Building the Snail

The Snail is my second custom design. The first was the Slug, way back around maybe 2012, when I lived in Fort Collins. Somewhat after the fact, I wrote a blog aritcle about that construction. The Slug ended up being very fast but had a lot of problems. After many years, I have learned much and decided to sort of try the design ideas of the Slug again, but with better construction techniques.

The differences in technique between the Slug and the Snail

Money.

The design philosophy

If you've read my other articles (who am I kidding? Of course you've read them because my only readers are my mom and my wife and they have read all my articles) you remember that I talked about how nobody interested in boat building really cares about your boat design ideas, so I will try to restrict my comments here to the bare minimum, but there are a couple features that actually impact the construction. First, my general vision for this design was a very fast but stable surf boat. I tried Benny's Mini Mako and it was painfully small, but I was jealous of his shreds at Skook. I wanted those super agressive edges (I don't care about the difference between a rail, edge, and chine) that flare out, but then I also wanted generous knee space. I also wanted to build a cockpit rim into the mold using the three part mold that Featherweight does. I noticed that with this strategy, I could make an overhanging sidewall - a concave sidewall where the knee was out farther than the edge, but the space above the edge still tucked in like a normal surf boat. This is impossible with a normal two-part mold because the top half of the mold has to be able to pop straight upwards to release off the boat. The three-part mold has two deck parts that release off kind of up but mostly sideways to clear the cockpit rim, so an overhanging sidewall would be no additional problem.

The "overhanging sidewall" is a little hard to describe so here is a picture that's slightly ahead of schedule.

Having described how that one aspect of the design really interfaces with the construction, I will now focus entirely on the actual process of construction. From here out, I don't think anything I say is specific to the Snail. It would be the same process for almost any homemade kayak.

Shaping

To ensure that my cockpit rim would release from the mold that I built, I copied the rim that I knew would release and fit my personal geometry: the XL featherweight rim. I had already made a couple copies and had a complete mold, so for this project I waxed it up and laid up a little ring that included the cockpit rim and a couple inches of the deck surrounding it. I used fiberglass and epoxy. I can't remember how many layers but I think it might have been 4 layers of 7 oz. glass cut into bias weave strips for the rim, and about 2 layers for the little ring surrounding the rim.

For the body of the boat, I went and bought some more styrofoam from the hardware store. This time I priced it out a little more like a non-idiot. I planned out how wide and long it would be (having a couple boats that fit me really helped there), and calculated the volume of foam I needed. Then I stood at the hardware store register and pulled out my calculator and crunched the numbers on what thickness would be cheapest. Turned out that getting 9 half-sheets of 3 inch foam was the cheapest at that particular store. It was a little amusing that half-sheets were cheaper but if you got two of them they would just give you a whole sheet. Once back at home, I glued the styrofoam into a rough block using gorilla glue. The seams ran vertically front to back, so that there would be a convenient centerline seam down the whole length of the top and bottom.

This was also when the first tools came into play. This time I bought a hot wire cutter for the large cuts to the styrofoam. I also had a couple Stanley Sureform drywall tools (also handy for shaping hip pads) and a couple nice sharp saws, and a big drywall square, but the hot wire cutter was new. I experimented with the cutter a bit and quickly learned that although it was way faster and cleaner than a hand saw, freehand cuts with the hot wire were pretty impossible.

My solution for making the big cuts was to make a series of forms or guides. I got some hardboard (not cardboard) and drew the shape I wanted on there with a marker, then cut it out and sanded the edges smooth. I laid two pieces of hardboard back to back to get a copy of the guide for both sides of the block. I would then take some time to carefully measure out where the guides should be, and tape them in place. I would rest the cutter against the guides and cut sections out, keeping it pretty much perfectly perpendicular to the correct surfaces. I would have to avoid the parts where the tape was holding the guide in place. Then once the first few cuts were done, I would add tape in the cut sections to hold the guides in place, and then remove the old tape and cut those sections so that I had an overall shape matching the guides. Obviously I first used this process to get the rough block nice and rectilinear.

The hot wire cutter

The not-so rough block, with straight edge forms still attached.

The plug with the side and top profiles cut in.

Once I had the side and top profiles cut to about where I wanted, I started digging in to the top to seat the cockpit rim ring. This was a ton of work. Once I started getting close, I put chalk on the bottom of the rim ring and wiggled it a little to transfer the chalk to the styrofoam so that I could tell where it was hitting. This was a long slow process, made longer by the fact that the ring I had molded was asymmetric. I think I pulled it out of the mold too early so that it got warped a little. I ignored this at the time, for some stupid reason, and just made the styrofoam a little asymmetric to match the rim. It might have been nice at this stage to have some giant calipers to check the height. Surf board makers have these, and you can even buy them, although I'm not sure if they open wide enough for most kayak deck heights. They're probably pretty easy to build. I just eyeballed it.

The rim seated and glued in place, beginning the rounding out.

Eventually, the cockpit rim was seated at the right height in the top surface of the styrofoam. I used a bunch of spray foam and some two-part expanding foam to stick it in place and fill in some of the remaining gaps underneath it. Then I began attacking the squarish edges of the deck, to smoothly match on to the ring around the cockpit rim and transition down to the rails of the boat. Again, this was a simple but slow process. I mostly used the drywall surfacing tools but occasionally made a few cuts with the hand saws. The hot wire cutter was not much use in this phase.

As the deck and sidewalls got closer and closer, I also worked on the bottom part of the edges. I didn't have to do anywhere near as much work on the bottom, since the hot wire cutter had left it almost perfect right from the get-go. The bow was a little tricky but fortunately the connection between the edges and the bow itself was revealed to me one night in a dream, which I quickly transferred to a small-scale model so that I wouldn't forget the vision.

The maquette showing the bow mockup, as revealed in a dream.

Rough draft of the actual bow lines.

Surfacing and sealing the plug

After a few months of work, and tons of people telling me that there wasn't enough bow rocker, I finally had the plug at a point that I decided was good enough to move to the next stage: creating a solid surface that would seal the plug. This surface needs to be solid enough to sand and hold a polish for easy releasing of the mold, and has to make a good seal because I planned to use polyester resin for the mold and polyester resins will dissolve styrofoam.

I started out by applying a layer of 7 oz. fiberglass (it was a nice drapable 2x2 twill) using epoxy. This did an amazing job of highlighting all the lumps and imperfections that I thought I had already sanded away. I sanded to clear as many high spots as I could and to rough up the surface for a good bond to the next stages. I then filled in a ton of fairing compound all over. This is basically Bondo, but beware because actual Bondo is a polyester based resin, so if it comes in contact with your styrofoam it will melt it. During the first sanding pass I had opened up several air pockets and sanded through the fiberglass in several places, so Bondo was off the table. I used Totalboat's epoxy fairing compound. It was nice.

The plug with one layer of glass, with some sanded and some unsanded fairing compound.

Typical burn-through to the foam underneath the glass. Cut away the loose stuff, fill with compound, sand again.

Vacuum bagging part of the second layer of glass.

The start of a large fairing compound pass.

Sanded, almost ready to apply primer.

Once that fairing compound was sanded pretty much smooth, I applied another layer of glass, again using epoxy resin. Somewhere in here I ran out of my 2x2 twill and switched to a much thinner glass with a fancy harness weave. I also decided to vaccuum bag at least part of this layer onto the plug. This helped eliminate some of the little air pockets that formed when laying up earlier stages. This did an amazing job of highlighting all the lumps and imperfections that I thought I had already sanded away. Again, I applied fairing compound, sanded, and applied more, and sanded more. Each cycle of fairing compound was exponentially closer to perfection. The first pass used something like 2 pints of compound, and I stopped sanding it with lots of really rough areas left. The next pass used less than half as much compound and took less than half as much time to sand, and subsequent passes followed that trend. Eventually I could get the sandpaper to scuff pretty much every square inch of the plug, with no low spots that it wouldn't touch, and I was chasing down tiny pinholes and scratches with my fairing compound.

During all this sanding I also introduced another new tool. I got a couple bendy longboards. They're basically pieces of foam with velcro on the bottom so that you can stick on sandpaper. Having that little bit of flex allowed me to get slightly curved surfaces to sand really smooth. You can probably build one of these yourself pretty easily. The main revelation for me was that you can get rolls of sandpaper that are designed to stick on longboards. If you've got some of that stuff, the board itself can be made of almost anything.

Eventually, after those two layers of glass and many rounds of fairing compound, I decided the plug had reached a good enough state to move to the next phase: applying a uniform primer coat. This did an amazing job of highlighting all the lumps and imperfections that I thought I had already sanded away. I started off by putting on a couple coats of an epoxy primer from Totalboat. I read the directions on the Totalfair compound and it said to seal it with Totalprotect primer or something along those lines. I applied it with a roller, because I didn't feel like dealing with my spray gun and because I had ordered a new spray gun that hadn't arrived yet.

Epoxy primer, freshly applied

Some pros and cons for that primer: it didn't smell super toxic, it was pretty easy to apply with a roller, overcoating was also easy and pretty fast, but then to sand it I had to wait a full 48 hours. I tried sanding after about 24 hours and the sandpaper gummed very quickly. Another fun anecdote: I tried applying a fancy guide coat to test it out while sanding the hull. I got it pretty smooth pretty fast, but decided the guide coat wasn't really that helpful. Then I started trying to clean off the remains of the guide coat. It wouldn't clean off. I tried everything. When I looked closer, I realized that it was still there because I hadn't sanded the hull smooth yet. The leftover guide coat was doing its job perfectly. I tried using water, soap, pretty much everything I had available, and it turned out that sanding was the only thing that would work. So the guide coat kept me honest and made me get that primer layer really smooth.

After prepping the epoxy primer, which did an amazing job of highlighting all the lumps and imperfections that I thought I had already sanded away, I sprayed with a couple coats of Duratech polyester primer. This sanded more easily than the epoxy primer, and had this cool kind of automatic guide coat. The outer skin of the Duratech cured to black, but the interior was a kind of blueish gray, so you could instantly tell when you'd sanded away the orange peel from spraying. I took it to about 600 grit. The first few passes went very cleanly and quickly, but as I got past about 220 grit the paper started gumming up (as the instructions had warned me). However, I sacrificed a couple sheets to get a slightly nicer finish, and eventually decided that it was time to build the mold.

Duratech primer, freshly applied

Duratech after some sanding

Building the mold is a completely different process, so I will split that into a separate article.

Applying the first bit of mold release wax

Until then, enjoy...

My other composites articles:

Introduction to Composite boatbuilding

Composite boat repair for the clueless

Building the Slug

Resins for the Clueless

Or, more useful, click the little "composites" label thing below, because who knows if I'll remember to update these links as I write more articles?