Canon says: 13 months to the year; 40 year mortgages with 480 monthly payments; only annual maintenance is an annual expense, and takes an average of 2 weeks.
Okay, but the two statements are in conflict.
Library Data, A-M:
Dating Systems. Three major dating systems are in use when referring to historical events— Terran, Vilani, and Imperial. A fourth system (Zhodani olympiads) is of passing interest.
... Terran years have 365 days and are considered a standard for length of year. Years are further subdivided into months and weeks, although these divisions have fallen into disuse outside the Solomani Sphere.
...Imperial dates count from the year of the founding of the Third Imperium,
specifying the year zero as a holiday year. ... Imperial dating uses a Julian system for specifying days. Each day in the year is consecutively numbered beginning with 001. Thus, in the year 1105, the first day of the year is 001-1105. Weeks of seven days and months of 28 days are used to refer to lengths of time, but rarely to establish dates."
480 months is not 40 years under Imperial convention; it's 36 years and 12 months. Canon doesn't mention having any sort of an annual holiday from the mortgage payment. Book 2 rules, if I recall, were adopted before there was much canon about the Imperium and its practices. They were based on the conventional Earth/Gregorian 12-month calendar that players are accustomed to - thus 480 months is 40 years. The Imperial calendar arrived later.
I don't know of any canon source that's settled the conflict, but there are several ways to handle it. One could, as Rancke suggests, make payments due every 30th day of the year. One could make payments due every 4 weeks and declare the 13th month a mortgage holiday month - no payments due that month. One could require payments every 4 weeks and ignore the Book-2 reference to a 40-year mortgage, with the mortgage paid off in 37 years. One could recalculate the payment period to cover 520 q-4-week installments instead of 480 installments - which does have the advantage of making them a little easier to meet. As there is no canon solution, any solution is by definition an IMTU solution, though the first clearly hews closest to canon intent than the others.
We can dicker till the cows come home but my estimate was based on a 52 week year, which is pretty much on target whether your year is 13 months and a day or 12 months and a 5-day. About the only mistake I can find is that some of the numbers assume income when there isn't any - in that month of down time. I didn't calculate for 800 dTonners because, as far as I know, he wasn't asking about 800 dTonners: an 800 dTonner implies daily traffic of 1400 or more passengers. I don't know if he's thinking about a starport with that level of passenger activity.
OK, revise:
TL8 95t 1G shuttle costs MCr17.86, needs to make MCr 0.893 annually to cover the mortgage.
Annual overhaul costs MCr0.01786.
Fuel costs: one dTon every 4 weeks in service, 4 weeks annual downtime planned for 2 weeks of overhaul and 14 days of random unexpected events through the year. MCr 0.006 for the year
No data on life support costs for short-hauling.
Crew costs: Cr 6000 for 4 weeks, we're going to be generous and pay the 4 weeks when it's not running 'cause we don't want our pilots wandering off to work for someone else. 6000 x 4 crew x 13 pay periods = Cr312,000 annual budget for crew. Likely to be other personnel needs, but we'll put that aside for the moment.
Annual break-even budget: 0.893+0.01786+0.006+0.312=MCr1.22886
Available working days: 336
Minimum income needed: 3658 daily
Cargo space available: 69.3 dTons, assuming no crew cabin.
Minimum income per dTon of space per day: about Cr53.
Optimal income per dTon of space per day: about Cr 69.
Factoring in a crew cabin adds about Cr 2 to that.
___
TL8 95t 2G shuttle costs MCr27.36, needs to make MCr 1.368 annually to cover the mortgage.
Annual overhaul costs MCr0.02736.
Fuel costs: 1.9 dTon every 4 weeks in service, 4 weeks annual downtime planned for 2 weeks of overhaul and 14 days of random unexpected events through the year. MCr 0.0114 for the year
No data on life support costs for short-hauling.
Crew costs: Cr 6000 x 4 crew x 13 pay periods = Cr312,000 annual budget for crew.
Annual break-even budget: 1.368+0.02736+0.0114+0.312=MCr1.71876
Available working days: 336
Minimum income needed: 5116 daily
Cargo space available: 61.75 dTons, assuming no crew cabin.
Minimum income per dTon of space per day: about Cr83.
Optimal income per dTon of space per day: about Cr 108.
We won't factor in a crew cabin 'cause this is supposed to be a passenger flyer.
So for Rancke's purposes we're getting cargo rates of about Cr 70 per dTon and passenger ticket rates of about Cr 54 per person. His Cr50 tickets cover costs nicely and give him a 20% profit margin, which gives him an annual profit of ~Cr 352,000 from which to fund any other infrastructure and pay the owners.
The 800 dTonner would indeed be more profitable, with 2.5% of tonnage in bridge instead of 20%, assuming there's traffic to support it. Also means a much lower percentage of personnel expenses. I'm getting minimum overhead of Cr55 per dTon per day for a 2G 800 dTonner, so the 800 dTonners support passenger tickets as low as Cr 36 per person with a 30% profit margin.
I think Rancke's more looking at what's reasonable for his setting. If his concept of the starport involves heavier traffic, he can scale up the size of his shuttles and scale down ticket prices proportionally and end up with something reasonable.
