Plywood canoe

Discussion in 'Wooden Boat Building and Restoration' started by latestarter, Oct 2, 2012.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    The (few) S&G boats I helped with - or watched being built - were rightside-up allowing access to the seams, with minimal forms and a couple of simple female chocks or slings to prevent rolling. If planks are cut accurately from proper developments an S&G hull should “fall into shape” when the planks are stitched snugly together with very little support; if this doesn’t happen the hull is not ideal for S&G. It seems to me that the forms aren’t needed to define the shape, just for support until the seams are bonded. I’ve observed that the designer’s form dimensions are often not an exact fit and presumably don’t need to be.
     
  2. LP
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    LP Flying Boatman

    Ahhhh....We just having fun.:D

    Very true. That is the important part.

    Here is a photo of a support jig that I used for this very short kayak. I also reused the supports on a 12' kayak by mounting them on saw horses. You've already cut the outside shapes and it would be simple enough to turn them over and mount them right side up and do something similar. On yours, you might want a third support in the middle to control sag. The internal shapes would still be you primary guidance with the outside forms just holding your boat up. Before doing anything permanent you check twist and sag. :cool: Then after you do something pemanent, you check for twist and sag. ;) An hour later, you check for twist and sag. :D I have caught my kayaks with a bit of twist, put some big clamps (for weight only) on opposite sheers to counter with opposite twist and after curing, the hull was straight.

    IMG_0148.jpg



    I can understand your apprehension about sheathing the exterior. It's a daunting task if you have never done it before. If you go that route and you fillet and tape the inside first, it will result in less work and a better finish than taping the exterior seams. Working the interior first really solidifies the build and the resulting task of sheathing becomes much easier.

    When you say tacking, are you talking about tacking the seams on the inside or outside? Tacking the inside would be the best if you can get up inside of the hull without too much difficulty. Make sure that you tacks are no larger than your fillets are going to be. This will allow you to run nice, consistent fillets over them. Whats most important is setting and keeping your hull shape when you remove your stiches and tape, regardless of it being right side up or up side down to begin with.

    Sometimes you just gotta do what you gotta do.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    When building upside down, it's usually best to just crawl under the thing and "tack weld" the seams with thickened goo, possably some short lengths of tape in highly stressed areas. After going to all the trouble of aligning panels, it seems silly to screw it up in a roll over, without the inside corners having sufficient stiffness, to hold the shapes you've worked so hard to get. This means all of the outside seams can be filled and taped, plus you could also sheath the exterior at this time too, not to mention paint, so when it does get flipped over, you're pretty much done on the exterior. Of course if electing to sheath and paint while upside down, the inside corners will need considerable reinforcement and the temporary molds would need a different fastening method than typically used. These are not necessarily the forethought and planning that go into home builds, but it's possible and exactly the way I did the last taped seam build here. Once the boat was rolled over, all that was left on the exterior were rub rails, a bolt on skeg, keel guard and other minor trim or paint concerns.
     
  4. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    I was talking about tacking on the outside only but can see the benefit of the inside as well. Most of the upside down builds that I have seen have been on a long bench which restricted access to the underside but using these stands make it easy.

    I bought a tube of West System Six10 two-part, gap-filling epoxy adhesive a couple of months ago, it should be ideal to do the insides, they claim it can be used upside down. It is used in a standard caulking gun and is self mixed in the nozzle. I have enough to do a third of the chines. However there will be storage/buoyancy compartments at each end so I could use goo there where it will not be seen instead.

    A great deal of forethought has gone into this build, it struck me during the amateur/professional debates if I was charging for the time I have spent reading and thinking about it, this canoe would cost thousands of pounds. :)
     

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  5. rwatson
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    rwatson Senior Member

    There is no need to do any 'tacking' inside the upside down hull at all. You tack the seams on the outside between the stitches, and that is plenty strong enough to be able to take all the stitches out.

    Check the videos out at this web site. You may get a few ideas for your own build

    http://www.pygmyboats.com/kit-construction-process.html
     
  6. pistnbroke
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    pistnbroke I try

    I can see if you are makeing a 20ft boat over a frame with ply then tacking on the4 outside and covering would be the way to go as you are going to put a thick layer of FG on the outside ..the ply is only there to make the shape like a permanent male mould...But on a small canoe it would seem a lot easier to do it on the inside..
    I personally find covering the outside with CLOTH to be a nightmare ..just cannot get the creases out so now I use chopped mat and a belt sander....
     
  7. LP
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    LP Flying Boatman

    Thanks for putting up with us cantankerous, crotchety old boat builders. Sounds like you have a plan and will end up with a nice canoe. ;)


    And to Brother Watson. May the wind always fill your sails and the skies be blue. Peace to you.
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    - a person can gain a great deal of wisdom from building that first boat!

    I'm not a devotee of S&G myself, having had the opportunity to watch others becoming wiser during their builds . . . as a consequence I prefer to build my canoes with chine logs instead of epoxy fillets (a lot cheaper too) which are glued to the planks before laying the planks over the mold. This stiffens the long, floppy planks making them easier to handle, and they seek smooth, fair curves when they bend.

    I prefer bungy cords and straps to stitches although I will use a few sometimes. It seems to me that the S&G concept was developed for a dinghy, rather more substantial than a canoe. Canoes with their long, narrow planks cut from thin, lightweight ply must be secured in many places to keep everything under control, but don't need a lot of force to pull the planks into position. For these, the use of wire stitches seems overkill: if adhesive tape does the job, then why not?

    The problem with building rightside up seems to be the need to turn the hull over while it is still relatively fragile. If you haven't already done this, I suggest first adding bands over the hull where the station forms are, and raising the boat using cords looped around the hull attached to the ceiling. The boat can then be gently turned while resting in the slings, and lowered onto female chocks (some folk use short slings) under the hull.
     
  9. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    Thanks for the info rwatson
    pistnbroke I would not describe the ply as just forming a mould, if it was mainly acting as a core you would need a thick and heavy covering of fibreglass and epoxy.
    I have been advised that the covering is more effective on the inside as waves and bumps usually put the inside in tension.

    LP thanks for your post 47, very helpful, you also wrote "Thanks for putting up with us cantankerous, crotchety old boat builders. Sounds like you have a plan and will end up with a nice canoe."
    I found it amusing and instructive when people were advocating their different methods. I am not sure about nice, but unorthodox, bordering on unique.

    AK wrote "- a person can gain a great deal of wisdom from building that first boat!"
    Very true. The plan is subject to the experiences I have gained as work proceeds and advice given to me on this thread.
    I am well aware this experiment could have failed with a different design, or had my beginners luck not got the planks there or thereabouts.

    Surfing the internet I have only come across 4 people using adhesive tape, none of them went into detail apart from a series of photos.
    When I got the tape first I stuck it to my computer desk about 10 inches in contact and pulling down at a slight angle with reasonable force the adhesive held but the tape eventually started stretching.
    The way I used the tape was to firmly press it on to the upper plank, hold the lower plank tight to the upper with my left hand and pull the tape firmly with my right hand, then drop it down onto the lower plank. It surprised me how much friction it created. I used 2 hacksaw blades similar to how you use tyre levers to adjust the alignment.
    This afternoon I used the West six10, very easy to use and will stay on upside down surfaces, applied to joints and spread along with the curved end of a mixing stick. The main reason is that the further taping, masking and filleting would disturb the position so once cured I can relax.
     

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  10. txriverrat
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    txriverrat Senior Member

    I build my hulls upside down for a couple reasons,it doesnt take a strong back or long table,just two saw horses leveled side to side,it is much easier to eyeball your hull upside down and to get the edges straight and everything lined up
    I usually run my outside filets sand the hull and then apply my cloth on the outside before I ever flip tthe hull,by then it is pretty stiff.
    Ron
     
  11. rwatson
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    rwatson Senior Member

    yes, thats as good a way as any. The only variation in my current design plan specifies, is to lay it right way up temporarily, after the fillets have been done, so you can pin the flat bit of the keel down to a flat plank, to ensure an even keel line. Then, you flip it back upside down, and apply the outer layers.

    The secret is to insist on your cloth being rolled around a tube at the shop, even if you have to take a bit of PVC pipe to the FG shop yourself. otherwise, as you say, its f&^^(ed.

    Its also makes it easier to apply to the hull when its on a roll.




    The most exciting part is wetting out the 16ft of cloth in one go, when you plan for a clear finish. Just did it twice recently.

    Start at the middle, and work towards the ends. Each time you get a new pot of goo, make sure you wet out at least 12 inches adjoining the first batches 'wet edge', at both the the bow and stern ends, before working further towards the pointy bits. ( see attached illustration )

    That way, if the first batch starts to go off, you have a 'wet edge' to work from. If the edge of the saturated area goes hard, you will never be able to lay the cloth flat for subsequent 'wets', and you will end up with an unattractive 'partially wet' strip.

    I cant remember who first wrote about it, but if the glass is being tricky to wet out, a short blast of warm air from a heat gun (not too hot or long, otherwise it foams) makes it spread through the fibres like butter.
     

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  12. latestarter
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    latestarter Senior Member

    txriverrat, I totally agreed with your eyeball and adjustment point especially on this build as along a significant length of 2 chines they would not be visible right way up.

    Could you expand on the above. Is the plank on the outside and are the outer layers just on the chines?
    My canoe is very wide and only 3 planks a side so even with the support from the frames it tends to droop on the keel, the twist in the adjoining plank stops the adjoining plank sagging.
    Eventually the design calls for an internal 4 inch wide butt strap on the centreline, which will be fixed when right way up. I am assuming, that part of the hull will still be very floppy and I plan to sit it on a row of cross pieces to create a smooth curve for the rocker.

    Regarding the temperature of the resin, I thought I would use my ultrasonic cleaner, it has a separate thermostatically controlled heater for the water bath so the epoxy resin and hardener could be kept "poaching" at the desired temperature.

    Do you glass cloth on your own? If I decide to use glass cloth I will get someone experienced to do it. The time to try and do it by myself would be the outriggers.

    An important factor in how I am planning the boat is to try and avoid set backs, as I have a tendency to start projects and not see them to a conclusion.
     
  13. rwatson
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    rwatson Senior Member

    very true

    Planning and going over it in your mind is the absolute way to go. Persistance after failure can be essential too :)

    Yes. That is the major problem.

    You really should go through those Youtube links I gave you, it is all described in them. Particularly

    and


    Essentially, once the panels have been wired together, you turn the hull right way up, and pin the keel along a solid, straight plank. Then you tack the keel line solidly. that will ensure a straight keel. Then you can turn the boat upside down, secure it firmly and straight, then take out all the wires, and start the glassing on the outside of the hull.

    That should work ok, but might be a bit severe. A lightbulb is all that is needed. Just keep the resin and hardener in pre-measured containers for rapid mixing in the process.

    More hands would help, but it is possible do do it yourself with planning and dexterity. Check out
     
  14. latestarter
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    latestarter Senior Member

    Thanks again rwatson.
    I did watch the glass clothing and it confirmed I would be mad to try it for the first time on a canoe this size, it is 33% wider than a typical canoe of this length. Glad of the reminder about hot glue gun. I bought a cheap one months ago and forgot about it.

    Regarding the keel, my boat is different in that the keel line is glued rather than S & G to create a flat bottom. It is the first job you do. That is another reason why this system worked for me as the keel plank gives a straight datum line to build from. Originally I had intended to set up the frames with perfect alignment but in the end it was the keel plank that defined where I put the frames.
     

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  15. LP
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    LP Flying Boatman

    I'm not pushing in this direction, but another option would be to sheath each side separately (different gluing sessions) with them joining or overlapping in the middle. I'm curious about your keel. I don't see it in your photos so it must be inside the canoe. Here is a link to one of my builts again. Post #31 has a series of photos showing my wet out sequence on the deck. Just a fair bit smaller than what you would be doing. :D Only 12' X 2'.

    http://www.boatdesign.net/forums/wo...tion/mysticshore-12-gets-started-39315-4.html

    Slow harder, small batches and spreading your mixed quickly ensures the maximum amount working life. Typically, I will dump/dribble my whole batch on the boat and quickly do a rough smear with a scraper to stop runs. It also avoids an exotherm reaction caused by leaving your epoxy in it's mixing pot. With 2-1 mix ratios, my batches are either 6, 3 or 1.5 oz. On vertical and near vertical surfaces, I'll use a chipbrush to quasi-uniformly "glob" epoxy onto the cloth and then quickly go over it with the scraper to spead it to the other areas. It takes little practice, but you can control the direction of flow of epoxy off of your scaper, much like a plow moving soil. A upright scraper with tend to pick up the epoxy, while laying over in the direction you are moving the scraper with tend to lay down the epoxy and force it into the weave. Turning the scraper, relative to it motion, will push the epoxy in that direction. When initially wetting the glass, you'll lay the blade over to push the epoxy into the weave and once it's saturated, you'll use a more vertical blade to push the excess epoxy to other areas in need of saturation.
     
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