Plywood canoe

Marking out and cutting the panels. The regulars on here will probably find my comments pretty routine but this is aimed at first timers like myself.

I drew the lines parallel to the short side at 305mm spacing and marked off the dimensions on the plan. I also marked lines parallel to the long side as a reference when aligning the panels later. I found it more comfortable to work on the floor rather than leaning across a table.

Joining up the dots to get the curves I used a plastic curtain rail I bought a while back but not got around to fitting. Nails in the marked points and bricks to hold the rail in place. There are small triangular pieces of ply between the rail and bricks to create a point load in line with the nails to avoid twist.

Cutting was with a jigsaw one sheet at a time. Some people do all 4 together but with my woodworking skills I prefer my mistakes to ruin 1 sheet rather than 4. I have seen it recommended that you have some scrap ply under the sheet to stop the edge chipping but I used a new fine blade and any damage will be hidden by fillets or paint.

Working alone I needed some way of supporting the panel being cut and came up with 3 3x2 timbers and clamps leant to me by a neighbour. They just needed moving back and forward as the saw approached them.

I shaped one of each type of panel down to the line using a Stanley Surform (red handled tool in the photo) which worked well.
The edges of this plank was marked with coloured chalk and then clamped to the other 3 planks. They were filed down with the Surform to the correct shape, checking with a set square as I went. If the chalk started disappearing I knew to stop. I then sanded them down with 80 grit Aluminium Oxide paper until all the chalk was removed. I am using 4mm ply, it might be rather slow with 6mm.

 

All good but if I can te you what I have found over the years...
A stitch and glue is a fits where it touches project ..if you pull too hard on the cable ties to close gaps you can get a wobby chine..better to fill ...Mix epoxy with flour ..glass balls too brital....use slow set it still goes off too fast !!!
When you tape up do it between the cable ties and then take them out and do the gaps ..or glass over them and cut out with and angle grinder and spot repair ..dont leave them in ..look at the photo below where the guy left them in ...horrible.
When you do the outside I dont recomend taping over the joints with an extra layer ..look at the bump in this photo ...you can fair it out with filler but just one outer coth layer is simplest.
For hardwood rubbing strakes buy harwood decking from Wickes and cut it on a saw/router to the section you want . If you want to save money use epoxy on the inside and poly on the outside ...remember poly does not stick to wood very well....by the way dont varnish it .roller some epoxy on the inside....

 

Thanks for your tips.
On another thread PAR jokingly suggested using a hatchet, to point out you do not need to get too precise.
I am a bit of a heretic regarding stitch and tape/glue. I am trying to keep the number of ties to a minimum. Using adhesive tape mainly and building over 3 frames. Wrestling single handed with 7 planks weighing 40 lbs did not appeal to me.
The reason for the varnish was that I have read epoxy is affected by UV light and most people seem to epoxy then rub down and varnish on top for protection, however my boat will be stored inside so probably not a problem.

 

Having shaped the panels, the next move was to glue 2 panels side by side to form the flat bottom.

There were almost no voids in the plywood but there were a couple on one edge so I clamped it vertically and added unthickened epoxy until they were filled.

I primed the edges with epoxy and left it to soak in for 30 minutes.
I then used epoxy, thickened with microfibres and wood flour to glue the panels together. The panels were held in place with bricks. There was a short length where the panels did not line up perfectly but it will be covered by a butt strap on the inside and a rubbing strip on the outside.
The warnings were not to squeeze in the joint too hard but I under did it, this left me with a slight gap between the planks.

For joining the planks end to end, I laid 2 sheets of ply beyond each end of the 8x4 sheet weighed down with dense concrete blocks to create a fixed base to set up the position of the planks. I butted the planks end to end then hammered a nail into the ply wood base beside the last available reference line on the plank nearest the bow/stern. By subtracting the dimension on that reference line from that at the middle station gave the offset required. I tried using a laser for the alignment but found a string line easier and better, so long as you remember which side of the string you are measuring to.

When satisfied with the position I drew lines either side of the planks as a guide. Glued the ends as before and weighed them down with bricks.

The joint was then reinforced both sides with tape left 25mm short from the sides to allow the tape on the chines to run through later.
I use grease proof paper for masking.

To taper the edges of the cured tape I used the same surform that was used on the planks. It is very effective, does not damage the adjacent wood and it comes off as shavings rather than dust.

 

A tip - dont use cable ties. Get some galvinised wire (wont mark the wood) used to tie concrete reinforcing together. Its flexible and very strong.

You can then drill the holes half the size, but even better, the ability to apply tension on either side of the plywood with a twist of the pliers.

 

Another product I've thought about using is the wire used to hang suspended ceilings. It looks smaller than stove pipe wire, but I have not investigated the pricing. Stove pipe wire was stupidly expensive the last time I bought it.


Here is a deal for your from TSC:

$3 for a hundred foot of galvanised wire.

http://www.tractorsupply.com/fi-shock-trade-steel-wire-17-gauge-100-ft--3600419

 

I have been very lucky in choosing a design that needs very little force to bring the planks together.

Using the dimensions on the drawings I marked out 3 frames from 12mm scrap plywood. I also offset to the outside by the thickness of the hull so I have internal and external frames. The internal frames were then mounted in the workmates.

I intended to do a trial run of fitting the planks temporarily, to see what the problems were, but it has gone so well I will stick with it now.

Tape used is a clear packing tape which I was advised was less likely to transfer its adhesive to the ply than the brown version.

I just laid the flat bottom on top of the frames and the garboards (if you can use that term on a canoe) beside it and taped from the middle towards the ends. The next plank was temporarily supported by resting it on clamps attached to the frames. The last planks are large, so I clamped a piece of wood to it to strengthen the join and raised it into position with ropes.

Inevitably the frames and hull are not a perfect match. Originally I had intended to bolt the workmates to a steel channel (you can see it resting on the cross members of the workmates)to give a rigid backbone and perfect alignment, now I shuffle them about to get best fit and check they are level side to side and the rocker is correct. The curve of the chines are so smooth I would not consider adjusting them.

So far I have used 6 cable ties and 4 copper wire ties. The only force other than fingers used are 2 Spanish windlasses to bring the garboards into line with the planks below. In the last photo you can follow the string up to where it is.

Any tips you have on getting a pleasing profile to the bow I would welcome.

 

Thats where the re-inforcing wire comes in - strength and adjustability. Get it from a steel merchant.

Copper wire is too weak, cable ties can only pull the planks together, not force them inwards and various other directions.

The wire for ceilings is a waste of time, too thick and too hard to bend.

The wire i am suggesting was a whole $12 for about 100 feet.

You might think the pressure can be held with tape, but if it starts to let go when you are applying the fg, then the whole hull will be out of whack.

 

Cable tie is way strong enough for any pulling of the bow you may ever need...Thin steel wire could /may pull through the ply.

 

I am not knocking how stitch and tape is normally used. There must be hundreds of thousands if not millions of boats successfully built using the system. But there are disadvantages which I hope to avoid.

My plan is to fillet the chines between the adhesive tape then when set remove the tape and finish filleting the chines.

The tape is low residue and I shall not be using resin on the outside of the hull other than the chines.

I am not ruling out ties, I am already using some. It just seems odd to cover the boat in ties when there are only 4 small areas where the forces are significant and over the rest of the boat, they are negligible.

It is the shape of the bow from the side view I was enquiring about, do you make a template or draw on the ply and trim to the line?

 

if you cut the panels exactly as the computer/plans dictated then it should all go together perfect with no adjustment .You normally put all the panels together to make the complete boat then start poxing it together...if you try to fasten two together and then add more you will be in troube.....filling the chines and then taping over is standard practice...wet the ply with resin first then with your thickend resin mix..flour is the cheapest...

 

Strength is not the problem. If you dont want it to pull through, dont tighten it so much !

The point is smaller holes, and the ability to be tensioned and positioned in much more useful ways.

 

oh please god send Frosty to our aid.......

 

You have to rely totally on the accuracy of the cuts.

You pull them together, and measure them to make sure they are symmetrical, but the shape and the position of the panels dictates the profile and shape of the hull.

once again, in order to force symmetry, you are going to need to force it not just in tension, but also in side force, to ensure proper positioning. All designs I have seen need some strong 'persuasion' on the forefoot of the craft. Sometimes, you may even need to run a wire from one side to the other, to pull the chines closer.

 

Bow and stern profiles can be somewhat arbitary. S and G is not an exact science and the shape that you are getting right now is a combination of all of the tolerances, deviations and errors in design, cut-out and assembly.

If it were mine, I secure everything as rigidly as possible; permanently or temporarily. What ever works best for your situation. Then I would take my low-angle block plane and work the strake ends, as a unit, until I had a pleasing and fair profile. It could also be done with a rasp, a file or even some aggressive sand paper attached to a block. The key though is to make sure nothing shifts once you do this or you'll have to do it again. You could fillet and tape the entire inside before finalizing bow and stern profiles.

Good luck and have fun.