[help] gelcoat chicken skin

   
What a disaster.
Checked it after a few months of storage. The deck (fiberglass) is covered by bubbles, the hull (carbon-kevlar) is not.
What could it be? fiberglass osmosis or a gelcoat problem?
The ski was stored outside, wrapped in a nylon black sheet and a silver tarp, sheltered from the sun and rain by a roof.
Hot and dry climate, rain just in the past days.

Are the little 1 mm bumps the bubbles you are referring to?  How old is the ski?  

yes, those bumps are about 1mm diameter and 0.5mm high, the sky is 9 years old and probably repainted

I can't be certain without a physical inspection, but it looks to me like it was repainted without proper surface preparation.  I bet that if you make a little cut in the paint and start peeling, that it will come off in sheets kind of like tape.  The only cure is to completely remove the paint and start over, with proper surface prep.  Sorry

I suggest you pop one or two of the little bubbles with a pin and see what comes out. If a polyester resin was used for the deck layup and the blister exudes acetic acid (vinegar) then you probably have an osmosis problem. 

My experience is with a boat I painted that developed similar blisters about a year and half later. I was told that the epoxy primer used had chalk in it and was hygroscopic. Real bummer.
The way your ski was stored may have contributed to the problem. Kind of like putting the ski in a plastic bag and them putting it in a microwave. A surfski will most likely have residual moisture no matter how dry you think it is.
  All that being said, if it is only on the deck, leave it. It looks pretty cool!
You can tell people that it is a new super secret proprietary texture that makes the ski faster. (Maybe it is faster?) Or it's a new non skid technique.