On Jun 9, 2014, at 4:19 PM, Timothy Collinson <timothy.collinson@port.ac.uk> wrote:
> I'm using the rule of thumb that says deck plans should have twice the number of squares of the tonnage.

That’s basically correct.  A standard deck square is 1.5 meters square and 3 meters tall:
1.5m x 1.5m x 3m = 6.75m^3.  Two squares is therefore 13.5 cubic meters.

The Traveller volume standard is a ton of liquid hydrogen; the density varies with temperature, but is typically between 70.85 and 71.00 kg/m3.  That works out to just over 14 cubic meters per ton (14.08 to 14.11).  Slush hydrogen has a density of about 85 kg/m3, which would put a ton at 11.76 cubic meters.

Slush hydrogen is a mixture of solid, liquid, and gas at the triple point.  For hydrogen, this is a lower temperature and higher density than liquid hydrogen - about 14K (-259C) and and 7 kPa (about 1 PSI, or about 1/14th of an atmosphere).

IMTU, I figure that typical Traveller starships aim to keep their fuel as slush hydrogen at the triple point, and provide about 15% extra space in the tankage to accommodate chillers and to contain temperature excursions.

> So a 400-ton ship would have 800 one point five metre squares.

Yep.

> So if I have four decks of 200 squares and a fuel deck (not shown on the plans) as well.  That's NOT a 400 ton ship but a 500 ton ship, right?

Right.  A 400-ton J-1 ship will need 40 tons (or 80 squares) of fuel.

---Derek