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02-03-2016, 04:02 AM | #1 |
Join Date: Feb 2005
Location: Doncaster, UK
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Empty Cargo Holds
Hello, this has probably already been answered somewhere but I can't find anything related through Search. Maybe there's a FAQ I don't know about?
In Spaceships, if I have empty cargo holds, my ship has less mass. Is it reasonable to have each empty cargo hold "count as" a fuel tank for the purposes of delta-V increase (GURPS Spaceships p. 17) ? |
02-03-2016, 07:09 AM | #2 |
Join Date: Jun 2006
Location: On the road again...
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Re: Empty Cargo Holds
I believe your logic is sound, but I'm not entirely sure treating an empty cargo hold as a fuel tank is the right way to go about it. Isn't there something in a later chapter for when fuel tanks start to get empty?
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02-03-2016, 02:34 PM | #4 | |
Join Date: Feb 2005
Location: Doncaster, UK
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Re: Empty Cargo Holds
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I'm wondering if the math is correct If we say, well I have 8 fuel tanks and two full cargo holds, my effective dV is x1.2. On the return trip I have two empty cargo holds, my effective dV is x1.4 (the next step on that table, 10 tanks). Writing it out now, I have a feeling it's not correct. Per what Ulzgoroth said. |
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02-03-2016, 03:59 PM | #5 | |
Join Date: Jul 2008
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Re: Empty Cargo Holds
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Which, um. Should give a better number than your way, but doesn't. (It gives one-tank delta-V x 8*10/9*1.2 = 8*1.33..., if one applies the rules.) Probably to do with multiplier table breakpoints, I can check the rocket equation math later.
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. |
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02-04-2016, 01:16 AM | #6 |
Join Date: Feb 2005
Location: Doncaster, UK
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Re: Empty Cargo Holds
What about the mass driver/powered rock example, in which fuel tanks and cargo holds are one and the same? The rocket equation surely wouldn't care if it's a fuel tank being emptied of fuel, or a cargo hold being emptied of fuel, its still a reduction in mass?
Related question: Does the dV multiplier hold true when looking at partially full tanks? e.g. If I have 6 fuel tanks in total, but only one is full (e.g. 3 mps of argon), do I still get the x1.2 multiplier (I get 3.6 mps)? Sorry for being dumb. Last edited by Marasmusine; 02-04-2016 at 01:42 AM. |
02-04-2016, 02:05 AM | #7 |
Join Date: Oct 2004
Location: Yorkshire, UK
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Re: Empty Cargo Holds
Spaceships is an intentionally simplified system, and the dV multiplier table is a simplification of what the rocket equation would give for reduced mass from empty fuel tanks if you did the calculation.
If you really wanted to be accurate, you would need to be recalculating the delta-v per mass of fuel every time the mass of the spaceship change - from burning fuel, firing missiles, taking damage, jettisoning cargo, being boarded, launching vessels from hangers, etc. - which would be no fun (for most people). For quick play at the table, treating empty cargo holds as empty fuel tanks for the dV multiplier is going to be close enough for game purposes and most people. |
02-04-2016, 02:39 AM | #8 | ||
Join Date: Jul 2008
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Re: Empty Cargo Holds
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As seen before, what empty tanks are equivalent to is making your ship less massive. So with 1 full tank and 5 empty tanks, your ship is only 3/4s its rated mass. So your one tank is equivalent to 4/3s of a tank, and should provide delta-V according to that. (Which is slightly better than 1.2x one tank, again. Because the last bit of reaction mass you use is the most effective.)
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. |
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02-03-2016, 07:29 AM | #9 | |
Join Date: Oct 2004
Location: Yorkshire, UK
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Re: Empty Cargo Holds
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SM+8/TL10: Fusion Torch (15mps on Hydrogen), 5 Fuel Tanks (250 tons of fuel, 75mps Total); 4 Cargo Bays - where 2 are empty. Treating the empty cargo bays as empty fuel tanks raises the Delta-V by 1.2 to 90mps. This would be the same calculation for if you had 7 fuels tanks giving 126mps; If you burn 36mps of fuel, you've emptied 2 fuel tanks, and have 5 fuel tanks of hydrogen left. i.e. 2 empty fuel tanks has the same state as 2 empty cargo bays - just without that initial 36mps of fuel! Calculating the actual effect requires the rocket formula which is somewhere here on the forums, but it does not seem necessary. |
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02-03-2016, 09:46 AM | #10 | |
Join Date: Apr 2011
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Re: Empty Cargo Holds
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That should only count for Cargo Hold modules, and a damaged cargo hold won't count until you've actually taken the time to empty the ruined cargo from it. Empty Hangars... well, I suppose you could say that every 2 empty Hangars could count as one empty fuel tank for delta V purposes. But that's starting to get fiddly. I'd absolutely not allow that for steerage cargo you get from a habitat module. |
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