Building a flat bottomed canoe

[troy2000]

The shut-in Romany dogs heard them [the Dalmatians] and shook the caravans in their efforts to get out. ‥‘The caravans bark but the dogs move on,’ remarked Pongo, when he felt they were out of danger.
[1956 D. Smith Hundred & One Dalmatians xiv.]

I think I sprained something in my brain reading that....

 

[hoytedow]

 

[troy2000]

Question: the bottom of this boat is going to be 3/8" plywood. I'm planning to nail it to the side planks using 5d hot-dipped galvanized nails, with some sort of glue or adhesive caulk in the seam. Keeping in mind that it's going to be dry sailed and cooking in the Southern California sun, does anyone have any recommendations on what to use? Aside from epoxy and tape, of course....

I was thinking about just using the Gorilla Glue, since I have a bottle already and a little goes a long ways. But I'm not sure a nail every few inches would clamp it properly. And the plywood and pine will probably swell and shrink at different rates, since one is solid wood and the other is glue-impregnated laminates.

At the stem and the frames, I was thinking of paying everything with an interior/exterior acrylic caulk and adhesive (after priming with paint). But I was wandering through some instant boat sites, and some of the guys were swearing by PL Premium. So I'm considering using that everywhere instead, including at the chines. Any opinions?

 

[lewisboats]

Pl works similar to Gorilla glue...moisten the surfaces prior to application and it sticks like....welll....glue! It guns well too and doesn't require precisely fitted joints or very high clamping pressure.

 

[troy2000]

I'm thinking of changing my signature line to "Life is what happens while you're busy making other plans." We intended to mostly finish the canoe this weekend, but wound up having to take care of other stuff instead.

When we finally shook free this afternoon, we figured we still had time to shape a stem and scarph the plywood together. So we laid out the tools and a power cord, rough-cut the plywood to shape.....and I said to my son, "I smell smoke. There's a brush fire somewhere."

It was just one light whiff, but I know the smell of chaparral burning. So we started looking upwind (south of us), and a couple of minutes later saw a small, light plume of smoke behind a hill. Ten minutes later the flames were coming over the hilltop, and the whole neighborhood was blanketed with smoke. We spent the rest of the afternoon with shovels and water hoses, protecting our property from flying embers.

Right before sundown the fire was under control enough for us to relax, so we managed to make the two scarph cuts in the plywood. But we ran out of time before we could get the joint glued up. That isn't something to be rushed in failing light, especially since less than a 1/8" misalignment of the joint could cock the pieces enough to keep the bottom from fitting.

Hopefully I'll have time to set the joint up properly and glue it before I leave tomorrow. Whether we do or don't, I won't be home to work on the canoe again until the Tuesday after this coming one.

I'll get some pictures of the scarph cuts in the morning, and of the Skilsaw jig I used to make them. I copied it straight from another website. If I had the job to do over again, I'd probably make a wider version of the jig I used on the pine planks instead, since the joint is only 28 inches wide. Of course I'd add some stiffeners to the longer slide, to make sure it stayed straight.

But we wound up with a couple of decent 6:1 cuts anyway. I think that's strong enough for our purposes.

 

[troy2000]

Here are a couple of pictures of the jig I made for the Skilsaw. The idea is that it rides on the plywood with the saw base against the edge, and the blade extends under the plywood to cut the bevel. Instead of depending on setting the angle perfectly on the saw, I used my jointer to put a 6 degree angle on the jig.

It's laying upside down in the first picture so you can see the angle between it and the blade, and set up like I'm cutting in the second one. I wouldn't normally be cutting left-handed (or single-handed) in that particular situation, although I'm left-handed. I was just holding the camera in my right hand to get the picture, because it's easier to push the button that way....

Unlike the guy whose setup I copied, I clamped a 2 x 4 on the plywood for a straight edge, instead of depending on a steady grip to keep from bobbling the cut at the beginning and end.

 

[troy2000]

Here's a photo of the burn area yesterday. I turned my pickup around for a minute to snap it on my way to work, a couple of miles from home. The reddish strip along the left edge of the burn is fire retardant that was dropped by an airplane.

 

[troy2000]

I should have been more careful about giving credit for the Skilsaw jig. I found it at the website for Libby Small Craft:

http://fivenineclimber.com/boats_sailing/articles/scarphing_jig.htm

Apparently that gentleman learned it from a set of drift boat plans drawn by Tracy O'Brien. So here's O"Brien's website:

http://www.tracyobrien.com/showcat.asp?id=2

It's simple, it's cheap, and it works for thin plywood (although like I've already said, I prefer to put a straight edge behind it to keep the cut straight at the ends)

But I'm not completely satisfied with it; it's kind of a clunky, Mickey Mouse solution. If I made a habit of scarphing plywood, I'd have to come up with something a little more elegant.

 

[hoytedow]

Here's a photo of the burn area yesterday. I turned my pickup around for a minute to snap it on my way to work, a couple of miles from home. The reddish strip along the left edge of the burn is fire retardant that was dropped by an airplane.

How did the fire start? Was it anthropogenic?

 

[troy2000]

How did the fire start? Was it anthropogenic?

I'm sure it was. The area the first plume of smoke came from is a little dish or valley behind the hill, where we normally go to shoot because it's surrounded by hillsides that act as backstops. It's accessible by a dirt road that kind of swings around the right side of it. Dirt bikers also love it, because they can enjoy nature by mindlessly running circles in it.

Twenty years ago you could drive a car up that road. But the dirt bikers combined with the rains have stripped it down to bedrock in so many places that now it takes a bike or a decent 4 x 4 to make it.

Given how close the 4th is, my guess is that idiot teenagers were up there playing with fireworks and rockets.

 

[hoytedow]

Our anthropogenic fires in Florida are usually in the winter time - our dry season. One cigarette ember will level many acres of woodlands.

 

[troy2000]

OK, home long enough to get a little more done.

While I was gone for a week, the wind blew the canoe off the sawhorses onto the ground. I should've thought of that one, but didn't. Laying there for days tweaked it a little, and we had to twist it straight again. No serious problem.

But a freaky bit of damage: there was a little bit of breakout on one plank around a couple of spike knots when we finished planing it. No big deal; nothing a little putty or patching compound of some sort wouldn't hide. But while the canoe was sitting on the ground, some !@#$ rodent (a field mouse, judging by the size of the toothmarks) decided those were great places to start chewing, and did some serious damage--enough to weaken the plank, I'd say.

I'm not quite sure what to do about it, but I'm leaning towards routing out the damage and installing a couple of dutchmen. Forgot to get pictures of what the despicable little critter did; I'll take some tomorrow.

Here, I'm spreading PL Premium on either side of the inner stem, made of second-growth Douglas fir. We've been using paint stirring sticks for glue spreaders, and just cutting off the dried glue before the next use to give us a fresh stick.

Here it is with the stem and transom installed. The bar clamp holding the starboard quarter to the sawhorse, and the can of paint hanging from the other side amidships, were how we held the twist out of the boat while we were working. And the stem got more fasteners before we were done with it.

A shot of the oak transom. The bottom hasn't been planed yet, or the plank ends sanded or planed flush. I rough-cut the transom top by free-handing on my table saw, because I didn't feel like setting up a bandsaw or jigsaw; we had enough tools dragged out already. As long as you don't take too big a bite and bind the blade, you'd be surprised how close you can shave out a shape like that on a table saw (with a little practice). But I finished it on a small tabletop disc sander and belt sander combo.

Here, I'm using a drywall square off the center mold to mark the frame locations.

We also ripped and planed enough oak for the frames, and rough-cut the pieces to length, and that's as far as we got today.

to be continued...

 

[hoytedow]

The boat is looking good.

 

[troy2000]

Worked on the frames today. Didn't get as far as I had hoped; We got a late start, and we kept getting distracted by by my son's cute little girlfriend and old high school buddies dropping by to check progress, drag him off to Starbucks, so on and so forth. Our work area looked more like a social center than an outdoor workshop....

That's OK. He enjoyed himself, and we got something done anyway. We planed the bottom edges of the side planks to fit the plywood, and flushed the plank ends at the stem and transom. We built the three sets of frames, beveled them and temporarily installed them. Tomorrow morning we'll cut and round the ends, set them in permanently, then attach and trim the bottom.

The frames are 3/4" x 1 1/2" oak. We drilled and screwed them together with 3 1/2' coated deck screws. We did glue the joints, and watched in amazement as the Gorilla glue sucked straight into the end grain. I doubt it's adding much to the strength, but what the heck: at least it should seal the joints a little to keep water out.

We sandwiched the joints between plywood gussets anyway, glued and fastened with 1" nails--mostly for clamping pressure until the glue set.

Then we tacked the frames into place to check the bevels, and the overall boat shape. By then the sun was going down, so we called it a day. Next step is to pop the frames out one at a time to cut and round the upper ends, then reinstall them permanently. Since the planks will swell and shrink more than the oak frames, we won't try gluing the frames into place. Instead, we'll pay between the frames and planks with a waterproof adhesive caulk that stays flexible, and fasten everything with screws.

Then we'll nail the plywood bottom on with PL Premium in the joint, trim it and it should look like a boat....

Here's where we were at sundown:

Tomorrow evening I have to be back at work for four nights; then I'm off for a week. So even at the snail's pace we're moving, it should be done and in the water soon.

 

[ancient kayaker]

Interesting thread. I liked the circular saw scarfing jig, neat idea to take off the material from the bottom, it would solve the problem I had keeping 3 and 4 mm marine ply sheets flat, and much simpler than the jig I tried. Just in time for the next build I have planned!

The sheer planks look like they have straight, parallel edges: is that the case? Then the sheerline and rocker is determined by the flare angle and the plan curve. This is something I have tried and got good results with.

I read that ring nails are good for attaching the bottom ply to the sheer planks; you may want to try them.

Like most of the builders on the forum I am not a fan of Gorilla glue although I used it on my first effort; it worked OK for a dry docked boat but too expensive. Also although it fills a gap, it does so by becoming a foam and expanding, which makes it much weaker, so for a strong joint it does require a fairly good joint fit. But too much pressure and it squeezes out, unlike thickened epoxy.

Nothing seems to work really well on end grain, not even screws! Epoxy can be made to work however. I have tried warming the wood before applying the epoxy and letting it draw into the grain as the wood cools, adding more as required. A thick epoxy works best but not too thick, a balance has to be struck between having it all soak into the grain or not penetrating enough to match the strength of the wood. My theory is, the glue only has to penetrate about twice as deep as the average pore diameter, which is not very far at all.