Epoxy and Cyanoacrylate (SuperGlue) on Plywood Boats

Tacks on the inside take only seconds to write, but on two boats, stern and bow, very narrow hard hull to access, widening up the seam is the method that appeals at the moment.

Hopefully I can get the results without getting out the 'hatchet', but I hear what you say about not having to be too fussy.

re the 'machined bevels', I got the 'omigod, how fussy' response when I requested predrilled wire holes in the panels. I even had to buy the drilling tool for the cnc machine. But in the end, it made the process way easier and neater, especially for two hulls.

I also got some 'positioning' holes drilled for the temporary frames, and these saved half a day of measuring and re-checking.

Its amazing how much the 'little' improvements can add up. However, the bevels may remove the option to choose an 'outside' from the panels, which could be important for a clear hull finish.

 

For reference, the Dremel bit was a waste of time - it didnt cut for &*^&^%$.

New strategy, I used a sharp chisel on the bottom plank. I also pushed the top plank out by one mil, to encourage the epoxy to ooze into the gap.

I leaned the kayaks over on the rotisserie, and used a heat gun to thin out the epoxy as I applied it into the gaps, in an effort to get as much epoxy into the gap as possible.

Over the next few days, I will check the strength of the plank joins, and decide if it will hold when the wires come out.

 

You could just stand them on their bow and pour in a loose mix. Tape over the seam so it doesn't leak out.

 

I like your style and will be more relaxed about the odd millimetre. Thinking about it, I will not be needing a measurement certificate so if it looks right it will do me, probably if building for others I would be more concerned.

Sounds good to me. What tools do you use?

 

Taped seam builds, by their nature are quite imprecise. The only real advantage is the jigless build method, though typically a few molds, some temporary are used. Like I said earlier, I don't use "stitches" but prefer to use tape, ratchet straps, clamps what ever I can to eliminate things blocking the seams, so I can lay a continuous bead and fillet on the inside. This is the key for me, one fillet run for each seam on the inside, followed by tape, which greatly speeds things up. Especially if I don't have to go back and remove stitches, fill holes etc.

I've never had issue with bows before, in spite of a few designs having quite fine entries. The plywood is precoated and usually still "green" when the fillets go down, so not much of a adhesion concern. On a few I've use a hot glue gun and straps of fabric to hold the seam closed, so I can do the inside. If you use relatively short straps, the outside seam taping will cover any damage received during their removal. Mostly I prefer things that come off quickly, like clamps, tape, straps, Spanish windlasses, etc.

To open a seam there's plenty of tools to choose from, angle grinders are a favorite. I've not found the multi tool to be a big help on most new construction, though in repairs it can be. I'm also not a fan of the "floppy" nature of these builds. Even with CNC cut panels, distortions and hull twists have to be constantly checked, which I don't find to be the case with a build over molds. If I'm building more then one boat, I'll make a jig. This way they're both the same. In fact, the last time I did this, I cut both boat's panels at the same time, saving one set, until the first was off the jig.

 

Theoretically a good idea, but as you so correctly point out, the potential problem is hull distortion if the hull gets moved around too much. Epoxying in the steel 'stitches' is also another potential risk.

If I stood the hulls on end ( hard when your gantry is less than 16ft high), I run the risk of the hull being bent when the goo hardens.

As it was, I had to rotate the hulls upright after the 'pour', as the hulls flexed slightly on the angle as the building beam twisted slightly.

As it turns out, I didn't hack many joins. I found by making the top plank ( on the bottom) stick out by a mil, there was enough of a ledge to lay the epoxy bead.

As Par says, the problem with S&G is the lack of accuracy without a frame.

The kit manufacturers gloss over the potential hazard of making a bent boat, and it requires constant vigilance to ensure the hull stays as accurate as it needs to be.

 

Many thanks PAR for the comprehensive reply.

I came across the idea of using tape instead of stitches here
via a link on this site, see post dated 28 February 2010
http://www.songofthepaddle.co.uk/forum/showthread.php?18033-osprey-glue-and-stitch

or going direct http://www.flickr.com/photos/24154262@N05/4384142890/in/set-72157623401088153/

As I will be working alone, I will cut 3 external frames from some scrap ply and clamp the external frames in 3 workmate benches. It should help control the planks.

I bought a hot glue gun recently it is a bit 'Mickey Mouse' but at £5.90 including 50 sticks I can't really complain.

Thanks also to rwatson, this thread has been a big help to me.

 

I thought I might need some sort of 'container' like that to hold the long floppy planks, but I perfected a method that saved me the trouble. The trick is to wire the bow and stern stems first, then tie the middle of the plans with a piece of string a bit wider than the boats hull (like a wide pair of handcuffs) . When you 'open' the planks, they form a controllable boat shape, that you can sit upright on the bench, and start wiring into the hull starting from the stern or bow. Par will also tell you that 'external' ( I presume you mean female moulds ) create problems lining up the hull planks by eye.

You have to be very careful in the S&G type of build, as you can only rely on the frames position IF the designer has given you the measurements.

For some reason, maybe some misguided effort to protect their design, they provide very little info on the positioning of temporary frames, expecting you to calculate it based on a distance on installed planks.

The benefit of using wires is that they are easier to tighten, and re-tighten, (from either side) than tapes. Tapes can also have problems with sticking reliably. For that reasons you need to pick your tape carefully.

Tape has the advantage of not needing to drill holes, but when the hull doesn't have a precise and solid frame underneath, wire is by far the most adjustable and rugged method of holding the 'planks' together.

Plastic ties have the problem of only being able to be tightened from one side, and have very little 'push' on the plank, only a lot of 'pull'. They also require bigger holes.

 

I am treating this build as an experiment so will try a method, if it works, fine, if not I can start drilling holes with no harm done.

I have just ordered the ply, it will be a few days before I can collect it. As I am retired, cutting out some moulds will keep me occupied.

The design is from http://www.selway-fisher.com/index.htm who provides exact dimensions for the centre section and a section roughly half way between centre and bow/stern.

He also has a site just for canoes http://www.makeacanoe.com/index.htm where he includes DXF files for cutting out the planks on a CNC machine.

I shall start a thread when I get going so you can all learn from my mistakes.

 

Holding planks in place while wiring

I thought I had a photo of the method to hold planks in place, but I have done a simple diagram instead.

It shows the orange rope holding the centre of the two joined planks wider than the hull, with two green wires holding the stems together.

The blue lines represent the three wire ties in the photo , as some planks are getting added to the bottom of the hull.

This technique does away with the need to have some sort of female (outside) support for the planks you are wiring in, as the new set of planks will not fall over when the two ends are joined together. I found that this is far more effective method of controlling the planks.

 

Getting the cnc cutting done on the panels is a big help - its so much more accurate.

I found that making the frames was a real nuisance- trying to get accurate cuts on fairly heavy timber or particle board. A couple of mm error makes life difficult.

I had the best success tracing a really accurate outline on paper, and then hotgluing small strips of plywood around the edges of the frame shape on the paper.

I then cut out a rougher, slightly smaller version of the frame, and screwed that down on the bits of plywood. I then peeled the paper off.

It sounds harder than it was. Example below

 

A local kayak builder who builds inlayed wood kayaks uses straight pins at an angle to hold the bows and decks in shape, the holes left are smaller than from the wires.

Nice looking job!

 

I dunno. We didn't think about this too much. We just chamfered the side
of the stempiece so that the planking laid flat and fair on it, and then epoxied and screwed the end s of the planking down. The front edges were then faired and a stempiece moulded from a cedar 4 X 4 was epoxy glued to the front. The Cedar piece was sacrificial and easy to repair when you notched it on that dock edge, or someone else's gunnel.

 

The problem isnt with the end of the hull planks, its sealing the stressed chine joins close to the two ends, to be strong enough to take the wires out.
You cant hold the chine edges in position by fastening the ends only.

For historical purposes, I can reveal the results now that the hulls have had their final coat of epoxy.

The suggestion above works fine unless you are trying for a clear finish. Messing with the gap produces visible joins that dont look all that good being uneven.

My preference now for the process would be to apply an initial sealing coat of epoxy on the joins, making sure to not get a lot on the hull sides.

Then, I would do a careful colour match of thickened epoxy in the joins.

By sealing the edges first, the thickened epoxy has got a good enough 'grab' surface, so that it has enough strength to hold the stressed plank joins solid when the wires are removed.

Thickened epoxy by itself on the join seems to produce a few resin starved sections on the roughened plywood edges.

I know a few people recommend holding the planks together with anything but holes. This kind of build would be worth it when using the super expensive clear epoxy, but for a 'working boat', I dont think its worth the trouble

I have figures of between $10K and $20K for total cost of super finish kyaks, and you wouldnt dare take them near rocks and sand.

I am much happier with $3K boats that dont matter if they get dropped or run up onto rocks. Having the holes drilled really evenly during CNC cutting improves the 'look' a lot.

 

I'm much happier with $150 boats from the tip shop. Who cares if you paddle onto an oyster bar....

PDW