GT Streamlined Starships

Kenneth Witt:


The rules for streamlining vehicles in the GURPS vehicles book (VE2) were apparently never designed to operate with volume dependent systems like the Jump drives as used in the Traveller Universe. The formula used for calculating the surface area of an un-streamlined (USL) vehicle assumes the hull is shaped like a cube. To anyone with a basic understanding of solid geometry, it is intuitively obvious that when a cube is streamlined, it will require more surface area to enclose the same volume. However, instead of treating streamlining as a modifier in the formula for calculating surface area, VE2 uses the same formula for all hulls and increases the ratio of surface area to volume by adding unusable (fake) volume to the vehicle. Or, as presented in the GURPS Traveller book, by reducing the useable internal volume for streamlined ships. The standard GT streamlined starship hull, as used in all the ships below, incorporates Very Good Streamlining (VGSL) and the lifting body option. This is interpreted in GT as a 20% reduction in the usable volume. This would not be a terrible way to handle streamlining if the Jump drive and Jump fuel requirements were calculated based on this actual volume, but for some unfathomable reason, the official GT rules for Jump drives in streamlined ships require that they be sized to include the non-existent volume which was used to increase the ratio of surface area to volume for streamlining. This results in a ship like the standard 100-ton scout having a 80-ton hull and a 100-ton Jump field. (Actually it is 83 tons when you include the 3 tons of the turret that stick out of the main hull, but thatís another issue; see below.) In any case, the Jump drive capacity is oversized by at least 17 displacement tons.

The streamlining rules, as interpreted in the official GT universe, have created a large difference in performance between SL and USL starships that exists in no other version of the Traveller rules. The logical result of the huge disparity in performance is that streamlined starships would not be able to compete economically or militarily with un-streamlined starships and would not be built or used by any reasonable organization that was concerned about either performance or profits. Since it is canon in the Traveller Universe that streamlined starships are very common and may even outnumber USL starships, the official GURPS Traveller method of streamlining creates a serious problem.

Fortunately, if you donít mind thumbing your nose at the official rules, there are two very simple fixes to the problem. One method is to size the jump capacity to the actual volume of the starship, such as 83 tons for the Scout/Courier. The second method, which I greatly prefer is to treat streamlining as a modifier to surface area rather than volume. The details of this method can be found in a message that I posted to the Journal of the Travellersí Aid Society (JTAS) starship design discussion board, but the short version is that VGSL adds 16% to the calculated USL surface area of the starship. All of the standard streamlined starships below have been redesigned using the streamlining as a modifier to surface area method.

Design Notes: The standard turret in GT displaces a total of four tons. One ton is inside the hull of the starship and contains the rotation space for the turret and the crew station. The other three tons are outside the hull proper and contain the actual weapon systems. There has been a long running discussion about counting the exterior three tons of the turret into the total displacement of the ship for Jump drive and Jump fuel requirements. In order to avoid the issue and keep the Jump requirements in whole numbers, I have used pop turrets in all the designs. Pop turrets displace their entire four tons inside the main hull of the ship and need only be extended outside the hull to fire. Pop turrets also make a good fit with streamlined hulls because when retracted, they will not produce atmospheric drag like conventional turrets. They have the additional advantage of making it very difficult for a casual observer to determine the armament of the ship, or even if the ship is armed.

The Ships

Sulieman-class 100-ton Scout/Courier (TL10)
Including Seeker variant.
Beowulf-class 200-ton Free Trader (TL10)
Now with a sickbay!
Empress Marava-class 200-ton Far Trader (TL10)
Increased cargo capacity.
Animal-class 200-ton Safari Ship (TL10)
Includes Kitten-class hunting launch and enclosed air/raft.
Akkigish-class 400-ton Subsidized Merchant (TL10)
Including a J2 Far Trader variant.


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Last updated: 28 July 2007