I admit it, I have a problem. Designing and building foam boats has turned out to be addicting.
My first foam boat was Toad, a 4 x 10.5 Jon boat. It was quite a success. It was a simple craft: flat panels of 2” expanded polystyrene (aka EPS, beadboard) glued together and covered with epoxy and fiberglass. But I got to wondering, could this foam be bent into curved shapes?
But why wonder? I'm an engineer and know how to calculate this stuff. I used published data for flexure strength and modulus; the results were surprising. EPS should easily take a 75” radius.
As a proof of concept I designed Woodstock (named after the bird in the Snoopy comic strip). It's an 11 ’8” pack canoe. I came up with a dead-simple construction method that would yield an efficient shape. I didn’t put a lot of time into thinking through the aesthetics - I wanted to be afloat by year's end (the paint was almost dry).
A small canoe made a suitable project for a number of reasons. There is no transom to build. Flare isn't necessary (amidship flare simply makes paddling more difficult). There is lots of curvature. And it would be super light; perfect for a post-work paddle in the park. Besides, I've never owned one of those cute little canoes like the Wee Lassie.
I decided on a 32 inch beam – a little wide for a solo canoe but good for beginners and those who hate getting wet in the wintertime. The flat bottom increases initial stability and ease of building. One thing that I wrestled with was the amount of rocker. I did some online research and discovered that short canoes vary between 0 inches and 2 inches of rocker. I compromised with 1 inch, both fore and aft.
The overall length is under 12 feet so it could be gotten out of two 4' x 8' sheets. Its half entrance angle of 12° and a prismatic coefficient in the low 50s should be ideal for paddling speeds.
I considered going with a flat sheer to reduce building time. Instead I came up with a trick that allows a curved shear with little additional work.
I made the sides out of one sheet of EPS, sliced lengthwise into three pieces and spliced into two 12 footers. I simply glued the foam end to end using PL Premium. After the glue had set, I shaped the two sides together. Unfortunately, I discovered that I hadn't done a very good job of splicing – they cracked apart just as I was finishing. After I calmed down, I carefully reglued them. There must be a better way to do this.
Another error I made in the building was in applying glue all the way out to the edges. I knew I wasn't supposed to but I forgot. This made trimming and sanding more difficult. Note to self: Jon boats are rectangles, canoes are not.
When I shaped the sheer line I left about 9” of the ends and center at full plank width. The extra material supports everything level while attaching the bottom. Afterward, I sliced off the extra material and sanded the curve smooth. The bottom pieces were made with a few straight cuts – leaving them oversize for trimming.
A word on cutting tools for EPS foam. Only three tools are necessary: I used an inexpensive 24 inch rip saw for cutting out the panels. A hacksaw with an 18 TPI blade turned sideways handled the rough shaping of the shear, rocker, chine radii and the ends. All final shaping was done with a 47 grit sanding sponge. Power saws would not have saved any time – the foam is so easy to cut. I have a jigsaw, a skillsaw, and a table saw. None of them were used on this boat.
But I tend to be impatient – so I used a random orbital sander for part of the rough shaping and for paint preparation. I have a Makita BO5041 (about $79). I like the dual handles. It has variable speeds but I always leave it on the highest setting. The tiny dust collector bag actually works quite well. It's not an overly powerful sander - an advantage when machining foam. So far I've used one 60 grit pad for each boat.
A single-edge razor in a window scraper handle is useful for carefully slicing off hardened glue - if you're one of those people who puts glue where you shouldn't. I used one tool you might not have on hand – a hot wire cutter. This was an experiment and I probably won't use it again. Saw cuts are much less wobbly.
Three more super cheap tools are necessary:
Clamps: I did all “clamping” with 8 x 8 x 8 inch hollow concrete blocks. I needed 8 when installing the bottom. The hollow shape makes them easy to grasp and, at $1.26 each, they're a steal. Just don't drop them on the foam (or your foot).
Fairing Battens: These are supposed to be made from clear, straight-grained wood. Good luck finding that! I saw a picture online of someone using PVC pipe to do the job, so bought two 10 foot lengths of 1/2” pipe and a slip coupler ($4.95). It worked! Offset the batten by half of the pen diameter and hold the pen straight up and down. The 1/2” pipe, however, isn't very stiff. Next time I'll splurge and get 3/4”, which is twice as stiff. I think I can afford the extra dollar.
Marking Gauge: I “built” my own. A tongue depressor (a.k.a. epoxy mixing stick) with a 5/32” hole drilled near one end. Measure your offset distance from the center of the hole and draw a line. Put the tip of your sharpie pen in the hole and grip it so your finger slides along the edge of the foam. I probably wouldn't use this for marking plywood (splinters).
I began the build on December 19 and, working an hour or two each day, launched on January 2. Total building time was 18 hours. This includes overall sanding and one coat of paint.
Now, my building situation isn't ideal. I work in an open carport in the front of the house; I have to put all of my tools away at the end of each session and round them up again before starting. This added to the time. I also had to do a complete cleanup at the end of each work session. The neighbors might be upset by Styrofoam blowing onto their lawns. With a dedicated workshop I could have done it in 16 hours. A real boatbuilder could do it a lot faster!
I was impressed with Woodstock's performance. It was easy to paddle and tracked quite well. As should be obvious, I tend to focus more on efficiency than aesthetics. I could have done a prettier job. The plumb bow is especially unappealing to me.
The winter turned unusually cold and stormy immediately after launch day. Six weeks passed before we again saw suitable weather for testing. Now I've noted the need for a couple of improvements.
First, it is too deep amidships for easy use with a double-blade paddle. A single-blade paddle works fine, but many people prefer the doubles for small canoes. The technique is much easier to learn. Along the same lines, a little tumblehome would also help.
Speaking of lines, the sheer didn't turn out as nicely as I hoped. I laid it out as a simple arc but it should have been more of an elliptical shape – flatter in the middle and rising more quickly at the ends. It's time to break out the hacksaw and make a few modifications.
In spite of the above, I managed to “built a better boat than I could buy.” As Josh Withe pointed out in his article on building Sawfish, an ultralight boat can be a real joy. It's so easy to go paddling on the spur of the moment - even in city parks. Owning the “perfect” boat might be nice, but frequent practice makes for a stronger, more skillful paddler. This translates directly into increased speed, range, seaworthiness, and safety. What more could I want?
Same as LWL
From gunwale to waterline
Equal fore and aft
Way too much!
With one coat paint
Yes, we tested it!
Note on costs: This is an honest “you can build it for this much” price. For instance, commercial epoxy is sold in 1.5 gallon units. I included the cost ($35) of the half-gallon that will be left over. There are also consumables - stuff you use up that isn't part of the finished boat. This includes roller covers, mixing tubs, sandpaper, etc. I made a comprehensive list of everything I used - 14 different items! To buy all of it at once would cost $75 (included above). Again, there will be leftovers because of package size.
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