My dad let me bring an aluminum bass boat from Maine when we moved to The Keys, so I could hit the flats for bones and cuda. It was in the water for about 8 weeks when it became unable to get up on plane, regardless of throttle. I pull the boat and what I find takes me three days to remove with power washer and manual scrapping. >100lbs of barnacle and shellfish buildup, looked a lot like that (sans prop tho, mine was outboard). Learned my lesson. Salt water crazy.
And
that's why hulls are sealed with copper paint. Or hot pepper sauce, if you're Trini.