Let's play numbers!
Akerut 5000 dT liner
Mortgage: MCr989.01 in volume, therefore ~MCr4.121 per month. For the purpose of this exercise, we will arbitrarily declare that a month is 4 weeks and every 13th month, coinciding with the maintenance month, is a morgage holiday. No debate, please: it makes the math easier. Buying into the declaration for the purpose of this exercise shall not be construed as waiving your right to argue about the length of the month or the structure of the mortgage payment in another thread at a later date.
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Crew cost: Cr45,000 per month plus whatever a pinnace pilot earns. Call it Cr50,000?
Fuel costs: Cr5000 for the power plant for a month. Cr250,000 per jump
Life support: Cr30,000 per two week period, or Cr 60,000 per month.
Routine maintenance: Cr989,010 annually. Spread over 52 weeks, comes to Cr76,084 per 4-week "month".
Berthing costs: HowdaheckshouldIknow. We will consider it insignificantly small for this exercise.
Total monthly costs, normally: 4,121,000+50,000+5,000+jump1x2jumps500,000+60,000+76,084=Cr4,812,084
Total monthly costs, 2 parsec jump: 4,121,000+50,000+5,000+average4xjump1severy3monthsis666,666permonth+60,000+76,084=Cr4,978,750
Total monthly costs, 3 parsec jump: 4,121,000+50,000+5,000+jump1x3jumps750,000+60,000+76,084=Cr5,062,084
The Hercules must make a bit over 2.4 million credits per normal jump (1 week in jump space, 1 week in port) to break even. For a 2 parsec jump, figure 4 jumps in 3 months, about 3.73 million credits per jump (2 weeks in jump space, 1 week in port). For a 3 parsec jump, a bit over 5 million credits per jump (3 weeks in jump space, 1 week in port).
Hercules available tonnage is actually 4069 dTons. It can make money nicely doing only transport with 1-parsec jumps between worlds. Loses tonnage for a 2-jumper, down to 3569 dTons, which means the 2-jump loses money. And, the 3 jump loses money in a big way.
Now, this can be made up handily by speculation, but ... if you can do that, then you can do it faster and make more money with a ship that can make two jumps per month instead of just one.
So, let's turn the problem upside down and ask the question: what would prompt Akerut to use jump-1 freighters instead of jump-3 freighters?
Top of my list: the ships are mostly free. Something McEvans said makes me think of this: Tukera buys the ships, runs them for 40 years, gives them a recondition job and then "sells" the old refurbs off to Akerut. Akerut hires the kind of spacers who couldn't get in the door at Tukera and are willing to fly an older ship for a chance at a job, pays a bit more in maintenance perhaps, forwards an annual share of profits to Tukera as the purchase price of the ship - and if anything disastrous happens, it's Akerut facing the music, not Tukera. If Akerut goes down into bankruptcy because, say, one of their ships crashed someplace populated, Tukera's primary leinholder on the company's chief assets.
Under that model, the ship need no longer be making 5 million credits a month. It needs only to cover the other expenses and enough to justify the arrangement: whatever value a 40-year old ship might have on the open market, amortized over whatever useful years it has left.
Second on the list: captive market. Whatever's most worth having on this world is already tied up by Tukera, or enough of it that competition isn't economically feasible for an up-n-coming company with a jump-3 freighter. We already know Tukera had most of the market for Zilan wine sewed up, but that's a seasonal market. Perhaps they are also heavily invested in other export commodities. If you have the market pretty much cornered and have an available ship that's close to free, then it may be more profitable to use the old asset and move slowly than to sink a billion credits into a fast new asset.
We know Imperiallines runs a route between Zila and Pysadi and from there to Aramis, but Imperiallines - well, read the entry in TA. Oberlindes runs a route into the area but has only a feeder to Zila, and the story revolves around Oberlindes' effort to alter that state of affairs.