Swallow Yachts Forum > Technical
GRP or ply?
Craic:
--- Quote from: Julian Swindell on 08 Mar 2011, 09:47 ---... It isn't a big job ... . The outside of the hull takes about half an hour to mask with tape and maybe 45 minutes to roller dark green. It has come up like a mirror, which has surprised me. ...
--- End quote ---
What? No sanding of the old coat?
Last -and only- time I did that it came up like a mirror too. Only, parts of it came off again in flakes half through the season and then things looked -and were- really horrid.
Re damages in a plywood hull: If you have a splintered indentation in a plywood hull, and cannot get at it from inside, you sure can patch it over on the outside. But that is only superficial. The structure underneath remains broken and inside the inaccessible cavity the wood fibres remain to lie open and remain unprotected against the moisture inside the cavity. Plywood is no plastic, it deteriorates faster where you have moisture getting in.
Tony:
Hi, Nick.
I have a Cardigan Bay Lugger in ‘poxy ply.
I probably would have asked for GRP but she was the prototype so it wasn’t an option. With a production run of 3 so far (unless I’ve missed something) chances are there never WILL be a GRP version!
Am I bovvered, though? No! The boat is a total delight to trail and sail being so light. I rather think the cabin is better insulated, too, but comparisons are subjective and difficult.
Downsides to EP? Very few with this modern stuff. True, the sanding is a pain in the proverbial - and I have to call my splodgey attempts at re-painting “Workboat Chic” but I feel more comfortable with wood than GRP. Just lack of practice with latex gloves, really.
Just one point. Where I sail the surrounding geography makes the bit of water just around the pontoon subject to really fluky winds at times, gusting from different directions without warning. (They call it a Rotator.... or some such.)
I “tut tutted “ smugly when a chap in a nice new (and solid-looking) plastic gaffer got caught out recently. What was a measured approach suddenly turned into panic stations as he careered into the pontoon at a rate of knots, flexing the port bow with a nasty splintering noise. Sounded expensive. I wasn’t so smug when I did the same thing myself a week or so later! If anything I was moving faster but I just bounced off with a solid sounding “Thunk”! Bit of varnish off the rubbing strake otherwise nothing. Nada. Ziich! (No wonder Matt can afford to give a 6 year hull warrantee.) I did something similar a month later....this time I went up the beach like a D-day Landing Craft. No rocks, thank Goodness, so I didn’t even lose any paint. Stepped nonchalantly over the bow and fetched the trailer as if I do it all the time!
(I might be a slow learner but now I drop the sails and row in from 200 yards out..... discretion being the better part of seamanship!)
Tony:
Hi, Nick,yet again...
Forgot to say (too busy spinning a yarn, as usual) Claus is dead right about the insidious effects of water ingress at the site of damage - or old screw holes.
Wood rots.
Its supposed to rot. The bacteria and fungi responsible have had millions of years to perfect the cellulase enzymes that do the job. Before they recycle your wooden boat, develop the habit of slathering every ding with epoxy (after a suitable drying out period) to keep 'em at bay for as long as possible. I think, with care though, I should be able to pass my Lugger on to the Grandchildren. (Unless they carry out their threat to pack me off to a Care Home...in which case all bets are off!)
Ah! but just wait till the Diesel Bug evolves a new set of enzymes. Crisp packets, polycarbonate bottles ( and plastic BayRaiders) will become Biodegradable overnight!
Craic:
Nick,
you will have got the message now that plywood boats are not as maintenance free as you may wish, and are ready to rot if you neglect that maintenance.
Your other concern was that you may have difficulty handling the somewhat heavier plastic version of the S17. Absolutely no reason to be concerned about that, as most of us here can handle the really much bigger plastic BR 20 without assistance.
Hope this helps.
Anthony Huggett:
I understand from Matt that Swallow Boats build all their wooden boats by pre-coating the plywood with epoxy (I'm still doing this step on my home built BR17).
Regarding Claus' point on repairing a punctured wooden hull, leaving exposed fibres is certainly undesirable. How about the following method? Suggestions for improvements welcome!
1) First make the hole bigger, back to firm wood and get the edges smooth with sandpaper. It must be made oval rather than round, or rectangular rather than square.
2) Make an inside patch, larger than the hole all the way around by say 1 inch. If your hole is now 1 inch by 3, the inside patch will be
3 inches by 5. Make a couple of finger holes in the middle of the patch piece.
3) Seal the inside patch with epoxy, including the finger holes. Do the same around the edges of the hole. Allow to cure fully. Sand to remove amine blush. Also poke your finger into the hole in the boat, and sand around the inside of the hole to provide a key for the glue. You want to remove any bilge/locker paint, into the epoxy or bare wood.
4) This is the hard part. Put epoxy all around the inside of the hole. Now you have to post the inside patch into the boat, without losing it into the tank, and draw it back towards the hull. To do this, put a piece of thin rope through one finger hole, and back though the other. Keeping hold of both ends of the rope, post the inside patch into the boat, draw it back so it is flush with the inside of the hull. Fiddle with it so it is nicely over (or should that be under) the hole, and tie rope tightly around a batten on the outside of the boat so that it pulls the patch tight. Clean up any excess glue and allow to cure.
5) Remove the thin rope and batten. You now have a recess into which you can simply epoxy a second piece of (pre-sealed) plywood from the outside, and finish off.
Caveat - this is just a suggestion, I haven't actually tried it and I hope I never have to.
Anthony
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