Plywood canoe

When I bought the plans it was for a motor canoe so the specification was for a dinghy. It showed a transom, 2 intermediate frames and 3 fixed seats supported by 50 x 25mm cross members. The inwale was 15 x 35mm and the outwale 15 x 15 or 15 x 35. So a robust construction to cope with an outboard and no support from thwarts.

What I am building is more like a compromise between a double ended dinghy and a canoe. I am using 19 x 25mm for the 'wales.

This is an experiment and the boat will need further stiffening. The temporary seat will be designed to assist the floor structure.

 

I have now completed the inwales.
I glued on the blocks with thickened epoxy then measured the offset from the string for the curve I needed.
I hung the boat from the lifting beam to give me some floor space. Due to the limited headroom I finished up walking like Groucho Marx
Then connected some plywood boards together, screwed blocks at 1 foot centres at double the offset needed to the plywood.
Steamed the inwale and clamped it to the blocks, it was trying to twist so put more force into the clamps. Unfortunately when I took it off there are some dents. I will try and steam them out later. The second one was bent over the first, so not a problem.
Taking out the first inwale from the steamer I chucked a section of pipe to one side only to find that it was bent, so had to steam the pipe to get it straight enough for the second one.

To cut the ends to match the partitions I used a piece of plywood held against the partition and a pencil laid flat to give the lines to cut to.
As recommended by AK and Michael, I did each gunwale in 2 stages, so much easier. There was still some West Six10 left in the cartridge from tacking the chines, so squeezed the epoxy and hardener out and hand mixed rather using the mixing nozzles. It is much easier to work with than thickened epoxy.

I was wondering how stiff the gunnels were so did a crude experiment. I rigged up a dial gauge and a baggage scale. Unfortunately the blocks were already glued on as I would have liked to measure with just the outer gunwale only. The finished gunnels turned out to be 5.5 times stiffer than the outer gunwale with the blocks. My questimate of how much stiffer the blocks made the outer gunwale is 3.5 so the gunnels could be about 19 times stiffer than the outer gunwale alone. In theory a complete triple gunnel should be 27 times stiffer.
A force of 20lb produced a combined deflection of 60 thousandth of an inch.

 

Sweet!

 

The 'triple gunnel' theory doesnt work like that. The 'middle' gunnel doesnt have much effect on the stiffness. Making the blocks wider would be a lot more efficient. This has been discussed a few times in the forums.

How much weight do you think theses gunnels have added to the boat ?

How much does the boat weigh now ?

 

This type of sheer clamp is an old school way of doing things and heavy too. Of course how much depends on several factors. The distance between the inner and outer portion of the assembly is the key to it's strength and stiffness, not the spacers count. The wider apart you can make the inner and outer elements, the smaller and fewer the spacers need to be. It's not necessarily the best approach from a weight stand point.

A much lighter method, particularly seeing this is a taped seam build, would be to place a perpendicular to the top strake and fillet and tape in in, just as the rest of the boat appears to be. Some hanging knees, widely spaced to support the mini side deck (of sorts) of the same material and building method, possibly with a midship drain hole, hand hold or two. On this boat, 1/4" plywood, say 2" - 3"wide, running full length, 1/4" plywood knees on 24" centers, possibly wider spacing, all filleted and taped, will be much lighter, stronger and stiffer too. Admittedly, it doesn't look as traditional as the faux frame head spacers style, but it's a taped seam build, so how traditional can you make it anyway.

 

LateStarter isn't really thinking "canoe" - the first post says this will be an electric-powered boat.that isn't unstable and wet. A 16 x 44 doubled ended canoe isn't going to be an easy one-handed carry like my 12 x 27 ultra-light, and is too wide for a comfortable solo paddle, although just right for rowing.

So he has informal launching facilities, car-topping, narow waters and maybe not facing forward to deal with - and some physical challenges I gather. There is potential for the boat to get banged about so he is over-building it. Makes sense. Not my own approach but it's a nice boat and different strokes . . .

 

Thanks for the feedback guys.
The moment of inertia for a rectangular section is related to the cube of its height or in this case the width as it is being bent sideways so if it is 3 times bigger it will be 27 times stiffer.

I agree that the material in the middle is less effective than at the edges which is one reason why I did not build a triple gunwale.

I have calculated the weight of the gunwales specified by the designer at 13.2lbs. The gunwales as built are about 14.2lbs. I think you may be being mislead by optical distortion of the camera into thinking they are more massive than they are. I estimate the gunwales are about 2.2 times stiffer the original specification.

The weight of the boat is about 68lbs.

PAR, I had considered something along those lines similar to the side decks on some dinghies but I have hopes to rig the boat for sailing and had fears if I sat on something like that above a knee it might punch a hole in the topsides which are only 4mm thick. I have an idea to put temporary padding to the tops of the gunwales for sitting on while sailing, comfort is more important these days than an unnoticeable increase in speed.

You are right Terry, if I was wanting just a paddling canoe I would not have gone to this trouble. By the way I am in better shape now as a result of the exercises involved in building the boat. I hope your recovery is progressing.

I am worried that I will become a serial boat builder, I am already reading up about skin on frame for the next project.

 

- glad to hear you are better. My own recovery has gone well - not likely to be any better unless someone comes up with an anti-ageing treatment! Life gets in the way of boatbuilding however.

 

While waiting in the pharmacy the other day, as the other half picked up a script, I came across a bottle of skin restorer, with remarkable abilities. So, after reading the label, I'm convinced I can fix a few things. First of all, I'm hoping after judicious use, I can grow my foreskin back, if for only a place to carry my car keys and wallet when in the shower, at the local gym. The biggest issue I see is trying to get a 55 gallon drum of the stuff, so I can dip myself bodily and possible beat back the aging process.

 

Be careful how you use that stuff, Par! Sounds like it's already changing you in ways unpredictable . . .

 

Many thanks SCHWIMMWANNEN for removing your post so quickly.
You can see that post here
http://www.boatdesign.net/forums/boat-design/canoe-inboard-motor-6-5hp-long-tail-indor-47169.html

Also his post
http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-127.html#post631006 is worth a look.

 

The marathon continues, hopefully the end is in sight. On the designer's website it says it can be ready for painting in 30 hours.

Working on the outside, when I taped the lowest chines, after a day I used the Surform to take off the raised edges. Now I used a sharp chisel to feather the edges then epoxy thickened with Q cells to fair them.

A centre runner was attached, a separate tapered piece at each end. I scabbled a recess in the bottom of the boat in front of the runner and filled it with epoxy as protection against hitting something that could get under the runner. I topped it all off with 3 layers of 81 gram/m^2 cloth and later finished it off with epoxy thickened with silica.

I have primed and added a few undercoats on the outside. Given it is now past midsummer's day I am not going to spend a lot of time on smoothing, just have good protection to the wood now and leave the better finish for winter time.

 

nice job ...takes longer than you think ...what summer ??

 

Looks nice. The white really accentuates the hull/chine lines and the multiple chines are verging on looking like a lapstrake.

I think she'll be a keeper.

 

- oh, that has given me such a guilt feeling. I don't even remember when I started my one-sheet special . . .