Falling off a ship in rough water can be dangerous, and the rules provided outline the mechanics and consequences of such a situation. Here's a summary of the rules:
The Fall:
- Falling overboard places you 1d6+5 feet away from the ship, while being pushed overboard puts you 2d6+5 feet away.
- To enter the water without taking damage, you must succeed on a DC 10 Dexterity (Acrobatics) check. Failure results in 1d6 hit points of damage from the fall.
Swimming:
- Each foot you swim costs you one extra foot of speed.
- If you are within 5 feet of a moving ship or one involved in a ramming or grappling maneuver, you must make a DC 10 Strength (Athletics) check. Failure means you cannot move that round, using all your strength to stay afloat.
- Climbing back onto the ship requires a DC 15 Strength (Athletics) check. Failure results in falling back into the water.
- Carried items that are not specifically waterproof will get wet and commonly carried items like rations, paper, and spell scrolls will be ruined and made unusable.
Underwater:
- You can swim underwater as long as you can hold your breath. Your underwater swimming speed is the same as your surface swimming speed.
- Swimming straight down is possible at half your swimming speed, or 15 feet per round if holding the equivalent of medium armor, or 25 feet per round if holding the equivalent of heavy armor.
- If unencumbered, you can swim straight up at 20 feet per round.
Armor:
- Swimming with light armor requires a DC 10 Strength (Athletics) check each round. Failure results in a speed of 0 for that round, going underwater, and losing one carried item (shield or weapon).
- Removing light armor takes one minute (10 rounds), or half that time with a successful DC 15 Dexterity (Acrobatics) check. Failure to remove armor after three rounds results in one level of exhaustion.
- Swimming with medium armor requires a DC 15 Strength (Athletics) check each round. Success allows you to stay on the surface, while failure results in sinking 10 feet and losing carried shields or weapons.
- Removing medium armor takes 1 minute, or half that time with a successful DC 15 Dexterity (Acrobatics) check. Without armor, swimming towards the surface is possible at a rate of 20 feet per round.
- Swimming with heavy armor is not possible, as it gives an effective speed of 0. Sinking occurs, and a DC 25 Strength (Athletics) check is required each round to stay above water or swim towards the surface.
- Removing heavy armor takes 5 minutes (50 rounds), or half that time with a successful DC 15 Dexterity (Acrobatics) check. Without armor, swimming towards the surface is possible at a rate of 20 feet per round.
Drowning:
- After a certain amount of time holding your breath underwater (1+(Constitution bonus) minutes), you fall unconscious and start making death saving throws if still underwater.
- If you become stable but are still underwater, you cannot remain stable and must start making death saving throws again. This continues until you die unless you are saved.
These rules provide mechanics for handling falling off a ship, swimming, and the effects of different types of armor in water. They add realism and consequences to underwater situations and require checks to stay afloat and survive.