Originally posted by Sigg Oddra:
Why oh why do we insist on thinking of starships being built like ocean going ships?
Keel first? How very two dimensional... must resist temptation to use quotes from cheesey Sci-Fi movies...
Submarines have to be your starting model, and modern subs are just about built from the inside out because once the pressure hull is in place it becomes several orders of magnitude greater to work on anything major.
Not 2-d, when the keel is running down the spinal mount... rather than being the bottom of the displacement hull of a modern craft. (And, in modern airliners, there really is no keel equivalent.)
But, for anything which is going to subject itself for high-multiple-g accellerations (modern airliners seldom exceed 2G loading in operation, and 3G loading in certain take-off and landing maneuvers), some centralized mass linking structure is a necessity.
In MT, the rules seem to assume this is the shell. TNE assumes a shell and spine (minimum armour and minimum spine). CT implies a spine.
The keel of a naval craft is also sometimes refered to as the spine and/or backbone, sometimes just back (As in, "The mine broke her back, and she foundered then and there."). Some (very few, actually, btu they do exist) ships have separate spines and keels, and subs use a shell-integrity model.
Now, apllying the term keel to a spacecraft, it refers to the main structural integrity member, rather than the "Bottom of the hull", and is more properly a spine, but the two terms have been used nigh interchangeably on the TML for well over a decade now.
And note that I said "keel out" rather than "keel up".
(Boy, am I in pedanatic mode right now... apologies for tone...)
We have many different ship building rulesets (CT/B2, CT/B5, MT, TNE/BL, TNE/FF&S, T4/QSDS, T4/SSDS, T4/FF&S2, GT, T20. Plus, for the further afield, 2300 Starship Architecht's Manual (from Star Cruiser), Star Hero, CORPS VDS, Space Opera, Space Master (in two editions), Alternity GM's and Starships books, Starfire, and Star Frontiers Knight Hawks; all of these have been used at some point for traveller games of one sort or another, and have ship design sequences. One friend of mine still uses 1st ed starfire for his ship design system. He assumes a small ship universe (8-250 spaces, roughly 10 Td per space based upon his notes...)
Now, lets assume a 50 year lifespan. (We know this to be low... but in the long run, a fair assumption due to non-wear losses.) This means that we need to replace the tonnage every 50 years. We'll assume a 6 months-imperial time frame; we'll assume an A port provides all the ships it encounters (in the core, this is way wrong, but in the marches, it may be providing far more than it encounters month to month. We'll also assume 1 month per year down time for self-maintenance (actually only 2 weeks for maintenance bays, to make math easier...). 13 months per year. 4 weeks per month.
Step one: tonnage replacement, is two times 6-month capacity... or 1 % per 6 months of the overall tonnage.
so monthly capacity is 1/6% per month.
Plus, the entire tonnage requires maintenance, at 2 weeks per year; assuming perfect distibution, and no construction bays used, that's 25 units, each of 2 weeks and 4% of serviced tonnage. We'll assume that this is actually 1 week, plus queuing time so tonnage for maintenance yards is halved, to make required service ammount 2% per 2 weeks, or 4 % per month. So we need a yard which can build/maintain 4_1/6% of it's serviced fleet per month.
step two: serviced tonnage from WTN. WTN is in credits... there are tonnage values based upon median cargo sizes.
Let us assume, however, that those figures are accurate. Now we need to turn those tonnages into tonnages of ships...
let's assume J2, 1G, 10% overhead above that (bridge and staterooms, 200+ tons). 23% for Jump, 4% for PP (2% for the PP, 2% for the fuel), 3% for the maneuver drive. That gives us 40% overhead. So cargo tonnage * 10/6, 1_2/3. Lets assume that this needs to be adjusted further to account for non-merchant craft, to a nice round number... say 2x or 3x (depending on YOUR TU's millitancy, maybe as much as x5).
So take the median monthly trade volume for the A port's WTN, and multiply by 2 for a laizze faire TU, 3 for a more normal one, 5 for a paranoid one. Let's assume x3 (or, roughly 1/2 of all tonnage is NON merchants.)
Step three: How much tonnage capacity: roughly 25/6% of the shipping tonnage! Round up to 5% on the frontier. In the core, you may as well halve this, or even less.
step four: integrate it:
3x the trade volume and 1/20th the tonnage: 15% of the monthly tade volume in tonnage per month on the frontier.
half that in the core. Or even less.