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Old 10 February 2004, 16:15   #21
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Plywood RIBs

Most RIB builder still use plywood in hull structures. Just so say few, for example Avon, Delta and Tornado use that material. It's risky and I really don't wonder that wooden parts had rottened in the boat illustrated. If you open a 5-10 year old RIB, you'll be more than likely to find out wet plywood inside even though there were laminated layers used for protection. And everyone understands what it means if you RIB's bulkhead is rottening...
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Old 10 February 2004, 17:10   #22
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foam

The recent gallery post showed foam bulkheads in the prosport, so yeah it doesnt have to be ply
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Old 10 February 2004, 18:06   #23
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Re: Plywood RIBs

Quote:
Originally posted by Pitkis
If you open a 5-10 year old RIB, you'll be more than likely to find out wet plywood inside ...
I have just cut 2 holes in the deck of my 6 year old and the ply was very damp. It did not even scorch during pauses with the router when cutting the holes. Deck construction is 1/2" marine ply with 3-4mm GRP on top and a good coat of resin on the underside. There is no sign (yet - fingers crossed) of any softness or rot. If anyone wants an 8" dia. sample it's in my bin.
Reason for cutting one of the holes :- to fit a bilge pump to get the water out from under the deck. Now all I have to do is find a way of stopping it running in down the control cables, wires and pipes!!!
I now have a hatch each end of the deck and during this dry weather they are both open to let a bit of air circulate. I am also thinking of rigging a fan to force air thro' as well. Hopefully this will lengthen the life somewhat.
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Old 10 February 2004, 19:55   #24
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Mark, Spongy plywood decks are really common, as soon as water gets in, the problems start, and a few years down the line you will start noticing it. However it is the simplest & cheapest form of construction. A better way is a fully moulded deck insert which is moulded up, turned over and dropped on the hull.

However you will generally still have a core to leak. One problem is all the fittings & holes drilled. Water as you will know finds its way everywhere! The best way is to touch up the sides of any holes drilled with epoxy which will soak in to the core material, and then finish off with a sikaflex or similar sealant.

We also use a sealant called polysulphide, it comes in a mastic type cartridge, and never really cures - well it does cure but still remains really soft and tacky - it is great for covers & hatches that dont get lifted frequently, and then we finish that seal off with a light bead of sikaflex which gives a very durable and watertight finish. These items can be found in a builders merchants - polysulphide is white and costs about 3 a cartridge and the sikaflex equivalant is polyurethane sealant (not silicon) and costs normally about 4 with a choice of colours - beats the prices you will pay in your chandlers for the same product.
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Old 11 February 2004, 04:34   #25
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Thanks Neville

Have to say that I usually get my sealants from a builders merchant, as you say the price is far better than a marine outlet and the choice is wider. My favoured method of sealing end grain edges in ply is to apply several coats of 50/50 varnish/thinners to the cut edges. This give excelent penetration. Once there is moisture in the structure, as in this case I prefer to leave the grain open to the air so the moisture has a way out. Hence the desire to keep the voids well ventilated now.

I am very pleased that after 6 years of soaking there is no sign of softness, delaminating, blistering or rot in the bits that I have removed. I doubt the under deck void has been drained on anything like a regular basis in that time. Going by the "tide line" there has been a good couple of gallons of water under there for most of her life.
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Old 11 February 2004, 07:31   #26
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What i normally do when leaving the boat parked up is jack up the front of the trailer as high as possible and leave out all bungs so that any water that may be in the boat will be able to drain out. I have found that jacking it up so the tow hitch is about 1000 from the ground seems to do the trick, lower than that and water stays in. i then put a couple of axle stands under the front of the trailer. makes it a bit more difficult to nick it as well.
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