Swimming (drowning) rules.
"Only characters with proficiency in swimming" can swim.
Rules are provided for encumbrance on swimming and its effect on endurance, speed, diving and surfacing.
Endurance (turns of swimming) = experience level + constitution score
Speed = base (40 feet / round humans, demihumans 30') modified by strength, current, above or below the surface.
Diving and surfacing base = 20' per round.
Treading water (turns) = double endurance
No proficiency in swimming = tread water for strength score in rounds.
Breath holding - did this one in A (2011) Dungeoneers Survival Guide
1/3 Constitution in rounds
Not too bad.
Shipping (more boating) rules follow with capsizing rules depending on boat size and wind, portaging, movement modifications for large move (miles / day) and small move (feet / round) covering normal sail, max sail, normal oar and max oar.