tonnages was RE: DS2 Resins to FT or FTFB Mass

On Tue, 24 Nov 1998, George,Eugene M wrote:
> Ack! Now I'm confused again. 

ok, here is my attempt at clearing it out. this may or may not be
correct.

note that for floating ships, the mass of the water displaced is equal
to
the mass of the ship (Archimedes' principle), so mass and displacement
volume can be used interchangeably. note that this works for floating in
anything, so the displacements measured in liquid hydrogen that were
mooted from traveller work out the same as water displacements. unless
they were just measures of volume, of course.

> DWT is the whole shebang, or equal to FT's Mass.

no - that's gross tonnage (grt).

grt : fully laden ship.
dwt : cargo plus fuel plus stores
net : unladen ship.

grt = net + dwt
dwt = grt - net

> This I get from the "a
> vessels cargo capacity is less than it's total deadweight tonnage..."
bit
> from the definition. DWT is the maximum displacement of the vessel
under a
> FULL LOAD, hence the total filled tonnage.

since dwt includes fuel and stores, which have non-negative masses
(well,
mostly; exotic matter fuel anyone?), cargo is less than deadweight.

> DWT = Structure + Max Cargo

grt = net + dwt
dwt = cargo + bunker + stores
grt = net + cargo + bunker + stores

> Gross Tonnage is cargo volume and hull/systems, similar to Mass in
FTFB and
> FT2

cargo volume does not come into it anywhere. for floating ships, 
displacement is a measure of mass. however, gross displacement is the
total mass of the ship, just like total mass in FT. star freighters
would
be designed with a specific maximum mass of cargo in mind; if
extra-bulky
cargo (such as expanded polystyrene) was to be transported, the ship
would
either be underloaded or would have to strap on extra cargo barges to
the
hull.

have suggestions been made concerning the thrusts of underloaded
freighters? it would be simple to work out, if it were not for the silly
way bigger ships have less efficient drives in FT2. is this fixed in
ft2.5? if power is proportional to mass times acceleration (which it
isn;t, i think), then the thrust of a freighter is given by:

t	actual thrust
T	nominal thrust
N	net tonnage (not cargo - hull plus systems)
c	actual cargo
C	nominal cargo

	t	=	T * (N + C) / (N + c)

i seem to remember that 40% of a freighter's mass is cargo in ft2. given
that, for FT2 freighters:

	C/0.4	=	N/0.6
	C	=	2/3 . N

so when unloaded:

	c	=	0
	t	=	T * (N + C) / (N + c)
		=	T * 5/3 N / N
		=	5/3 T

so if the Sturmey-Archer (below) had thrust 4 and went unloaded, it
would
have thrust 4 * 5/3 = 20/3 = 6.6, not bad at all.

this leads to the possibility that a carrier might dump its fighters or
a
missile ship its missiles in order to boost thrust and run away. not
very
clever if there is a chance you will have to fight, but if an FFG runs
into an enemy battle fleet, it might be wise.

> but more for the purposes of registration/ cargo costing.

i think it does actually correspond to the mass of the ship.

> I don't know
> if this is identical to DWT but it sounds like it.

nope : grt = dwt + net

> GT = Structure + Cargo Volume

well, cargo mass rather than volume, and remember to include the mass of
fuel and stores in that figure, and yes.

> Gross Registered Tonnage is the Cargo Space ONLY. Identical to Net
Tonnage.

nope : grt = net + dwt

> GRT = Cargo Volume

> Net Tonnage would be the FT equivalent of the 50% for weapons, cargo
and
> systems. It corresponds to the FTFB equivalent of everything but
drives,
> weapons and systems. A pure expression of the cargo capacity of the
ship.

gross tonnage is the total mass. net tonnage is the mass used for the
hull, equipment, armour, etc (everything but fuel, stores and cargo).
some
of this is accounted for by the 50% overhead (hull, engine, hyperdrive, 
firecons, life support plant, computers), some by the 50% designed mass
(weapons, armour). however, note that both of these contribute to dwt
too
- missiles, magazines for SMs and RGs, fighters and fuel (allowed for in
engine mass) are all part of dwt. for freighters, cargo mass is also all
part of dwt.

> Deadweight (gross tonnage?) is the theoretical maximum displacement of
the
> vessel (Mass 200 bulk carrier)
>
> Net Tonnage/ Gross Registered Tonnage for said Mass 200 Bulk Carrier =
4
> holds of 149 Mass total.
> 
> So the Shimano Maru a 200,000 ton ore carrier, will depart from New
Albion
> on the 21st of December, carrying 20 crew and 149,000 tons of
diatomaceous
> earth from the toothpaste mines.

whilst the RMS Sturmey-Archer, a 50 000 tonne tramp bulker, will be
recieiving cargo at Balder HiBase from 23 Dec 2148 until 27 Dec 2148,
departing 0730 UT, carrying 20 000 tonnes of small painted plastic cubes
discarded by Front Admiral Indy following failed pulse torpedo tests.

incidentally, 'tramp' just means that she does not sail a fixed route
(ships that do this are 'liners') but rather wanders among the stars,
going where the contracts take her. it says nothing about her state of
repair.

> (on the DS2 table top it would be about 14
> inches long by 3 wide by 2 and a quarter tall.... :) )

speaking of which, does anyone know why there are three explosions when
the Nostromo goes down (up?) at the end of Alien? and why was there a
self
destruct system on a freighter? seems sort of risky, especially at
office
parties ...

> Sound good (whether or not it's right in the real world)?

it does so.

hope (a) i have this right (b) this helps,
Tom