Dink build on foam and glass...

[maxiSwede]

.....using my current plywood/epoxi dinghy as mold.

I've got a 8' rowing dinghy as some of you may know. I am quite happy with it, rows we'll and all but it's a wee bit heavy at 25-30 kg, so I am playing with the idea of building one in 12 mm/ 1/2" foam glass and epoxi to get a lighter yet more buoyant dinghy clearly easier on maintenance too.

I am quite familiar with laminating and all that, but never did a"new build" before, so wonder a bit on how many plus of glass I would need.

Thinking 3 on outer skin (300 g/m bidirectional) and one as inner skin to get it as light as possible. It would have to be rigid enough to take a bit of a beating, since it will be our daily "utility truck" since we are full time live aboard cruisers.


Anyone with experience? Also a few facts to calculate the finsished weight, it's a "2sheetofplywood" size dink. Solid wood in the thwarts and rail today would be foam and glass fillets on the new one.

Cheers, Magnus

[CharlieJ]

Graham Byrnes (  B and B Yachts) tried a foam dinghy. turned out heavier than a normal plywood one, once enough glass was added to maintain strength. Sounds good but be careful

Just for kicks, here's a pic of me and a 6'6" Minipaw I built some time ago. It did NOT have the seats in it yet, but was all glassed. I was younger then also :)

[maxiSwede]

Charlie, thanks for replying, I kinda hoped you'd chime in... ;-)

It looks like some lines and blocks on top on your photo, no? .....ok, ok, you were younger, no prob :-D

Interesting the comment on glass on foam would be heavier. I guess it depends on the stiffness needed/wanted. It would have to be stiff, so too much movement obviously could grind down the foam to powder over time.

Still, Derek Kelsall pioneered foam and glass on his early racing tris, (notably the one he designed, built, AND sailed AND won the Ostar single handed in 1964(?). A record that still stands I believe). Is still sailing and holding up fine as other from his early days in the trade. Quite amazing. I've seen and visited one built a few years later along the same lines, also An Ostar boat, and it's certainly not a beefy build.

I don't think 3 plys of glass would suffice as an outer skin though so possibly the weight gain wouldn't be that great...?

In the meantime, our dink becomes ever more "composite". Nicely built, the original owner/builder only coated the outside of the hull with epoxi, so on each haul-out I replace some rotten wood with foam an glass. Not the hull itself, but "bulkheads"/ seat supports and the thwarts themselves. Same thing will happen with the lovely laminated wood along the gunwale, which were only varnished. I painted over all this to make the appearance unattractive for folks with longer fingers. So far so good, no matter what it will need stripping off all old paint, partially chipped and flaked to start from bare wood again. Hard to be able to get proper conditions for painting here due to humidity unfortunately

Cheers, Magnus

[CharlieJ]

LOL- no lines from ceiling. At that point the dink weighted, I believe, 30 pounds. You'll notice- no sheer clamps, and as I said, at that point no interior Strictly the hull. My new one, (same model) finished, weighs 60 pounds and I modified the seats a lot.

3 layers of 10 oz cloth, of itself is 30 oz per square yd- close to 2 pounds per yd, not counting the epoxy weight. A layer of 6 mm Okume is about the weight of the foam.

I'm sure it would work out but would likely not be as sturdy banging around behind a big boat.

A guy over on the Cruising Sailor BB (Todd Dunn) built a dink from Blue foam. He used it, but I don't think he was all that happy with it. Too far back to be in their archives- links all gone elsewhere also

[maxiSwede]

3 layers of 10 oz cloth, of itself is 30 oz per square yd- close to 2 pounds per yd, not counting the epoxy weight. A layer of 6 mm Okume is about the weight of the foam

Ah, there you are, I wondered!!  6 mm okoume - mine is from what I can gather from the Bulkheads/frames inside the hull 12 mm(1/2" more likely since it was built in the Sea of Cortez) as of the density or overall quality of the plywood I have no idea, it was bought locally in La Paz for sure. The builder did, slightly grumpily, mutter about selling it for less than the cost of the materials when I bought it for 400 $.  He had already put his boat up for sale, so whatever he could get in side-deals would be a ' bonus' of course.

6 mm ply with one ply of thinner glass inside and out....would it be stiff enough according to your experience?  Would be close to half the weight which is what I am looking for....