Steve Jackson Games Forums FTL rate of movement for GURPS SPACESHIPS
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 02-19-2019, 10:49 PM #1 hal   Join Date: Aug 2004 Location: Buffalo, New York FTL rate of movement for GURPS SPACESHIPS Hello Folks, In digging up some of my older material from FULL THRUST, and jogged by a memory elsewhere in this forum, I thought I'd bring up the idea of making smaller ships move more quickly via FTL than larger ships. In a nutshell, the rate a ship travels is equal to its mass^.2 such that a 1000 ton ship would 3.98 days to travel 1 light year. A 1,000,000 ton ship would take 15.85 days per light year to travel. It is an easy enough formula to utilize - but you can always customize it to some extent. For instance, if you want a 1,000 ton hull to be able to travel at about 1 light year per day, you could simply make the formula as being .25 * Mass^.2. Thus, smaller ships can fast without needing to do much to change how the game works when designing ships in general. If you really want to have fun? Make it simply that the ship moves at a rate of Mass^.20 days per light year PER FTL engine. Thus, with two such engines, you halve the time required to travel 1 light year. If you don't like the fifth root of mass, then use some other value such as cube root or log of, etc. Just a way to maybe fiddle with the formula to make things work in a manner that might be more fun. Maybe.
 02-19-2019, 11:12 PM #2 Rupert     Join Date: Aug 2004 Location: Wellington, NZ Re: FTL rate of movement for GURPS SPACESHIPS Is there any particular reason to want small ships to move between systems aster than large ones? __________________ Rupert Boleyn "A pessimist is an optimist with a sense of history."
02-19-2019, 11:21 PM   #3
Agemegos

Join Date: May 2005
Location: Oz
Re: FTL rate of movement for GURPS SPACESHIPS

Quote:
 Originally Posted by Rupert Is there any particular reason to want small ships to move between systems aster than large ones?
Is it so that small, unmanned message torpedoes can carry communications and other information far faster than people can travel? Is it so that transport will be divided among a myriad of small ships so that there is always a number of starships in any system and rarely only one to deal with an unexpected event?
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 02-19-2019, 11:58 PM #4 hal   Join Date: Aug 2004 Location: Buffalo, New York Re: FTL rate of movement for GURPS SPACESHIPS When I was handling FULL TRUST campaigns back in the day when it was JUST the original FULL THRUST rules - there wasn't all too much to difference the smaller ships from the larger ones. The "mass rules" were different for that game, but I recall working on that problem so as to give a reason for having "Scouts" that were smaller. They could get to a trouble spot faster, scout things out and possibly even return. The larger ships, taking longer to arrive, were massive firepower platforms, but if they took longer to arrive - it allowed for smaller ships of a destroyer class or corvette class or what have you, to engage in smaller ship actions. Is it worth it to have for use with GURPS SPACESHIPS? Can't say, it would be up to the GM or player to suggest to a GM "Hey, what are the implications of this". In the end? It is an idea being tossed out there for any who might like it enough to try it. If even one person gives it a shot, or it gives someone an idea on how to customize their own FTL ratings for their games, I can rest happy that a few electrons died for this. ;) Seriously though. What WOULD be the implications? As was pointed out, it would allow for smaller ships to make good couriers. It would also perhaps allow for smaller ships to be able to outrun the larger ships? Suppose you had a 300 ton hull flee a star system with a 1,000 ton hull in hot pursuit. Let's say that they're both trying to reach a destination that is 3 light years away. The 300 ton hull will take 9.38 days to reach its destination. The 1,000 ton hull will take 11.94 days to reach its destination. That makes a difference no? If the ability to have FTL-2 makes it such that you halve the time taken, if both have FTL-2, the smaller ship STILL retains an advantage. Now suppose we're dealing with a game universe where the GM uses reaction drives, or solar sails or what have you, no "reactionless" drives at all? What if the "FTL limit of a star is based on solar masses and the limit was 2 AUs x Solor Masses? Now we have something Traveller-like in that ships can approach up to a give point, but then have to rely upon good old fashioned newtonian movement. For every ship system that is given up for FLT drives, the ship's fighting capabilities become weakened. But take a hard look at what happens when dealing with a Dreadnaught class ship at say, 30 million tons.It would take 93.88 days per light year of travel. Even with FTL-5, that Dreadnaught will take 18.77 days to arrive. Compare this with the 300 ton hull taking only 9.39 days to travel the same distance. In the end, it is an easy way to handicap the larger ships in speed where FTL is concerned. Some might not like that idea (many probably won't). That is, until they need to be on a FAST ship. Fast and Fragile, or Slow and sledgehammers?
 02-20-2019, 12:10 AM #5 Rupert     Join Date: Aug 2004 Location: Wellington, NZ Re: FTL rate of movement for GURPS SPACESHIPS It will certainly encourage the use of message torpedoes/probes. If you use Spaceships there's already incentive to use many small ships over few large ones, even for civilian use - the cost per ton is the same, the payload per ton is the same, and the 'small ship fleet' is more flexible. For military purposes, the small ships are even more strongly selected for - missiles make ships eggshells with hammers, so you want each egg to be as cheap as possible. The proposed FTL system hammers this home, even with a relatively slow loss of speed with increasing mass. It would likely kill carrier+fighter and carrier+rider concepts, because the big carrier would be strategically slow compared to a fleet of small ships. It would make small PC-owned ships faster than the lumbering great warships of the Evil Empire. However, if two FTL drives means you go twice as fast, a 30,000 ton ship with two drives is very nearly as fast as a 1,000 ton ship with just one, which might not be a strong enough speed difference to really differentiate ships by speed. __________________ Rupert Boleyn "A pessimist is an optimist with a sense of history."
02-20-2019, 12:16 AM   #6
Rupert

Join Date: Aug 2004
Location: Wellington, NZ
Re: FTL rate of movement for GURPS SPACESHIPS

Quote:
 Originally Posted by hal In the end, it is an easy way to handicap the larger ships in speed where FTL is concerned. Some might not like that idea (many probably won't). That is, until they need to be on a FAST ship. Fast and Fragile, or Slow and sledgehammers?
I generally have FTL drives give more speed when you have more of them and/or put more power into them (assuming they're designed for that - or even if they're not if you're willing to risk Bad Things happening). My current rule is: [Power Points used by Stardrives]^0.5 x 5 lightyears/day (round to the nearest whole number), and you can have any mix of Stardrives and Super Stardrives, but they have to all be in the same hull section. Thus the most speed you can get is with seven Super Stardrives, consuming 14 power points, for 19 LY/day (and as at TL10-11 it takes four power plant systems to power these drives, 55% of the ship is just FTL drive and power for it). Most ships just have drives good for one or two points, and thus 5-7 LY/day.

I think most fast ships will tend to be relatively small, because most of the time you don't need to move massive amounts of stuff very fast at considerable expense. There will be some fast larger ships, of course - the rich might well pay for faster travel, the military will probably like some decent sized ships capable of fast interventions, etc., but most big ships won't, IMO, be especially fast.
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Last edited by Rupert; 02-20-2019 at 12:24 AM.

02-20-2019, 12:51 AM   #7
David Johnston2

Join Date: Dec 2007
Re: FTL rate of movement for GURPS SPACESHIPS

Quote:
 Originally Posted by Rupert It will certainly encourage the use of message torpedoes/probes. If you use Spaceships there's already incentive to use many small ships over few large ones, even for civilian use - the cost per ton is the same, the payload per ton is the same, and the 'small ship fleet' is more flexible. For military purposes, the small ships are even more strongly selected for - missiles make ships eggshells with hammers, so you want each egg to be as cheap as possible. The proposed FTL system hammers this home, even with a relatively slow loss of speed with increasing mass. It would likely kill carrier+fighter and carrier+rider concepts, because the big carrier would be strategically slow compared to a fleet of small ships. It would make small PC-owned ships faster than the lumbering great warships of the Evil Empire. However, if two FTL drives means you go twice as fast, a 30,000 ton ship with two drives is very nearly as fast as a 1,000 ton ship with just one, which might not be a strong enough speed difference to really differentiate ships by speed.
Assuming that you include the defense favouring switches then it creates the early 20th century paradigm of battleships for heavy firepower, destroyers for speed and cruisers to catch destroyers.

02-20-2019, 01:19 AM   #8
Agemegos

Join Date: May 2005
Location: Oz
Re: FTL rate of movement for GURPS SPACESHIPS

Quote:
 Originally Posted by Rupert If you use Spaceships there's already incentive to use many small ships over few large ones, even for civilian use - the cost per ton is the same, the payload per ton is the same, and the 'small ship fleet' is more flexible.
On the other hand, the larger ships don't need engine rooms and can be automated more cheaply. I recently did a cost study for a particular set of assumptions, and found that a highly-automated SM+12 ship came in 30% cheaper per ton-lightyear than an SM+9 ship with an engine room.
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02-20-2019, 02:39 AM   #9
ericbsmith

Join Date: Aug 2004
Location: Binghamton, NY, USA. Near the river Styx in the 5th Circle.
Re: FTL rate of movement for GURPS SPACESHIPS

Quote:
 Originally Posted by Rupert It would likely kill carrier+fighter and carrier+rider concepts, because the big carrier would be strategically slow compared to a fleet of small ships.
I disagree. Modern day carriers are lumbering hulks compared to jet planes. However, modern day carriers are not meant to be front line vessels, they are meant to serve as a base of operation for the much faster fighters, a place where the pilots can take their fighters to rest, refuel, rearm, and repair.

I see nothing about the proposed setup that would change that, though it does open the door for a different class of medium-occupancy "corsair" fighter which has limited fuel, repair/maintenance capabilities, and extremely cramped living space but is based out of a carrier allowing the crew to rotate and any necessary repair/maintenance to be done back on board the carrier. These would be larger than your typical fighter, capable of operating on their own for a few weeks, but smaller than your typical independent ship. Given the background description such vessels could dart around ahead of the larger fleet, performing reconnaissance or hit-and-run operations.
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Last edited by ericbsmith; 02-20-2019 at 02:43 AM.

 02-20-2019, 05:15 AM #10 AlexanderHowl On Notice   Join Date: Feb 2016 Re: FTL rate of movement for GURPS SPACESHIPS What would happen if you flipped the assumption? For example, that spacecraft possessed a speed equal to ((mass^0.5) × (FTL engines^0.5))c? In that case, a 100 metric ton smallcraft with four FTL engines would have a maximum velocity of 20c while a 10 million metric ton capital ship with one FTL engine would have a maximum velocity of 3,160c. It would give a military reason for large ships and a logical reason for carrers.

 Tags ftl, spaceships

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