My husband and son spearfish in those waters and it’s cold right now (low 60’s.) Without a wetsuit, hypothermia probably set in quickly. These guys had no body fat either, they were athletes, I’d imagine low body fat could bring on hypothermia more quickly.
Good point; they were ‘big’ but no doubt; more ‘muscled’ than most non-athletes, their same size. Had not thought of how important real ‘fat’ is; in THIS situation. . .