The Jump Tug

(by Terl Obar)

Ever wonder how all those star systems that don't have a Starship Construction Center get their system ships? If they can't make them and the ships are not Jump capable, how did they get there? The answer: The Jump Tug. This vessel consists of little more than a small crew module, some massive engines and a long boom used to attach the ships it transports. Unloaded, it is one of the fastest ship on the Frontier (especially the smaller model). With crews of three to six beings, these ships traverse the space lanes moving other ships throughout the Frontier.

Characteristics

Jump tugs are based on a size 5 hull. Any smaller and the hull can't support the stresses. While they could be larger, you are decreasing towing capacity and increasing cost for no real benefit. Despite their relatively large size on paper, the hulls of these ships are in truth physically small as most of the hull material has been used in reinforcing the engine struts to handle the massive engines mounted on these small hulls and to create the boom, which is 350m long. Although their small hull size would normally use Class B engines, Jump Tugs sport 4 Class C Atomic engines. The relatively small hull size combined with the large engines give the Jump Tug some unique characteristics that make it ideally suited for the role of interstellar ship transport.

 

Sporting the Class C Atomic Engines, the Jump Tug only needs an overhaul once every twelve jumps through the Void. This means that a Jump Tug is able to make at least one round trip from any SSC to any system in the Frontier without an overhaul.

Because of the over-sized engines on the small hulls, these ships are able to move a large number of other ships all at once. The Jump Tug can ferry ships up to a total combined hull size of between 25. To put that into perspective, it would only take 4 Jump Tugs to move any one of the UPF Task Forces (Cassidine, Prenglar or Nova) between systems. (5 to take Prenglar if you took the Minelayers)

The large engines also mean that, unloaded, these ship are fast. Unloaded, they have ADF and MR values of 6¹. In fact, it's not uncommon for Jump Tug captains to hold impromptu “drag races” on off days for bragging rights on who has the fastest ship around.

 

Of course having these large engines mounted on these small hulls comes at a price. The hulls have to be incredibly reinforced to withstand the large stresses placed on the ship. This extra reinforcement uses up most of the available hull material leaving little to be used for actual crew space. As a result the crew area is smaller than an entire hull size 2 vessel! On the plus side, because of the reinforced hull, these ships are sturdier than their traditional counterparts and have more hull points.

Crew

Because of the limited space available for the crew, Jump Tug crews are small, typically three to four beings and never more than six. At a minimum the crew needs a pilot, an astrogator and an engineer. Many times the crew will include a second astrogator to speed up jump calculations. Crews, especially on independently owned tugs, may have a few extra engineers in the crew to speed up the overhauls when they are needed. (It can be a drag to overhaul four Class C Atomics all by yourself.) While crews are typically in the three to six range, there are tugs out there that are run by a single, albeit highly skilled, being. Whether because they like the solitude, just need more personal space or some other reasons, these spacers choose a solitary life among the stars.

Hauling Capacity

Jump Tugs can haul up to 5 times their own hull size in towed ships Their actual performance (ADF/MR) depends on the total hull sizes of all the ships being towed on a specific jump. Table 1 summarizes some basic performance information about the Jump Tug giving the total Hull Size that can be towed for a given ADF/MR.

Tug Hull Size	5
Number of Engines	4
Maximum Total HS of Ships Hauled	25
Unloaded Max ADF/MR	6
Max total HS towable with ADF/MR of 1	25
Max total HS towable with ADF/MR of 2	10
Max total HS towable with ADF/MR of 3	5
Max total HS towable with ADF/MR of 4	2
Max total HS towable with ADF/MR of 5	1
Max total HS towable with ADF/MR of 6	0

Ships are towed by attaching them to the long boom extending from the bow of the tug. Generally, the ships are arranged around the boom to balance out the center of mass and keep it in line with the center of mass of the tug. However, if hauling a ship of HS 13 or larger (or any single large vessel and a bunch of smaller ones), the large vessel is attached at the tip of the boom via the large force diffusing plate at the end of the boom. This allows the mass to be balanced properly for the trip.

Economics

While it is possible to make a bigger tug (based on a hull size 6 or 7 hull) with more (6 or 8) engines that could haul slightly more ships per jump, they are not cost effective. The hull size 5 ship described here cheaper to both purchase and operate and any potentially larger version. One Class C Atomic engine costs more than all of the rest of the ship systems combined. Thus, adding more engines, the most important part of the hauling power, dramatically increases the cost. On the other hand, it doesn't drastically increase the towing capacity. Doubling the engine count, nearly doubles the cost of the ship but only gives a 32% increase in towing capacity. In addition, the larger ship would require more fuel per jump and more maintenance down time for overhauls.

 

Typical charges for a tow is 5000 cr per point of hull size per jump. However, depending on circumstances it could be as low as 2000 cr per point of hull size or as high as 16000 cr per point of hull size per jump. depending on the destination, age of ship, number of ships being towed, etc. Details are left to the discretion of the Referee (see “Operating a Jump Tug” below).

Operating a Jump Tug

Based on the Knight Hawks stats given below, the cost of a Jump Tug is 3,621,100 cr unfueled. It takes another 400,000 cr to completely fuel the tug enabling 10 jumps. Assuming the tug makes 40 jumps a year, has a crew of three (Pilot 4, Astrogator 3, Engineer 3) and spends an average of 10.5 days in annual maintenance. The total operating cost of the tug (maintenance cost, fuel and salaries) is 1,890,500 cr per year. Amortized over 40 jumps that reduces to 47,263 credits per jump. With a full load of 25 hull size worth of ships per jump this comes to 1891 cr per hull size per jump. This gives us the bare minimum a tug captain can charge and still break even, namely 2000 cr per hull size per jump.

 

However, this makes several assumptions. The biggest is that the ship is completely paid for! Assuming the captain financed 3.5 million cr (nearly all) of the cost of the ship for 10 years. That adds another 1,428,350 cr per year to the operating costs. Again amortized over the 40 jumps per year adds 35,709 cr per jump or 1429 cr per hull size.

 

Another assumption is that the tug makes all jumps completely full, i.e. hauling a full 25 hull sizes worth of ships. This is rarely the case, there are usually a few slots unfilled. In addition, if the tug is delivering ships to a remote system, there may be nothing to haul back to the SSC where the tug makes its base. In this case, there is nothing to defray the costs of the jump so they have to be absorbed into the cost of other jumps. Of course if they are not hauling anything they can simply operate 2 of the four engines to save some cash.

 

In the end all, of these things go into figuring the cost of operating the the Jump Tug. The 5,000 cr per hull size per jump is just an average number assuming the ship is mostly paid for, the tug is relatively full and can usually bring back a few ships on a return trip.

Deck Plans

The Jump Tug has four decks. They are, from top to bottom: the bridge, the crew deck, the airlock and engineering. Figure 1 shows the deck plans for the Jump Tug. Descriptions of the labeled areas of the ship are given below.

 

1. Elevator – The decks are connected by a single elevator (1.5m diameter) designed to carry a single being at a time. However, two can squeeze in if they want to get cozy. This elevator runs to all four decks of the ship

2. Pilot's Station – This computer station is the pilot's seat on the ship and has all of the controls for flying the ship.

3. Astrogator's Station – This is the astrogator's work station for plotting out the ship's jumps.

4. Main Computer – This is the main computer system for the ship housing all the ships functions and programs.

5. Crew rooms – Each room can be used by up to two beings. The rooms each contain a desk and chair as well as a bunk bed. The bed is mounted in such a way that one or both of the beds can be stowed up into the ceiling of the room to make additional floor space if desired. If only one being is using the room, the second bed can be permanently stowed with the first one being either at ground level or raised. In addition, if one of the inhabitants is a Vrusk, the second bed can be stowed with the first one raised and specialized Vrusk resting couch/bed can be placed on the ground level.

6. Restroom – This room contains a small sink, toilet facilities and a shower.

7. Common room – The common room contains a small table, four additional chairs and the galley. There is also an entertainment center (area 8).

8. Entertainment Center and Life Support Machinery – This part of the ship is filled with an entertainment center to keep the crew occupied during the long voyages as well as part of the ship's life support equipment.

9. Ship Machinery – various parts of the ships life support system, computer, and other machinery fill up the majority of this deck.

10. Spacesuit storage locker – This room is primarily designed to hold the crews' spacesuits but can be used for miscellaneous storage as well.

11. Airlock – This is the ship's airlock. It can hold up to 3 spacesuited beings at one time.

12. Entryway – Small entry room that beings entering or leaving the ship can use to remove or don their spacesuits.

13. Engineer's station – This is the engineering station on the ship and has the computer the engineer uses to monitor and control the ship. Can be used as an auxiliary bridge.

14. Storage – General storage locker for the ship.

15. Ship Machinery – More space taken up by general ship machinery.

16. Workpod – The ship's workpod. Used for hull repairs and to assist in mounting ships to be towed. Access is through a pressure door that links with the airlock of the workpod.

17. Engine access tunnels – These tunnels allow access the the engines from with the ship.

 

Figure 2 shows the full ship to scale with its engines and the boom for attaching the ships to be towed. The boom is a solid piece of hull metal, 350m long and 2 m in diameter. The force diffusion plate on the end is a 1m thick plate 30m in diameter. Figure 3 is a close up of the body of the ship showing the relative placement of the decks inside the hull.

Full KH Stats

Here are the full KH statistics for the Jump Tug.

¹ Assuming the Referee allows performance like this in the campaign. If not the upper limit can be whatever the Referee decides applies.

Author's Note:

The baseline for the calculations in this article is the fact that a HS 15 ship requires 4 Class C Atomic engines and has an ADF/MR of 2. All of the math that went into ADF/MR and towing calculations were done using the hull size of the ships being towed, not their volume/mass as would be more realistic. This was done in keeping with the simplicity that is Star Frontiers. Anyone who has ever really looked at the Knight Hawks “Hull Specification Chart” (p11 of the KH Campaign Book) has probably realized that the size of the ships do not increase linearly with hull size, rather they increase exponentially, i.e a HS 10 ship is not 10 times bigger than a HS 1 ship. Rather it is almost 10,000 times bigger. And a HS 20 ship is 150,000 times bigger than a HS 1 ship, not just 20 times larger. Thus in reality, if my tug could tow one battleship (HS 20), it should be able to tow 150,000 fighters (HS 1) or 4800 Assault Scouts (HS 3) if you just looked at volume/mass. Obviously that doesn't fit within the Knight Hawks cannon framework. Plus the math required on the part of the GM/players gets really involved and the point is to keep it simple. If it helps, you can think of the limitations imposed by using the hull size as coming from the attachment points on the towing boom. You can only cluster so many ships around the towing boom before all the attachment points are filled. To do this properly, where the ADF/MR reduction and number of ships towed was based on volume/mass instead of hull size, would actually require a rewriting of the star ship construction rules to bring hull size, ship volume and engine characteristics onto a consistent and realistic framework.