Don't forget guys, that large liners need support to be profitable. I've always assumed that the freight and speculative cargo rules were designed for the fly traders who trawl through the starport on the hunt for something profitable on the grounds that the larger ships have already taken anything worthwhile, hence the rules for freight and speculative cargo simply represent the leftovers of the corporate table.
Any liner of that size (8000 tons) would have dedicated cargo and freight offices on every world along its route that would source profitable cargos for the liner, and have dedicated holding warehouses and storage depots, to facilitate this, hence when the liner arrived it might spend only one day unloading, whilst loading up on the next day and immediately jumping to its next destination, thus achieving more jumps per month. I would also expect the owning corporation to have profitable deals set up with the local government or dominant on planet corporations and be a 'preferred carrier' which might involve charging a set fee per amount of hold space allocated, regardless of how full it actually is as per the mail rules. Hence the organisation that actually pays for that space would find the expenditure to be more profitable the fuller it is, in much the same way that full mail van is obviously more cost effective for the mail company than a half empty one.
As in real life, its a rare large company that actually pays any taxes, and hence if your liner is serving the same group worlds all of the time and giving a reliable and constant, predictable service then why not demand a government subsidy, in lieu of taxes paid.
As an aside, what pirates do you have in your TU who would willingly attack an 8000 ton liner, afterall a ship this size with minimal defences should easily swot the typical 200-400 ton raider.
Dont forget you are also a bulk consumer of fuel so a discount is in order there, and as for berthing they should be paying you or giving you a kickback on money spent when your passengers disembark and flood the starport bars, hotels and restaurants.
Also I would imagine that financing would be different, in much the same way that a man buying a small speed boat would purchase it with different terms to the multimillion pound shipping company commisioning the build of a new new ocean liner. Vessells as large as this one, are seriously good for the economy of any world with a shipyard, hence the 80% standard design discount should be thrown out, take bids from competing shipyards, and lower that price, perhaps to 50% even...
Coming back to financing, dividing the purchase price by 240 and paying that each month over 40 years actually returns double the value of the ship. If your going to finance it through a bank mortgage, negotiate and get it down to 1 1/2 of the ships purchase price or even lowe if applicable, hence lowering the monthly mortgage payment.
However if you are financing on your own paper (paying for it yourself) then don't go for profit, just get enough money in each month (all revenue streams) to meet costs, because once year 40 has come you will have made 100% on the purchase price of your ship or 1 1/2 if you give yourself a discount. Pretty handy when the going gets tough or subsector wide financial collapse is imminent(bottom of the trade cycle).
Other forms of income can be gained by floating yourdself on the local stock exchanges, (long term investors like stable companies that show steady growth) and you could also set up your own merchant academy, attracting the best and brightest people from all over the subsector or sector to attend and pay for the privilige of your expertise and training. (the added advantage that they or their families are paying you to teach them how to become your crew - Priceless!).
One day when I get time, I might even write up some rules for large ships, hope this helps.
