The following proficiencies are either limited to spelljammers or have applications that are uniquely or extraordinarily useful for spelljammers.

Artillerist: A character with this proficiency can direct the siting and operation of bombardment engines. The maximum number of engines the character can control is equal to 1/3 of his Charisma (Leadership) score, provided that the engines are no farther apart than the character can sprint in a single round.

Astronomy: A character proficient in this skill has a detailed knowledge of the relative movement of stars, moons, and planets. On his home planet the character can predict with complete accuracy the arrival of eclipses, comets, and other cosmic phenomena (evening and morning stars, full moons, etc.) The astronomer can identify numerous stars and constellations, and gains a -3 bonus to all checks made using the navigation proficiency, providing that the stars can be seen.

Aboard a spelljammer an astronomer can mitigate the effects of critically failed navigation checks. When arriving at an unfamiliar DP, the astronomy proficiency may decrease the amount of time spent manoeuvring into DP jump position. A successful proficiency check with a penalty of +2 reduces the time from 200% (doubled) to 150%. Instead of becoming hopelessly lost, if an astronomer rolls a successful proficiency check with a penalty of +5, he recognizes enough stellar landmarks to plot a course back into Known Space.

Bo's'n: The bo's'n is the deck officer, in charge of and necessarily highly skilled in the supervision, management and discipline of the ship's crew, and in all aspects of marlinespike (rope and rigging maintenance and operations, including the knowledge of and ability to use knots, hitches, bends, whipping, and splices as needed to perform tasks such as mooring a vessel and safely operate a windlass), ship's anchors, sails, colours, and the ship's boats. His duties usually include supervising the cleaning, painting, and maintaining of the vessel's hull, superstructure and deck equipment.

To become a bo's'n requires as a prerequisite a double proficiency in spacemanship, and proficiencies in at least two of the following: freefall; rope use; sailmaking; shipwright; signalling.

Freefall: Characters with this proficiency are skilled at fighting and working in the absence of gravity. They can use all of their applicable (including those involving gross dexterity) nonweapon proficiencies without additional hindrance, suffer only 1/2 the penalty of a non-proficient character on initiative and attack rolls (+3 and -1 vs +6 and -2), can attack every round as level and specialisation permit (non-proficient can attack only once per round and must pass a successful Dexterity check or rebound away from their target for 1d4 rounds), can use special combat abilities (such as wrestling) while drifting in space, and with a successful check can roughly steer his course through space by body mechanics. A second slot allocated to this proficiency negates all penalties.

Navigation (Space): A proficient character can navigate through wildspace (within a crystal sphere) avoiding hazards and using planetary motion to improve speed over long journeys. A successful proficiency check allows the vessel to arrive at its destination 10% faster than normal. A failed check indicates no time is saved; on a roll of 20, time increases by 20%.

Without this proficiency and access to a full library of star charts, a ship between spheres, within the Flow, moves randomly between and through Discontinuity Points, usually arriving at some other sphere within 10-100 days, but occasionally becoming hopelessly lost. A successful check means the ship arrives at the chosen destination within that time. A failed check indicates a random terminus; a roll of 20 means the terminus point is unfamiliar to the navigator and the time spent manoeuvring into DP jump position is doubled. A second roll of 20 on the same voyage (before reaching safe, known harbour) means the ship has become hopelessly lost.

Planetology: A planetologist has studied the various types of planets to be found within crystal spheres, and is able to identify the various types from space. Can differentiate hostile and hospitable environments (gravity, air composition, climate, etc) as well as the existence and probable type of groundling civilizations from space.

Rope Use: This proficiency enables a character to accomplish amazing feats with rope. A character with rope use proficiency is familiar with all sorts of knots and can tie knots that slip, hold tightly, slide slowly, or loosen with a quick tug. If the character's hands are bound and held with a knot, he can roll a proficiency check (with a -6 penalty) to escape the bonds.

This character gains a +2 bonus to all attacks made with a lasso. The character also receives a +10% bonus to all climbing checks made while he is using a rope, including attempts to belay (secure the end of a climbing rope) companions.

Characters with this proficiency can set rigging (with instruction) and construct cargo nets and other useful items without a proficiency check.

Sailmaking: The character with this proficiency is capable of making and maintaining all types of ships' sails and other canvas work, including pennants and jacks, deck buckets, ditty bags and so forth. They also know how to rig, set and trim the sails to best advantage, and make, splice and tie ropes.

Shipwright: The shipwright is knowledgeable regarding techniques for ship construction and repair. He can design and supervise the building of common ships of all types, without a proficiency check being required. (However, unusual features may require checks.)

He is also skilful in all the carpentry skills related to ships, and can perform routine maintenance on spelljamming vessels, excluding the sails and metal components, consequently, shipwrights are highly valued as ship carpenters.

A shipwright will need a crew of workmen to build any but the smallest vessels.

Signalling: This proficiency gives the character the ability to use signalling equipment, including mirrors, lights and flags, to send complex messages across interspheral space. The semaphore signal transmitted by a proficient character can cross up to 10 miles, provided nothing obstructs direct line-of-sight between the sender and the recipient. Under favourable conditions, heliographic and light signals can travel considerably further. A trained signaller can send as many as 10 words a minute.

To send a message and have it understood, both the sender and the receiver must be proficient and both must roll proficiency checks. If both succeed, the message is understood perfectly. If one fails, the message is garbled in an obvious way that merely necessitates re-transmission next round. If both checks fail, or if either rolls a natural 20, an erroneous message is received that seems valid, but--depending on the content--could have disastrous consequences.

To prevent miscommunication, most Captains require all but the most trivial messages to be repeated. Custom calls for the sender who is repeating a message to say ''I repeat'' and for a recipient who missed the message to say ''Say again.'' This at least clarifies who is supposed to do the repeating.

On Dominion ships communication operations are usually conducted by four sailors. On the ship that originates the transmission, the ''caller'' reads the written message and calls out the letters to the ''sender'' who operates the mirrors, lights, or flags. The receiving ship has a ''reader'', often equipped with a spyglass, who watches and interprets the transmission, calling out the letters to a ''writer'' who writes them down. On the largest ships a fifth sailor, usually a trainee, works as an ''answer reader'' and watches the receiving ship for acknowledgment of a word.

Spacemanship: An ABS (Able Bodied Spaceman) is qualified to work as a crewman on a spelljammer. Has general knowledge of all parts of a ship, can recognize the insignia of all ship's ranks, knows basic information about air consumption, gravity and freefall orientation, sails, ropes and rigging. Can perform all shipboard tasks under the direction of the bo's'n, sailmaster or shipwright.

Spelljamming: Proficient characters are expert at manipulating a spelljamming helm to Manoeuvre a vessel. Any spell-caster can operate a helm, but only those with specialized training are competent to use the polydiscontinuity points, guide a ship through a dweometric storm or take one down through a thick, turbulent planetary atmosphere.

Additionally, on a successful check a helmsman can boost either the SR or the Manoeuvrability of his ship by 1 for one combat turn. He cannot boost both the SR and the Manoeuvrability at the same time. He also gains a -1 to the dice roll that determines which ship gets initiative in combat. In order to use these benefits, the character must be the one operating the helm. Bystanders cannot help, regardless of their proficiency.