OK I just got out my starboard Rio only to discover thousands of tiny (matchhead) size soft bumps all over the underneath, I always have slackened off the air valve after use and have looked after this board. Is this delamination? its only a few months old and used about 20 times so would it be repaired under waranty?
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It sounds like osmosis damage to me, probably caused by storing a wet board in a board bag. The good news is that it's unlikely to have affected the structure of the board. It's probably just the paint blistering. If you're very lucky, the blisters may subside as the board dries. However it may need sanding down and (if you care about the finish) respraying. Try and dry it out first though, and then maybe have a chat with a board repairer before attacking the blisters.

It's a winsurfer, it's meant to get wet and go in a board bag.

Take it back to the supplier and tell them that it is not fit for purpose.

"I always have slackened off the air valve after use"

You should only be messing with the air valve in the following conditions (per Starbaord's instructions):

Always ensure that the vent is closed prior to any contact with water, and opened when either stored in extreme temperatures or transported through large changes in altitude.

Keep opening and closing it will wreck the seal.