Painting below the waterline

[Michael Rogers]

Last week it occurred to me that I hadn't inspected Cavatina's bottom for some time, in case there were significant scratches or whatever requiring attention. So I had a look – and was glad I did and simultaneously wished I hadn't. There weren't scratches: there were areas (not huge, but 'significant') where the paint had peeled right off, with ragged edges where the paint was lifting – like the edges of a big burst blister. So far as I could tell, this involved only the top layers, not the primer underneath (and, when I built her, I coated every single ply part with epoxy before starting assembly): so I am hopeful that the underlying plywood (which is either 9mm or 12mm on the bottom, ie quite substantial) won't have soaked up significant water.

She clearly needs to be brought back here (I usually leave her at Studland over winter) to go under cover, be turned over and have her entire underneath stripped back to the wood. But I have two questions – 1) why has this happened? 2) exactly what should I do in terms of re-coating?

By way of explanation, I painted her (in 2011) with Jotun two-pot paint, following precisely the instructions which came with it, careful attention to mixing, over coating times etc etc. Two- pot painting is time-consuming, BUT it was time well spent because the results are vastly better than with 'conventional' paint (I used one-pot on my first build), particularly in terms of toughness and longevity: there really is no comparison. The paint work is still in amazingly good condition, with no work on it needed – except for this now serious problem on the bottom.

Back in 2011, aware that the paint I used was sold as topsides paint, I rang my Jotun supplier about using it on the boat bottom. The reply was that topsides paint would be fine if I was storing the boat out of the water, ie not on a mooring. Made sense, but the bottom has, over 8 seasons, been submerged for periods up to 10 – 12 hours, in contrast to the topsides. So it has presumably eventually given way, and water has got in through scratches or whatever.

I would welcome advice about what to do this time round. My inclination would be to put on 3 coats of bog-standard epoxy resin as basic protection, and then do primer and top coats in something designed for below-waterline. I'd look for something really 'tough'. Question – what do people like Swallow Yachts use for this purpose? (I don't need antifouling as such, because weed growth etc is clearly not a problem) I'm aware, obviously, that SY don't do many, if any, builds in epoxy-ply these days.

Comments much appreciated.

Michael Rogers (Trouper 12 'Cavatina')

[garethrow]

I have always used International 2 pot Michael on Gwennol Teifi, above and below the waterline and find it lasts for ages without trouble.

Regards
Gareth Rowlands