Spelljammer Architecture

Ships in space have a number of attributes and statistics that describe their performance and capabilities. The most important contributing factor to a ship's maneuverability, speed and self-defense is her crew, navigator, gunner and spelljammer — though her armor, weapons or other devices that augment her performance will prove invaluable as well, especially in the event of attack by neogi slavers!


A ship's bulk size is defined in tonnage (T) — literally the amount of displacement the ship takes up. Since this displacement also influences the amount of breathable air surrounding the ship in space, a ship's tonnage is also a reflection of both its crew capacity and requirements. One ton is not a measure of weight in this context; instead, it is arbitrarily set to equal 100 cubic yards. A mass that large will allow a man to breathe comfortably for roughly 5 months.

Ship's Speed Rating

A ship's Speed Rating (SR) is a reflection of the ship's speed and relative power, and to a lesser extent its maneuverability. A ship with a high SR can move faster than one with a low SR. The ship's Speed Rating is dependent on the individual powering the Spelljamming Helm, on the design of the Helm itself and on other factors (including the mass of the ship and her cargo and the current of the Flow if she is in the Phlogiston, for example). In general, a ship with a more powerful mage at the Helm will have a higher SR than a similar ship with a weaker Helmsman. Of course larger, bulkier ships tend to have lower base SR than small, darting frigates and scouts.

Ship's Crew

Each ship has a certain minimum number of crewmen required to operate her. Of course the maximum number of creatures which can occupy a ship depends more upon her supplies (including food, water and of course air!), though some especially small craft are simply not designed to carry many people.

When talking about maximum crew numbers and the air requirements of various races, man-sized (SM 0) creatures are the default assumption. You will need to adjust your calculations about supplies needed based on the actual occupants' needs.

Maneuverability Class

Maneuverability Class (MC) refers to the tactical maneuverability of the craft — when her speed in a straight line is much less important than her agility. Her SR does help, of course, but it is also a matter of sails, oars, fins and other controlling devices over and above her SR. In general, the hull design of a ship determines its MC, with the quickest typically being the graceful flitters of the elves and the most sluggish being sea vessels that have been converted into spacecraft. A ship might be powered by a weak mage (and therefore have a low SR) but still have a high MC that allows her to function well in tactical combat. The ship's Maneuverability Class functions much as a character's Dodge does: add 3 to her Speed Rating and then add any bonuses or penalties from the hull's design.

Hull Points

Hull Points (HP) are a method of assessing damage to a ship, whether inflicted by small arms' fire (perhaps a suicidal musketeer?) or the siege weaponry of another ship. Initially, a ship has Hull Points equal to half her tonnage (a 30-ton ship has 15 HP by default). Some ships are fortified and armored, sacrificing maneuverability and crew space for protection.

Hull Points are similar to a character's Hit Points, though ships are obviously much more durable than a man. Attacks from ordinary weaponry (swords, arrows and musket balls, for example) are not usually enough to deal more than cosmetic damage to a ship on their own. Ships automatically reduce such "small arms" damage to 10% of its total, rounding down, before applying it against their armor's DR (if any). If this would reduce incoming damage to less than 1.0, the ship's HP ignores it. A ship that lost half its HP has many rents and holes in it, while one that has lost all its HP has broken apart and is destroyed.

Power Type

Power type defines the type of Helm, engine or other motive force that causes the ship to go through space. Most Helms gather and concentrate magical or other mystical energy and convert it into motive force. Different power types have different limitations and capabilities. A ship with no power is adrift, unable to control her motion. A ship can have multiple power sources. The one "on-line" is the primary power source, while the others (including any spells) are back-ups. The most common power types (discussed in more detail in their sections) are:

Major Helms an elegant (of course elvish) improvement on the basic Spelljamming Helm design, it is more efficient and more powerful
Minor Helms the most common Spelljamming Helm design, it is also the cheapest or at least the most readily available
Series Helms alien psionic sciences have devised a means of deriving motive power from the minds of gifted psions; these devices are exotic and rare
Forges fabulously expensive, but tremendously large and powerful, these dwarvish engines power colossal asteroid vessels
Furnaces primitive and inefficient, these early designs are still used in some areas and draw power from magical items rather than mages directly
Gnomish Drives defying the foundational principles of thaumaturgic laws, these devices are impossible: they simply should not function — of course, being gnomish, they work anyway.
Lifejammers horrifying devices, these engines of evil draw their energy from the life force of victims held within over the course of a slow, agonizing process


The weaponry a ship can mount and bring to bear varies from ship to ship. In a typical ship description, the Standard Armament (SA) is provided. The ship may be outfitted with additional or customized armament, though this cuts down on cargo space (the room that would normally be used for cargo is instead used to provide space for large weaponry and its ammunition). A ship's description will say how many "hardpoints" are built into its hull which are available for weapons to be mounted upon. Further additions can be made, though each weapon and its ammunition occupy a certain amount of space otherwise allocated for cargo (check the weapon's description).

Cargo Space

Cargo Space is the amount of stuff the ship can contain. This is generally related to the ship's bulk size in Tonnage (T). Each ton of a ship's size generally allows 50 cubic yards of space that may be used for carrying (nonliving or non-breathing) cargo. A 30-ton frigate could carry 15 tons of cargo (the ship's cargo space should be noted with its Tonnage). The remaining interior space is needed for crew and supplies. Space taken up by cargo does not add breathable atmosphere — it merely occupies a volume within the ship. In this sense, the "ton" occupied by cargo is not the same thing as the "ton" unit used to denote a ship's displacement.

Keel Length

Keel Length (KL) is the longest dimension of the ship, usually but not always measured along the ship's keel. This is the long dimension of the ship's gravity plane.

Beam Length

Beam Length (BL) is the width of the ship, measured at the ship's widest point, but not counting any oars, poles or sails that may widen the ship without effectively contributing to her real Tonnage.


A ship's armor is her most effective defense at close range when siege missiles are unlikely to miss. Most armor will provide DR or extra HP at the expense of speed (SR and MC). The ship's sheet needs to note her outfitted armor as well as her weaponry and other devices of course.

Spelljammer Architecture

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