What is 'Osmosis' in fiberglass (PRFV / GRP) boat hulls, what is its primary symptom, and how is it prevented?

1. Water penetration through the outer gelcoat reacting with unreacted polyester resins to form acidic blisters; prevented by applying epoxy barrier coats to a dry hull
2. Corrosion of bronze thru-hulls caused by stray electrical current; prevented by wooden plugs
3. Fouling of the bottom by marine barnacles; prevented by high engine speeds
4. Cracking of the deck due to excessive sail halyard tension; prevented by nylon ropes