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11 March 2017 at 02:02 #70233
Andy Stoneman
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@andystoneman15177
Hi, I am intending to build a Thames sailing barge in the near future, Thinking ahead as I often`sometimes do, I have a question which is one of those how long is a bit of string types, With any boat i know how important it is to be buoyant and have a low centre of gravity, Heres the scenario, I know the best thing would be to plank the hull with balsa, its customary these days to resin the sides to strengthen the hull, Ok so this makes the hull heavier, I would like to use 3mm MDF or 4mm plywood, So bearing in mind the MDF is slightly heavier but not so much Should I plank in balsa and glass it up for strength or just use the MDF and use half a dozen coats of varnish, which is going to be the heavier hull

Andy
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11 March 2017 at 02:02 #4395
Andy Stoneman
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@andystoneman15177
Hull building materials
11 March 2017 at 08:34 #70234
Malcolm Frary
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@malcolmfrary95515
In any sailing boat you only want weight at the lowest possible point, so you need the lightest possible hull consistent with it being strong enough. Anything else, you have a display model than can only be put on the water when there isn't enough wind to make it go.
11 March 2017 at 08:34 #70235
Dave Milbourn
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@davemilbourn48782
Andy

Whatever else you do avoid MDF. It soaks up water like a sponge then swells up and turns to mush. If you use it as planking then you'll need to sand it to shape and I wouldn't like to try getting a decent finish on it afterwards.Yes – I know there's probably someone out there who routinely uses it for planking, frames, masts etc but the closest I would allow it to water is as a boat stand – and that would have five or six coats of varnish.
Balsa is OK for planking a small hull but you need to get exactly the right grade. Too hard will be difficult to bend and too soft will either crack and/or sag between frames (so-called starved horse effect). I've made three POF models around 30" – 40" long and used obechi each time. It's a relatively straight-grained, knot-free wood, not too hard to bend and sands easily. It has a consistent hardness from one sheet to the next and also takes up aliphatic resin glue very well. SLEC sell it in various sizes of strip or you could save money and strip it down from sheet. Others rate lime as good for planking but I've not used that myself.

Dave M
11 March 2017 at 09:38 #70239
John W E
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@johnwe
Many moons ago, there used to be a bloke called Mike Mayhew; he used to build Thames Barges from cornflake boxes and they used to sail. The old Man Dave Milbourn's friend Riggers, used to know him well. How he used to seal them, I believe he used to coat them with resin I believe. As has already been stated personally I wouldn't use MDF in water due to the fact that it falls apart when damp. Plank with either cedar or lime and plywood frames and make plenty provision for lead ballast in the bottom of the hull. Seal the hull with epoxy resin.

john

Edited By bluebird on 11/03/2017 09:39:57
11 March 2017 at 19:05 #70255
Andy Stoneman
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@andystoneman15177
Thanks Dave and Bluey, Maybe what Ive got hold of isn't MDF then as I've soaked it for over an hour untreated and measured the thickness and theres very little change overall, However I liked the cornflake box idea but will stick to your suggestion Dave. Most of the hull length of a model barge is virtually a straight box affair except the two ends, So Obechi or Lime it will be for planking and Definitely plywood frames ! The ballast will be a removable lead keel trying to keep the weight as low as possible, Thanks again for your help.

Andy
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