Strengthing dinghy hull

[lumphammer]

For reasons of cost when building my Phantom dinghy I used a cheaper grade of marine ply, which I now regret as on the areas under tension round the bows and other places it looks like the wood is starting to split along the grain of the top laminate.

Please no comments about using cheap wood, I have already kicked myself enough, I don;t need any more reminding about what a bad idea it was.

What I'm thinking of doing this winter is taking everything back to bare wood, making good where necessary then applying a coat of epoxy, which I hope will stabilise the top layer.

I would like to know first, will this do any good, and second what preparation should I do to repaint. I'm thinking of using a marine gloss e.g. Toplac or similar?

 

[Lakesailor]

I've found that once you've got the ply really dry, 2 or 3 months stripped bare, dry and reasonably warm, then epoxy resin will soak right into the laminates. I used a slow setting epoxy and mixed it without any fillers. I poured it onto the ply and worked it around with a spatula (old credit card or similar). I found using some discarded old ply that if you cut it after applying the resin it had soaked through the top veneer into the first layer of adhesive. Whether it bonds to that is a bit in the lap of the gods of course, but assuming most of the adhesive is OK then you will have a rigid skin of epoxy-soaked ply encasing your dinghy.
You could then put a layer of glass material bonded to the outside of the hull in the same way as stitch and glue builders do. It may be OTT, but would form another strength layer and bond well to you newly impregnated ply. (it has to be specifically for use with epoxy)

Pic from www.Fyneboatkits.co.uk

 

[NickiCrutchfield]

Hi,
I'd second what Lakesailor says about the epoxy,and add, depending on whether the dinghy is finished bright or painted, that it could make sense to screw through the ply into ply strips on the outside to pull the laminate up firmly. Not tight obvioulsy. Also be a good idea to place a plastic membrane between the hull and the temporary stringer just in case a bit of stray epoxy glues the tempory piece to the hull. The holes can easily be filled and your ply will be as good as it can be made.
Nicki Crutchfield

 

[oldsaltoz]

G'day Richard,

Coating with epoxy will fix the flaking ply but will add some weight.

If you mix about half a cup of epoxy resin and hardener then add one third of a cup of Methylated spirits and mix well you will a thinner resin that will penetrate into the ply, roll or brush in adding extra near any end grain joints (Like the bow and transom and chines). Apply wet on tacky to avoid sanding between coats, as the thickness builds up tip off with a brush to maintain a smooth finis, and avoid more sanding.

You may have to this more than once, the idea is to saturate the surface, so any areas showing grain lines (very fine cracks) will need more.

When you have enough on let it cure for 24 hours minimum, then wash under a running hose starting at the highest point and working down rub with a scotch brite pad till the water no longer forms beads.

Let it dry and then give it light sanding, just enough to dull the high gloss, but not so it's all dull and flat looking, use a 250 grit for rapid results. Clean off all dust, I wash it and let it dry.

Now add a coat of epoxy primer and let it cure as per the manufacturer's instructions then give it a light sand and clean before painting with your choice of paints.

Hope this helps.

Avagoodweekend......

 

[davidfox]

You could either just use epoxy after stripping back, say 2 coats or put a layer of glass cloth on and put some filler into the 2nd coat and fair it.

 

[William_H]

Years back the material to use in stead of fibreglass for this express purpose was called Dynell. It is a soft fabric which is more suitable to following the contours of the outside of the plywood. (Kevlar would be good but V expensive) This will hold a good layer of epoxy but while having less strength than glass will give a better job. However I would go with just a thin coat of epoxy t0o fill the gaps and splits. Then paint it. good luck olewill