Ship Design

Trying to duplicate Erin's design was the first time, ever, I'd attempted to use the GURPS: Traveller modular ship design system.

It's not laid out as I would have liked, but it will suffice.

I think I can live with the change from the maneuver drive pulling a volume to pushing a mass.

There's a bit more book-keeping since you need to figure out the mass of the ship to get the acceleration and that can be a big factor on whether you can take-off!

The standard assumption is 5 sTon per dTon of cargo.  That's 10,000 lbs per 500 cu ft.  20 lbs per cubic foot.  Less than a third of the density of water...

Cast iron is 112.5 sTon per dTon.  Water is 15.6 sTon/dTon.  Bulk wheat would be 12.1 sTon/dTon!

So the 146 tons of cargo space in a Subsidized Merchant is rated for 730 tons of weight.  That mass rating means that just under 6.5 dTons of cast iron could be carried without affecting performance.  That's a cube of iron 14.8 feet per side or a cube of water 28.6 ft across.

A full (mass) load of wheat would take up less than half the cargo hold (60.5 cu ft).

Clearly the game designers weren't thinking of tramp freighters a bulk material haulers.  Bulk hauling really requires specialized ships anyway otherwise loading and unloading is a labor intensive chore.

Hmmm.

Real world comparison:

C-5M.  Cargo compartment there is 73.359 dTon.  Max payload on that is a mere 135 tons (7.36 lb. per cu ft).

747 LCF.  130 dTon.  Max payload, just 44.673 tons at max fuel.  1.38 lb/cu ft.

747-400F.  43.34 dTon.  Max payload, 68.315 tons with max fuel.  6.31 lb. per cu ft.

It does very well against modern aircraft, especially when you consider it can pull 1.01g with that 730 ton load.  It's capable of out accelerating many modern fighters.

The jump drive still seems to work on a volume rather than a mass, so if you've some means of hauling the iron from the surface to orbit you can pack in 16,425 tons of cast iron where only being able to accelerate at 0.08g isn't QUITE the liability it is while parked on the surface.  From orbit it takes just a bit over 11 hours to get to jump distance from an Earth sized world at 0.08g.  If we restrict our cargo to the standard amount 1.01g carries us to the jump point from the surface in about three hours thirty minutes.

Traveller numbers in GURPS are still miraculous!

Update: the value of a 730 tons of... in USD today is:

Iron $429,240.
Wheat $223,635.50.

Hauling at the normal 600 Cr per dTon per parsec; 87,600 Cr.  Hauling that Cube of iron, 3,900 Cr, half a hold of wheat; 36,300 Cr.  Because there's such a loss in getting massed out, the shrewd captain treats hauling the block of iron as a charter and charges the customer for the hold that cannot be used because of the mass of the load.  The client IS using the entire hold after all...

It doesn't pay to leave the hold empty, so hauling the less dense breakbulk and containerized cargos is the way to go.  As we can see from our airplane example, such loads do abound.