Stitch and Glue Boat Construction

Intro: Stitch and Glue Boat Construction

The "Stitch and Glue" method of boat construction is one of the most popular methods of plywood boat construction today. It allows for easy test fits, fast assembly, and simple fixes. I recently modified the Mini-Cup Sailboat plans, normally calling for assembly with wooden stringers, to stitch and glue.

I apologize for the lack of some crucial photos, as once the process is started and the gloves are on, the epoxy usually gets everywhere so I try to limit my camera's exposure to it.

STEP 1: Tools and Materials

Tools:

• 
  Epoxy brush
  
• 
  Sharp scissors
  
• 
  Saw
  
• 
  Drill
  
• 
  Drillbits
  
• 
  Latex gloves
  
• 
  Plastic scraper
  

Materials:

• 
  Epoxy resin (marine-grade)
  
• 
  Zip/cable/wire-ties
  
• 
  Fiberglass tape (11.1 Oz best for structural, bi-directional not necessary)
  

Most of these materials can be purchased at a marine supply store.

STEP 2: Cut It Out

First you need to have your parts to be stitched and glued cut out. For my boat's 1/4 inch plywood hull, I used a Jigsaw to cut out the pieces I had lofted from the plans.



If your pieces are joined at odd angles, you can choose to cut the pieces out at an angle, or just use a file to shape it later.

STEP 3: Drill Some Holes

Depending on the amount of curve in the pieces you're stitching, drill holes that will accommodate your Zip-ties anywhere from 3" apart to 6" apart, about 1/4" to 1/2" in from one of the piece's edges to be joined. This definitely does not have to be exact.



Now mock up the two edges to be joined, the one with holes in it and the one without. Try to clamp it as best you can for at least a few feet, especially if it's curved. Then, drill holes in the untouched piece that line up with the holes in the other piece. Again, this really does not have to be exact.

STEP 4: Tie It Up

Now start loosely attaching Zip ties through every set of holes. Start tightening them evenly from the middle outwards, until you have it exactly how you'd like it to stay, forever.

You should consider which side of the joint the locking part will be on. If you can access both sides when everything's in place, make the locks on the part that will not be taped, so you can take them off later.



Note about alternate "stitch" methods:

Though traditionally the stitch in stitch and glue has been copper wire, I find cable ties to be better for a few reasons. Mainly, they are easier to tighten and remove (in some instances), and they have a safety feature integrated into them in the sense that they usually break before the wood breaks in the event of over-tightening. However, it should be noted that the advantages of copper wire are that it can be completely removed from epoxy if already covered in it by simply heating it up and pulling it out, and also wire is stronger and normally skinnier than cable ties, which allows for a closer bond, which is especially helpful in tight curves, and a smaller hole drilled into the hull. Copper wire has to usually be cut to length as well, whereas cable ties are pre-cut, and have to be tightened either painfully by hand or with a pliers which can be cumbersome.

STEP 5: Joint Specific Instructions

There are a few things you need to worry about if you're gluing an "inside" edge, where the tape will be folded inwards. In order to have a strong bond, you need to create a rounded epoxy fillet to fill the corner. Thicken some epoxy to the consistency of peanut butter, and apply the rounded fillet using a popsicle stick evenly throughout the joint. You can leave the ties in, as long as the locking part is on the outside, where it can be removed later.



If you have to glue on the same side that the locking part of the tie is on, then apply "welds" of rounded, thickended epoxy in between the ties, let it dry, remove the ties, and then fill in the gaps with rounded fillets. Be sure to sand the epoxy before you apply the tape if it has dried.



If you're working on an "outside" edge, and you have access to the inside, then go through with the same rounded fillet of epoxy on the inside, and just go over the ties. Once it's dry, you can remove the bulky locking portions on the outside, and continue.



If you're working on an outside edge and do not have access to the inside, then you're in a sticky situation. Your best bet is to space the edges using 1/4 or 1/8 inch dowel inside the loops of cable tie, so that you can then apply thickened epoxy inside of the joint as "welds" in between the ties. Once it dries, remove the ties, fill in the rest of the joint with thickened epoxy, and continue.



Note that before thickened epoxy is ever applied, you should first "wet out" the surface with epoxy by coating the area in unthickened epoxy. Use your epoxy brush to evenly coat the surface, and don't worry about getting it on the cable-ties.

STEP 6: Start Taping

After you've got your joint somewhat solidified with a weld of thickened epoxy, you can remove the cable ties. you may need to cut them, but just get out what you can, and don't tape over the locking part. Sand the area smooth (and rounded if an outside edge) so that it's ready for epoxy.



If your joint required you to "weld" it together so that you could take out the cable ties (especially the locking part), make sure to sand the area roughly before you start to apply the tape. Epoxy generally does not stick to itself very well. Remember to wet out the surface once again if you've had to wait for the first coat to dry.



If the joint is all ready and set, cut a length of fiberglass tape to fit the joint. You can leave about a quarter inch of extra on each side if you want, but for inside joints especially it's best to cut it exactly. Roughly pat down the tape to the wet epoxy surface, and then starting at one end with a fresh batch of unthickened epoxy, brush on epoxy until the tape becomes relatively clear. You may need to finesse the bubbles out with a finger, but generally fiberglass tape is pretty easy to get right.



Use a plastic scraper to help you get out any bubbles and to spread the epoxy along evenly. Generally I'll wet out around a 1 foot section with a brush first, and then get another foot out of it using the plastic scraper. You just want the fiberglass tape to be impregnated in epoxy, not necessarily coated. A thin layer of epoxy is flexible, and the fiberglass gives it the tensile strength it needs, whereas a thick layer of epoxy is more likely to crack.



If you're going around curves, you may need to "kerf" the tape around the edge by making a few 1' cuts into the tape along the inside and outside radius of the curve. The tape stretches pretty well though, and try pulling on the ends of the tape before you make any cuts, which decrease the strength of the joint.

STEP 7: Drying and Finishing

Follow the epoxy's instructions on drying time and curing (generally 6-12 hours to touch). Try to keep dust and insects off of it in the meantime.



If you're okay with the slightly raised and bumpy texture of the fiberglass tape, you can cover the seam in a polypropylene drop cloth, which doesn't stick to the epoxy and will create a nice and smooth surface.

If you want it to be smoother, then suit up in a jumper or long sleeves and pants (with legs and arms taped) and sand it out. Fiberglass gets everywhere, so to avoid itching for weeks, do everything you can to keep dust from flying around.



If your joint needs to be super strong, then do a few more seams of tape overlapping the original seam. This is common on large boats (20 ft+).

STEP 8: Epilogue: Mini-Cup Mods and Suggestions

I made a few modifications to the original plans. For one, Instead of having stringers and screws fastening each piece of plywood, I use the stitch-and-glue method outlined here. I also rotated the original cockpit dimensions so that the rounded end was towards the stern. Additionally, I placed deckplates in the cockpit for access to the five watertight compartments. In the two foreward compartments I added two non-watertight bulkheads at the fore end of the daggerboard box to stop any cargo in those compartments from sliding around too much. I also added an additional support beam at the top of the stern between the rear bulkhead and transom. I coated the entire hull, inside and out, in epoxy for longevity.

In terms of the rigging, I kept the general rig dimensions, but added outhaul, downhaul, and traveller lines feeding into clam cleats at the cockpit. The spars are 1.25 in aluminum T6 tubing and the mast is a 2.25 in alumunim T6 pipe. I made the sail with a sail-making neighbor of mine, and it is based of off the given dimensions with the shape "eyeballed". The The mainsheet goes through a swiveling fairlead and cam cleat located directly aft the daggerboard, with an accompanying block directly above on the boom. I may try and make a higher performance sloop rig; I'm not sure the lateen rig does it justice.

On deck, I added a cleat and set of chocks at the bow and an additional cleat as a handle on the daggerboard. I put an adjustable hiking strap in the center of the cockpit at the floor, which certainly sees use. The hull's nearly flat-bottomed design means that in the water, the Mini-Cup likes to be sailed flat, and tends to turn into the wind with even small angles of heel.

Comments

[DylanB91]

How much does it weigh?

[bcrocker1]

Awesome project and great modifications to accommodate stitch and glue construction for novices such as myself! Just curious as to how you joined the hull bottom to form the V. Can't tell if you used stringers in the bow... If you didn't, then did you just use zip ties to join the pieces? Also, would you recommend completing this step earlier than the PDF suggests? Thanks!

[Z.Backas]

I used a ratchet strap to bring the bow up before I zip-tied it and removed the strap. There are no stringers anywhere in the boat. The progression the PDF suggests that goes from cockpit to daggerboard/mast box and then bow stiffener is appropriate, but it is important to make sure that the curvature in the bow stiffener does not put too much stress on the bottom ply.

[hyperfocused72]

Even easier than epoxy is to use PL Premium construction adhesive. It comes out of a caulk gun and allows you to spread it like peanut butter. 24 hours later it is as hard as a rock. Just make sure you use gloves. You can make fillets just like with epoxy. I built a Puddle Duck Racer this way. The PL Premium is a polyurethane adhesive that sticks to almost everything, wood, metal, etc.

[pete.oconnell.75]

How does the PL Premium construction adhesive finish. Does it have a wood tone, is it clear, or is there some other appearance?

[pete.oconnell.75]

Thanks for the feedback hyper. Its probably not sandable either. Soo, I'll go with the epoxy method

[hyperfocused72]

Although you could probably cut the PL with power tools, I don't think you can really finish it. It is sort of a brownish yellow when it cures.

[bo88y]

PL is awesome stuff. We used to have a lot of PL 400 around for gluing subfloors to joists, and we used it to strengthen our saw horses. Once the guy driving the Lull ran over one of the horses, and the wood broke before the joint glued with the PL.

[chud9]

I love the finish in the pictures. How did you pull that off? Did you use resin pigment for the epoxy and split it into different sections (one w/ pigment, one w/o) or did you use spray-on boat paint, or something else? I'd love to get mine looking like that.

[Medic55]

Good Job.

[Fuddmaster]

What kind of plywood did you use? Curious if it is marine grade or not?

[Z.Backas]

I used two sheets of 1/4" Marine Grade Fir for the boat, and sealed it completely with epoxy.

[Tanzer26]

I built a Stevenson design "Weekender" back in the 80's. Also flat bottom and liked to round up when the winds picked up and she heeled over. Third year in the water, I modified the swing board to a fixed fin keel, moved the centre of resistance aft almost a foot and what a world of difference.
I don't know your sailing background,but boat balance is all about the centre of effort of the sail in relation to the center of sideway resistance of the boat. If you've ever been on a sailboard, moving the centre of effort is how you steer.
Sailing fairly flat is usually fastest, , I found the weekend we wwamted at least 5° heel. On your mini cup, modifying the centreboard is a no go, but getting the upper spar mor upright, moving the 2 mounting points forward or shortening the boom, would all move the CE forward. Letting out the boom, to flatten the boat, else moves the CE forward, but may sacrifice power.
I'd be curious how it would do with a sailboard type rig. Taller mast, shorter wishbone boom, also give you better headroom in the cockpit.

[Tanzer26]

Can you provide a link to the plans you used? I like the idea of converting to a sloop rig, it might balance better.

[Tanzer26]

Wrong button. Your mast looks quite bendy. I you're rounding up too much when you heel, it could be a sail balance issue (ie too long a boom/not enough area ahead of the mast. Could also be some loss of depth of the rudder, so less area giving less control. generally, sailing flatter is faster, but you usually want a few degrees of heel.

[Z.Backas]

I just added the instructions I used in the last step as a .pdf file, hope that helps.

The mast in the picture was what I initially used because I was able to procure the material for free, though I soon learned that it was not nearly strong enough. I now have a 2.25" aluminum T6 mast that works perfectly, I recommend a material with at least a 2" diameter.

Though the sail is probably not perfectly balanced, I do believe that it's mainly the flat bottomed nature of the boat that causes it to head upwind when heeled. The boat simply needs to be sailed as flat as possible, it's as simple as that!

[amajchrzak]

beautiful sailboat. I love buying and fixing up older boats. would love to try this.

[jmwells]

Just a note: I'm an electrician. We use tons of zip ties. If you go to an electrical supply store, or an aircraft parts store; they sell a tool made for tightening and cutting zip ties. It looks like a gun, most have a tightness adjustment. When you've squeezed the trigger to the adjusted tightness it automatically cuts off the tail flush with the lock. No tail in the way, and, no sharp points to get snagged/cut on.

[cesar harada]

thanks for the ectra step. That's helpful

[cesar harada]

wonderful set of instructions. Inspirational. I want to build a few of these, but I want to make super super light... I'm in Hong Kong, so maybe bamboo + fiberglassed epoxy... I'll report for sure :)