A Guide to Hull Blisters There is one phrase that causes a lot of anxiety during a haul-out: "Blisters have been observed on the hull" It’s often treated like a terminal diagnosis for a fiberglass hull, conjuring up images of a boat slowly dissolving from the inside out. But anyone gets too excited and assumes the boat is destined for the scrap heap— take a deep breath. While hull blisters are certainly a nuisance and can be expensive to fix, they are rarely fatal. Let's peel back the layers on what causes these bumps, why the "O-word" (osmosis) gets thrown around too much, and what it actually takes to fix them. What Exactly is a Hull Blister? In simple terms, a hull blister is a fluid-filled bubble that forms underneath or within the fiberglass laminate and the outermost protective layer of your boat, known as the gelcoat . When we pop them during a survey, they usually expel a pressurized fluid. If that fluid smells like strong vinegar, it’s a classic sig...
