Prep for Glassing Plywood - to fill or not

I will be using frames and intend using just tape but if locally the forces warrant it I shall reluctantly revert to stitches.

in post 20 of your 'Epoxy and Cyanoacrylate (SuperGlue) on Plywood Boats' thread PAR wrote :-
"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."

http://www.boatdesign.net/forums/wo...acrylate-superglue-plywood-boats-44010-2.html

In that thread Gelmagic non sagging epoxy was mentioned but not obtainable everywhere. An alternative is West System Six10 two part thickened epoxy adhesive cartridge for use in a caulking gun.

 

Just another thought - are you trying for a really high quality clear finish, with no holes, then there is thing to consider.

The normal West System epoxy is 'not recomended for clear finish' according to their manuals, and my experience. You need the special 207 hardener. The only trouble is, its really expensive.

ie.
http://www.westsystem.com/ss/hardener-selection-guide/

Unless you need perfection, avoiding wire holes is not going to matter that much.

 

I am aiming for the minimum effort possible. Keeping the water out and going in a straight line are my primary aims. Anything more will be a bonus.
Paint outside, varnish inside. no glass cloth and no epoxy coating.
I am old enough to have learnt to sail in plywood dinghies which despite hard racing survived many seasons.
This canoe will be lightly used on canals and lakes.
To me drilling holes in a hull is best avoided.
I learnt a lot from your threads and look forward to your input as my project progresses.

 

Like rwatson said. Don't use adhesive tape for this application. It will be a great disappointment if you try it. Better to use small cable ties every decimeter or so.

 

Congratulations on your boat, it has been interesting following its construction.
My apologies for taking it off topic with the clogs.
A lot will depend how 'tortured' the panels will be in the design I am building.
It can be done, see this link:- http://s387.photobucket.com/albums/...16 - tape glue and glass/?albumview=slideshow

The photos run backwards in time, scroll to the end of the photos with the arrow in the bottom right corner.

 

The clogs discussion was very entertaining. No apology necessary.

 

Wow - doing that without epoxy would be tricky without any chine logs.

There is plenty of pressure on the 'feet' at each end.

I have used wire and plastic ties. You need bigger holes for plastic ties, and they have the disadvantage of not being able to be tightened from either side. With wire, you can use pliers to kink the wire for a super tight hold without having to fiddle with the twisted ends.

make sure you get the super strong flexible galvanized wire they use for tying reinforcing bars together, not the harder to bend garden stake variety.

 

that design you linked to requires glass and epoxy - how are you going to do it ?

 

How is it your are going to bond the panels together, without epoxy and fabric? That canoe wouldn't exist without the taped seam method.



This is how the butt joints where handled (read more epoxy and fabric). The only interesting thing about this technique is the seams are all taped at once (mostly). This is likely because of the desire for a bright finish.

 

What I said was "Paint outside, varnish inside. no glass cloth and no epoxy coating"

All I was interested in, was how he managed to get the panels into position, not his subsequent method.
I am using 4mm marine plywood which is very flexible, in theory it is over 3 times more flexible than 6mm ply. I have just fixed one end of a half panel and managed to twist the other end more than 90 degrees using my thumb and one finger.
I trained as an engineer and dealt with structural matters some of the time throughout my career. I have considered every step in the construction and kept asking myself why.

The scheme at the moment is to use the above technique to get the shape, tack it with the West System Six10. Turn it over then fillet and tape the chines.
Turn it back over and finish the joints with epoxy and filler. If you remember rwatson, we discussed bevelling the edges where the panels butt up to each other to get a reasonable gap to ensure a good joint, which is what I intend to do.

 

I think Par will concur with me - without the exterior glass, the structure will be quite a bit weaker, especially with thinner ply - if the original plans called for 6mm

It takes both layers to establish structural integrity.

If you are doing this in an attempt for a great finish, its at the expense of the structural integrity.

 

Latestarter: I too build plywood canoes for light duty without glassing. I have found 3 mm marine ply is fine for a solo and 4 mm should be OK on a two seater. Given good quality ply the key is the strength of the seams as any engineer or designer knows.

To date I have used chine logs which is equivalent to epoxy fillets plus glass tape and suits boats with 3 to 5 planks but as the plank count climbs the angles between planks become to obtuse and most folk go with S&G. For really high plank counts S&G there are so many stitches and the planks are so floppy that S&G becomes tedious.

Holding planks together without stitches is not the hard part. Adhesive tape, bungies, nylon cord strung gunnel to gunnel with wire hooks at each end, they all work, at least for canoes which tend to have gentle plank bends with little force required.

The problem is getting and keeping the edges aligned; stitches allow the builder to do this a bit at a time. One idea I came up with is discussed at http://www.boatdesign.net/forums/wo...storation/zipper-seam-construction-18316.html - I haven’t tried it full size yet although it works well in mockups - but the thread has a good discussion and related techniques are mentioned that may be of interest to you.

BTW: I'm not saying glassing is to be avoided: it greatly increases both strength and stiffness and is useful in severe duty boats such as whitewater kayaks and performance sail and power craft. Just that it needn't be used where it's not necessary.

 

rwatson, nothing that I am suggesting is intended as criticism of your build, from some of your comments you are interested in building for other people and as you have no way of knowing how they will use it, glassing makes sense for strength, stiffness and low maintenance.

I am looking for adequate strength and stiffness for my proposed modest uses, it will not be used on rapids or going over weirs etc.

I do not have the patience for a great finish, my hope is for a suitable boat with the minimum of effort.
The designer gives the option of 4, 5 or 6mm. The point I was making was the the huge difference in forces required for a thinner board.

This article I came across a couple of months ago by John Welsford struck a chord with me:- http://www.duckworksmagazine.com/03/r/columns/welsford/011/john.htm

AK we seem to on the same wave length. I have seen you post on http://www.songofthepaddle.co.uk which specializes in canoes and kayaks.

My canoe is wider than normal and I will have a heavy battery, to feed a small electric trolling motor, in the middle of it. For these reasons I will be stiffening the floor.

Aligning the edges may defeat me as I will be working alone and it looks like a 2 person job, one to align while the other tapes.

Thanks for reminding me about the Zipper thread, I had read it before but there were some useful pointers I had forgotten.