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Old 03-20-2023, 10:29 PM   #1
Outlaw
 
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Default ST to Horsepower

Apologies if this has been discussed before but I couldn't find anything directly related in my searches.

Is there a direct conversion of ST to maximum (short burst) horsepower a humanoid can generate? The BL rules state how much one can lift over their head in one second with one hand but is that from the ground or some other datum?
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Old 03-20-2023, 10:49 PM   #2
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Default Re: ST to Horsepower

According to Wikipedia, a typical adult can generate about 1.2 hp briefly and 0.1 sustained. Elite athletes can generate 2.5 or more (Usain Bolt's record run peaked at 3.5 HP), and sustain 0.35.
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Old 03-21-2023, 02:25 AM   #3
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Default Re: ST to Horsepower

According to Basic p460, horses have somewhere between ST20-25, with 'ordinary horse' having ST21. There's other stats, too, if ST doesn't correlate to horsepower.
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Old 03-21-2023, 03:24 AM   #4
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Default Re: ST to Horsepower

Bear in mind that a horsepower actually exceeds the typical work output of a horse.

My unofficial rule of thumb has been that sustainable work output, in watts, is the product of Basic Lift and Basic Move. So a typical human, with Basic Lift 20 pounds and Basic Move 5, delivers 100 watts. For comparison, a draft horse has ST 25, Basic Lift 125 pounds, and Basic Move 6, which gives 750 watts, which is almost exactly 746 watts, the customary definition of a horsepower. Neither of those figures is better than an approximation for gaming purposes, but they're at least the right order of magnitude. (Both are actually a bit high—see Cotterell and Kamminga's Mechanics of Pre-industrial Technology for some human figures—but that may be appropriate for adventure games.)
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Old 03-21-2023, 04:11 AM   #5
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Default Re: ST to Horsepower

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Originally Posted by whswhs View Post
Bear in mind that a horsepower actually exceeds the typical work output of a horse.

My unofficial rule of thumb has been that sustainable work output, in watts, is the product of Basic Lift and Basic Move. So a typical human, with Basic Lift 20 pounds and Basic Move 5, delivers 100 watts. For comparison, a draft horse has ST 25, Basic Lift 125 pounds, and Basic Move 6, which gives 750 watts, which is almost exactly 746 watts, the customary definition of a horsepower. Neither of those figures is better than an approximation for gaming purposes, but they're at least the right order of magnitude. (Both are actually a bit high—see Cotterell and Kamminga's Mechanics of Pre-industrial Technology for some human figures—but that may be appropriate for adventure games.)
If it matters, I use 9 for typical humans because 10 is the 'adventurer' average (9.5 if I want to be more exact). BL18 * 4.75 comes out to 85.5 watts with 9.5, BL16 * 4.5 is 72 watts with 9, which might be closer than 100 watts.

I didn't even consider Basic Move, but that does make sense. I wonder if we can reverse engineer ST for machines this way, but being Unliving could easily throw a wrench in the works.
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Old 03-21-2023, 04:21 AM   #6
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Default Re: ST to Horsepower

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Originally Posted by kirbwarrior View Post
If it matters, I use 9 for typical humans because 10 is the 'adventurer' average (9.5 if I want to be more exact). BL18 * 4.75 comes out to 85.5 watts with 9.5, BL16 * 4.5 is 72 watts with 9, which might be closer than 100 watts.

I didn't even consider Basic Move, but that does make sense. I wonder if we can reverse engineer ST for machines this way, but being Unliving could easily throw a wrench in the works.
Using ST 9 gives you BL 16 lbs., and multiplying by Basic Move 5 gives you 80 watts. Several of the 8-hour figures in Cotterell and Kamminga range between 70 and 90 watts, so that may be plausible.

Basic Lift has the dimensions of force, and Basic Move has the dimensions of velocity. The product of force and velocity has the dimensions of power. So that seems as if it might scale correctly and not give absurd results, even if it's a bit off.
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Old 03-21-2023, 07:09 AM   #7
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Default Re: ST to Horsepower

My general rule of thumb is 4xBL to get Watts for sustained power (losing FP at a rate akin to Hiking - that is, 1 FP per hour), 8xBL to get Watts for more intense but ultimately unsustainable output (losing FP at a rate akin to Jogging - that is, roughly 1 FP every 2 minutes for someone with HT 10), and 16xBL to get Watts for ~peak output that can only be done for rather brief periods (losing FP at a rate akin to Sprinting - that is, roughly 1 FP every 30 seconds for someone with HT 10). This was based on humans averaging around 80 Watts for sustained output in most sources I could find, with the jogging/sprinting-equivalent boosts being based on the speed boosts associated with such (jogging - or paced running - is about twice as fast as hiking, sprinting is twice as fast as jogging). Boosting these to 5xBL, 10xBL, and 20xBL as a GURPS "heroic average" (as well as to adhere to GURPS' love of multiples of 5) is probably acceptable (particularly if you're assuming actual human average to be around ST 9).

Part of me likes the idea of bringing in Basic Move, and part of me dislikes it, so I'm not sure on where exactly I stand. For the "realistic" scale (80W, 160W, 320W), you could replace BLx4 with BLxMovex0.8 (and BLx8 with BLxMovex1.6, and BLx16 with BLxMovex3.2). For the "heroic" scale (100W, 200W, 400W), you would instead replace BLx5 with BLxMove (and BLx10 with BLxMovex2, and BLx20 with BLxMovex4).

Those figures are probably appropriate for devices/exercises where you are essentially using your whole body. Something where you just use your legs (like a hands-free treadmill) might be more appropriately something like 70% of the above values, while something where you just use your upper body (like a winch) might be something like 50% instead (both versions involve incorporating your core, hence the sum being greater than 100%). Optionally, only things that use your legs would use Basic Move (but this would make the above equations much more complicated for those with Move other than 5).

EDIT: With the note that a typical human can apparently manage ~1.2 HP (so around 900 W) briefly, another level - probably burning around 1 FP per second - that is somewhere around BLx45 (BLxMovex9) or BLx50 (BLxMovex10) might be feasible. This would be "peak output" (rename the sprinting-analogue something else) and probably a form of Extra Effort (calling for a Will roll, and risking causing physical damage to yourself).
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Old 03-21-2023, 07:22 AM   #8
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Default Re: ST to Horsepower

Well, if you are hauling stuff, the power you expend certainly is affected by your speed. That's why I figured in Move.
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Old 03-21-2023, 07:55 AM   #9
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Well, if you are hauling stuff, the power you expend certainly is affected by your speed. That's why I figured in Move.
Realistically, I think incorporating Move is the right call. From a gamist perspective, however, it feels like "power generation" would be a function of strength, and strength and speed are separate stats (although realistically the two should be linked to a certain degree - fast runners aren't muscular just for show). And in GURPS, things get even more complex when considering various Advantages. If someone is a faster swimmer than a runner, do you use their swim speed instead? What about Flight - where the exact details of how you fly might influence how much power you're outputting when doing so? Then there's Telekinesis - at first glance one would think that TK 10 would be able to generate as much power as a typical person with ST 10, but because TK Move actually matches your TK level, it would actually generate twice as much power. But then there's the further issue that TK 10 cannot move that ST 10 person a fast as that power output implies - that is, that ST 10 person can output 80W or 100W to move at around Move 1.5, but when TK 10 outputs 160W or 200W on that same person, it can only manage Move 2 (twice as much energy to move ~1.5x as fast, while if that ST 10 person had Move 10, that same 160W/200W would move them at Move 3). And then you realize that body weight should play a factor (if someone is ST 10, Move 5, and 150 lb, they are demonstrably outputting less energy than someone who is ST 10, Move 5, and 200 lb when moving around, so why should the two generate the same energy when running on, say, a treadmill?), but then you have to account for the character's weight which is supposed to be a Feature, and then *froths at the mouth and collapses*
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Old 03-21-2023, 09:22 AM   #10
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Default Re: ST to Horsepower

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Originally Posted by Varyon View Post
Realistically, I think incorporating Move is the right call. From a gamist perspective, however, it feels like "power generation" would be a function of strength, and strength and speed are separate stats (although realistically the two should be linked to a certain degree - fast runners aren't muscular just for show). And in GURPS, things get even more complex when considering various Advantages. If someone is a faster swimmer than a runner, do you use their swim speed instead? What about Flight - where the exact details of how you fly might influence how much power you're outputting when doing so? Then there's Telekinesis - at first glance one would think that TK 10 would be able to generate as much power as a typical person with ST 10, but because TK Move actually matches your TK level, it would actually generate twice as much power. But then there's the further issue that TK 10 cannot move that ST 10 person a fast as that power output implies - that is, that ST 10 person can output 80W or 100W to move at around Move 1.5, but when TK 10 outputs 160W or 200W on that same person, it can only manage Move 2 (twice as much energy to move ~1.5x as fast, while if that ST 10 person had Move 10, that same 160W/200W would move them at Move 3). And then you realize that body weight should play a factor (if someone is ST 10, Move 5, and 150 lb, they are demonstrably outputting less energy than someone who is ST 10, Move 5, and 200 lb when moving around, so why should the two generate the same energy when running on, say, a treadmill?), but then you have to account for the character's weight which is supposed to be a Feature, and then *froths at the mouth and collapses*
Since I'm doing this as a house rule, it only has to suit my own approaches, and I'm primarily a simulationist and secondarily a narrativist; I don't pay a lot of attention to gamist issues.

Of course you would have to use different approaches for forms of movement other than walking. In the case of flying, for example, I would probably estimate power as body weight times the cube of air speed, with a multiplicative constant based on the ratio of flying to walking/running. Though I haven't done a full dimensional analysis, so I'm not 100% sure how good a fit that would be. I'm mainly thinking that where ground movement is primarily impeded by friction, air movement is primarily impeded by aerial drag; if your ground movement is fast enough so that streamlining is important, then the power relationship is going to change. But living organisms don't get into that speed range except in brief bursts like a cheetah's run.
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