Here’s one more attempt on my part to nail down types of ship – and, hey, to avoid the acronym “SEx” in the process!
Longhex (“Longship”)
(interstellar-ranged hyperdistortion drive)
A fully self-sufficient craft with fully HEx-capable distortion drive, crew accomodations, and – above all – the fuel stores to travel faster-than-light for weeks at a time.
Most Hammer Lord and merchant princes prefer longhex ships, large or small, because of the attractions of (1) the strategic/commercial flexibility of being able to move interstellar and (2) the self-sufficiency of not needing tankers, carriers, drop tanks, or any other specialized support to do it. But that same flexibility and self-sufficiency means that longhex ships spend more of their mass on propulsion (drives plus fuel) and are therefore less efficient than specialist ships.
Shorthex
(intrasystem-ranged hyperdistortion drive)
A craft with a fully HEX-capable distortion drive but only enough fuel storage for a few days or even hours of faster-than-light travel: sufficient to zip around a system at faster-than-light speeds (once you’ve accelerated clear of the Disk) but only a tenth or a hundredth of what’s required to make it to the next star system.
Shorthex ships are ideal for system defense outside the disk (“North Watch” and “South Watch”) and for fast commercial transit (e.g. first class passengers) within systems that have more than one settled body. They can also be converted to longhex ships relatively simply, by adding (massive) drop tanks.
Sublight
(intrasystem-ranged subliminal distortion drive)
A craft with a subliminal-only distortion drive, capable only of sublight travel. They are adequate for short flights in the Disk of a system where HEx doesn’t function anyway – say two worlds so close together, or so deep in an unusually dense Disk, that taking the “shortcut” into HExable space is worthwhile – or for slow hauls between planets for non-time-critical cargoes – say bulk supplies or raw materials.
Militarily, sublight ships are of very limited use, able to defend a single planet and its satellites, but on a system-wise scale all too easily outmaneuvered by HEx ships taking “shortcuts” in and out of the Disk.
A sublight ship can be converted into a shorthex ship, or even a longship, by adding a HEx array and appropriate fuel tanks, but this is effectively bolting on a second drive and requires some technical sophistication to make it work.
Thruster
(conventional reaction-based thrusters only)
A craft without a distortion drive at all. (Distortion drive ships have CTA thrusters to give the vectors that the artificial and localized distortion of the space-time continuum then magnifies). Such craft are outmaneuvered by distortion-drive ships, HEx or sub, beyond the Well of a specific world, and they are outmanuevered by grav/pressor sleds within the atmosphere. So thruster craft are optimized for, and capable of dominating, only one narrow shell of space, whose upper boundary is the radius from the planet at which dust levels attenuate to allow subliminal distortion drives to engage, and whose lower boundary is the radius from the planet at which gravity is strong enough for grav/pressor systems to work efficiently.
Commercially, thruster-only ships are commonplace: They are a cheap and effective way of shuttling between a planet’s surface, its orbiting satellites or space stations, and any deep-space ships parked in high orbit that cannot land or do not want to bother to. Militarily, they are very narrowly useful either as landing craft, launched by distortion drive-equipped motherships, or as close-in defense craft for a particular planet, often as a Q-Beam equipped mobile extension of fortresses on the ground.
A crucial question to Chris: Which of these types do you want to be common and which rare specialists? Because we can justify the underlying technology cost-benefit tradeoffs however we want once we know the desired effect.
From what you’ve posted so far, I’m thinking that most craft fall at one or the other of the the extreme ends of the spectrum: There are lots of fully HEx-capable interstellar ships, lots of local shuttles with no distortion drives at all, and precious little in between.
But you also mentioned “drop tanks” at one point, and if the mass required for fuel is a really significant factor (as the Vaylen Wars rules state), then the idea of a “shorthex” ship that has everything it needs to go interstellar but the fuel is very attractive: You only have to haul around the mass of all that fuel when you really need it, and the rest of the time you can strip down and have a much higher thrust:weight ratio. (Now, if “fuel” is mostly water, then it’s a really good absorber of heat, making it potentially dual-use as a heat sink in combat when you can’t expose your fragile radiator vanes, and even perhaps as shielding). If the efficiencies are attractive enough, you could even justify battleships with drop tanks!
Likewise, it’s important what the cost/mass penalty difference is between having a HEx-capable drive with only enough fuel for intrasystem hops (shorthex) vs. a sublight-only drive vs. conventional thrusters only. If there’s not much difference between the cost and mass of a HEx drive with enough fuel for intrasystem travel only and a subliminal distortion drive, then there’s no point to building a sublight-only ship when a shorthex ship can just zip in and out of the Disk. And if there’s not much difference between the cost and mass of a sublight-only drive and conventional thrusters, there’s no point in building a thruster-only ship that’s optimized only for a narrow zone around a planet. But the bigger the difference between drive types, and the more cost and mass increase each step of the way from CTA-only to subliminal distortion to hyperdistortion, the more it’s attractive to build different specialized types of ship.