It's possible to power a ship using more than one engine, but doing so causes a cumulative -2 circumstance penalty to all Profession Airship Pilot checks for each engine beyond the first. Though some ships can overcome this problem by installing an engine sync (the piloting components section will be discussed later), most airships are simply not capable of fully suppressing the stresses caused by the additional engines.
*footnote - the engine cost is per power factor, engine hull points are per ton of engine size, and engine repair cost is per point repaired.
Arcane Engines While most types of Airship engine are designed to produce energy, which is then converted into motive power by various spells embedded in the engine. This type of engine is primarily used by sorceres and wizards who can fuel it with their magic. Bonus: Arcane engines are small and light, and do not require traditional fuel. Penalty: None Fuel Cost: None. It does require a link between an arcane caster and itself. The caster dedicates a number of spell slots to the engine while the link is in place. For every spell slots level, the engine produces 20 power factors for one hour. Forging a link requires the caster to place hands on the engine for 15 minutes, and allowing the arcane magic to work. The caster may then dedicate any spell slots at any time he wishes to the engine. Dedicating slots is a free action that does not provoke. Size: 1 ton per 50 power factors or fraction thereof, 1 critical hit slot per 100 power factors or fraction thereof. Catastrophic Failures Result: If the engine is reduced to zero hull points, it is considered to have suffered a catastrophic failure - any spellcaster currently linked to the engine suffers 1d4 damage / level of each dedicated slot.
Divine Engines The divine engine is identical to the arcane engine, save that it uses divine energy for its source.
This is apparently the "most common" of the elemental engines, providing excellent lift, but are prone to being damaged easily. The work by imprisoning summoned air elementals and converting their energy into lift for your ship. These engines rise higher than others, and their lifting capacity attenuates slower. The engine doesn't come with an elemental, but is later summoned by it's user.
Bonus: Does not suffer attenuation of lifting capacity as rapidly as others, and may rise up to 750' in altitude without difficulty. Gains +1 maneuverability rating.
Penalty: These engines are constructed of glass, crystal, and fragiles. This equates into a low hardness, and half the number of hit points of other engines of its size. It also requires a mage or cleric to cast Summon Monster or Heal spells when appropriate.
Fuel Cost: Energy is drawn from the life force of the elemental. When summoned it is trapped inside the engine until consumed, even beyond the spell's normal duration. An engine may hold up to 2HD of elementals for every 5 power factors of its capacity. For every hit point burned from the elemental provides the engine with 2 power factors for one hour. Bound elementals that are not fully consumed regenerate at 5 per hour of rest. An elemental may be fully restored with the Heal spell, but cure wounds type spells are ineffective. An engine burns one elemental at time, starting with the largest.
Size: 1 ton per 50 power factors, 1 critical hit slot per 100 power factors or fractions thereof.
Catastrophic Failure Result: If the engine is reduced to zero hull points, the elemental inside is immediately freed. The extraplanar rift formed (although only for a split second), causes 1 hull point of damage to the ship per 20 power factors of the engine.
These engines are good for speed, but are both that great at maneuverability. Like the air version, they do not come with an elemental when created. Military vessels prefer this type of elemental engine for their speed and destructive power. The engine itself can be used as a weapon itself against vessels approaching from the rear, and some alterations (covered in the Shipboard Weapons section later on) can allow the exhaust to be used as a fire projected missle weapon. Bonus: increases maximum speed by 20 mph. Penalty: due to the massive exhaust engines, maneuverability is decreased by 2. It also requires a mage or cleric to cast summon monster and heal spell when appropriate. Fuel Cost: Taking the life force of fire elementals as fuel, the elemental remains trapped there until consumed, regardless if the spell's duration expires. The engine can hold up to 2 HD worth of elementals per every 5 power factors of its capacity. The larger elementals are always consumed first. Each hp burned provides two power factors for 1 hour. Elementals not fully consumed regenerate their hps at 5/hour of rest. The elemental can be fully restored with a Heal spell, although cure wounds type spells have no effect. Size: 2 tons per 50 power factors, 1 critical hit slot per 50 power factors. Catastrophic Failure Result: If the engine is reduced to zero hull points, it suffers a catastrophic Failure. The elemental becomes freed, causing an extra planar rift lasting less than a second, but causing 1 hull point of damage to the airship per 5 power factors of the engine. This also starts a 10' square fire centered in the engines former location.
Energy Engines Similar in nature to elemental engines, these power plants derive their power from an extraplanar source. A pinprick portal to the positive energy plane allows a trickle of this potent energy to seep into the engines furnace. A second portal allows a trickle of negative energy to enter the furnace. When the two mix, they react violently and create a vast amount of energy considering the small size of the furnace. Because they require no fuel, these engines are used most often by airships that must travel long distances. Unfortunately, the engines are unable to generate energy quickly and require a great deal of time to lift an airship from the ground or to accelerate. Bonus: Requires no fuel. Penalty: Requires a whole hour to begin generating energy once turned on. It cannot accelerate faster than 10mph per round. Fuel Cost: None. Size: 1 ton per 25 power factors, 1 critical hit slot per 50 power power factors. Catastrophic Failure Results: The unrestrained reactions between positive and negative energy immediately causes an explosion that collapses the links between the two planes, causing 1d4 hull points of damage per 5 power factors of the engine.