Estimating ship sizes

Hey guys might not be the right place for this but how do you work out how big a space ship needs to be I ask this because I have been working on a scfi world for several years now and have written a number of wiki style articles detailing the military capacity’s and crew compliments of most ships in the military of this universe however I find it very hard to work out how big they are I know off course this largely depends on how much of a ship is needed for engines

But assuming engines and the like only make say a 1/3 of the mass how would I go about creating a formula that will tell me the rough size of a ship with say 30 or 500 or 2000 crew?

once done found deck plans for there 40 odd ship types will not be far off

For 'Space Opera' universes with 'magic' drives (like Traveller, Star Wars and Star Trek), the answer is 'whatever the plot requires'.

However, for answers dealing with hard science, this is the single best source of data that I know of:
http://www.projectrho.com/rocket/index.php

[The problem with 'realistic', is that 'realistic' ships are slow (months to the next planet and hundreds of years to the next star) and 90% reaction mass ... that's a lot of 'nothing' for a deck plan of a ship.]

For just the 'cargo' portion of the ship (including human cargo, but ignoring drives, fuel and reaction mass) this is a good source of data on how much room is needed for living space and food production:
http://www.nss.org/settlement/library.html

Hope that helps and Good Luck.

[PS. If you just want some quick and dirty answers, Traveller (the RPG) requires:
1. about 2000 cubic feet of living space (200 square feet of floor area) per person ... which includes all common areas, life support, living quarters, food storage etc.
2. about One crew member per 50,000 cubic feet of total ship.
3. about 15% of the ship dedicated to 'Engineering' (drives, power plant and fuel) per unit of speed ... which in traveller are gees of acceleration for normal travel and parsecs per week for faster than light travel.
4. each 2000 cubic feet of unused space can hold 1 passenger worth of accomodations or 1 TEU standard cargo container. ]

I ran across this cool poster online while I was looking up what a blueprint should look like on my latest lite challenge entry. It might be of some help since it compares pretty much all the well known sci-fi spaceships.

It's a cool chart: Sci-Fi Space ship Comparison chart

Hey nice find Jax, this could come in really handy.

Cheers,
-Arsheesh

It's intended for use in Roleplaying Games, but GURPS Spaceships would probably do a decent job of providing consistency of starship size without too much difficulty. GURPS books are pretty well researched so you can be reasonably confident that they aren't just making up numbers. The biggest downside is the use of US Customary units.

Yeah having now considered this question even more I think its more complex this for a space oprah thank you for that chart jaxlon right now I only have drawings of the style of each ship and the relative sizes of each ships and rough estimates of crew sizes im thinking the engines and like do not take up a huge part of the ship as you know it’s the future and all so I’m more inclined compare it to a Morden air craft carrier then anything else

What I might do when I get to the holidays is look at a whole lot of different ships from modern and historical naves looking at diagrams there engine rooms take up barely anything so I’m thinking I will try to work out what size of ship you need for what size crew then forming a spread sheet where you tell it what ratio of the ship is engine and what is crew space then tell it what level of luxury they can have on a scale form 10 a cruise ship to 1 a modern sub or a warship from the age of sail

And then you put whether the ship is military or cargo and its crew size and it will try to calculate a rough size for you

That said everything I just said is words right now lets see if I can find sources to give me the figures I need and get my head around the maths to do it all

Jaxlon if your chart says anything it is that there is no agreed size in scfi which I found stunning I somehow assumed they were all working of the same figures in working out how to build there models but very cool find none the less

While I’m doing this to try to make floor plans of some of the smaller ships the maps are really all in aid of a novel I have been writing

Realistic spaceships have large engines and huge fuel tanks because they need to carry (and accelerate) loads of reaction mass. There are plenty of design studies and examples out there, but the basic point is you'll end up with a huge percentage of fuel to propel even a tiny payload...

If you are going for space opera, then ships are any size you want. Most SF authors probably just make stuff up as they go along, some may have rough guidelines and I am guessing very few actually have set "rules" on ship design.

I've looked at ship sizes myself some time ago, mostly trying to figure out what a "tramp freighter" would be like, and I've based my comparison on Traveller, H. Beam Piper, and some real world stuff:

http://enderra.com/2011/10/14/starsship-sizes/

Here is a great site for ship size comparisons:

http://www.merzo.net/

Jeff Russells Star Ship Dimentions.