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R/C Sailboat Answered

I want to make a R/C sailboat, so far I have 4x32x1/4 inch balsa wood planks and they should last me the entire project. This weekend I'm going to visit a hobby store and get: waterproof wood glue, waterproofer for the wood. Then go to target and get a rotary tool. The boat will be 3 inches tall with a 1 inch keel (keeps the boat from tipping) 5 inches wide and 15 inches tall. I will get a cheap multi directional R/C car and use the steering mechanism to move the rudder and the drive motor to turn the sail. Once I make the boat I'll fill the gaps with wood paste and water proof everything hopefuly with a silicon based sealant. Any tips or flaws with my plans, please see the attached sketch.


Is there a particular reason that you are not basing your boat on existing plans? It would make life easier for you to follow a plan - there must be plenty of free plans floating about the Internet.


Pat. Pending


10 years ago

Well I reshaped the hull and keel today also designed a better rudder attachment. I'll start the actual cutting and gluing tomorrow. None of the wood glue at home depot was water-proof below the water line so I decided on getting a bottle of Gorilla Glue. Then I found a nice sized bottle of Thompson water sealer and it promises to make everything waterproof, oh plus its aerosol.


. What is the foot on the bottom of the keel for? Ballast? Looks? Seems to me it's just more drag. . Unless you need it for ballast, I'd get rid of the foot and then round the bottom front corner of the keel/centerboard a little bit (all to reduce drag).

Yeah thats for ballast the boat is half done and is very light plus its going to be top heavy because of the sail. Any Idea how to figure out how large each triangle has to be for the front of the sailboat, I know its geometry but I cant think of what to do. I started building the boat over the weekend, the most time consuming part was cutting out the jig it sits on. I used Gorilla glue which is really light and strong plus it expands when it dries so I

Hull 003.jpgHull 002.jpgHull 001.jpgHull 004.jpg

There are fairly well established techniques for 'developing' the lines of a boat (search for 'lofting' and 'lining off') but yours doesn't have any curved lines, so simple geometry will do.

Based on your drawing, you can easily find the 3D coordinates (height, width, length) for each point of the triangles. Now simply use the 3D distance formula:

D = sqr root( (x1-x2)2 + (y1-y2)2 + (z1-z2)2 )

Find the length of all three sides (of each triangle.) You now have the exact dimensions of your section.

Draw one side of the triangle, and use a compass set to the length of the 2nd and 3rd sides--draw each one from the endpoints of the first side. The arcs cross at the third point ...

I finished Geometry last year I don't really know how to apply the 3 dimension. I think I might me able to do this though. I'll get back to you

I'll do just one side of one triangle, to get you started (although I'm pretty sure you can figure this out yourself....)

x -- width (from center)
y -- height (from baseline)
z -- length (along baseline from bow)
(these are arbitrary, whatever dimension convention you choose, be consistent.)

point defined as -- pX(x, y, z)

For the garboard (lowest plank) triangle section of the bow, the bow stem length (the stem is the front of the boat that 'cuts' into the water):

p1 (0.0, 3.0, 0.0) (foremost point at bow--all the bow triangles will share this point)
p2 (0.0, 0.0, 3.5) (low point of the stem)
p3 (1.0, 0.5, 3.5) (the point off the center)

Distance(p1, p2) = ~4.60977 = sqr root( (0.0 - 0.0)2 + (3.0 - 0.0)2 + (0.0 - 3.5)2) )

Oh, yeah--only three triangles need to be developed, since the other side is identical...

(For the lining off techniques I mentioned, you'd need to change your drawing somewhat. With the distance formula, you can use your existing drawing.)

> Any Idea how to figure out how large each triangle has to be for the front of the sailboat, I know its geometry but I cant think of what to do.
. Hmmmmm. Not sure. Looks to me like it half-a-cone, so I think you can use the same formulas that welders use to build "cones" from pieces of plate. Pyramid calcs might work. A 3-D modeling program might help (check http://www.sourceforge.net/).

The stearing mechanism is called a servo (FYI), and when your sail is movable, you usually don.t have a rudder, just a keel. Once you make it, attach it to the end of a fishing pole for your first couple voyages, I'd hate to see your handiwork float away. Yay! I fullfilled my role as a Volunteer! WHOOOOOO!!!

Oh yes I'd deffinity attach it to a fishing line, but not a pole. All yachts have a rudder and a movable sail.

Correct yachets do but most models don't. There's bunch of guys who sail there boats at our park's pond every Saturday, and whatched them a few times, there pretty cool. RC cars don't usually have rack-and-pinion steering. They use a servo[] witch has a little arm hing that goes back and forth. If you use string to rig all of this up correctly, you will be able to make both the sail and rudder turn.

Most of the cars I've seen have rack and pinion. If I hook up the sail to the rudder mechanically then I can adjust the sail to the wind, decreasing its speed and it can tip over that way.

Make sure the motor that moves the sail is reversible (bi-directional). I know many R/C cars can back up, but some do not. The only other problem I see (and it is only a potential one) is over-steering the rudder if the sail is not synchronized with it (or vice versa).

Yes of course I'd get a multidirectional R/C car, and yes over steering could be a problem.

Ok, I wasn't trying to be a nit-picker, just checking :-)

yeah thats fine thanks for looking out

. It depends on your sail height/area, ballast, draft, &c;, but I'm guessing a 1" keel will be too short. I've never seen a formula for calculating keel depth, but most sailboats I've seen look like the keel/centerboard is about 1/3 to 1/2 the mast height. . I don't know enough about R/C gear to really tell what's going on with the steering, but something doesn't look right to me. Can't put my finger on it. . Any part of the rudder that is above water or blocked by the hull is wasted. It may help to move the rudder down a little bit. . . If the steering works, what you have should be good enough for a proof-of-concept run. You can always add to the keel or adjust the rudder, later (if even needed, I'm no boat designer). . . Good luck and keep us posted.

I'll keep the keel about 2- 2.5 inches that way I can always take off its much easier that way. I realize that part of the rudder would be wasted but its easier to keep it in one solid piece, I'd rather keep the rudder high because the little struts will be more then high enough above water.

Oh and I'll make this and iBle but post pictures of it during the process, I'll start this weekend. I also though about cutting out some plyboard in the shape of the outer hull that way I can just set the boards together and glue. No clamps nessesary.