Harry et al,

Thanks to all for the advice - there are so many possibilities here. I've re-examined the hulls are there are no blisters. Osmosis may be a factor, in that the last two years the hulls have taken on a small amount (~1 gallon during 5 months) of water without a discernable leak.

I'm hoping that a coat of anti-fouling paint (epaint?) after a winter in a dry garage (humidity is low up here, but the snow is high) will both seal things better against osmosis and prevent the algae growth.

I really wish I could store this lovely boat out of the water, but proximity to a good lake; the time, effort, and logistics of taking it in and out frequently would curtail my sailing time so much that I'd probably only take it out once or twice a year, and it would eventually die a sad death in a back yard. I'd rather do some extra work every year or two, sail frequently even if not at optimal speed; and thoroughly enjoy every day I'm out there.