(Iderati revision)
External Load Towing Capacity (homebrew house rule extrapolation/extension)
LBB2.81 standard drives follow a formula for drive throughput of Code: 1 @ 200 ton increments and the "yield" of the drive is simple multiplication/division (dropping fractions) for different hull sizes.
- Drive-A = Code: 1 in a 200 ton hull
- Drive-A = Code: 2 in a 100 ton hull
- Drive-A = Code: 3 in a 66 ton hull
- Drive-A = Code: 4 in a 50 ton hull
- Drive-A = Code: 5 in a 40 ton hull
- Drive-A = Code: 6 in a 33 ton hull
So in the context of a Five Sisters Clipper, when skipping the letters I and O (to avoid confusion with the numbers 1 and 0 in printed LBBs), M (jump and maneuver) and N (power plant) equate to multiples of 12 and 13 (respectively), yielding a performance of Code: 1 in 2400 tons and 2600 tons (respectively). This then means that the performance for Drive-M (jump and maneuver) has the following Code yield breakpoints:
- Drive-M = Code: 1 in a 2400 ton hull
- Drive-M = Code: 2 in a 1200 ton hull
- Drive-M = Code: 3 in a 800 ton hull
- Drive-M = Code: 4 in a 600 ton hull
- Drive-M = Code: 5 in a 480 ton hull
- Drive-M = Code: 6 in a 400 ton hull
However, a default (unmodified) hull is not (or at least, should not) be engineered to routinely "tow" external loads (safely) "for free" without any added expense for the capability. This is where Small Craft/Big Craft Launch Facilities (LBB5.80, p32) come into play and can be extrapolated from.
Small Craft (99 tons or less) can be carried at their own tonnage on ships 1000 tons and under, but require 130% of their tonnage on ships over 1000 tons.
Big Craft (100 tons or more) can be carried but require 110% of their tonnage on all ships.
In both cases, the carrying capacity requires Cr2000 per ton.
Internal hangar capacity will obviously require tonnage allocation within the hull, while external towing capacity costs no internal tonnage inside the hull. However, in both cases, the capacity (internal or external) still requires Cr2000 per ton of capacity. The difference between internal and external capacity is that internal capacity does not alter drive performance when loaded (the small/big craft tonnage is already "paid for" in the design), while towing external loads increases the (combined total) displacement the same way that external fuel tanks do (while mounted externally) which then reduces drive performance relative to their baseline. Additionally, external loads will follow the precedent of Exterior Demountable Tanks (LBB A5, p14) such that with an external load, ships are considered unstreamlined regardless of their hull configuration.
Most ships building for external load capacity will have Ordinary Launch Facilities (LBB5.80, p32) permitting a launch/recovery of one craft per 20 minute combat turn, which have no additional cost associated with them. Only Dispersed Structure (Configuration: 7) hulls can simply attach external loads to their hull exterior and be capable of launching/recovering all craft simultaneously in a single 20 minute combat turn.
So a 600 ton Five Sisters Clipper with Jump-M and Maneuver-M drives installed is J4/4G that also has 200 tons of external load capacity "occupied" by external loads functions (temporarily) as an 800 ton hull with J3/3G performance (see above). However, docking a 200 ton starship (such as a Free Trader, for example) would require 220 tons of external load capacity, which would then reduce drive performance of the Five Sisters Clipper down to J2/2G with a 200 ton ship being towed.
Furthermore, once 400 tons of external loading (the 1000 combined tons breakpoint) is exceeded, any individual components of the external load that are 99 tons or less consume 130% of their actual tonnage in terms of external load capacity. This is why the upper limit of J2/2G drive performance with a limit of +600 tons external load (1200 combined total tons) means that with small craft there is only 600/1.3=461 tons of small craft tonnage capacity available for external loading. 15x 30 ton
Modular Cutter Modules is 450 combined tons of small craft hulls … 450x1.3=585 tons of external docking capacity is required to tow that load (the less than 1:1 tonnage "efficiency" is due to all kinds of mechanical engineering stress limits and "packing losses" of needing to keep hulls from abutting one another "too tightly" and so on). The main point being that external load capacity cannot be utilized
as efficiently as internal cargo hold capacity.
Furthermore … in order for an operator to charge "full price" for transport services on external loads (such as a collection of
Modular Cutter Modules filled with cargo), the operator needs to provide the "external hull volume" themselves to receive the Cr1000 per ton per jump price for shipping. However, if a third party owns and operates the
Modular Cutter Modules instead, then the third party merely needs to charter the tonnage of their modules for transport, at Cr900 per ton per jump.
Starship operators who want to retain jump/maneuver flexibility in their operations will thus NOT want to own any external cargo capacity themselves, since they would need to "leave it behind" (with warehouse and security arrangements, just like with Demountable Tanks (LBB A5, p14)) if they want to "shed load" for a longer jump range. Consequently, it is entirely reasonable for operators with external load capacity available to simply charter that capacity to interested third parties, with the third parties then obliged to provide the necessary small craft/big craft hull "containers" to be transported externally (which can include other starships!). The third party only pays charter prices for the external tonnage they actually submit to be transported, not for the amount of external load capacity needed to actually carry that tonnage.
So a third party wanting to transport a 200 ton Free Trader through jump as an external load would charter 200 tons of external load at Cr900 per ton (total: Cr180,000), but because the 200 ton Free Trader is a big craft (100+ tons), it will require 220 tons of external load capacity.
Likewise, a third party wanting to transport 15x 30 ton
Modular Cutter Modules would charter 450 tons of external load at Cr900 per ton (total: Cr432,000), but because the combined tonnage of starship plus external small craft exceeds 1000 tons (600+450=1050) those 450 tons of external load would require 585 tons of external load capacity. That same third party wanting to transport 15x 30 ton
Modular Cutter Modules could sell their 450 tons of cargo capacity as a middleman service, charging their customers the full Cr1000 per ton price of shipping … in effect profiting off the arbitrage price differential of Cr100 per ton of cargo to earn their profit margins without needing to own, crew or maintain any actual starships themselves. Instead, the third party company would simply own, maintain and supply the cargo containers (at MCr2 each for 30 tons of cargo) and do all the "legwork" of drumming up business to fill those containers in preparation for a starship to transport them wherever they need to go, resulting in a containerization business model for interstellar shipping.
Note that such a formulation means that even if there is limited (to no) cargo available from an origin to a destination (LBB2.81, p11) to a starship operator for a direct contract ticket … it is always possible that the reason why that condition prevails is because third parties have already contracted for all of the cargo bound from the current origin to a destination and those third parties simply want to charter a starship (at a lower price) to transport their freight to wherever the starship is going next (declared destination). Alternatively, the Referee could decide that if the cargo tonnage available exceeds the starship's internal capacity that the excess cargo tonnage available for transport (full or partial) may instead be managed by a third party wanting to charter the starship operator's external load capacity for transport. An additional consideration could be that government subsidized ships on their "in subsidy" route may be given preferential treatment for charters by third parties, especially if the starship operator(s) have earned a reputation for "reliable service" at the point of origin. In other words, there are a variety of different ways to handle external load capacity potentials as a Referee.
