tonnages was RE: DS2 Resins to FT or FTFB Mass

> On Tue, 24 Nov 1998, George,Eugene M wrote:

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
bit
> from the definition. DWT is the maximum displacement of the vessel

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

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

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

nope : grt = net + dwt

> GRT = Cargo Volume

> Net Tonnage would be the FT equivalent of the 50% for weapons, cargo

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

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

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

> At 01:18 PM 11/25/98 +0000, you wrote:

I think that Traveller was using their displacement values simply as a measure
of volume, to simplify drawing deck plans. It works okay since
large portions of their ships _are_ filled with liquid H due to the fuel
tanks.

> have suggestions been made concerning the thrusts of underloaded

I asked the question in one of the DS2 "how many power armor troops can dance
in the hold of cargo vessel?" threads about a week ago.

> it would be simple to work out, if it were not for the silly way

I'm not sure how it would work in FT2. In 2.5, though, it makes a lot of
sense. Each point of thrust requires 5% of the ships total mass to be devoted
to engines.

For example:

A mass-200 freighter with FTL, thrust-2, and a fragile hull would have
25%
(10% + 5% x2 + 5%) of its mass devoted to structure and 75% to cargo
capacity. Realistically, if that ship was running "light" its total mass would
only be 50 and its engines would mass 20, so it should be able to
generate thrust-8.  Every 25 mass of cargo (or portion thereof) would
reduce thrust by a point.

A little tinkering and one could cook this into a spreadsheet which would
calculate the thrust/load ratios at the time of design.

> this leads to the possibility that a carrier might dump its

I would tend to discourage this however. IIRC, its been stated that FT
fighters mass less than one each. I think the mass requirements for fighters
and SLMs reflect the hangar bays, magazines and other support equipment which
would not be reduced significantly with a launch.

> On Wed, 25 Nov 1998, Jeff Lyon wrote:

> I'm not sure how it would work in FT2. In 2.5, though, it makes a lot

i see. very sensible; i'm glad to see that one fixed. i plugged this hole in
ft2 (all ships pay for drives as cruisers) and recalculated points
costs. suddenly, all-battleship fleets became very attractive. i then
changed the capitals to have better thrust, and it sort of balances out.
still very pro-battleship, though (not that there's anything wrong with
that - size does matter!).

> >this leads to the possibility that a carrier might dump its

quite; the mass a ship could lose by dumping stores is fairly minor. unless
you are the FCT or have one of beth's arsenal ships, of course
...

Tom