Open space is the space between worlds, where ships sail. It has no air, and it is very cold. A ship's helm holds a pocket of air around the ship, called the air bubble, so the crew can stand on deck and breathe.
Size. An air bubble reaches about 60 feet out from the hull in every direction. A warship's bubble reaches about 120 feet.
Air and Warmth. Inside the bubble, the air is fresh and warm. Creatures breathe and move normally.
Pull to the Deck. The helm also holds creatures and loose objects to the deck with normal weight. Inside the bubble, down is toward the deck. See the Gravity and Heavy Worlds rule.
Two Bubbles. When two ships come close, their bubbles join. Creatures can then cross from one deck to the other. See the Boarding Actions rule.
A helm stops when it runs out of crystal or is broken. It also stops when its mage leaves it with no course set, or when a Vhal creature drains it.
Stale Air. The bubble stays around the ship, but the air is no longer refreshed. The air stays good for 24 hours. After that, the air is stale. At the end of each hour in stale air, a creature must succeed on a DC 10 Constitution saving throw or gain 1 Exhaustion level.
Cold. One hour after the helm stops, the bubble is very cold. Use the Extreme Cold rules. A fur coat or a spacer cloak gives Advantage on the saving throw.
Weak Pull. The pull to the deck stays, but it is weak. Treat the ship as light gravity until the helm runs again.
Restarting. A working helm starts again with an action from a creature who can run it. Fresh air and warmth come back at once.
Some Vhal creatures can take a ship's bubble away. A ship with no bubble is in open space. Every creature on deck or inside an open part of the ship follows the open space rules below. Closed cabins and holds keep their air for 10 minutes for each creature inside them, then the creatures begin to suffocate.
A creature outside any air bubble is in open space.
No Air. The creature can't breathe. It can hold its breath for a number of minutes equal to 1 plus its Constitution modifier (minimum of 30 seconds). After that, it suffocates. It gains 1 Exhaustion level at the end of each of its turns. When it can breathe again, it removes all levels of Exhaustion it gained this way.
Deadly Cold. At the end of each minute in open space, the creature takes 2d6 Cold damage. Resistance to Cold damage halves this. Immunity to Cold damage prevents it.
No Weight. Nothing pulls a creature in open space. A creature with no Fly Speed can't move on its own. If it pushed off from something, it keeps drifting in a straight line at 30 feet per round. A creature with a Fly Speed, such as one under the Aether Wings spell, can fly normally in open space.
No Sound. Sound does not carry in open space. Creatures there can't hear each other unless they touch.
Protection. An air bubble charm, some class features and some spells give a creature its own small bubble. A creature that does not need to breathe ignores the No Air rule, but the cold still harms it.
A creature that falls off a deck or is pushed past the rail falls down past the hull.
Catching On. A creature that goes over the rail can make a DC 15 Dexterity saving throw as a Reaction. On a success, it grabs the rail or the hull and hangs there. Climbing back up takes 10 feet of movement.
Falling Out of the Bubble. A creature that does not catch on falls out of the bubble by the end of its next turn. It is then in open space. It drifts away from the ship at 30 feet per round.
Tether Line. A creature clipped to the ship with a tether line stops at the end of the line and does not leave the bubble. It can pull itself back on its turn with 20 feet of movement.
Throwing a Line. A crew member can throw a rope or tether line to a drifting creature within 50 feet as an action. The drifting creature catches it with a DC 10 Dexterity saving throw as a Reaction. Pulling it back to the deck takes one more action.
Turning Back. A ship can turn and pick up a drifting creature. The pilot makes a DC 12 Dexterity check with ship proficiency. On a success, the ship reaches the creature in 1 minute. On a failure, it takes 1d4 minutes.
A world has its own air and its own pull. Inside a world's sky, creatures breathe normally and fall toward the ground. If a ship's helm stops in a world's sky, the ship falls 500 feet each round. The pilot can slow the fall with a DC 15 Dexterity check with ship proficiency each round. On a success, the ship falls only 100 feet that round.