My issue with the in-system ferry is how it interacts with fuel/charging versus stock torchdrive. Like, if the ferry is moving dropships insystem, a thing designed to move on its own, how efficient they are runs into how efficient torchships are. Its like building a cargo ship to move slightly smaller cargo ships that would otherwise sail themselves just fine.
Like Sol/terra is a very well traveled system. If a ferry would work anywhere it would be there. The travel time is only 9-10 days from earth to zenith with a dropship. The cost of a dropship moving itself is 10 burn days is the same as 10 burn days of fuel you dump with reactor charging an engine, but the dropship has a very low tonnage cost per day. Now a tiny ferry drive rated to 1 LY presumably is so tiny it can affordably transport multiple dropships cheaper then they can move themselves. Also, if the drive is too efficient, then 1ly warships, which would quickcharge their way across conventional 30ly leaps, would have massively more room for weapons and armor at a fraction of the cost, only spending a little longer making big jumps but having far too great an efficiency once in system.
If the ferry is more efficient in both speed (charging time) and fuel (transporting multiple big civilian droppers for less fuel then the droppers would spend) then we wouldnt see dropships with interplanetary drives in the same manner. The ferry would be the defacto solution. Already, we can use civvy jumpships to spend 183 hours charging with a solar sail to bypass the dropship transit time, so the ferry needs to also be more efficient then civilian jumpers with a sail.
I dont see a great design space for the ferry without it just completely taking over how all travel is done.
The efficiencies don't pile up if you only have one inhabited world in a system, or in systems without extensive deep-system economies. (aka places with Belters or Belter equivalents). The reason is
time.
y'see, you can't go higher than one gee if you're carrying people any significant distance and want to deliver them alive and in good health.
that right there, limits your thrust duration, and if it takes a week under thrust (or two, or four) a ferry system pays for itself, presuming you have two of them or more to swap out.
particularly if you're developing a full
in system economy rather than boutique trips.
One way to consider this, is the difference in efficiencies between railways, and automobiles, when you start looking at continental length trips versus urban-core-to-the-suburbs. Your Econoline van might seem more efficient-until you have to drive from Minneapolis to Los Angeles on a regular basis, rather than once in a year.
same thing here; for systems with very long distances between points and planets, being able to make that trip in under two weeks or less than a month really stacks up, but if your jump limit is only 7 days? well...why woudn't you just run torch ships to the planet and back? It's the more sensible approach!
Kowloon's jump limit is four weeks. That's a month between the primary planet, and the Zenith or Nadir. The closer points include the planetary L1, (several days) Planet-Moon L1 (four to six hours) or the hot point between the two stars (better bring your sunscreen) which is still pretty close to a month at standard one-gee driving.
THAT system
needs a Ferry, because your emergency supplies can expire before you arrive, see? This ain't a system you'll need at somewhere like New Avalon, because the distance is reasonable from the Zenith/Nadir or the L1, and there isn't a lot of development
out-system into places like the local Kuiper belt, gas giants with Moons, etc.
chalk it up to New Avalon being a nice place, with a simple geometry that is one of the main reasons it became an Administrative Capital for an interstellar empire.
