My friend's cat (Nacra F18) had water in the mast. After a capsize recovery problem he decided it was time to remedy the situation and I wanted to help so I could have someone to race against. When he drilled out a rivet, there was the definite escape of air under pressure - I heard it from 10 metres away. When we drained it, we got something like a pint of water out.

1. Is that enough to worry about?
2. How can there be water in there AND positive air pressure? We'd expect that the air pressure would be equalised if there was even the smallest leak. Which begs the question as to how the water got in.

Any thoughts? Especially on how to find a leak that appears to be able to resist positive air pressure while letting water in!

We did find that two cleats low down the mast looked to have the white deposit typical after a water leak, and they were not fully flush with the mast (too concave to be a fit against the relatively flat surface), so had been fitted with a lot of sealant to fill the gap. Needless to say these look suspicious and will be replaced. But we still can't understand how there was air pressure and water in the mast.

Puzzled
Simon

Thats an interesting connundrum. My only (wild) guess would be that the water got into the mast previously through a hole in the base during a full-turtle capsize. The salt or corrosion plugged the initial leak. Then, the mast heated up in the sun to create the positive pressure immediately prior to your drilling.

Like I said...its just a wild guess. I would try to find any remaining leaks by lightly pressurizing the mast with air and using soapy water to detect leaks.

It could be that there is a piece of sealant loose and creating a flap, so when pushed from the outside by the water it gets in, but pushed from the inside by expanding air it closes up trapping air. Could be hard to find by pumping air into the mast, might take the full removal and submerging method to find the bubbles....