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Old 10-28-2011, 11:52 AM   #21
Bruno
 
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Default Re: Max Damage on Bows?

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Originally Posted by mhd View Post
Going just by the rules, I don't think so. A gastraphetes (TL2) has a maximum usable ST of 30 (3 * 10), whereas a Siege Crossbow (TL4) has a max usable ST of 21 (14*3 /2) (never mind a higher bulk and slower RoF).
... No, the /2 is for the rated ST ONLY, not for the maximum. 14*3 is still 38 - the rated ST for an effective ST 38 Siege Crossbow would be 76(!!), but it shoots like 38, which you can't get with a gastrophetes at all.
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Old 10-28-2011, 12:01 PM   #22
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Default Re: Max Damage on Bows?

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Originally Posted by mhd View Post
I thought that crossbows already exceeded that limit, at least steel ones…]
Crossbows aren't Muscle Powered Weapons. yes hey have a ST rating but ther damage is not based on the user's ST
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Old 10-28-2011, 12:03 PM   #23
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Default Re: Max Damage on Bows?

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Originally Posted by Jeminai View Post
.

I do like the idea that the arrows have to be heavier to withstand the pressures of the bow.
That's not really why you use heavier arrows. There's a fairly sharp limit as to how much speed you can get out of a bow. You can quickly reach a point where the limbs and string can not snap back any faster than they already are.

Then, since Kinetic energy is mass x velocity squared and you can't get any more velocity you have to use more mass.

You can get a very light arrow to break on a very heavy bow but you can get around that problem with stronger materials. You can't get around the speed limit.

You'll get a mechanical speed limti with pretty much any device built to shoot physical objects. Maybe 250-300 feet per second with bows, maybe a little higher with crossbows, 2000 or a little elss with black powder and not quite 3x that with smokeless and so on.
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Old 10-28-2011, 12:08 PM   #24
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Default Re: Max Damage on Bows?

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Originally Posted by Bruno View Post
... No, the /2 is for the rated ST ONLY, not for the maximum.
According to the table, the ST value bows and crossbows is the minimum rated ST (siege x-bow: 14M). So if the triple minimum rule applies, I'd triple that value (42). And according to the steel crossbow entry, I'd use half the rated ST for damage and range (21). Apparently my reading comprehension is already on its weekend levelů
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Old 10-28-2011, 12:16 PM   #25
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Default Re: Max Damage on Bows?

You can't have very arrows? I thought they were just +49 CF like other Very Fine Miscellany?
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Old 10-28-2011, 12:25 PM   #26
DouglasCole
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Default Re: Max Damage on Bows?

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Originally Posted by Jeminai View Post
So there really shouldn't be any sort of cost difference for higher strength bows? I just thought it would require more skill, better materials and more time to make a ST: 20 bow than a ST 12 one.

I do like the idea that the arrows have to be heavier to withstand the pressures of the bow.
Bows can cost very different amounts using the spreadsheet accompanying The Deadly Spring. You could always, if you want really cinematic bows, design the bow using the article, but then look up the damage based on, say, thr+2 for ALL bows, with ST looked up based on draw weight, etc.

It would get odd, since it takes a hyper-realistic and complicated design process (by my own admission) and at the very end, jump back to the Damage Table.
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Old 10-28-2011, 12:26 PM   #27
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Default Re: Max Damage on Bows?

Bows and crossbows were the topic of almost unending debate on the playtest. I finally went for a conservative treatment rather than a comprehensive alternative system, because I couldn't see agreement on any particular system.

Steel crossbows are a tricky case. I looked at the actual measured physical properties of steel by comparison with horn, sinew, and wood, and tried to express them through GURPS rules. My copy of the book with the relevant tables seems to be in hiding, but my recollection is that steel isn't really the best material for storing elastic energy; its advantages are more in durability and compactness than in energy per unit mass.

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Old 10-28-2011, 12:33 PM   #28
DouglasCole
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Default Re: Max Damage on Bows?

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Originally Posted by Jeminai View Post
I do like the idea that the arrows have to be heavier to withstand the pressures of the bow.
There are two basic reasons (though Fred touches on some very valid limiting steps) for bows needing heavier arrows.

The first is "spine." If you don't have an arrow shelf, releasing the bowstring causes the arrow to flex and deflect sideways. There's a "right" amount of deflection to make the bow shoot straight.

The second is efficiency, which is quite important. You want the arrow to be infinitely heavier than the deflecting mass of the limbs . . . since the energy you put into drawing the bow will accelerate the string and limbs as well as the arrow. Heavier arrows are more efficient in capturing maximum energy from the draw.

Range is proportional to velocity, though . . . so if you want to capture basically all the energy, but only have a few yards of range, have at. If you still want a DISTANCE weapon, you start to make compromises!
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Old 10-28-2011, 12:42 PM   #29
DouglasCole
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Default Re: Max Damage on Bows?

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Originally Posted by whswhs View Post
Bows and crossbows were the topic of almost unending debate on the playtest. I finally went for a conservative treatment rather than a comprehensive alternative system, because I couldn't see agreement on any particular system.
Bill already knows this, but for others: There were a few simple equations that some of us were converging on. Problem was, they really only "worked" for certain kinds of bows in a certain range. Beyond that, you started to get ugly quickly, and since we had steel bows, crossbows with wood, horn, and steel limbs, the simple scaling stuff that was proposed didn't cover the cases that already existed in the book.

So while the scaling equations were actually quite simple, the number of edge cases got out of hand.

As an example that happened after the playtest, here's an off-list post I made to a group of people:

Quote:
Originally Posted by Douglas Cole
Here are my bow design "rules." If SMarsh accepts it, I'll turn it
into a Pyramid article

Bow Efficiency Factor: (Height-Draw)/Height

Height = staff length of bow
Draw = draw length when used properly
Poundage = 2.5 X BL
ST = ST :-)

Bow Weight = ST^2 x Draw / 2625 for self bows
Damage = ST * sqrt(Draw) * BEF /12.75
Range = ST * SQRT(Draw) * BEF * 4.5

That's it. Some examples:

100# light warbow, 70" staff, 28" draw: ST14, 2lbs, 1d damage, 200yd
range
72# shortbow, 43" staff, 28" draw: ST12, 1.3lbs, 1d-2 damage (actually
2.0pts avg), 115yds range
1250# crossbow: 32" staff, 7" draw: ST49, 6.4lbs crosspiece weight,
7.9pts damage (call it 2d+1), 455yds range
You can see that where THIS started (and why I thought I could get away with 2,500 words!) and where The Deadly Spring ended up are rather far apart!



Quote:
Originally Posted by whswhs View Post
Steel crossbows are a tricky case. I looked at the actual measured physical properties of steel by comparison with horn, sinew, and wood, and tried to express them through GURPS rules. My copy of the book with the relevant tables seems to be in hiding, but my recollection is that steel isn't really the best material for storing elastic energy; its advantages are more in durability and compactness than in energy per unit mass.

Bill Stoddard

If one looks at the bow cost per pound in The Deadly Spring (pp. 5-6, I think), you'll see that most of the materials Bill mentions are much more expensive than steel. The cost is based on energy storage capacity per pound, and wood and horn are MUCH better! But they run into other problems, which is why you eventually need to use steel for really high-draw-weight crossbows. If you pound on my design system, I think you'll find that TL3 steel is not well suited to anything, TL4 steel is a strong competitor with natural materials, and TL5+ starts to do very well up until the engineered materials like fiberglass and carbon fiber come onto the scene and kick (archery) butt.
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Old 10-28-2011, 06:38 PM   #30
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Default Re: Max Damage on Bows?

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If one looks at the bow cost per pound in The Deadly Spring (pp. 5-6, I think), you'll see that most of the materials Bill mentions are much more expensive than steel. The cost is based on energy storage capacity per pound, and wood and horn are MUCH better! But they run into other problems, which is why you eventually need to use steel for really high-draw-weight crossbows. If you pound on my design system, I think you'll find that TL3 steel is not well suited to anything, TL4 steel is a strong competitor with natural materials, and TL5+ starts to do very well up until the engineered materials like fiberglass and carbon fiber come onto the scene and kick (archery) butt.
Well, part of that is because the cost of steel per pound falls sharply between TL3 and TL5, thanks to the shift in metallurgical techniques. But also, I was looking not at cost as the limiting factor, but at weight.

The other thing to note is that high draw weight is not the only factor. Steel is much stiffer than horn, and it takes much greater force to bend it, so it has a higher draw weight. But energy storage is force times distance, or stress times strain, and steel's elasticity reaches its limit at a lower strain than horn's, which more than cancels out the benefit of greater draw weight.

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