Introduction: How to Build and Arm a Scale Model Battleship From Scratch
Welcome to the fascinating world of R/C BIG GUN Warship Combat. So what exactly is R/C Warship combat? It is a hobby where scale model warships, armed with low-pressure CO2 cannons, fire small ball bearings at an opposing ship. When enough holes are put in the easily punctured balsa wood covered hull to overload the internal bilge pump, the ship will sink. All ships have a float and recovery line so there is no need to go swimming unless you want too. Yes, we shoot holes in our models on purpose. How else can you simulate real sea battles. It's Allied versus Axis; Battleships, and Cruisers and Destroyers maneuver for attack, or struggle to protect the cargo ships that are valiantly trying to get supplies through. Oh, and we cannot forget the need to defend your port city from bombardment from sea. Any questions? Good, you can ask any Midwest Battle Group member. But, we have to warn you, you're going to get hooked on this hobby.
The ships are 1/144 scale (range from 3 to 6+ feet in length), WWI - WWII era (1900-1946) warships, transport ships, and occasionally submarines. The wood or fiberglass hulls are covered with balsa wood skin. They have bilge pumps to simulate damage control, are electric powered, and are armed with low-pressure CO2 cannons, that can rotate and depress. The models are equipped with a float attached to a recovery line. This allows easy recovery of the ship when it sinks. The ships are quickly recovered, repaired, and put back in the game. The only damage is to the balsa wood on the hull, since the internal components are protected by shielding, and the electronic equipment is usually waterproofed.
This instructable walks you through the process of building a model warship from just a set of overhead and side views.
More about me....I've built 5 ships from scratch and used to run a small business selling supplies and building cannons for the ships. I made several design improvements to the cannon, but cost of having parts cnc'd drove the prices up to high. I sold my business to strike models http://www.strikemodels.com/.
More about the hobby. You can learn about the hobby from www.strikemodels.com they support both versions of this hobby small gun and big gun. Small gun limits the number of cannon and they are all bb size. Big Gun uses various ammo sizes upto 1/4" linked to the ships actual cannon size and allows you to arm all the guns. Big Gun is what is pictured in this instructable. The currently are selling everything you need to battle. They have a very good website which includes a list of currently active clubs.
The guns way anywhere from a 1 to 1.5 pounds. The ships themselves can get fairly heavy. A Yamato weighs around 40 pounds and is around 6 foot in length and 10 inches in beam.
Also new is our club's promotional video. Unfortunately the club has disbanded do to shrinking membership, but many clubs are still active across the US and Australia.
Step 1: SELECT a SHIP
First things first – decide what ship you want to build. This decision alone may take many months of procrastination while sorting our all the facts that seem pertinent when in reality, it doesn’t make all that much difference. I have participated in about 50 rc combat warship battles over the past 5 years and have followed the action of other clubs closely. One thing that I have learned is generally, there is no such thing as a bad boat. Assuming a boat is reliable and well balanced so it is seaworthy, and put in the hands of a skipper that has learned how to use the features of the particular ship to his advantage any ship can be an effective part of a team.
Ask yourself why you want to participate in this hobby. Presumably the reason is to occupy free time and consume some disposable cash, for this hobby will certainly do that, but more likely the real reason is to have fun. The best way to have fun is to have a ship that is reliable and seaworthy. It’s very frustrating to have your ship role over and sink as soon as it begins to take on water, or to spend the day sitting at the side of the pond working on your ship instead of participating in the game.
Consider a used ship as your first ship. This will allow you to begin playing the game sooner and there is no better way to decide what ship fits your style than to participate in the game for awhile in order to learn your strengths and weaknesses. Ideally the owner will allow you to battle the ship before you purchase it. If you like how it responds to your style of battling and it operates reliably through the day it is a good choice to get you in the game quickly. When you get a ship test all systems to ensure that they work, and how they work, then use this ship to gain combat experience and as a construction aid and test bed for your new ideas. That’s right. To test out your new ideas. About every modeler I have ever known has his or her own ways of accomplishing tasks and you will find yourself asking, “Why did the original builder do it this way?” Most often there was a reason, but sometimes it was just a mistake, an attempt to implement a new idea that didn’t work very well. There is no substitute for experience in building a ship and learning combat techniques.
Avoid small ships and complex ships for your first building experience. There are many operational systems in our warships and every system is equally important in its own right. Think about it, which is more important, cannon, drive motors, pump, steering, or balance? After a little reflection you will probably decide that all systems are equally important since your ship won’t be combat effective if any of these systems don’t work well. It’s by far and away easier to learn the basics of maintenance and installation on a ship that has fewer operational systems. It is easier to get the hardware installed in a larger ship. Small ships test the talents of the most skilled builder. For your first ship you will be well advised to build a larger ship rather than a smaller one. Larger ships are more survivable in combat as well.
Keep it simple. Another sound tidbit of advice would be – don’t try to reinvent the wheel. Stick to the basic and proven methods of implementing a function. Look at the ships of the seasoned skippers and pay attention to how they implement the various functions, then follow suit.
Step 2: OBTAIN a SET OF 1/144TH PLANS
I have often been asked what I felt was the best way to construct a hull “from scratch.” I’ve seen several methods used with some methods working better than others, yet still I’m not sure if there is one best method. I believe if the hull doesn’t warp, isn’t overly heavy, and floats somewhat level when empty (no major list) it’s a good hull. I suppose I should add in one other criterion as well, it shouldn’t leak. This article will cover: Making a Pattern Set, Selecting Construction Material, and Assembly.
The premise for developing patterns sets for a scratch built hull is that the ship will be built on a flat bottom plate with ribs, bow and stern keels being glued in vertically all topped by a caprail. BDE offers several such pattern sets ready for cutting and assembly, but this section will cover the basics of developing your own pattern sets should they not be commercially available. Using the baseplate method of building is recommended otherwise you will have to set the ribs on a keel, which requires jigs and fixtures to achieve good results and the keel will be in the way later anyway. Flat bottom boats are much easier to build, but don’t confuse a flat bottom with a shoebox shaped hull. The sides will still be rounded, as will most of the hull below the waterline. Real warships are generally flat on the bottom as can be verified by your ship plans.
First, obtain a set of plans for your ship. The greater the detail shown on the plans the better, but don’t be surprised if the detail is lacking. Often a set of plans consists of a top and side view of the hull and superstructure and a drawing of the ribs at a few stations along the hull, but this will suffice.
Step 3: BUY OR CREATE a PATTERN SET
A photo of a typical rib station drawing is shown to the right. The plans usually don’t provide enough ribs for the required spacing (1, 2, or 3 inches) so you will need to draw additional ribs. Look at the overhead view of the provided rib locations. Next decide the spacing you will use. Use of ¼” wide ribs on 2” spacing is the most common selection, but for large ships 3/8” wide ribs on 3” spacing is also used. With your spacing selected you will need to draw lines on your overhead view where you need to add ribs. You will often need to add one and sometimes up to three ribs in between those provided by the plane set. What I recommend is making a copy of the original ribs and hand sketching the correct number of ribs in-between the provided rib profiles. Just eyeball even spacing for the number of ribs you are adding. Be sure to reduce the overall rib width by the thickness of the balsa sheeting on the hull, and the overall height by the thickness of the caprail and bottom plate. Do this by drawing a line below (3/8” for plastic ¼” for wood) the top of the rib for your new rib top and a line 1/8” above the bottom of the boat. Also draw reference lines for the water line and a line one inch below the water line across the ribs. Note that often only half of the ribs are drawn, so you’ll have to draw the mirror image of each rib the best you can including the added ribs. When I do so I use a light tracing paper that you can see through easily, draw half the rib, fold the paper in half then copy the other half of the rib off the first half. Another method is to make a copy of the ribs then trace them on the back of the paper copy, thus making a mirror image. When you have a complete set of full width ribs COPY all of your work and save the original drawings. Make one copy for each of the ribs.
For each rib highlight the correct exterior hull line the top and bottom (remember to follow the lines that allow for the bottom plate and the caprail). Also on the exterior line mark an 1/8” deep notch on each side of the rib at a point starting one inch below the waterline and extending to the bottom of the rib. Hardwood stringers will be installed here later on to help form the impenetrable area of you hull. On some of the wider ribs you will not need a rib that goes completely across the bottom of the hull. If the flat spot in the rib is more than 4.5” wide then you will draw a left and right piece. You may wish to read the section on water channels at this point so you can design your rib patterns to accommodate water channeling. The water channel will be 2.75” wide so measure 1 and 5/8” inches left and right of the center point on the flat bottom of the rib profile to allow for the water channel stringer. Make these marks ¼” high. At the outer edge of the flat spot measure ½” up and draw a diagonal from that point to the top of the ¼” tall line that marked the top of the innermost edge of the rib’s bottom. Next sketch in a line about ½” in from the exterior hull line to complete the inside edge of your rib. You will want to mark the location of the prop shafts on the appropriate rib patterns, usually the rib just forward of the propeller and the two ribs forward of where the shaft enters the hull. For the rib just forward of the prop you will need to draw in braces to support a circle big enough to drill the hole through for the prop packing tube.
The next items to make patterns for are the bow and stern keel plates, the caprail, and the baseplate. Start with the base plate. Take your rib patterns and measure the “flat” width at the bottom of the ribs. For all ribs with a flat spot at least 3/8” wide and that touch the bottom plate transfer those measurements over to a sheet of paper. Remember to also measure the distance from the bow to each rib from your overhead view and transfer these to your base plate pattern. You should end up with a center line with rib locations marked and each rib location will have a perpendicular line centered on the center line that represents the width of the flat bottom of the rib. To complete the base plate pattern just connect the outer edge of the rib lines. Next to make the bow and stern keels trace the side view of the bow and stern profile. Measure in about ½” in from the profile and make another line. You will want to make the keels long enough to overlap the base plate at least 3 inches. Remember to make a 1/8” allowance for the base plate. Also note that a few of the forward and stern ribs will not attach to the base plate but to either the bow or stern keel. These rib drawings should be modified with a notch to slide onto the keel and remember to keep the depth of the ribs all the way to the bottom of the keel, since they do not rest on the bottom plate. Some ribs that are on the base plate may need to have a notch added to their pattern to allow for the overlapping bow and stern keels. To make a pattern for the caprail trace the outer edge of the ships deck from the overhead view (please note that some odd ships are wider at the waterline then at the deck or caprail level). Draw a second line a ½” in to complete the pattern. You may also wish to design in some cross braces into the caprail pattern. These help the ship maintain its desired width and to reinforce the hull should it ever need to be pulled from the water with 100 pounds of water in it!!!. Make copies of all these patterns as well.
Step 4: HULL CONSTRUCTION
You are now ready to select the material for your scratch built hull. Some people prefer 5-layer plywood, while the MBG now has three plastic hulled ships. The plastic is foamed PVC and can be obtained in various thickness’ from an industrial plastics supplier. Foamed PVC enjoys the advantage of being lightweight and strong, easily cut and glued with CA glue, is inherently waterproof and will not warp or rot. If you do chose to use plywood the following precautions must be followed. Cut your caprail and base plate patterns into pieces between 12 to 18 inches to prevent the wood from warping. Cuts should be made at a rib location.
Glue the copies of the tracings to plywood using Elmer’s glue, or some other water-soluble glue, then saw them out slightly oversize. Use material of the appropriate thickness corresponding to the rib spacing of your pattern. For the base plate use 1/8” and for the caprail use 3/8” for plastic and ¼” for wood. Next sand the pieces to the correct size. Finally remove the paper from the wood or plastic with warm soapy water, then dry the parts well. Don’t be concerned if the wood parts warp somewhat. If the wood is going to warp, now is the time to find out. If warping of the longest sections of the cap rail or bottom plate occurs just cut them into shorter sections, preferably at rib location. A little warp won’t hurt anything at this stage of construction. We’ll fix it later.
If you chose wood as your material you will need to glue sections of the caprail and base plate together, end to end on a flat surface and while laying over a tracing of the plans. This will ensure the sections have the proper curve to match the hull. Likewise, with the bottom sections of the hull. Epoxy glue works well for this purpose, but CA is too brittle and will not work well. Don’t be concerned if they look weak lying there. We’ll strengthen them plenty later on. When the glue dries, lay these sections over the plans and mark the positions where the ribs will attach. Now attach the ribs to the base plate with 1 or 2 drops of CA glue. Don’t glue them too well right now since you may need to remove the later if something doesn’t line up right. Next, look at the hull from the end and visually verify that the ribs are symmetrical on both sides of the hull. There’s a photo of this step later in this article. Now attach the cap rail to the top of the ribs. Some of the ribs may not line up with the cap rail well, but don’t force the caprail down, or up to the ribs. Trim or file the ribs as needed to line up with the level caprail. Note the word level! There are photos accompanying this article that will help you visualize how the hull will go together.
Once the hull is glued (tacked) together in this state it will still be very frail so handle with care, but don’t panic yet. Next will come the strengthening. Place the hull on a flat surface and inspect carefully to see if the hull has developed a warp. If so just break a few glue joints to relieve the pressure, then glue them again. You may also need to make a few cuts through the caprail or base plate to relieve pressure to eliminate the warp. You’ll find photos of this step ate the end of this article. Make as many cuts as needed to get the warp out. Once again, don’t worry, you’re not weakening your hull permanently.
Now the strengthening of the hull begins. For wood hulls install hardwood (spruce) strips the thickness of the balsa sheeting allowed (1/16 to 1/8 inch). These stringers will be 3/8” wide. This width will allow the strip to overlap the ribs by 1/8”, since the wood caprail is only ¼” thick. These strips are installed around the caprail on the inside and outside of the hull. You can cut the stringers into shorter sections, but make sure the joints are staggered and the inside stringer joint does not occur on the same rib as the outside stringer. Again installing them on the bow and the stern is the trickiest part to accomplish. To allow the hardwood to bend around the curved areas cut notches about 2/3 though the wood stringer about every ¼” in the inside the side that will be next to the hull, then bend the stringer until it cracks at the notches. I use the Dremel tool and cut off wheel to make the notches.
Next, install 1/8” by 1/8” stringers (preferably spruce) in the notched portion of the ribs that starts 1” below the waterline and extends down to the base plate. The stringers do not need to butt up closely together, as you will cover this portion of the hull with fiberglass. Assuming your hull is still true and not warped go back and brush epoxy glue on all wood joints that were tacked with CA glue. For plastic joints a bead of CA glue along both sides of the joint will permanently bond the plastic parts together. Invert the hull and brush the epoxy inside the sandwich formed by the two hardwood stringers and the caprail. Wait for the epoxy to cure and you’ll see that this step will have strengthened your hull dramatically.
Now the hull should look nearly complete save for the side skin. Sand all outer surfaces of the hull so that they are smooth in preparation for fiberglassing the bottom. Next, place the hull top down on a flat surface and add spacer beneath it to allow it to lay flat and be supported. If the hull has taken on any warp you must get the warp out at this time. Check the hull closely for warping. Don’t be afraid to cut the hull in two and glue it back together if needed to correct a warp. Now is the best time to fix them.
Fiberglass resin has quite an aroma (it stinks) so find an area to work with good ventilation. Cover the work area with a sheet of plastic. Now make a stand to hold the hull off the work so it can lay inverted (upside down) and be stable. The stand must hold the entire hull (for wood only) off the work area to include the bow and cap rail since we’ll be glassing them also.
Next, cut the lightweight fiberglass cloth in to small sections about 12” square, or whatever size or shape is needed to cover the hull. Small sections of cloth are easier to work with and to keep air pockets out of. At this point I would recommend purchasing an ultra violet cured resin sold by SolarEZ. This stuff is just like epoxy resin with the added bonus of only hardening when exposed to about 30 minutes of strong sunlight. If you keep the windows covered in your shop you will be able to work at your own pace rather than at the pace of the setting time of normal resin. Apply a thin coat of resin to the hull bottom and sides down to the penetrable area, then lay on a section of fiberglass cloth and apply another thin coat of resin over the cloth. Repeat this procedure to apply the next section of cloth, overlapping the previous section by ¼ to ½ inch. Continue laying cloth until all the wood stringers on the bottom of the hull are covered with fiberglass cloth and resin. Remember a thin coat of resin is all that is desired. Applying more resin just makes a mess and increases the amount of sanding needed. Sanding fiberglass is no fun. The cloth will try to “slip” across the wood as you brush resin on, so reverse directions of your brush strokes regularly and use a gloved hand to push or pull the cloth. As you are progressing smooth out the cloth, working out all air pockets and wrinkles. Cut the cloth with an Exacto knife to let the air escape if necessary and overlap the cloth at the cut then smooth it down. This will be especially necessary in the bow and stern where there are a lot of curves. Continue this effort until the hull is covered, bow to stern, to include the solid bow and stern blocks.
Allow the fiberglass resin to partially set, then using an Exacto knife cut away any excess fiberglass cloth that has extended into the penetrable areas of the ship. After cutting, smooth the cloth down again along the cut edge using a gloved hand. Wetting the resin with water first to provide some lubrication helps to keep the resin smooth. As soon as the resin on the bottom of the hull is set enough (but not fully cured) invert the hull and apply cloth and glass to the top of the bow stern and cap rail, overlapping the sides of the caprail down to the penetrable area. When you are through the entire outside of the hull will be covered with fiberglass cloth and resin except for the penetrable areas. Once the resin begins to set up trim away any cloth that extended into the penetrable areas and smooth down the cloth. Remember no wrinkles or air bubbles should be allowed in the cloth. Now invert the hull and sit it back on the wooden block upside down.
Apply another layer of glass cloth and resin down the center of the hull bottom from bow to stern. This sheet does not need to extend up the side of the hull to the penetrable area, but just cover the flat part of the hull bottom to provide more reinforcing in the base plate to strengthen the butt joints that were glued together.
At this point you may want to install optional frames to butt your balsa sheeting up against. Some people like these since they create a “window frame” that you cut the balsa to fit into. The advantage is that all the work in tapering the balsa sheet to the hull profile is done once with the frame the disadvantage is that when you install the balsa it has to be cut to fit this frame. If you decide to add this frame you’ll need to get some wood stringers that are 14” wide and the thickness of your balsa sheeting. Glue these 1.25” below the waterline (this gives a ¼” of hull for you balsa to glue on to) and ¼” fore and aft of the penetrable areas. Use automotive putty to taper the edge of the framing to the ship’s hull. Let dry and sand. You may need to apply a few layers to get it smooth.
Brush another thin coat of resin over the entire hull and caprail. As this coat of resin sets make sure the job “looks right.” Look for thin spots in the resin. If it looks good and you are happy with it then let the hull dry completely. Otherwise, apply another thin coat of resin. If there are a few “rough” areas it won’t make all that much difference and they will be corrected later. On a warm day this could take only a few hours for the resin to cure, other times it can take several days for all “tackiness” to vanish. Again the two part resins are tricky things to mix and the solar cured resin is preferred although use of an old mirror might be required to get the sun to all parts of the hull for complete curing.
Once the fiberglass resin has set completely sand lightly with fine grit (150) sandpaper on a sanding block or orbital sander. Sand lightly is a key word. You do not want to sand through the resin and into the cloth anywhere! After the sanding is complete wipe off the hull with a damp cloth then skim on a coat of automotive putty over the entire hull surface that was fiber glassed. A plastic putty knife works well to skim on the filler, allowing the filler to fill in only low spots and to smooth out rough areas. I recommend the automotive filler putty because it is easy to work with, is waterproof, and is easy to sand. Once it dries sand the hull again. You may have to repeat this procedure to get a really smooth finish, especially in the areas where the glass cloth was overlapped.
Step 5: MAKE THE PROP SHAFT STUFFING TUBES.
4.5 Making Prop Stuffing Tubes
The fabrication of prop shaft tubes can be a very simple task. Just visit your local model shop and find their assortment of brass tubing. Or purchase a stuffing tube kit from BDE. To do most jobs you need a 12” piece of 7/32” brass tubing for each prop stuffing tube, one 12” piece of 3/16” brass tubing, one 12” piece of 5/32” brass tubing, and one 12” piece of 1/4” brass tubing. You’ll also need some thin brass sheeting for your shaft stand-off supports, but you should have plenty left over from making your rudder. You may also consider buying a special fitting from BDE that will slip over your 7/32” tube and allow you to use a standard grease gun fitting to fill your prop shafts. I’ve used this on several boats and it sure beats filling a needle with grease and squirting it into the shaft.
You’ll also need something to cut the brass tubing with, a dremel tool with a fiberglass cut-off wheel is recommended. To solder the tubing together you’ll need a 100 Watt soldering gun or a small torch, a pair of modeler’s helping hands or a vise and some clamps, some flux, and a roll of silver solder.
Use your plan set to identify the location of your props and study your hull to determine where you will place your motors. Measure the length necessary for each of your prop tubes and subtract ¼” transfer these measurements to the 7/32” tubing and cut them to length. Next cut two 1” long pieces of 3/16” and 5/32” tubing and one 1” long 1/4” tube for each stuffing tube. Remove all burrs and use light sandpaper to clean all tubing till shiny.
Next to prepare your Hull standoff support cut one ½”x1” strip from your brass sheet for each stuffing tube. Use either your vise or helping hands to hold the ½” wide end of the brass strip against the 1” long section of 1/4” tubing. Apply flux and solder together. Let cool then slip over your 3/16” tubing. Make sure you keep this away from any soldering operations so that it does not become attached in the wrong place. You’ll be gluing it in place when you install it in the hull.
If you have the grease gun fitting from BDE slide it over your 3/16” tubing now and hold your tube over your boat and identify where would be the best place to have access to your grease gun fitting. Mark it and apply flux to the 3/16” tube and heat the BDE fitting and apply solder. You’ll need to take a 1/8” drill and use it to drill through your 7/32” brass tube going through the hole in the BDE fitting that the grease gun fitting screws into.
Next apply flux to your 3/16” sections and slip them into the 7/32” tubing leaving about 1/8” sticking out. Then apply flux to your 5/32” sections and slip them into the 3/16” sections leaving about 1/8” sticking out. You now have a the tube stepped down from 7/32 to 5/32 and ready to solder. Heat the 7/32” tubing just behind the two inserts and apply solder to both joints. Heating the bigger tube behind the joint helps draw solder into the joint.
Clean them up and you are ready to install them into your boat.
Step 6: INSTALLING THE PROP STUFFING TUBES
Before you get started locate the position of your rear cannons in your hull set them inside and determine approximately where you want to locate your motors and where you want the packing tubes to end. This will eliminate the need for modification of your prop stuffing tubes later on when you begin installing the hardware into your boat.
Installing prop shafts and packing tubes is far less difficult than most builders make it. An important thing to remember is not to be overly critical when cutting a hole(s) in you hull for the prop shafts. The holes will probably be in the wrong place no matter how much time you spend thinking about anyway, so just cut them. Oversize holes are easier to fill later.
If you have a wood frame hull you can install the prop shaft packing tubes before or after the hull is sheeted and fiberglassed. Due to the nature of the Iowa prop and skeg arrangement I chose to install them first. Just remember that it is very important to determine how and where your cannon will mount in the hull before installing the packing tubes, otherwise you will surely install them in the wrong place.
The upper photos show how the packing tubes were aligned parallel to one another and level, glued to a wood dowel that was carefully measured and marked. If you are using a fiberglass hull and brass stand-off supports for the ends of your packing tubes then use the dremel to cut a slot for your brass stand-off support near the end of the packing tube. Slide the brass support into the slot as you tilt your packing tube in place and glue to the wood dowel. Ribs were ground away as needed to allow the tubes to lie level with one another and fit in place at a slight downward angle. The tubes were secured in place with epoxy putty, which also reinforced the ribs that were ground down substantially.
If you are using the brass stand-off support for the end of your prop shaft and have not yet sheeted the bottom of your wood hull then glue cross support between ribs so that you have something to glue the supports to.
Wood sheeting was installed around the tubes and stand-offs (editors note: the above article on wood hull construction suggests the use of hardwood strips instead of balsa wood sheeting), but a small space was left open around the rib. This hole was filled with epoxy putty, which is a great water seal and also gives a nice appearance to the hull and looks like the packing boxes on real ships.
The third photo shows how the over size holes cut into a fiberglass hull were filled with epoxy putty. It also shows the extreme angle on the coupling for the motors that was required to allow the cannon to fit between the motors. As it turns out, the center motor was still in the way of the stern cannon and had to be removed and installed “backwards” above the packing tube using an o-ring drive or gear drive. The motors are installed by attaching small sections of brass tube to the hull with epoxy, then slipping plastic wire ties through the brass and around the motors. This is a system that has proven to work very well.
The bottom photo shows the running gear of the Scharnhorst, which is one of the most difficult ship hulls to outfit. Three props and two rudders fit into a very small space, but it can be done.
Step 7: Constructing the Water Channel
Have you ever wondered why some ships settle fairly evenly in the water when they flood internally while others take on a severe list? The reason is most likely inadequate water channeling. Water, being a liquid will seek out the lowest point of the ship and move in that direction. It also follows the laws of physics and reacts whenever the ship moves. If the ship turns right the water will move to the left, and visa-versa. Also, when the ship moves forward the water will run towards the back. This is why nearly all ships sink by their stern, rather than bow first. In fact, of the several dozen of ships I have seen sink I have never seen one sink bow first. Although sinking bow first would be a good feature since this has the potential to save the rudders and props from damage when the ship hits the bottom, or is recovered. I say “potential” damage because after 6 years of battling the MBG has yet to see any props or rudders damaged by sinking, but it could happen.
I’ve developed effective water channels with the past 9 ships I’ve constructed and the method I have come to like the best is the foam filled water channel. I like this method since I’ve found it the easiest to accomplish. To make the water channel I first installed two wood stringers down the center of the hull and separated by about 2.75 inches. The stringers should be ¼” x ¼” hardwood. These stringers also serve to add some strength since the bottom plate of this ship (wood construction) was made up of seven sections to prevent warping. Next grind down the portion of rib that is glued to the baseplate so that it will form a sloped line going from the ½” tall height of the rib to the center ¼” tall strip (editor’s note: its easier to layout the rib patterns with this slope in mind and save the grinding). In addition to the channel down the middle you may want to leave an open section sized for your batteries so you can keep this large piece of weight low in your hull. Make this battery space an 1” longer than the battery you intend to use and typically centered amidships with the batteries placed out towards the side of the ship to allow for a CO2 tank between them.
If you are putting a channel in a fiberglass hull your job is a bit easier. After attaching the sides of your channel to the bottom of the hull you will need to add a stringer that goes from the edge of the waterchannel out to the side of the hull about every 4” along the length of the hull. You will need to cut a slope on them such that they are ¼” tall on the waterchannel edge and ½” tall on the end near the side of the hull. I recommend you work with 3/4” by ¼” hardwood strips. Measure off the length of stringer that will fit in the section of hull you are currently working on and measure in ¼” on opposite ends of the rectangle and draw a diagonal line between the two. The result should be a matched pair of wedges that are the same length and ¼” tall on one end and ½” tall on the other. Make your diagonal cut first down the center then make the cross cut. Glue these two pieces to the hull and you’ve created your own “rib” stringers and you are ready for the next step.
I then installed a piece of balsa over the ribs between the water channel stringer and the side ribs of the ship as shown in the accompanying photos. Since the part of the ribs that were glued to the hull keel plate were sloped towards the center this allows any water coming in through holes on the sides to run into the water cannel and towards the pump. Then I drilled a hole in the balsa sheet between each rib and using a can of “Great Stuff” minimal expanding spray foam I filled each rib section with the foam. My first attempt at this several years ago the foam simply forced off the balsa, cracking it to pieces. The accompanying photo shows how even minimum expanding foam still expands greatly (there are some new very minimal expansion foams on the market get some and experiment). The spaces between the ribs were only 2/3 filled!
Using a small blade on my pocketknife I cut away the excess foam, which was quite easily accomplished, then sheeted over it with more 1/16” balsa sheet. Be sure to use epoxy glue for this since CA glue will melt foam, as will fiberglass resin. When the whole hull was sheeted on the inside so I couldn’t see foam anywhere I put a thin coat of “SolarEZ” UV cured polymer resin over the inside of the ship. This product won’t hurt the foam and cures more predictably than conventional fiberglass. The trick is sunlight must be able to reach it in order to cure the resin.
Now that the water channel is installed you should have a ship that will settle level as it takes on water.
Ship Construction Sequence
A detailed description of each item will follow the list below.
Step 8: Selecting and Assembling Your Cannon
There are only two basic types of cannon used in the hobby today those with a horizontal accumulator and ball valve and those with a vertical accumulator and ball valve. Of the horizontal type the most popular and successful to date has been the Indiana design cannon. These are currently being sold commercially through BDE.
Vertical (or canister) cannons have been developed by many folks including BDE and have meet with limited success do to the limiting nature of their design. Canister cannons main limitations are four fold. One the guns are tall and top heavy since the actuator is typically located in the top of the cannon. Second the cannons have limited volume for the accumulator because of height limitations. Third the cannon are often difficult to rotate. Fourth as the cannons become progressively bigger in diameter the ability to seal the top of the gun becomes extremely difficult in a 4” diameter cannon the upward force exerted on the magazine seal is approximately 1,800 pounds!!!
The main limitation of the Indiana cannon has always been their length, but BDE pioneered a tandem cannon design which allows two rotating magazines to be powered by a single accumulator. BDE also pioneered the use of 90 degree accumulators. These two new features have made arming many of the smaller battleships and cruisers feasible.
Cannon typically come about 80% assembled. Here are a few things you’ll need to do yourself: Install actuator and CO2 fittings, install barrels, install barrel bracket, Install Rotation system and install elevation system.
This one is easy just screw on the provided MPA-7 clippard actuator and add a 1/16” hose barb to the inlet and you are ready to connect to your CO2 plumbing. One side note you will see a small vent/drain hole on the MPA-7 on the cone shape near the threaded end that attaches to the cannon. You may want to add a few holes especially one at the bottom when the MPA-7 is on the gun. This will allow water to drain out in case it gets flooded when the boat takes on water. That way you don’t need to take it off when you do after battle maintenance, just squirt a little WD-40 in a couple of your extra holes.
Adjust Ball Height Setting If Applicable
Have you ever fired your cannon and noticed that one or more of the barrels did not fire? This may be the result of improperly adjusted breach set screws (not all cannon have these) that serve to position the ball for firing.
The adjustment of the breach and ball set screws, located in the cannon manifold assembly is critical to the proper performance of your cannon. On the Indiana cannon the set screws can be accessed from the bottom of the magazine assembly. This is a one-time adjustment that should be good for the life of your cannon, unless you switch the cannon to a different caliber than it was adjusted too. The ball height must be adjusted correctly or your cannon will not feed balls reliably, resulting in misfires from one or more barrels.
Figure 1 shows an incorrectly adjusted set screw. When loading or firing the cannon, motion of the balls will usually force a ball into the proper firing position. However, when the cannon is partially unloaded sometimes a ball will “hang up” on the set screw if it is set too high as shown in Figure 2. This will result in the ball be shot into the magazine instead of out the barrel.
The figure 3 to the shows a properly adjusted set screw and the position of the balls in the magazine.
Figure 4 shows how the ball will roll into the firing position after the cannon is fired.
Care must be also be taken not to adjust the set screws too low. Otherwise, the ball in the load tube will be sitting slightly over the ball in the firing position and this situation will dramatically reduce the fire power of the cannon.
When air cannons are received the barrels will not be installed. Since barrel height varies from ship to ship barrel installation must be accomplished by the user. To do so the barrels must be cut to length to achieve the proper vertical positioning above the deck (note your cannon should already be mounted on a platform and installed in the ship) and the proper overall length that the barrels protrude from the turret on a particular ship. For this operation you will need a Dremel tool with a fiberglass cut-off wheel, a small ball grinding stone, and safety glasses.
1. Put on your safety glasses and mark where you will need to cut the riser portion of the barrel. I like to put all barrels for the cannon in a vice at the same time so that I know they are all equal length. Your barrels may actually need some additional height if so you will need to cut a small piece of brass tubing of the appropriate i.d. to fill the space between the barrel and the cannon. Remember to leave a ¼” gap for flexibility.
2. Mark and cut all barrels to the correct horizontal length.
3. Using the ball grinding stone de-bur inside and outside of the barrels where cuts occurred and taper the inside surface of the barrel tube end that is located closest to and above the cannons riser tube to allow balls to enter the barrel easier.
4. Use poly-urethane tubing to attach the barrels to the cannon risers. When cutting your tubing remember to leave a ¼” gap between the cannon riser and the barrel inlet to prevent misfires when the barrels are depressed. All also want at least ½” overlap on both the riser and barrel. For ¼” barrels use 5/16” i.d. tubing and for 3/16” cannon use ¼” i.d. tubing.
5. Cut poly-urethane tubing to length and install barrels onto the cannon risers to ascertain proper fit and positioning, then disassemble.
6. Using the Dremel tool and cut off wheel cut shallow grooves or notches into the portion of barrel the tubing overlaps. Do not cut all the way through the barrel wall. These grooves will help the rubber-tubing grip onto the barrel.
7. Secure the precut lengths of tubing to riser end of the barrels using a small screw type hose clamp.
8. If you needed to add a brass spacer insert it into the tubing at this time. Then slip another hose clamp over the tubing before sliding the tubing over the cannons riser tube. Tighten the hose clamp again making sure you have left a ¼” space between barrel and riser.
Install Barrel Brackets
Figure shows how align the barrels properly in the barrel bracket. First slide the bracket over your barrels and loosely tighten. Set the barrels on a flat board then push the risers up against another straight edge. Ensure the barrels are square to the backboard and that the riser portion is vertical. Then tighten up the barrel bracket.
Install Rotation System
You should already have your cannon mounted on a platform with your sail winch servo installed as described in the construction section above.
There are two methods for setting up your rotation; Nylon coated steel wire in a no slip configuration or rubber tubing / belt drive. Which one to use depends on the type of drive you are using for rotation. For a proportional sail winch servo you will want to use the steel wire so you get pretty much the same position every time for a given transmitter setting. For a continuous rotation servo the rubber tubing / belt drive would be acceptable.
Starting with the Nylon coated steel wire setup I recommend you go to a sporting goods shop and purchase some line leader wire (braided steel, nylon coated 40 lb test) and the appropriate crimp connectors. I’ll describe driving a pair of turrets since this is the most complicated setup. I’ll refer to the forward cannon as the A cannon and the aft cannon as the B cannon. The front of the cannon will be referred to as the 12 o’clock position when view directly from overhead. First you need to connect the two turrets together. Start with the B turret pre-drill a pilot hole for a #4 x 3/8” wood screw near the top of the cannon’s drive track in the 12 o’clock position. Use one of your wire crimps to make a small loop in the end of the steel wire. The loop should be big enough for the wood screw to go through, but not so big that the head of the screw fits through easily. Hook the loop onto the screw and screw into the pilot hole. Looking from above route your steel cable clockwise around the drive drum of the B cannon for ¾ of a turn (moving from the 12 o’clock position around to the 9 o’clock position). Now take the wire forward to the A cannon’s 9 o’clock position on the drive drum and wrap the cable clockwise around the A cannon’s drive drum ¾ of a turn to the 6 o’clock position of the cannon add an extra ½” and cut the cable. Remove the cable and make another to match.
Now drill two pilot holes in the drive track of the A turret. The first hole should near the top of the drive track in the 5 o’clock position make sure you leave room for the head of the screw and a washer. The second hole should be near the bottom of the drive track in the 7 o’clock position. Place a #4 x 3/8” wood screw with washer in each hole and screw in about a ¼”. These two screws will be used to wrap the steel cable around and by adjusting where you tighten down the end of the two cables will allow you to easily adjust the alignment of the A turret to the B turret.
Use a 3 foot dowel rod inserted into the center barrel of the A and B turrets to align them pointing directly forward so the two rods are parallel and on top of one another and twist tie the dowels together to keep your two cannons aligned. Now place a washer on one of your screws and hook the looped ends of your identical pair of cables over your screw and tighten down the screw in it’s pilot hole in the 12 o’clock position of the B cannon’s drive track. Route the first cable as described above and when you get to the 5 o’clock position of the A cannons drive drum wrap the end of the wire clockwise around the screw starting from the bottom of the screw. Route your second cable counter-clockwise ¾ of a turn around the B cannon’s drive drum to the 3 o’clock position go forward to the A cannon’s drive drum 3 o’clock position and go counter-clockwise to the 7 o’clock position and wrap the wire clockwise around the screw starting from the top side of the screw. You may need to tweak the tension on the wires to get the alignment just right.
Install Elevation System
There are two types of elevation. Fixed and servo drive. The fixed is easiest so we will start with that one. You’ll need two sets of 2-56 threaded ball and socket connectors and some 2-56 threaded rod for each turret. You can get these from BDE or your local hobby shop. You’ll also need some ½”x ½” hardwood.
Now cut off a 1” long piece of your hardwood and epoxy it to the center of your magazine cover. You could also screw it on from the inside of the magazine cover with a #6x3/4” screw if you wish to have the option to switch to servos at a later date. Next drill a 1/16” pilot hole in the front of the post about a ¼” down from the top. Next screw a 2-56 threaded ball connector into this pilot hole. You may need to secure it with glue if you have trouble with the threads stripping out. Screw another ball connector into the cannon’s barrel bracket in the hole provided. Hold up the threaded rod and mark off a piece about 3/4” short of the distance between the two ball connectors (with the barrels raised to the horizontal position).
Screw a nylon socket joint onto each end of the 2-56 rod and adjust elevation by tightening or loosening the nylon sockets then snap them back into place.
Using a servo for elevation is very similar to the above except the servo replaces the wood post. To mount the servo cut a 1.25” post from your ½” x ½” hardwood and secure to the cover so that they are separated by the width of the servo and positioned so that the servo horn is close to the front center edge of the cannon. With the posts secured to the cover slip the sevo in-between them and drill pilot holes to line up with the servo’s mounting holes. I use #6 screws to lock down the servos. Drill a 1/16” pilot hole in about the middle hole of a standard servo’s arm to attach your 2-56 threaded ball. Then complete as above.
Install Feed Tube
Now that everything else that needs to be attached to your cannon has been put in place look for an open spot on the cover to locate the cannon’s feed tube. Use a dry erase marker to trace the outline of the feed tube’s base. Then remove the cannon barrels, barrel tubing and the cannon’s magazine cover. Turn the cover over and from the inside mark the center of the feed tube and the two attachment screw holes. CLAMP down the cover either by using screws to screw it into a scrap piece of wood or in a vice. If you don’t the cover may spin out of your hand as you drill through it. Use a 9/32” bit to drill out the center feed hole and a 3/32” bit to drill out the holes for the mounting screws. Attach the feed tube then reassemble the cannon.
On the cannons there is only one item that typically wears out and that is the ball valve spring. If your ball valve begins sticking open it is most likely time for a spring.
1. Go to an ACE hardware store and find their Century spring display. What you are looking for is a 7/32 diameter spring with a .022 wire that is 1” long.
2. Next empty the cannon and ensure there is no ammo left in the gun.
3. Remove the MPA-7 actuator and pressurize the accumulator. Pull the ball valve shut if you necessary to fill the cannon. This will lock the ball valve in place for the next step.
4. Remove the screw and washer from the end of the ball valve rod and replace the old spring with your new spring.
5. Replace the MPA-7 and test fire the cannon. Be careful where you aim just in case you missed step 2.
Step 9: INSTALL YOUR CANNON
Phil S. has long been a proponent of mounting your cannon on modular platforms that can be quickly installed by hooking, snapping, or bolting to the bottom of the ship. Tim M. took the modular platform on step further by attaching posts that are cut level to the deck and secured to the deck structure. Since Phil’s method is easily modified to Tim’s we’ll start with that one then finish with Tim’s idea. Personally I like Tim’s method since the screws that hold the platform assembly in place are much easier to access.
First create a paper pattern for your gun base plate. If you are mounting a pair of cannon on the same plate it works best if the baseplate is long enough so that it sticks at least ½” forward and aft of your two cannons. If you are rotating your cannon you will need to extend the length of your base plate to accommodate your rotation device. If you followed the instructions for the water channel you should cut a 2.5” wide piece of paper and tape it centered in the water channel. Make it more than long enough so you have paper to work with. Next measure the plans to determine the location of the center of the turret(s). Transfer this measurement(s) to the piece of paper in the bottom of the water channel. Also mark the waterchannel itself at these locations so you know where to put the platform later on. Sit the two cannons and your rotation servo in and measure to make sure they are in the correct positions and centered. Use a pencil to mark the forward and aft edge of your platform. You want to make the pattern long enough so that you can see and edge on both ends. This will give you a spot for attaching the platform to the bottom of the deck, which will be discussed later on. Remove the cannon. Remove the paper and draw in your for and aft ends of the plate. Now draw a ½” wide by 1” deep rectangle centered on the fore and aft ends of your base plate pattern. Draw an X in this rectangle as it will be cut out to make a fork shape on each end that will allow you to center your base plate. Cut the baseplate for your cannon from a ¼” thick piece of 5 layer plywood. Use your marks to locate the center position for each turret and drill a 9/32 whole through for attaching the cannon.
Set your baseplate back into the waterchannel and line it up with the marks on the water channel and make sure it is centered. Trace the sides of your forks on the bottom of the hull as well as the fore and aft edges of the baseplate and remove the baseplate. Cut two ¼” slices from a ½” by ½” piece of hardwood to form two guide blocks. Also cut four ½” long pieces of wood from ¼”x ¼” hardwood to form four stops. Next glue the guide blocks on the marks made in the bottom of the water channel with some epoxy so that they line up the outside edges of the baseplate and sit between the marks for the sides of the “fork”. Also glue the stops on the bottom of the hull at the end of each “tang” of the two “forks” of the baseplate. While you are waiting for the epoxy to set apply a good coat of either paint or epoxy to your baseplate. After the guide blocks have set mix up some more epoxy and coat the guide blocks and stop blocks completely. Note the guide blocks will center your gun baseplate, while the stops will keep it from moving for and aft.
When everything is dry attach the cannons to the baseplate with the screw provided. Use some silicon adhesive to ensure the cannons will not rotate. Test fit in the hull before the silicon sets up.
Now you need to install a platform for your rotation servo. First measure the depth of the hull in the location where you plan to put the servo (usually directly aft of the B cannon or foreward of the C cannon). If you have about 4” and at least one layer of superstructure above the servo position then you will be able to mount the servo upside down. Cut four pieces of 1/4” x 1/4” hardwood 1 and 7/8” inches long these will be your legs. Cut two pieces 3 inches long for rails and cut two pieces 2.5” long for servo supports. Epoxy two legs to each rail at either end, resulting in a C shape 3” high and 2.125” wide. Now epoxy the legs of each rail set to the outer edge of the cannon’s base plate so that the rails run parallel to the cannons accumulator and are close to the edge of the cannon’s magazine. Now drill 1/8” pilot holes in your servo supports so that the servo’s mounting holes are centered on the support. Sit the servo supports on the top side (drum side) of the servo’s mounting holes. You’ll probably need to use a dremel tool to grind down an annoying little tab there so the support sits level. Bolt the servo to the support with #6 x ¾” machine screws and nuts. Turn this assembly upside down and straddle the rails. You’ll want to string up your drive belts or wires at this point (see other article). With your drive system in place pull the servo along the rails till the drive belt/wires are taut. Then drill 1/8” pilot holes through the supports and into the rails. Fix in place with #6 x ¾” wood screws.
Now you need to decide how you wish to lock down the cannon platform. You can either put your lock down tabs on the bottom of the hull or extend pillars up from the cannon platform so the deck can be attached to it and then used to lock the guns in place. Like I said I prefer the deck method even though it is a little more work because as you plumb and wire your boat getting your hands down to the bottom to lock the platform in place can become tricky.
If you wish to use the simple method of the bottom lock down here is what to do. First drill an 1/8” hole through the center of your guide block right through the bottom of your hull. Yes through the bottom of the hull. Use the cone shaped sanding attachment for your Dremel tool to flare the hole on the outside of the hull so that you can flush mount a screw. Take a 1.25” long #8 flush mount machine screw and screw it from the outside in and cover over with some epoxy for a watertight seal. Next cut two pieces of ½” by ½” hardwood 1inch long. Drill a 9/32” hole through the center. Paint both pieces and let dry. Next slide these over the machine screw and secure with a nylon lock nut. Make it tight but not two tight to turn. Rotate this latch so it parallel with the sides of the waterchannel. If you attached the guide blocks in the correct place and cut the “forks” deep enough your baseplate should be able to go around the latches. Try rotating the latches if they clamp the baseplate too tightly remove the latch and install a thin washer between the guide block and the latch bar.
If you wish to attach the deck to your baseplate follow these steps. First carefully measure the height from four exposed parts of the cannon platform (two at each end) to the bottom of the deck and cut two pieces of ½” x ½” hardwood to this length and epoxy them to the platform. You should now have four pillars that extend from the gun platform up to the bottom of the ship’s deck. You’ll want to cover the tops of your pillars in epoxy and some thin fiberglass to prevent splitting the wood when you screw the deck to it (remember to drill pilot holes). Also paint all wood pieces to prevent water damage. Depending on how sturdy your pillars are you may need to add some cross braces diagonally from the top of each pillar to the platform about half way between pillars. Going across the cannon you’ll have to work around the cannon. Remember, once it’s in the boat your guide blocks and stops position the cannon the pillars just keep the cannon from popping up. Making the pillars sturdy is mostly so you can remove the cannon for maintenance
Step 10: Install Rudder and Rudder Shaft.
Building the rudder assembly is relatively simple. First locate where the rudder shaft should be located and transfer the measurement from your drawing to your ship’s hull. Next cut a block of balsa about 1” square and tall enough to go from the bottom of the hull to about 1” above the water line (or as high as possible). Take this block and sand the bottom contours so that it sits perpendicular in the hull. Then use a vice and drill press to drill a 5/32” hole down the center of the block. Then glue the block in the hull insuring the hole is correct location and the post is perpendicular to the hull. Now you can use a hand drill with the 5/32 bit to completely drill through the bottom of the hull. If the block is too deep for your bit a piece of 5/32 brass tubing with a roughened end can be chucked up in the drill and it will eventually cut its way through. This method is suggested since it is easier than trying to sit a battleship squarely under a drill press, however if your shop will support doing that it would be a quicker and perhaps more accurate alternative.
Next cut a section of 5/32 tubing that is a little longer than your rudder post block. Put a little CA glue on it and tap it through the wood support post. You will want to leave about a 1/16” of an inch above the post inside the hull and below the bottom outside the hull. Use a dremel to cut the tubing down if necessary.
Next cut an 1/8” solid brass rod the appropriate length for the rudder shaft. The shaft should extend ½” above the rudder support block (or higher depending on where your rudder servo is located) and the entire depth of the rudder below the hull. Test fit the shaft and check your measurements.
The next step is to cut out a rudder from thin brass sheeting. It should be thick enough so it does not bend easily, but not so thick you can’t cut it with metal sheers. My favorite method is to use very thin brass and layout a pattern such that you will fold mirror image rudders around the shaft. The thin brass is easy to cut and the finished rudder has a more hydrodynamic shape.
Next file the rudder shaft flat where you will be attaching the rudder. You will only need to flatten on one side if you are using a one sided rudder, but on both sides if you plan to use the wrap around rudder. Put flux on the flat side(s) of the shaft and then use vise grips to clamp the rudder in place. Use a small torch or a 100 Watt soldering gun to heat the rudder and shaft and apply silver solder.
When installing the rudder you will need some sort of bushing between the hull and the rudder. If your ship’s rudder is flush against the hull just use a small thin washer and slip it over the shaft then slide the rudder into place. If the rudder needs to stand off some distance then use a wheel collar to lock down the correct stand off distance.
The final step is to install the control arm. If your arm will be above your post you will also need a wheel collar to ride against the rudder stuffing tube. In most ships a simple lever that locks onto the shaft with a setscrew is sufficient, but for those really narrow sterns a toothed pulley and toothed belt can be used. The toothed pulley method works very well for the twin rudders in the narrow stern of a Scharnhorst. The belt goes around both rudder pulleys then around a matching pulley on your servo and you’ve got a quick and simple dual rudder drive. The caution is that belt driven rudders can slip easily if the rudder is bumped during ship launch or run aground when going in reverse, so use conventional control arms and wire rods where possible.
Step 11: Install Props and Prop Shafts.
You’ve already built and installed your prop stuffing tubes during your hull construction so all that is left to do is to install the shaft(s) and prop(s). First slide a piece of 1/8” brass rod into the prop stuffing tube. You will want to have 3/8” (you may need more depending of the type of drive system hardware you are using) of an inch protruding from the stuffing tube inside the hull and ½” protruding outside of the hull. Mark the shaft(s) and cut to length. Next locate where the setscrew for the prop will be on the shaft and mark. Use a file to flatten this spot. A trick I’ve learned is to hold the file at an angle so the flat spot is deeper on the ship’s side of the shaft. This makes it much harder for the prop to slide off the shaft since the setscrew would have to be forced up a ramp. Attach the prop with the setscrew sitting in your angled notch and slide into the stuffing box. Now double check the length inside the hull remember how much shaft you need will be a function of the type of drive system hardware you are using. Adjust the length if necessary. Mark the spot where the drive hardware’s set screw will be located on the shaft. Remove the shaft and cut an angled flat spot this time with the deeper end towards the prop side of the shaft. Next put the shaft back in and attach the drive hardware. Finally fill the stuffing box with grease. Pump the grease in till you see it squirt out both ends of the shaft. Just a few minutes of ungreased operation will destroy a shaft (been there done that).
Step 12: Select Drive Train and Motors
First some tips on selecting motors / batteries for your ship. It takes some form of propulsion to move your warship through the water and this power is provided by one or more relatively small, direct current (dc) drive motors. What size motor is required? Well, the power required to propel you ship can be defined as a force sufficient to overcome the frictional losses of the system. In this case the “system” is comprised of the friction of the drive components and the drag on the hull moving through the water at your design speed. While there are formulas for determining all of these losses for a given ship, not all of us are engineers. Even those of us who are find it much easier to ask some skippers (preferably those with ships of similar size and speed) what motors they used at what voltage and what size and pitch of prop. The Table 3 has some example drive setups.
This will get you close enough that you should be able to tweak your system to make speed. A good rule of thumb is to look for surplus motors that operate over the range of 6 to 12 volt and draw somewhere around 200-400 Millie-amps no load with an rpm range of 5,000 to 10,000. The dc motors used in radio control racecars and airplanes don’t work very well since they have far and away too much power. In short, they are overkill. They cost more money, require resistive speed control to slow them down and as a result waste a lot of battery power. Ideally you find someone that is running a 6-volt system in a boat similar to yours and be able to duplicate the drive setup. I recommend 6 volt since this gives you the option of running your motors, pump, and radio all off the same source. While this is very efficient in terms of the electrical system’s layout it has the extreme drawback of losing all systems at the same time due to battery failure, lose connection or broken switch. For battleships this is not a great concern since you can pack enough power to run all day, but use a good float charger to top off the batteries before a battle. For small ships this is attractive also to save on weight, but you will have a limited run time and setting a timer to tell you when to head home is a real good idea.
In our hobby you can drive all props on the ship, but not all props must be driven. This means that on a typical warship (if there is such a thing) with four props a skipper might choose to power only two of the four. The performance trade seems to be acceleration vs. maneuverability. Four props accelerate faster, but two props usually turn better (somewhat dependent on the number and location of the rudders). Other advantages of only two props is less space is taken up in the hull and the drive train is more efficient since you have half of the friction losses associated with turning the prop shafts. As for saving space, the need to conserve space in our ships cannot be overemphasized. As for power savings, if one or two motors of a given type have sufficient power to move your ship at the rated speed, but you install four motors anyway and run them lightly loaded you will most likely be wasting a lot of energy. In this case you could save energy by using just one fully loaded motor and a gear drive to power all props. Of course, if you could find 4 smaller motors and if the sum of the power from these motors was the exact amount needed to achieve the rated speed. Then this direct drive system would use less power than a gear drive system due to the lower friction in the system. A few examples of these trade-offs are given in the history of two rc warships below.
A photo of my second ship, the Richelieu, is shown above with 4 drive motors. I was really proud of this accomplishment. All motors fit in line well and the universal joints weren’t really needed since the motors lined up with the prop shafts so well. The ship ran right on rated speed at 12 volts dc at 2.2 amperes of current draw when running four 1.25” props. No speed control devise whatsoever was needed. The installation looked good and ran good and I was insufferably pleased with myself.
Still elated with myself, I bought the cannon and set them into the hull. At this moment reality struck me with a solid blow right up side my swollen head and a cold chill ran down my spine. The cannon wouldn’t fit! After much deliberation, and with as little fanfare as could be arranged I pulled out the 4 motors and installed 2 more powerful motors, driving only the inside 2 props. The motors had to be dramatically offset to allow the cannon to sit between them. The dog bones were at about a 40 degree angle from the prop shaft! But the cannon fit. With some degree of trepidation I put her into the water and made a startling discovery. She once again ran on speed, or ever so slightly under speed at 12 volts dc, but did so with only 1.9 amperes of current draw with 1.5” props. What’s more, the ship turned better than she did before. I loved it! The internal air compressor in my body turned on once again and my head started to swell. I promptly proclaimed the modification as a well-planned engineering masterpiece of power savings and ship outfitting. Life is good.
In another ship I built (I’ve built 7) the hull space was very limited. She was my third ship, the Capitani Romani. Initially I used 2 direct drive motors and tested the boat without any armament to see what was required to achieve her exceptional speed of 40 knots. Lead was laid in her hull to ballast her down to her heavy load waterline. In this case 8.4 volts were needed at 1.1 amps (9.24 watts) to achieve speed. Unfortunately, there was no room remaining for the need armament and CO2 system. To gain about 3 inches of linear hull space I used a gear drive with one larger motor mounted “backwards” over the prop shafts. This allowed all hardware to fit and the ship was armed with 2x2 torpedo tubes and a 2-ounce CO2 cartridge with regulator. This motor and gear drive system required 9.6 volts at 1.2 amps (11.04 watts) to achieve rated speed. Again the increase in power requirement was attributed to the added friction of the gears, but at least now all the equipment would fit!
On final discussion on selecting a drive system. If you can’t find a starting point from the above table then you will want to pick a pair of motors and props and install them. Now it is just a matter of using trial and error to determine what voltage you need. This is easy to do if you plan to use NiMH batteries, in which case you simply add or remove battery cells, which are 1.2 volts each, until the ship runs slightly over speed. If you are using sealed lead acid this is a bit harder since you will be working with either 2v or 6 volt increments. You may also need to use blade angle and prop diameter to fine-tune your speed. When using this method there are two things you need to watch out for that can actually cause ship speed to decrease when more power is applied: motor overload and prop cavitation.
When motor overload occurs adding more power will only cause the motor to overheat more, decreasing the boats speed. To check for motor overload run your ship for 15 minutes. If you see your speed start to decrease bring the ship in immediately you are either running out of battery power or your motors are cooking from an overload (editors note nearly burned up a destroyer once with overloaded motors). When the ship comes in touch the motors if they are hot you are trying to push more water with the size prop then your motor can handle. If you are under speed there is nothing you can do but put in more powerful motors.
Cavitation is the other problem that can cause ship speed to decrease (or remain the same) when power is increased. This condition occurs when the props are spinning too fast and operating very inefficiently, causing a loss of performance. When cavitation is present increasing the voltage will either not effect the ships speed or actually slow it down and decreasing the voltage may speed the ship up. To check for cavitation look for a visible stream of bubbles coming from the shafts. It is common for some cavitation to occur when starting from a dead stop, but no bubbles should be streaming from the props once the ship is at speed. To correct this problem you will need to slow the props down by either reducing voltage or by selecting a lower blade angle on the prop. Once you get cavitation to stop hopefully your ship is at the desired speed. If it is still to slow you will need to add a larger diameter prop
The purpose of the drive trains is to transfer power from the motors to the prop shaft(s) in a reliable, efficient manner. As the above examples show there are several factors one must consider before deciding which drive systems is best for a given ship. These include but are not limited to possible motor locations, motor speed, torque, number of shafts, and reliability. As for driving motors there are really only two methods in rc combat warships. These are direct drive and rpm reduction drive. Reduction drives are either gear or belt and pulley.
4.2 Direct Drive
This is perhaps the easiest and most reliable of the three. There are several advantages to using direct drive. It is very reliable because there are very few places that small wood shavings and combat debris can get in and foul things up. It also allows the motor to be mounted at an angle if you use the universal dog bones. Efficiency is relatively high, but they have the disadvantage of not being able to change the torque or rpm of the prop without swapping out motors.
4.3 Gear Drive
I’ve heard several skippers say, “Wow, my ship was running too fast so I installed a gear reduction and my power draw was cut dramatically! Gear drives really reduce power draw!” While this observation sure would make you think a power savings was the result of the gear drive, the savings was actually the result of slowing the props down and removing the resistive speed control. In this case using smaller motors with the original direct drive would have even greater savings.
Gear drives are perhaps the most tricky to setup if you try to do it yourself. The main problem lies in motor and shaft alignment. Not only do the motors have to be parallel to the shafts, they must also be the proper distance away. If they are too close, the teeth will start to wear and bind the system. If the gears are too far apart, you risk stripping the gears. The alignment problems can be solved if you purchase gear drives already assembled. You also have to worry about getting pieces of wood and other combat debris caught in the gears. However, gears do allow you to “gear up” or “gear down,” whether you need more RPM or more torque. You can also gear two shafts together and have them rotate opposite directions. Remember that when you gear to increase the torque, you will lose RPM and vice versa.
Examples of both are shown in photographs (volume I page 4).
4.4 Belt Drive
Belt drives offer a different set of challenges. They allow you to “gear up” and “gear down” motor speeds like gears, but all the shafts rotate in the same direction. This works well if you want to drive two props off one motor in the same direction. They are susceptible to foreign materials like gears as well. Another problem that crops up is slippage. You need to put a higher tension on the belt to keep it from slipping, but that puts increased stress on the shafts. One way to get around this is to use a belt with teeth on it, but then you need to find matching pulleys.
One word of caution while o-rings are cheap they will only work well for a few hours. They have low tensile strength, which causes them to wear out quickly when stretched around the outside of a pulley.
Step 13: Install Drive Motors.
Once you’ve selected the type of drive system (see later chapter) how do you secure your motor(s) to your hull. The most simple method is to buy a plastic motor mount from BDE or you can build your own with some thin walled PVC tubing that just fits over your selected motor(s)’ diameter. Then cut off a length to match the motor’s length. Then cut off about the top third of the tube and epoxy two lengths of ¼”x ¼” hardwood perpendicular to the bottom of the tube to make legs. The legs serve two purposes first the raise the motor up a little off the bottom and second provide a space to slide two zip ties under the pull the tube tightly around your motor. With the motor strapped in and the legs firmly attached, mix up another batch of epoxy and coat all sides of the legs and set into the desired location in the boat. Hook up the motors to the shaft and hold in place while you test the drive. If it runs quite and the props are turning then everything is lined up correctly and you can let the epoxy set up on the stand. Now when you need to swap out motors just cut the zip ties put in a new one and cinch it back up.
Step 14: Battery Basics - Selecting a Battery That's Right for Your Ship
Since RC combat warships are battery powered selecting batteries for a ship is something all skippers must do. Two different types of batteries are typically used 1) Nickel Cadmium and Nickel Metal Hydroxide (NiCad and NiMH) and 2) Sealed lead acid (SLA). There are also other types of batteries available, but they are more expensive and require specialized chargers so they are rarely used in our hobby.
NiCad/NiMH batteries typically have about twice the power density of a SLA battery, but cost 2 to 4 times as much. NiMH is much better than the old technology (NiCad) that it is replacing. . NiMH is a newer version of NiCad batteries, which not only packs in more power in the same size cell, but also eliminates the need for complete cycling (running the battery till dead). NiMH typically, however, do not support fast charging. NiCad batteries on the other hand support fast charging, but require complete cycling for the maximum service life. Because of the cost NiMH packs are typically used in boats where space and weight are a premium and long run times are not required, i.e. medium cruisers down to destroyers. I recommend buying NiMH over NiCad and both types of cells can be found at reasonable prices from surplus houses or new from internet suppliers such as www.houseofbatteries.com or www.cheapbatteries.com.
As stated above SLA batteries are heavier, but much cheaper than NiMH/NiCad batteries. When you need to pack 14 amp hours of power into a battleship SLA batteries are the only economical choice. Sealed lead acid (SLA) batteries require a slow or moderate charging rate and fast charging can destroy the battery. Therefore you must either size your SLA to last all day or carry a charged set of spares since you will not be able to recharge them quickly enough pond side. SLAs also have a maximum discharge rate limit that is lower than a similarly sized NiMH battery. SLAs can be used for transports, cruisers and battleships, although the cruiser application may be a bit tricky if your weight is at a premium. SLA batteries can be obtained through BDE, surplus houses or online distributors such as www.aventrade.com.
Typically, each of these types of battery requires its own charger and using the wrong charger will reduce battery performance and possibly lessen the life of, or even destroy the battery. Any battery can be destroyed by over charging. There are commercially available chargers for all batteries, but not all battery chargers are created equal.
For NiCad/NiMH a good charger will support a range of voltages automatically, have adjustable current charge rate and a flat-peak voltage detection circuit, which reduces the charge rate to a trickle or stops the charging altogether when the battery is fully charged. Another good feature is a temperature probe that attaches to your pack to ensure you don’t cook the batteries. Moderately priced chargers may support only two voltages at a fixed charge rate with peak voltage detection and trickle charge. Less expensive chargers employ a timer to shut off the charger or reduce the charge rate to a trickle after a preset time. The cheapest just charge at a preset rate until you remember to remove the battery from the charger. I do not recommend this type of charger at all, but if you can’t afford better do not use a charge rating higher than 1/20th of the amp hour rating since most batteries can tolerate this load indefinitely without significant damage to the battery.
For SLA batteries a good charger will support both 6 and 12 volt, have adjustable current charge rate and a peak voltage detection circuit, which reduces the charge rate to a trickle or stops the charging altogether when the battery is fully charged. Moderately priced down to cheap have the same characteristics as those for NiMH above, but typically will have a max of 1 to 2 amp current rating to prevent damage to the battery (you’ll need less than that if sizing the cheap option i.e. 1/20th of the amp hour rating).
How long will a battery power your boat on combat day? At a given load this is determined by the amp hour capacity of the battery. The ampere hour capacity of a battery is defined as the time required to discharge a battery to a specified point on its voltage discharge curve at a rate of 1 ampere per hour. For example, if a NiCad battery pack is rated for 1.2 amp hours it will in theory support a discharge rate of 1 amp for 1.2 hours. However, it will support a discharge rate of 1.2 amps for only about 50 minutes or 2 amps for only about 25 minutes. In other words, the discharge rate is not linear as shown in the discharge curves in figure below.
Extending Battery Capacity
Assuming that your ship can support the added weight, you can extend the amp hour capacity by adding batteries connected in a parallel configuration. To accomplish this the batteries must be of identical voltage and amp hour rating. This is accomplished simply by connecting the positive terminals of each battery together to make one common positive lead and likewise with the negative terminals. This connection scheme will split your boats current draw between the two batteries, which improves your run time by shifting you to a more favorable curve on the discharge chart. From the figure above if you moved from the C/2 curve to the C/4 curve your run time would go from 1.5 hours to about 3.3 hours.
Special care must be taken when charging batteries connected in parallel. Due to differences in internal resistance of the batteries charging in parallel is not recommended. It is almost certain that one battery will achieve its full charge before the other. To charge the batteries they should be disconnected from one another and charged individually, or a special wiring scheme must be implemented.
Words of Caution
No sealed type lead acid batteries will support their rated amp hour capacity continuously. The data sheet for a typical 7 amp hour, 12 volt battery we use clearly states the maximum charge or discharge rate is only 2.5 amps per hour. Charging or discharging at a greater sustained rate will cause internal gassing, which will cause the batter to vent gasses and be destroyed. This venting will cause the electrolyte level to lessen much the same as the battery acid in your car battery gets low sometimes. The difference is that the electrolyte in SLA batteries can not be replaced.
Caution is in order when working with batteries. If a battery vents gasses extreme care must be taken since this liquid is acid that is extremely caustic and will burn skin and clothing. The gas that escapes is hydrogen, which is flammable and explosive. While the previous caution is in order I must also state that I have never seen a SLA battery vent, but then again I have never abused one to this extent either.
I have seen NiCad batteries explode inside a ship on more than one occasion. This has always occurred when overcharging the battery pack. Extreme heat is generated inside the battery when this occurs and usually the resulting explosion is limited to “popping” a hole in the battery case, followed by a hissing sound as battery acid is squirted sometimes up to 20 feet away! This is not particularly destructive to the ship, but it does destroy the battery pack and the batteries remain hot for a long time. If you have this happen exercise caution when cleaning it up as it will burn skin and eat holes through clothes.
Selecting Batteries for Your Ship
With all the above data freshly in mind the next question is how do I go about selecting a set of batteries for my ship? First you must ask yourself if you want a simple system (cheaper, lighter, but a single point failure) or a more complex system (independent systems and hence more survivability, more weight, and more cost).
If you choose the simple system that means you’ll be operating in the 4.8v to 6v range so that you can run your receiver and servos off of the ship’s battery. For this simple system everything will run from the main battery, so if your battery goes dead your pump stops, the receiver quits and the boat stops! For some skippers this is just too scary to even contemplate, but I’ve driven my WWI South Dakota class battleship for two years now with this setup and 14 amp hours of battery power and have never run out of power. Cruisers and smaller will not have the luxury of large power reserves so for this type of system you really need to know the maximum run time before the ship stops dead and set an alarm so you know when you have to return to port.
For the complicated system you will have three batteries; receiver, pump, and motors. Receivers should be run at 6 volts to give the extra speed and power to servos. The pump can be run at 6 volts, but may need a higher voltage to achieve the desired pump rate for large battleships. The drive motors can be any voltage from 6 to 12 depending on the motors, props, and drive system you have selected.
Now on to the business of sizing your power requirements. Below Table 1 is intended to be a helpful guide by giving you some average current draws to expect from your system. You may want to actually measure the current draw for your system UNDERLOAD if you know you need to make the system as light as possible and still meet your desired run time. Most combat skirmishes will only last 30 to 45 minutes before most ships return to port low on gas or pumping hard. A reliable battleship that is spared significant damage could run up to 4 continuous hours on a really good day, but 2 hours would be more typical.
From the above table a fast battleship planning to use a single battery system you would expect a current draw in the neighborhood of 5.4 amps. Now since you’ve got plenty of room and weight you decide 2 hours of continuous run time would be a good starting point. Now you will want to find a representative discharge curve for your battery (see figures above for NiMH and SLA). You’ll probably run a matched pair of batteries so the draw per battery will be about 2.7 amps. So go the SLA chart look up your desired run time (2 hours) and find the value that it intersects the curve. For this example for the SLA to run 2 hours the curve that intersects that value is the C/2.5 curve. To turn this into a battery size you multiply your current draw (2.7) by 2.5 or rounding up 7 amp hours. For a 4 hour runtime the chart reads C/5, which would mean you would need two 15 amp hour (2.7*5) batteries.
Generally, I think its safe to say that more amp hour capacity is better, so if you have to add ballast weight to your ship consider doing so by adding more/larger batteries.
Checking you Juice
To perform a simple test on the performance of your battery(s) you’ll need a volt-ohm meter, an amp meter, and a variable resistor would be nice, but is not absolutely necessary. Also a calculator would be nice unless you really like doing math the old fashioned way, using your head. With these tools measuring the performance of your battery is simple. First, make sure your batteries are fully charged. Then run the motors with the props loaded by putting them in the water and measure the current draw of one of your motors by installing the amp meter in line with the motor. If your boat will fit into a bathtub this will work, otherwise a larger body of water will be needed. If using an amp meter, record this current measurement and multiply by the number of motors in the ship to derive the total current draw of the drive motors. This can also be accomplished with the pump motor while it is actually pumping water at the desired flow rate. Once the actual current draw is known you can then substitute the load of the motors with a load resistor, or just perform the test using the ship in the water. In either case you’ll need to know the actual load on the battery to ensure you’re not overloading the batteries, which means drawing more current from them than they were designed to supply. Now that you have the actual current draw of the load you can proceed with the test.
First use the discharge curve appropriate for your batteries to determine your theoretical run time. Remember that the different curves represent different current draws labeled as C/X where C is the amp hour rating of your battery and X is equal to the amp hour rating of your battery divided by the current draw on that battery. If your draw is 3.5 amps on a 7 amp hour battery then the curve to use would be the C/2 curve.
To test your batteries, simply fully charge them then run the motors under load and time how long it takes the batteries to drop to their rated voltage, or until a significant reduction in running speed of the props is observed.
If your ship won’t fit in the bathtub another method using a load resistor can be used. To calculate the equivalent resistance divide the battery’s full charge voltage by the current draw you measured above the result is the number of ohms of resistance you need to simulate your motors. Make sure the resistor you use can handle the load otherwise it will overheat and burn up. The load capacity of resistors is measured in watts. To determine the wattage of your system multiply your current draw by the voltage of the battery. Once you’ve selected the appropriate resistance just short it across the battery terminals and time how long it takes for the voltage to drop to the rated voltage. This will give you a good indication of your run time. In either case the time should be fairly close to the theoretical run time you extrapolated from the battery’s discharge curve. If there is a significantly shorter run time then it is probably time to replace those worn out batteries.
Step 15: Install Batteries.
You should already have a space laid out in your water channel in which to sit your batteries. You want to keep the weight as low in the hull as possible and to lay large lead acid batteries on their side. The quickest and easiest method is to put some self adhesive Velcro loop strips on the bottom of the battery and the matching Velcro hook strips where you want to attach the batteries. If you left sufficient space to move the batteries fore and aft and a little side to side the Velcro allows for quick changes in battery location and hence the trim of the ship. If the Velcro ever starts to peel off, just use a little CA glue to tack it back onto the battery/ship.
Step 16: Install the CO2 Tank
First do you have the right size of tank? An initial estimate would be 2oz of capacity for every 3” diameter cannon, 4oz of capacity for every 4” diameter cannon, and 6oz capacity for every 5” diameter cannon. This first estimate should completely empty the cannons with enough gas for about another half a magazine load of ammo. This means you do not need to refill the tank between your first and second sortie, just the ammo. Of course the size of the ship may force you into a smaller/lighter tank.
Typically the tank is located near the center of the ship either between or on top of the batteries. The tank should be mounted so the valve end is inclined slightly. This helps to prevent liquid CO2 from getting into the cannon, which could cause a dangerous overpressure condition. The tank must also be on the centerline or it will cause the ship to list as it empties. Install the CO2 tank near the center of the ship. Otherwise as the CO2 is used and the tank gets lighter the ship will take on a bow down or stern down list. Install the tank such that it can be easily removed from the ship for refilling. Removing a dozen screws to fill the tank is a real time waster on battle day.
To build a mounting platform trace the outline of the diameter of the tank on a piece of 1/8 plywood or plastic and draw a line across the middle of the circle. Pick two places where your stand will rest either on top of the batteries or the hull. It is best if they can be attached to the hull. Mark these lengths on either side of the line on your stand pattern. Make the stand as wide as practical and at least as wide as the tank itself. You can get creative and make a chalice type shape for each stand in order to save weight and space for plumbing. Next glue the stands centered on the hull. The stand should not impede the flow of water through your water channel. You can use hooks and rubber bands to secure the tank to you stand. Most tanks with an anti-siphon tube have the tube pointing towards the on/off knob on the valve. So when strapping in the tank make sure the knob is pointing up.
Step 17: Install the Pump
should be placed as far aft in the water channel as possible, but you need enough room to allow you to easily remove the pump for maintenance. Commercial pumps should come with a screen over the pump inlet. The purpose of this screen is to prevent damage to the pump from any items that might get sucked into it. This screen will clog quickly if debris is allowed to get under the pump. My favorite method of installing the pump is to make a rectangular “tube” from some fine screen mesh. The tube should be big enough to slide over the pump and 2” longer than the pump. Then cut four flaps (1/2” deep) on the tube like you would have flaps on a box. Glue the “flaps” of the screen tube onto the bottom of the water channel where you want to place the pump. Now slide the pump down the tube till it rests on the bottom of the water channel. Then use a rubber band to secure the top of the tube to the wires and pump outlet hose. This type of installation should prevent your pump from becoming clogged with combat debris.
Step 18: Install the Electrical Wiring
You will now need to locate two major components of your system the positive/negative power busses and the switch panel. The power busses should be located in the hull somewhere near the batteries amid ships. Ideally you will run all electrical wires on one side of the ship and all CO2 plumbing and servo wires on the other side of the ship. The power buss can be mounted on the ship’s ribs just above the batteries. The switch panel should be located under either quickly removable superstructure or under a hinged deck section. This panel should have room for your switch that will supply battery power to your positive power buss, your CO2 safety switch, your radio and pump switches (optional), and if possible your gun pressure regulators and speed control resistor. That’s a lot of stuff for one panel so your ship may require multiple panels. In that case you want at least the electrical switches and the CO2 safety on the same panel so you can power up and arm the boat quickly.
Like many things, wiring a ship is fairly simple after you have done it once. However, the routing of wiring is another matter altogether. The wiring of some ships looks like a rat’s nest, while the wiring of other ships looks neat and orderly. As long as it works I guess that’s all that really matters, but a new wiring job will certainly make trouble shooting and maintenance a lot easier. Also, a well-laid out wiring system will lessen the potential for electrical interference problems, which can be a nightmare to resolve and often requires adding electronic filters or rewiring to correct the problem.
Always install a fuse near the positive battery terminal. Install one fuse for each battery. The fuses are intended to keep the wiring from melting if an electrical short occurs, not to protect the motors or other hardware. Therefore for a single battery a 5 amp fuse will work well whereas for two batteries in parallel a 3 amp fuse will work well. Slow blow fuses are recommended to handle motor start stop spikes.
Always install a main power interrupt switch in an easily accessible place. By easily accessible I mean that you shouldn’t have to remove screws or nuts to get to it, but the switch must be shielded from cannon fire. I’ve found it’s convenient to group the main power switch, receiver switch and the CO2 (air cannon) safety switch together in a protected area above deck, or below deck under an easily opened hatch.
Avoid “daisy chains,” which means do not run one wire from the battery to the pump motor, to the drive motor, etc. This type of wiring is really hard to trouble shoot and maintain and can be easily overloaded by the sum of the current flowing through it. I once borrowed a battleship from a generous captain when I was getting into the hobby. The wiring was so convoluted that it took two of us a good 1-hour just to figure out where to plug in the main batteries!
If auxiliary electronic items such as a Switch 8 or 16 channel expander are used always connect the ground terminals of all batteries together to form a “common ground” and connect this common ground to the circuit card of the electronics. Installing common ground points is a good idea for any system. Likewise having a common distribution point for the positive leads for all subsystems is also a good idea. If you are running multiple batteries of different types then you will need a positive distribution buss for each type of battery.
Make your subsystems modular and connect them via quick disconnects to the distribution busses. Thus each subsystem can be quickly removed for repair. An rc warship has three electrical subsystems; drive motor speed control, pump, and radio.
When routing the wiring throughout the ship physically separate the antenna, receiver and servo wiring from the pump and drive motor wiring. Run the pump and drive motor supply wires together in a bundle and route them down one side of the hull, twisting the wires together if possible. Run the receiver and servo wires together in a bundle and route them down the opposite side of the hull. This will help to reduce electrical interference. Run the antenna wire outside the ship above deck. Keep the antenna away from electrical wiring for any electric motor.
To minimize electrical interference install a .1 micro-farad capacitor between the leads of the pump motor and each of the drive motors. Install the capacitors very near to the motors keeping the leads as short as possible. Cut of the excess wire leads of the capacitors to prevent a short.
Physically locate the receiver and to the extent possible the servos as far away as possible from the electric motors to minimize interference potential.
Your antenna wire is cut to a particular frequency length for your radio. Do not cut the antenna wire shorter, or lengthen it. Also, do not coil up the antenna wire to make it shorter. Radio interference problems will result.
Keep all wiring as short as possible. If the wires running to your pump and drive motors are 12 inches too long then cut them off. Don’t coil them up. This will help reduce radio interference problems and reduce “clutter” and cramped spaces in your ship.
Methods of Speed Control
Some form of speed control is usually necessary to certify your warship at its rated speed. To accomplish the speed control it is common practice to select a drive system that will get you running (see appropriate section later in this manual for more details) slightly above your rated speed, then provide a means to reduce the speed using a speed control apparatus. Once the ship speed is nearly correct, slowing down the ship to critical certification speed using a speed control apparatus may be accomplished in several ways. Perhaps the most common method of obtaining the required speed is to install an adjustable resistor with a rating of about 3 to 10 ohms at 25 watts power dissipation in line with the motor(s). This method is inexpensive, simple, reliable and effective. Ship speed is reduced by increasing the resistance thereby dropping the voltage across the motor(s). This generates heat so mount the resistor well away from any parts that will melt or burn, to include the PVC cannon, electrical wiring, electronic components, and plastic blast shields or wood. If you were able to get close to your desired speed through drive train adjustments the amount of heat generated will be minimal. There is a minor down side to this method of speed control in that as the battery discharges the voltage will drop and the ship will slow down below rated speed, but so will most of the other ships you are competing against so the loss of the performance is somewhat negated.
If you want to eliminate this problem an electronic regulated speed control is required. These devices work well and maintain the voltage at the set point as the battery discharges. However, they are expensive and fragile, being easily destroyed by static electricity during handling, water immersion, or by an improperly wired motor circuit. I used to use these devices in all my ships, but after I replaced the 5th or 6th one of them I quit buying them and went to alternate methods. If you decide to pursue this method be sure you buy a regulated electronic speed control. An electronic control that does not claim to be regulated may allow your set speed to drop as your power supply voltage drops. Also make sure you get one with reverse, most do not have this feature since they are designed for airplanes! Generally, I do not recommend these devises. In my opinion the cost and sensitivity to damage outweigh any benefit.
A crude method of speed control entails tweaking your props. You must be very close to your desired speed before you can use this method since only minor speed changes will be possible. The first and easiest is to turn on your props and use either some sand paper or a metal file to grind down the diameter of the prop. Try to keep the amount of sanding you do on both props equal. I recommend about 10 seconds of grinding with a course metal file then drop the boat in the pond and check your speed again. You can also use pliers to slightly twist the prop blades so that you reduce their angle. This is harder to achieve uniform results though and you can crack the solder joint on the prop, which is very hard to repair without a jig. I used the sanding method to grind down the props on the USS Indiana from the standard 1” four bladed to ¾” bladed props. She was still running just a bit fast at this point so I gave up and installed an inline resistor because the props were getting ridiculously small.
Wiring Diagram for a Simple Three Speed Control (Forward, Off, and Reverse)
Now that you have the motors and props installed you’ll need some means to turn the motors forward, off, and reverse. If you choose to use an electronic speed control unit with reverse then this is already taken care of. However, if you were lucky enough to tweak your drive train to the desired speed or opted for an inline resistor you will need to install motor power and reversing switches. Double pole, double throw micro switches are most commonly used and these are available at Radio Shack or about any electronic store. Simply attach the switches to the side of a servo (or to a servo mount, editors preference) with CA glue and modify a standard servo control disk into a half circle as shown in figure above. The key is to set up the servo so the half circle operates as follows. When the servo is centered neither of the switches are touched by the half circle so that they both are in the normally open position (NO). This is the off position. Then when rotated one direction only one switch is depressed (forward) and when rotated the other direction the other switch is depressed (reverse). NEVER, NEVER, depress both switches at the same time as this will short the power supply and burn up your wiring. Which switch is forward and which is reverse will depend on the rotation of the motor and the prop blade angle (left or right hand) when power is applied. It really does not matter as long as your transmitter has the servo reversing feature.
The switches must then be electrically wired as shown in figure above. There will be 3 contacts on each switch. These will be labeled (NO), (NC) and (C). First, connect the (NO) terminals of each switch together, then connect the (NC) terminals of each switch together. Run one wire from the connected (NO) terminals to your positive power distribution bus (remember think modular). If you did plan to use an inline adjustable resistor then connect the positive line to the sliding brush of the resistor. Then connect one fixed end of the resistor to the positive distribution bus. Next run another wire from the connected (NC) terminals to the negative distribution bus. Then run a wire from one of the (C) terminals to one side of the motor. Finally run a wire from the other (C) terminal to the other side of the motor. If more than one motor is used, observe the polarity of the terminals of the first motor and connect the terminals of this motor to the opposite polarity terminals of the second motor. This will counter rotate the motors, which when used with a left and right handed props will eliminate drive torque from your ship.
Wiring a Pump
Your pump system will consist of the following components a power source, a switch (optional), a variable resistor (optional), and the pump. Your power source will either be a dedicated battery (sized appropriately) or the main power bus of the ship. If you chose to connect your pump to the main power bus of the ship and you have plenty of amp hours aboard I would recommend the following setup. First skip using a switch and run the pump continuously. I know of at least three ships that sank because the skipper forgot to turn the pump on until it was too late. Pumps draw little power when they are running dry and a centrifugal pump (BDE’s is this type) can run dry indefinitely. The next thing to consider will be how you will adjust the flow rate of the pump to meet your ship’s requirement as set by your clubs rules. There are two methods to do this the first is to restrict the outlet area of the pump, but this can cause excessive back pressure. The other method is to drop the voltage to slow the pump down, you must be careful not to drop the voltage too low or the pump may fail to prime. Often a combination of both is best therefore I suggest installing an adjustable resistor into your pumps wiring circuit. First run a wire from the positive distribution buss to a fixed end of the adjustable resistor. Then run a wire from the adjustable brush to the positive terminal of the pump. Your pump will typically only prime in one direction and running it backwards is not recommended. Finally connect the negative terminal of the pump to the negative distribution buss.
If you chose to use an independent power supply you will need to set it up as follows. Starting from the positive terminal of the battery connect a line to an inline fuse holder containing a 2 amp slow blow fuse. Next run a line from the other end of the fuse holder to a double throw single pole switch. Note you can either mount this switch on your main switch panel (recommended) or use a servo to actuate it (use only if power is limited or your pump can not run dry for long periods of time). The normally open side of the switch should be connected to the positive terminal of your charge connector this will allow you to charge your pump battery without removing it from the ship. The negative terminal of your charge connector should be connected to the negative terminal of the battery. Next connect the normally closed side of the switch to the variable resistor then to the positive terminal of the pump as described above. Finally close the circuit by connecting the negative terminal of the pump to the negative terminal of the battery.
Step 19: Install the CO2 Plumbing
Hopefully you were able to install a panel big enough to hold all of your electrical and CO2 switches and pressure/power regulators. If not find an easily accessible space in your hull to install another panel for your CO2 controls.
Next select a location for your firing valves and their servo(s). Remember to make servos easily removable from the ship and mount them as high in the hull as possible. Ideally you will build a servo mount that holds your firing valves in place as well so that a servos can be quickly swapped in and out without having to remove or disconnect any of your plumbing.
A later chapter in this book discusses various plumbing layouts and includes diagrams. Refer to this section when connecting the various components.
Other general advise would be to avoid excessive lengths of tubing and put all CO2 plumbing on one side of the ship and zip tie it together in bundles.
There are 5 colors of tubing generally available for CO2. I recommend color coding your firing valve plumbing different from your gun accumulator plumbing and bow different from stern. This will aid when trouble shooting any malfunctions.
Use either thread compound or pipe tape on all screw connections even if they have washers. Use the appropriate hose clamps over all hose/hose barb connections.
A mixture of dish soap and water brushed over your connections will quickly isolate any leaks that you may have.
2.5.10 Install the Hardware for Removable Deck Sections
Now that you have located all items which need to have easy access you can go about installing hardware to make these sections of the deck easily removable. For the large section over your batteries and CO2 bottle I recommend placing your piece of deck in place over these items and clamp into place. Then drill a 1/8” hole at the four corners of the. Drill all the way through the middle of your caprail. You’ll want to make sure when you drill that you are between ribs, move your hole location if you are not. With the holes drilled take a 5/8” long #6 machine screw and put a small dab of CA glue on it and screw it into the caprail from the BOTTOM side of the caprail so that you have the threaded end sticking up through the caprail. Your deck will slip over these threaded studs and you can use either wing nuts or thumb nuts to batten down the deck. The reason you want to screw this down is so your batteries and tank don’t fall out if the boat gets sunk.
For the sections of deck over your electrical/CO2 switch panels I recommend either a removable section of super structure or a hinged deck depending on where the panel is located. Superstructure can be made removable by clamping it to the main deck and drilling a hole 5/8” deep from the bottom of the deck up into the superstructure at the four corners of the removable section. Use a drop of CA and machine screws as above to create studs in your deck, but in this case you will just sit the superstructure down on the threaded screws. If you would like to use this piece of superstructure to double as your float use 1/8” pieces of brass rod instead of #6 screws so the superstructure section will slip off easily enough that it will come lose during a sink. For hinged decks you can use a piece of anchor chain if the panel is located in the bow and the plans show anchor chain in the area of the hinge. This makes for a decorative and functional hinge.
Step 20: Install the Hull Skin
To sheet the hull, install the sheeting in sections 8 to 16 inches wide for the bow and stern. The middle section can usually be done in one piece, but it can be cut in two if necessary. The end joint always occurs on a rib center and the grain of the wood should run fore to aft, horizontal. As you install the sections from the stern forward use a permanent marker to mark the caprail where each section starts and ends. This makes removing damaged panels easier for repair. Now lay a new sheet of balsa over the hull and cut it to fit the shape of the hull as shown in figures xx and xx. This may take several tries to get a good fit, so cut the new skin a little wide the first time. Once you have the sheet trimmed to fit well at the top and bottom, cut it for length such that it ends at the center point of a rib. When this is accomplished submerge the balsa in warm water for 5 minutes (usually only necessary for bow and stern sections). Remove it and wipe it off. Then spray the inside of the balsa section with CA acellerant. Next coat each rib and the top and bottom of the hull edges the balsa will contact with thick CA glue. Now carefully set the hull section in place and press it against the hull until the glue sets. This will happen very quickly. If there are any gaps or voids along the seams apply another bead of CA glue then spray with acellerant. You don’t need to fill the gap completely just make sure its sealed. Once the section is installed proceed onward with the covering process until the entire hull is re-skinned. I usually work from the stern (most difficult) forward to the bow.
Once all the hull skin is installed trim off any balsa that protrudes out too far and sand the seams until smooth. Next, use automotive putty to fill in any holes or gaps in the seams. This gives a smooth appearance to the hull and helps to prevent water leaks. When the filler dries, sand the hull until smooth. Figure xx shows applying the filler while Figure xx shows the hull before final sanding.
Step 21: Apply Silkspan and Paint
Silk span provides several desirable functions to our warships. It provides a smooth surface and hides all wood grain. It adds a small amount of strength to the wood and helps to prevent cracking and splintering. But most important, it seals seams in the wood paneling and seals potential leaks very well if applied properly.
When applying silk span it is best to use only model dope as the paint and sealer. For some unknown reason dope has proven to work best to adhere silk span to balsa.
First, sand your hull lightly after filling any voids with automotive putty, then wipe off all dust with a damp cloth. Next apply a coat of dope sanding sealer to the entire wood surface. Next, cut the silk span into sections that are a size easy to work with. The size isn’t all that important. Now prepare your tools.
You will need a water spray bottle or a bowl of water and two towels, a few bottles clear dope, a paintbrush, and rubber gloves.
Spray a precut section of silk span with the spray bottle of water, or dip it in the bowl of water then lay it on the towel and blot away excess water. Apply dope only to the hull area where the damp silk span will be applied then lay the damp silk span over the wet dope. Allow the silk span to overlap the cap rail and at least an inch around the bottom of the penetrable area. The excess over the caprail will be cut off when the dope dries. Now apply a coat of dope over the silk span and work out all air pockets with the paintbrush, or your fingers. This is where the rubber gloves come in handy.
Now repeat the procedure overlapping all silk span sections about ¼” or so. Take care to cut the sections into the proper size and make the overlapped area uniform so the finished job will look neat. Use an exacto knife or razor blade to cut away any silk span that is hanging over the top of the hull (caprail), but wait till the dope dries and the job will be easier.
Some areas with a curve or sloping area, such as the bow or stern can be a bit tricky to cover without air pockets forming under the silk span. If you find and air pocket just apply more dope and rub your finger over the area slowly and gently. Continue this until the silk span stretches to conform to the sloped area. It may take several tries, but keep working at it and keep the silk span damp with dope while working it.
Some skippers prefer to have the silk span on the inside surfaces of their hull, thinking that this works better to prevent splintering. If you want to try this approach just silk span your balsa sheets before you sheet your hull, then install the sheeting with the silk span inside. You will probably still need to apply sections of silk span to the outside of the hull to cover all seams in the balsa to control leaks. I have tried both methods, inside and out, and I see little difference in performance. I just apply the silk span to the outside of my ships.
Silk span is available in three thicknesses. Remember that our rules specify the usage of lightest weight silk span. This stuff is hard to work with without tearing it or getting wrinkles. Life is rough sometimes. Be careful when applying wet silk span, as it is more likely to tear. This is easier said than done. If a tear occurs it’s really no big deal. Just apply some dope to the torn area and work in with your finger. The tear will barely be visible and won’t effect the strength or performance much at all so long as it’s not right on a seam in the balsa sheeting. If so, just apply a small silk span patch over the tear. In all likelihood you’ll have quite a lot of similar looking patches after your first combat sortie anyway.
Step 22: If You Have Room for a Watertight Box or Tube Install It Now
My favorite boxes are O-ring sealed PVC project boxes that can be purchased in various sizes from an electronic supply catalog, some even come with clear lids. Using micro servos a 3.5” x 3” x 2” box can hold three servos and the receiver. You can even attach the firing valves through the wall of the box as well as your power leads for the motors. The best way to keep the box water tight is to pass all electrical connections through the wall of the box via a screw and bolt, since wires are hard to seal around and water can leak down the inside of the wire as well. The key to making this easy on yourself is to remember that you only need two terminals for receiver power, one terminal per radio channel located outside of the box and a pair of power leads for the input and output of your speed control if you locate it inside your box. Also you can save space inside your box by removing the receiver board from its box and placing only the board inside your watertight box.
At this point your ship will be running out of real estate quickly. If you have a large open space you can follow the guidance in the radio section of this manual to construct a water-resistant box. To mount your box I recommend the use of Velcro to attach the box to the bottom of the boat.
Step 23: Mount All Radio Control Gear
If you have the luxury of a water-resistant box you’ll want to stuff as many servos into it as will fit. For those servos outside of your box you’ll want to mount them as high in the hull as possible and upside down if possible. This will give them the most protection from water at least until the ship goes under. A good mounting device is to cut an “H” shaped piece of ¼” plywood or plastic with the space between the “legs” of the “H” wide enough to fit a servo. Put the servo in one side and use the other “legs” to screw onto the caprail.
Step 24: Install Recovery Line
First look for an open spot in your ship near either the bow or stern. Ideally you will be able to place your float on the same end of the boat as your power and CO2 switches. Now you need to secure your line to the boat. If you have a good solid section of caprail to tie to use that or you’ll need to epoxy in a loop of 8 guage solid copper wire into the bottom of your boat to tie to.
Next cut a length of recovery line at least 5’ longer than the known maximum depth of the pond. Don’t count on being able to get close to shore before sinking. Boats often go down in the deepest part of the pond. I use braided nylon string with a 150+ pound test. Make sure the weight of your recovery line is not more than your float will be able to pull to the surface. If your not sure bundle your line so it is just hanging from your float then put it in a bucket. If it pulls the float under you need a bigger float.
Next you will need to make a float. I prefer cutting a large block of balsa (1”x1”x3”) and gluing it to the bottom of a piece of unsecured decking. The balsa block should help keep the deck/float from being blow or shot loose of the ship prematurely, while being able to float free of the hull. Make sure that cannon barrels or other superstructure will not block or entangle the float as it deploys. Secure your recovery line to the float with either an eyelet screw or by drilling a hole through the balsa block. Coat all knots with CA glue so the line does not untie itself. Paint the float so it doesn’t get waterlogged.
You’ll want to get a paint can cap or some other plastic cup to glue to the bottom of your hull to coil your recovery line into. Start with the boat end of the string and carefully coil it into the cup. A tangled recovery line will prevent your float from reaching the surface.
Your boat will not weigh more than it was floating until you try and pull it out of the water. A battleship can hold a good 100 pounds of water so once you pull the ship to the surface grab hold of the hull, shut down the electrical and CO2 systems and to pull the ship into the recovery boat.
Step 25: Conduct Initial Sea Trials Ship Stability
our models exhibit a variety of symptoms indicating some degree of instability. This varies from the barely noticeable to the outright thrashing that would beat do death any humans on a real ship like that. Not only can it look silly, but more importantly, it’s a potential safety problem because of cannon “elevation” during the moments of roll-over. So is there one off-the-shelf solution to this problem? To some degree, yes. There are formulas and rules-of-thumb all over the place – mostly about real ships – not too much about models. And absolutely nothing but speculation when it comes to R/C Combat models. R/C combat models are unique in the ship-modeling world because most of their ballast is functional and bulky, unlike the little slabs of lead that can be neatly tucked into the “perfect” lowest places on a non-combat hull. So we have two problems: 1) how to stabilize a model’s hull in general and 2) how to stabilize a hull full of; tall bottles, gun systems, batteries and radio boxes. The first step towards solving this problem is getting some insight on what actually happens to a hull when it heels over.
All hulls have a Center of Buoyancy (CoB) and a Center of Gravity (CG). The CoB is mainly related to the hull shape, whereas the CG is related to where the weight is placed in the hull. The higher the CG is above the COB, the less stable the hull. No matter how you move the hull, the CG is always in the same place (assuming no equipment shifts). However, the CoB moves when the hull rolls over because the hull shape in not symmetrical (a floating cylinder would be symmetric). See Figure 1 by the way, what is buoyancy? Well basically, the weight of your model hull is pushing a hole into the water and gravity is screaming at the water to fill it back up again. So the water’s weight is pushing in from the sides and up from the bottom, trying for all the world to pop your boat out of the water like a nasty zit. There’s more to it than that, but hey, we’re trying to keep this non-technical.
Okay, back to more technical mumbo-jumbo. A ship’s hull has a point called the Metacenter (M) and a measurement called the Metacentric height (GM) that is used to define the relative stability of a hull. See figure 3. Take a minute to look up “metacenter” in whatever references you’ve got at home. As you can see, the CoB moves away from the CG when the hull tilts over. This is the main reason that the hull will right itself. The CoB is the center of the upward force floating your boat. As long as this point is further away from the CG, the hull will right itself. Generally speaking, the CoB will shift less with narrow, round bilge hulls than it will with wide, flat-bottomed hulls. The CoB shift in a wide flat bottomed hull can compensate for a much higher center of gravity- that’s why big battleship models are generally more stable than little CLs or DDs. As long as the CG stays between the hull centerline and the CoB, gravity and the upward force at the new CoB will cause it to right itself when the force(s) causing it to roll subside.
Forces that cause a hull to roll are 1) wave action, 2) centrifugal force while turning, 3) temporary weight shift due to rotation of unbalanced turret, 4) weight changes due to depletion of ammo and gas, 5) the wind, and 6) prop and rudder torque. Suffice it to say, when some force wants to roll your hull over, you want the hull to resist and come back to upright without delay.
A hull will capsize when the CG moves further out towards the low beam than does the CoB. See figure 4. Once a hull is able to sit upright in the water and resist forces that want to heel it over, another problem may come up, oscillation, or the pendulum effect. The hull gets pushed over, the shifted CoB pushes it back too far, causing it to start rocking back and forth like one of those inflatable punching bags. Damping this effect is important unless you like your model to rock like a cradle. This happens when the CG is extremely low and all the mass is on the centerline and the beam is small compared to the draught and there is nothing on the submerged outer hull to help brake this problem.
2.6.2 The Solution
Ironically, the answer to some of these problems will seem contrary to common sense, but trust me, I’m old. Obviously, get all the weight as low as possible in the hull. This includes your construction techniques, as well as the placement of your equipment.
Building a strong frame is a given, but starting with the deck, build LIGHT. 1/8” decks are very sturdy, but on smaller models, they are the beginning of top-heaviness. Consider using 1/16” on cruisers and 1/32” on destroyers.
Ultra lightweight super-structure is a bit of a pain, but any mass up there is potentially destabilizing. Beside reducing highly placed weight, whatever you save by building light can be put back where you need it to increase stability. My personal rule is to never use plywood, hardwood, or plastic in the superstructure. Editors note: the above section on superstructure recommends the use of hollowed out foam and thin lexan for superstructure. This should meet the stability requirements, but you may need to look at how thick the upper lexan decks are and you may need to “hollow” out the plastic decks as well to further reduce weight.
Believe it or not, paint is heavy, particularly the sandable primers. Although it hardly matters on a battleship, too much paint on a destroyer’s superstructure can contribute to a problem. By the way, clear paints are the lightest.
Once the ship sits upright in the water, tip it over 30 degrees and watch it right itself. It should come back quickly with little or no rocking. If it rocks more than twice, you need to dampen that effect. Remember all that weight you saved in construction? Well now you can use a small amount of that to dampen the oscillation. See figure 6.
Last, but not by any means least, make sure everything is BOLTED DOWN, as in secure, fixed, etc. Anything that can shift will, upsetting the stability you have worked so hard to achieve. In small models the location of everything must be precisely repeatable. Your method of strapping things down must also position them precisely so that when you remove that CO2 bottle and battery pack and put them back in the boat the boat will not take on a list.
To deal with roll oscillation the use of bilge keels to dampen (slow down) roll oscillations by friction with the water. These are not too effective on our models because of their small size, but they are however, an excellent place to add more of that weight you saved! Ron K and I stabilized his LeTerrible destroyer by shaving 3 oz off the top and putting it back on the bilge keels with metal-filled epoxy. By placing these weights far from the ships CG you increase the roll moment of inertia which will also tend to dampen roll oscillations. Another technique is to place a very small weight at the top of the tallest mast. While this will raise the CG a little it will increase the roll inertia significantly.
Most of us don’t experience prop torque problems because we use multiple counter rotating shafts, but rudder torque is a common problem for small models. Every time these models turn the rudder rolls the model into the turn (way too much) and then thrashes back the other way so much that a roll oscillation is started. There are too methods to reduce rudder roll. First reduce the distance between the center of the rudder plate and the ships CG. This can be done by lowering the ship’s CG or by cutting off an 1/8” from the bottom edge of the rudder. Rudder induced roll and also be reduced by increasing the rolling inertial as mentioned above. See figure 7.
If you’ve tried all of these suggestions and your ship is still unstable there is two tricks left that will require a waiver from your club so please try all the solutions above before you try these. The first trick is to add buoyancy where your keels are. This will raise your ship a little in the water, but more importantly change the way the CoB moves as the ship rolls so that it develops more restoring force. The extra buoyancy can be achieved with either oversized balsa bilge keels or by placing an air filled tube under the bilge keels. This extra displacement will also allow you to place more weight on the bottom of the hull. The second trick is very radical and involves suspending a flat weighted plate several inches below the hull on a pair of metal rods. The plate should be horizontal not vertical. A horizontal plate will not improve your turning ability where a vertical plate could.
In conclusion, model ship stability is not a result of only one factor, but several: 1) CG height, 2) CoB location/shift, 3) hull shape, and 4) shifting weight. No matter how the components are arranged in you ship, it cannot capsize as long as the CG does not cross over the CoB when the model heels over. If your model wants to roll over, then your CG is too high for that particular hull, or something heavy is moving around. If you can't reposition weight your equipment in the hull, then you need to reduce top weight (superstructure, deck, etc.) and put that weight back on in the hull bottom – that’s why the rules allow a lead strip to be attached to the outside bottom hull of small vessels.
Step 26: Build Deck and Superstructure
When building superstructure think light. I recommend using closed cell gasket foam, “Crosslink” is a brand name, for your levels of superstructure. This can be found at an industrial gasket supply store or BDE. For your main deck that will be screwed to the caprail I recommend either 1/8” thick foamed PVC. For your decking I recommend using thin Lexan (.04 to .06). These can be obtained from an industrial plastic supply store or BDE. You’ll need to create patterns for your superstructure as a first step. Look carefully at the side and overhead views of your ship and any cutaways or superstructure drawings it has. You should isolate the outlines of each level of superstructure and the deck that goes underneath it and trace it onto separate sheets of paper.
For wide and long sections of superstructure levels/decks you do not need to cut a solid layer, but can cut a hollowed out superstructure. Your levels do not need to be more than 1.5” deep from the sides, but make sure before you cut out the center that the next layer of superstructure will cover the hole with significant overlap (1”). You will find from the side view that the height of most superstructure layers will be either .75” or 1.5” with the occasional ½” or 1” tall sections.
To assemble the superstructure you simply glue the first level to the main deck. Then the second level deck on top of the first level. Then the second level onto the second level deck, etc. until you run out of layers for your “cake”. For “frosting” I recommend using a silicon adhesive such as plumber’s or marine goop to glue your layers and decks together.
When building masts use either wood dowel rod or brass tubing.
Step 27: Back to the Pond for the Final Check Out
Runner Up in the
Make It Real Challenge
Second Prize in the
Remote Control Challenge
Participated in the