Bendability of Robbins Ply for Rolled-in Decks

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jpa_wfsc
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by jpa_wfsc »

chris wrote:
But have just done an experiment with plywood ( see photo) the ply is 3ply 3mm poplar from avon plywoods cost about £17 for a full sheet. It is very light indeed but only graded as water resistant so don't use it for a hull. I used a piece about 7" x2" . The method of steaming is a little eccentric but only OK for small pieces, on the other hand very quick.
1 soaked material for about 1/2 hour
2 wrap in wet paper towel
3 wrap in cling film.
4 Microwave for one -two minutes
5 bend round wine bottle.
6 remove after a minute
7 remove cling film etc
8 tied string round it to hold shape.
9 Microwave for 1/2 minute to dry it,

It has held its shape very well, has not split or delaminated. it very stiff and strong. The tightest curve has a radius of about 3". Grain follows round the curve.
If one added step 10 - treat bent section using SP systems epoxy which is bourne into the wood by an evaporating carrier and then cures deep inside - would you end up with both a light and long lasting bent bit of marine ply?
j./

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JimC
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by JimC »

jpa_wfsc wrote: would you end up with both a light and long lasting bent bit of marine ply?
I fear not. The glue between the layers again. It would surely inhibit your epoxy reaching the middle veneer, and also would be prone to fail...
But I sometimes wonder if we get over struck on marine ply for dry sailed dinghies. If you are really diligent about maintenance and coatings, store indoors for the winter etc then I bet you'd get a pretty good life out of the cheap stuff. Don't think I'm going to volunteer to try though.
chris
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by chris »

jpa_wfsc wrote:But I sometimes wonder if we get over struck on marine ply for dry sailed dinghies.
Last century, in '95, I built a very simple 15' lapstrack, flat bottomed rowing boat. We rowed and camped down the Thames from Lechlade. It's been used only a few times since and has spent most of the rest of its life outside upside down under a tarp. It was made from exterior grade ply from the local builders supplies. It's only had one or two coats of varnish since and the underwater parts were painted with marine paint ( one more coat since. I think exterior ply is expected to be OK for about twenty years and I can confirm that. None has gone soft but there are a few black areas where the varnish has gone and I ought to treat it a lot better than I have done. But it was made for fun on the water with the children rather than heirloom. So yes exterior ply will not fail that quickly but I still would not choose it for decent job.

The British Standards for ply refer to the timber used and the bonding glue as two separate issues:
Class 3 : Exterior Conditions
Capable of withstanding exposure to weathering conditions and liquid
water over sustained periods of time.
Replacing WBP (Weather and Boil Proof)
Nessa
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by Nessa »

The pic of the FM skeleton reminds me of the Peril. It also has the rolled in decks, which are currently separating from the gunnel.

It's going to be interesting to see the boats side by side as I think the Peril has more in common with this than the more recent machines.
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Rupert
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by Rupert »

The marine and exterior grade plys use the same glues, I believe. What I was taught was that it is the number of joins in the face ply and the size of voids inside that are different. You can get experior ply of higher quality wood than cheap marine ply.
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by Obscured by clouds »

Yup. that's my experience too Rupert. There's a sheet of superb 9mm ply left over from my fathers boatbuilding stock. I always thought it was marine ply. Imagine my surprise when I discovered the WBP stamps on it.
An expensive sheet of 'marine ply', again 9mm, that I bought locally to form the bulkheads on Sibrwd turned out to be rather less 'marine' than I was led to believe.

I'm still arguing over that with the place I got it from.
Tony



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JimC
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by JimC »

I was actually thinking below exterior grade...
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Re: Bendability of Robbins Ply for Rolled-in Decks

Post by JimC »

On a related subject, here's my staple removing tool.
https://flic.kr/p/pMANZB

Note the heavy duty plastic packing tape to protect the wood. Picked up some of this from the builders merchants skip. Epoxy doesn't stick to it, all sorts of uses. Under g cramps is a good one
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