07-23-2011, 03:37 AM | #1 | |
Join Date: Jun 2006
Location: Portsmouth, VA, USA
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Water Move for Spaceships
I'm attempting to work out a proper method for giving a spaceship design (from GURPS Spaceships by the most excellent Mr. Pulver) a water-based movement. Other than the maddeningly unhelpful line from the Star Galleon, there seems to be no easy way to do it.
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So thanks much for anyone who replies! Ghostdancer
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07-23-2011, 04:31 AM | #2 |
GURPS FAQ Keeper
Join Date: Mar 2006
Location: Kyïv, Ukraine
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Re: Water Move for Spaceships
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07-30-2011, 02:45 AM | #3 | |
Join Date: Jun 2006
Location: Portsmouth, VA, USA
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Re: Water Move for Spaceships
Quote:
Ghostdancer
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07-30-2011, 04:54 AM | #4 |
Join Date: Oct 2004
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Re: Water Move for Spaceships
Water speed (surface speed in mph) - no contragrav...
6 * (LWt * 2000)^(1/9) * (Acceleration)^(1/3) * (Modifier)^(1/3) LWt is the ships rated mass, Acceleration is the space acceleration in Gs (though some notes state that rockets and rams give only 1/2 their rated thrust in water and should cost a bit more to retain full thrust in space and air), ^(1/9) is ninth root and ^(1/3) third or cube root. Modifier is the hydrodynamic lines modifier, something from 1 to 20 (avg lines are at 10). Same works for underwater performance just as well, except the modifiers are different (avg nautical at 3). To make it into 4th ed stat line i suppose you need to further divide the result (in mph) by two. Acceleration rate is same as air acceleration. Crush depth (yards) is different... but i suppose... dDR being the lowest armor rating on the ship. 10 * (dDR + 1) * Frame * Shape / SM Frame probably should default to 1 and Shape to 3 (maximums being 4 & 24 respectively) (30 * (dDR + 1)) / SM No guarantees for the math nor for any of them notes. |
07-30-2011, 09:51 AM | #5 |
Join Date: Aug 2004
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Re: Water Move for Spaceships
If you happen to have Gurps Vehicles, p.26 of that book has a very familiar looking table. You can work backwards from that, submerged weight, and your own judgement on how good your ships hydrodynamic lines are to get a surface water speed and a submerged speed.
I didnt concern myself with my ram-rockets differing performance in the much denser water than air, since I had already made it a reconfigurable system (to switch between high and low thrust options) and figured the cost and tech needed to adjust nozzles for space, air, and water all fell under that. Given how much a reconfigurable system costs, using that to cover your ability to get full rocket thrust underwater should do, Id think. I do wonder if we could figure out a vortex system to get underwater speed up. It seems to be a TL 9 design feature if the real world is any indication, and spaceships like the Vorpal Blade feature it prominently. But I digress. |
07-30-2011, 10:45 AM | #6 |
Join Date: Oct 2004
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Re: Water Move for Spaceships
Well... I was referring to Vehicles expansion 1 which has some content about underwater propulsion, including vortex combustion, underwater & adaptive rockets and rams, as well as supercavitation.
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07-30-2011, 10:57 AM | #7 |
Join Date: Aug 2004
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Re: Water Move for Spaceships
Ah my apologies Wanderer, I dont have VEX1 so I didnt make the connection. Thanks for letting me know though, maybe I should pick it up.
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design switch, naval, spaceships |
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