Campaign Guide

Underwater Combat

In an environment like Marhaven, it should be obvious that there will be numerous and frequent underwater combat situations and encounters. The various rules governing these things are spread out between the Player's Handbook, the Dungeon Master's Guide, and Stormwrack. For easy reference, here is a summary of how we will handle the situation in Marhaven.

Movement

A character that does not have a natural swim speed can swim up to half their land speed in a full round, or one quarter their land speed in a single move action. A normal human, for example, has a land speed of 30. On land that human can move 60 feet in a full round or 30 feet in a move action. In the water, that same human can swim 15 feet in a full round or 7.5 feet (which rounds to a single 5-foot square) in a move action. Creatures without a natural swim speed cannot use the run action to swim faster.

Normally a DC10 Swim check is required in order to be able to move at all underwater. Since players have the option of taking 10 on Swim checks anyway and the penalty for most light armors is negligable, as a house rule I will only require Swim checks from creatures wearing Medium or Heavy armor or who are carrying an abnormally heavy load.

Some races, including aquatic elves, darfellans, and aventi, have a natural swim speed. Characters of those races can move their normal speed in a move action, just as a land-based creature can on land. Creatures with a natural swim speed can also run (move at 4 times speed in a straight line as a full round action).

Breathing

A normal non-aquatic creature can hold their breath for 2 rounds per point of Constitution while swimming under water. Taking any strenuous action -- making an attack, grappling, casting a spell, making a Strength check, etc. -- reduces this time by 1 round for each such action. A dwarf with a 15 Constitution score can therefore stay underwater for 30 rounds if all he does is swim. If he enters combat and uses one attack action per round, he can only stay under for 15 rounds.

A creature holding his breath can restart the 2-rounds-per-point-of-CON by spending a full round breathing air (ie, head above water). If the time limit runs out, he must make a Constitution check every round to avoid drowning.

Some races, such as darfellans and seacliff dwarves, can hold their breath for longer than 2 rounds per point of Constitution. Aside from that difference the same rules and limits apply.

Drowning

If a creature stays underwater past the limit for holding his breath, he must make a Constitution check each round or begin to drown. The check starts at DC15 and the DC increases by one for each round the creature remains under water. As soon as the creature fails a Constitution check he becomes unconscious (zero hit points). On the next round the creature goes to -1hp, and on the round after that he is dead.

Weapons in the Water

Only melee piercing weapons work normally under water. All creatures using slashing and bludgeoning weapons take a -2 penalty on their attack rolls and do only half damage on a successful hit. Ranged weapons suffer a -2 penalty per 5 feet of distance to the target regardless of the weapon's normal range increment. Thrown weapons of any type cannot be used underwater at all.

Creatures in water have total concealment against attackers who are out of the water (50 percent miss chance) because of the water's refraction and surface tension.

Some weapons are designed to be used in water and are subject to different penalties and limits. An aquatic crossbow has no penalties underwater and a 40-foot range increment; an aquatic longbow works underwater with a range increment of 10 feet but no penalties. Both work above water as well.

Spellcasting

A creature that cannot breathe water cannot speak underwater; therefore a spellcaster who cannot breathe water cannot cast spells with a verbal component while under water. This also applies to command-word-activated magic items and language-dependent spells, obviously.

Spells with the Fire descriptor require the caster to make a Spellcraft check (DC20 + spell level). On a successful check the spell produces steam instead of fire but otherwise works normally. On a failed check the spell is wasted.

Workarounds

A number of spells and feats can impact a character's ability to function underwater. Some of them are:

• Water Breathing -- Will allow a non-aquatic creature to breathe and speak normally (including spellcasting) under water. This does not provide any benefit to swimming ability.
• Freedom of Movement -- Eliminates all penalties associated with slashing and bludgeoning melee weapons and allows a non-aquatic creature to swim at their normal land speed. This does not confer any ability to breathe or speak under water.
• Airy Water -- Surrounds a creature in a 20-foot-radius bubble of frothy, breathable air/water. Allows a non-aquatic creature to swim at half their land speed or walk on the bottom at full speed and eliminates the penalties for slashing and bludgeoning melee weapons.
• Aquatic Shot feat -- Reduces the penalties for using normal ranged weapons and allows limited use of thrown piercing weapons underwater.
• Expert Swimmer feat -- Increases the time a character can hold his/her breath by 50 percent (3 rounds per CON point) and increases the movement rate while swimming.
• Steam Magic feat -- Eliminates the Spellcraft check to cast fire-based spells under water.

All of the above can be used by creatures with or without any aquatic racial features. For those with a natural swim speed there are many more choices in both Stormwrack and the Player's Handbook.