Gravity and the Air Envelope

Gravity

Gravity behaves differently in space. Any object or creature of about 1 tonnage in size will create a gravitation field around it. This field expands to form a bubble around the object to a distance of three times its cross section. Gravity as a force is binary; it is either on or off, there is no micro gravity. On any object that is smaller than a planetary body this field manifests itself as a two-dimensional plane that runs through the longest axis of the object; for most ships this maps to its deck. As it is a 2-d plane; gravity falls towards both sides of the plane. Many ships have the gravity plane bisect it, and it is not uncommon to have gravity spin 180 degrees on you when you climb through a hold or for you to have duels while standing on the bottom of a ship. Anyone who falls overboard of a ship in wildspace just bobs up and down when they come to rest on the plane; but there is a subtle push from the plane that move everything resting on it towards the edge of the envelope at a rate of 5ft every round.
Each gravity bubble moves relative to the object that creates it. This means there is no relative motion on a deck of a ship due to its movement, you do not feel the force of acceleration (much like you do not feel the rotation of a planet when standing on it). Outside forces such as collisions or turbulence when surfing the flow will still cause movement for those standing on a ship. An object will retain its own gravitational orientation even if it is inside the gravitational bubble of another object such as another ship or a planet; up to the point that they make substantial contact. Once this contact is made the plane of the smaller object shifts to align with that of the larger one. Most humanoid captains maintain a decorum of aligning their planes when they come across each other in wildspace, it's just hard to have a conversation when you have to crane your head back 90 degrees to talk to a ship that is oriented differently.
Substantial contact is defined as an integral part of the object; accessories such as ropes, anchors, and boarding planks do not shift a plane.

Air Envelope

Most creatures need fresh air to breath and that is a commodity that is in short supply in wildspace. If a creature that isn't large enough to create a gravity bubble found themselves suddenly propelled into wildspace; they will drag enough air with them to last for approximately 3 minutes. But if you’re shooting for longer habitation, you will need enough mass to create the gravity needed to hold in your precious air. This air diffuses to the extent of the gravity bubble to make up the air envelope. Any creature inside the envelope can breathe freely, even if they are overboard and floating away. Convections inside the envelope keep the quality makeup of the air uniform. Most ships gravity bubbles capture enough air to support their crews for months at a time, but only the largest of ships like the Dwarven Citadel have the space needed to grow enough plants to generate new air. For everyone else in wildspace your air envelope will slowly deteriorate, and if you cannot replenish it, you will eventually suffocate. Wise captains plan their voyages to allow for fly-bys of planets with known good air or build magical contingency plans to refresh their envelope.

Calculating the capacity of the enelope

Each ship has a listed stat for the number of air days that it's gravity bubble will retain. Each air day is enough for 1 medium creature for 24hrs. Different sized creatures place different strain on the envelope; Small creatures use half as much air, and every step above medium doubles the required amount of air. Total the daily strain for all living breathing creatures of at least small size and divide by the ships air day rating to get the duration of how long a voyage the ship can take on one charge (Tiny or smaller are a negligible strain on the envelope; don't add the ships cat to the calculations).

Size	Air Day per 24hr
Small	1/2
Medium	1
Large	2
Huge	4

Air Quality

It can be dangerous to push your air enveolpe to it's limit. The captain that does push their luck can find their air getting stale and their crew suffering from the fouled air.
A full charge of air will become fouled after it's been roughly half depleeted (3d10+40%). Being on a ship with fouled air is extremly difficult, and often one of the most harrowing experiences for anyone. Many a mutany has been caused due to a reckless captain pushing a journey too far. When exposed to fouled air, a creatures that need to breath will be Hypoxic and will not be able to remove the condition until they have access to fresh air. In the event where an unfortunate ship does not have access to a source of air to refresh their air envelope, after it has expended its air days the air will become Spent. Spent air does not have any life giving vitality left in it, and any creature that needs to breath will begin to Suffocate when eposed to spent air. Anyone who is unfortunate enough to fall(or be thrown) overboard in the Phlogiston is lucky enough to become Calcified. In this state they can wait for days, weeks, or millennia and still be revived when brought on a ship that has air; thought those who spend too much time calcified loose their sanity reporting they hear whispers in the flow.

Fires

Nothing causes primal fear in a spelljamming crew like fire. Not only are most ships made of wood, and therefor ready fuel for a fire, but fire also eats through the ships air envelope. A ship fire will quickly foul the air with smoke, and if it burns long enough it will completely deplete the air and render it spent.

Definitions

Air Days

A statistic of a ship that represents the approximate size of its air envelope. A medium creature consumes 1 Air Day worth of air in 24hrs. Different sized creatures consume different amounts of air.

Fouled Air

Air that has been degraded by either breathing it for too long or due to a ship fire. Creatures that are exposed to Fouled air gain the Hypoxic condition

Spent Air

Air that has no vitality left in it. Creatures that need to breath immediately start to Suffocate when exposed to spent air

Tonnage

A quasi-abstract unit of measurement used to approximate when objects are large enough to create a gravitational field. It equates to roughly a 15ft cube of matter, though it can be in any shape.

• Gargantuan creatures are generaly large enough to qualify as at least 1 Tonnage
• Ship size is measured in Tonnage

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