Thanks Tom, PM sent

More than happy to do either, happy to help you repair it or do it all for you.

Thanks dbcrx and Dravis, I think first things first then, getting it washed out and dried to hopefully stop it getting any worse, then wait for the warmer weather before attempting a repair. Thanks for the boot drier tip.

To me that looks like blisters in paint... The layer just seems way too thin to be gelcoat..  I would definitely wash out any traces of salt in the "lockers" and try to dry them out, maybe using some sort of tubing and a "boot dryer"
(The ones you can buy for drying your boots, with a small fan and heating element that blows warm air out through "tubes" you put your boots on..  Am i making any sense here... )

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

When I say popping open, what I mean is the whole blister will break off leaving a small circle of exposed fiber, not just release the air/fluid inside and settle down. Osmosis also takes longer to develop normally. You can tell if it is by bursting one of the blisters. If moisture comes out and it smells like vinager then it is osmosis. If the gel coat is very thin, then it could be a combination of the damp lockers and air expanding pushing the gelcoat out through pinholes in the laminate. To dry the lockers you will have to flush them. Salt water will never dry out fully as the salt remains and then reabsorbs moisture.

Hi Chris,
Unfortunately, it was bought second hand so the warranty does not extend to us.
And in any case I now think it is due to the salt water in the bulkhead - fault of the previous owner and our lack of knowledge in not checking and leaving it.
We would be interested in finding someone who can do this repair. I've done my share of car body repair but Im daunted by this because of how thin the gelcoat is.

Hi 

Hi drcx, they are popping (see pic) and there is no sign that they are going away, in fact I dont see that they can, they are too big and even if they do the gelcoat where they were will be detached from the carbon.

I think that the fact there is salt water within the bulkheads is the cause as the bubbles are limited to area of the hull and deck above and below the bulkheads - there is no bubbling to the hull below the cockpit.

I cant see any alternative but to sand and refill but do I need to wash out the bulkheads or will allowing them to dry properly (with salt still in) be sufficient. I'm not sure of the best way to ensure the salt is removed other then run fresh water into them for quite a while.

Those don't look like osmosis blisters. Osmosis blisters tend to bubble to the point where they will pop open. And osmosis blisters won't just go away when left to dry out, once it's there it need to be opened up and washed and dried. What you have looks more like some kind of contamination in a painted surface. Either way the only fix is as suggested. Grind or sand them out and either refill the gel coat, or fill/fair and repaint.

Thanks for your replies,

ChrisR, unfortunately bringing it indoors is not an option being 7.5m (23ft) long, although I am trying to find a secure barn or such like to rent some space, so I may have to wait for the warmer weather for it to dry out properly.

Since my first post I've noticed that the bubbling is not around the open cockpit area but only around each of the bulkheads, which are sealed except for a small bung. Removing the bung revealed that both bulkheads are very wet inside (although no water seems to be flowing around in them), but there is crystalised salt inside - the previous owner used the boat on the sea. I'm leaving the bungs out but they are very small so will take a long time to dry out, would it be better to wash them out with fresh water first or just leave them to dry?

Interesting what you say about not storing it in a sock - it has been stored outside on tressles, upside down so water has not collected in it, but the nylon sock has been repeatedly wet and dried with the weather, so I this wont have helped. I will do as you suggest and remove the sock and if I can't get storage I will make something like an open ended poly-tunnel.

Warren, how easy is it to match the colour (white)?