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Old 12-07-2018, 08:00 AM   #7
Mako
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City: Seattle
Join Date: Jun 2012
Posts: 3,312
So it turns out that the bottom insulation, which was standard polyurethane open cell (the yellow stuff) was completely saturated with water. Insulation with water does not insulate. There must have been a small break in the past that allowed a tiny bit of condensation, which then snowballed. It would have been impractical to scrape out the entire layer (plus honestly not worth the effort) so I heavily caulked a thick polystyrene board to the bottom, sealing it tight. It looks great and we'll see how well it works over the next few months.

However this drives home the disadvantages of spray in foam for metal boats, which a lot of people love - when it gets wet it is a big gruesome worthless mess. And a boat is on the water.

Pretty much every commercial shipyard that I have visited and discussed builds with, have stated that they only install rock wool.
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