Bows:From the Ground Up

[Nymdok]

Originally Posted by DouglasCole

The only issue I have here is that having a 50lb bow be ST8 is a bit harsh. In a different thread, we'd come to the conclusion that a person could draw a bow of BLx2 lbs, with StrongBow adding +0.5BL at DX and another at DX+2; Special Exercises (Arm ST) could be applied in two levels for the same bonus. So a specialized archer with good skill and special exercises could draw the bow with 4xBL of pull.

Otherwise, I worry that the damage of these bows will be extremely unrealistic. Using the firearms scaling style, I figured a 180lb warbow would likely only do 1d+2 damage...

BLX2 Doesnt reflect the 2 second effort [Rof 1(2)] that is used to draw a bow with both arms. I designed these rules to mesh fairly homogenously with the existing rules.

The Unrealistic nature of the damage again, is a function of the rules as written. The rules use strength based damage, I maintain that convention here.

The strength scale fits fairly well with Current world records for bow draw strength.

Nymdok

[Nymdok]

Originally Posted by SuedodeuS

I like it. You might want to consider editing your initial post to include units, however. Also, I'm curious as to why you used 48 instead of 51 in your calculation. Finally, what is your justification for using the .67 conversion factor? I seem to recall you justifying it, but can't find that anymore.

50# does seem rather high for ST 8. I personally struggle with a 50# compound bow, and my ST is probably around that level. I can do it, but (in GURPS terms) it costs FP for each shot. Were it not for the let-off of compounds, however, I probably wouldn't be able to manage at all.

The .67 conversion factor means I normalize everything versus Yew, the most famous of bow woods and the one for which an abundance of data is available.

As for 50# at Str 8, the struggle is well represented by being a 2 second effort, but a repeatable one.

Nymdok

[DouglasCole]

Originally Posted by Nymdok

BLX2 Doesnt reflect the 2 second effort [Rof 1(2)] that is used to draw a bow with both arms. I designed these rules to mesh fairly homogenously with the existing rules.

The only issue I have with this is that there are strategies that increase drastically the RoF of the bow in RAW GURPS.

The bow RoF is Ready Arrow, Ready Bow, Fire. This can be dropped to Ready Bow, Fire with Fast-Draw (Arrow), and Heroic Archer I believe can even Fast-Ready bows.

I would suggest that BLx2 is what you can do with a one second effort, and that if you take two seconds, you may certainly draw a stronger bow; you may also draw a stronger bow by expending fatigue.

I'd base the calculations on the one-second ready, because that has a good chance of being the heroic base-case from which we scale.

[Polydamas]

Hi Nymdock,

Originally Posted by Nymdok

BLX2 Doesnt reflect the 2 second effort [Rof 1(2)] that is used to draw a bow with both arms. I designed these rules to mesh fairly homogenously with the existing rules.

The Unrealistic nature of the damage again, is a function of the rules as written. The rules use strength based damage, I maintain that convention here.

The strength scale fits fairly well with Current world records for bow draw strength.

Nymdok

Basing bow draw on the rules for how much weight you can lift off the ground and stagger around with seems sort of odd, and it isn't part of the rules as written but an interpretation. I wouldn't make draw weight 4 x BL, because then a ST 10 man with one point in Bow skill could use an 80 lb bow effectively. I would make a 50 lb draw standard for ST 10, so draw is 2.5 x BL. A lot of hunting bows have a similar draw, and I have heard of semi-skilled archers who could use 50 lb self bows effectively. I haven't heard of novice archers using 80 lb bows. A 150 lb bow using these rules would be ST 13-14, and there are only a few archers worldwide who can use a self bow that strong.

Originally Posted by Nymdock

Optional Additional Rules:

Crosssection: The D shaped cross section is the WORST possible shape and, sadly, is how english Longbows were made. The ideal shape is rectangular as used by the Native North Americans. The difference in energy transfer is a factor of 2 (40% to 80%). If your a simulationist, treat english bows as having 1/2 the listed strength for Damage and Range or Treat the Rectangualr crss section as having Double. I dont know which the Tables in Gurps are based on, so I cant say which way is the right way.

That doesn't agree with most of what I've read. Long D-sectioned self bows wouldn't have been used across a warlike continent for 3,000 years if they weren't effective. Blyth's appendix to Hardy's Longbow suggests that D-sectioned bows can tolerate more strain than flatbows. Pratt's appendix gives 67% efficiency for a 70 lb English longbow firing long bodkin or broadhead arrows. It suggests a lower efficiency for target or flight arrows which are probably what Klopsteg used in 1963. A couple of German scholars got around 40-50% efficiency firing various arrows from several sinew-backed Scythian bows.

Efficiency also varies with arrow weight and type. Light, long-ranged arrows tend to have less energy (but higher velocity) than heavy, destructive arrows. I don't recall why.

[DouglasCole]

Originally Posted by Polydamas

I would make a 50 lb draw standard for ST 10, so draw is 2.5 x BL.

Yeah...I misremembered my original post, and 2.5xBL for a fairly unskilled, nonspecialized archer works well for my sense of reality. If you know what you're doing (DX, DX+1, or DX+2, depending on how Strongbow is implemented) then a ST10 person could draw a bow of up to 3.5xBL, or 70lbs.

An average guy ranging from 50 to 70# draw weight works for me. If you add special exercises, that ST10 person can draw up to a 90# bow. To draw a 125lb warbow, then, would require a minimum of BL27, or ST11.8 (ST12).

For a professional warrior, ST12, Strongbow, and Special Exercises (Arm ST or Draw a Really Heavy Bow) works for me.

[Anthony]

I can't think of any immediate reason a D-shaped bow would be a factor of two less efficient, though it depends on your materials. It might have a factor of two lower energy storage at a given weight, but the relationship between weight and efficiency is complex.

The basic way a bow stores energy is that it compresses the material on the near side of the bow, and stretches the material on the far side of the bow. Material near the center of the bow is neither compressed nor stretched, and thus stores no energy; as such, the ideal bow shape is two sheets of material with a minimum weight filler between them. In addition, at maximum extension, both materials should be near their yield point; thus, if the compressive strength of the inner material is greater than the tensile strength of the outer material, you will use less material on the inner surface; if compressive strength is lower, you will use less material on the outer surface. A D shape is a decent option if the two strengths are unequal.

As far as efficiency of bows, there are two ways a bow loses energy:
1) Bow materials are not perfect springs; some energy will simply be lost as heat. This effect is almost entirely a function of the material used.
2) When a bow contracts, it must use its stored energy to accelerate the arrow, the string, and the ends of the bow. Any energy used to accelerate things other than the arrow is wasted. You maximize efficiency here by maximizing the ratio of arrow weight to bow weight. Also, not all parts of the bow move equally, so if you can trade off weight in an area that doesn't move much for weight in an area that moves a lot, you should do so. This is a major reason to make bows that taper near the ends.

[Nymdok]

Originally Posted by Polydamas

Basing bow draw on the rules for how much weight you can lift off the ground and stagger around with seems sort of odd, and it isn't part of the rules as written but an interpretation...... I would make a 50 lb draw standard for ST 10, so draw is 2.5 x BL. ... A 150 lb bow using these rules would be ST 13-14, and there are only a few archers worldwide who can use a self bow that strong.

Its an interpretation but not a total leap. I took the 2 second effort and assumed it was for 2 hands. Perhaps a 2 second 1 handed effort of BLx2 would be more representative.

Again using the reocrd value of 200lbs using my method gives ST16, using yours its ST20. I chose not to use Non integer values to keep the math easier, and BL x 3 although a suitable ST:18-19, didnt seem to fit in with the progression laid out in B353

At any rate, because the equations are laid out here for you to see, feel free to use them as YOU see fit. That was the Purpose of this exercise, to make them customizeable and set up a relationship so that GM's could fiddle with the dials themselves. So customize away and enjoy!

Originally Posted by Polydamas

That doesn't agree with most of what I've read. Long D-sectioned self bows wouldn't have been used across a warlike continent for 3,000 years if they weren't effective.....

Witness the 'power' of tradition. In an apprenticed trade like bowyer, and in the absense of outside influence, that they would do it wrong because thats how they had done it for hundreds of years doesnt suprise me at all.

Originally Posted by Polydamas

Blyth's appendix to Hardy's Longbow suggests that D-sectioned bows can tolerate more strain than flatbows. Pratt's appendix gives 67% efficiency for a 70 lb English longbow firing long bodkin or broadhead arrows. It suggests a lower efficiency for target or flight arrows which are probably what Klopsteg used in 1963. A couple of German scholars got around 40-50% efficiency firing various arrows from several sinew-backed Scythian bows... .

That the D shaped cross section could handle signifigant strain does not suprise me. Its virtual mass (the resorative energy used up to bring the bow stave to its rest position) will also be increased however and THIS is where the efficiency drops.

I made no presumtion on the kind of arrows Klopsteg used, and I find his derivations to be reasonable.
The discrepancy is why I made the efficency argument Optional.

Originally Posted by Polydamas

Efficiency also varies with arrow weight and type. Light, long-ranged arrows tend to have less energy (but higher velocity) than heavy, destructive arrows. I don't recall why.

That would mean that the mass would have to plummet and QUICKLY to offset the velocity squared term in Kinetic energy equation which we all remember as

1/2(mass)(velocity squared)

are you sure your remembering that correctly?

Either way, I tried not to treat the arrows with too much detail, but that may be an area worth exploring.

[Nymdok]

Originally Posted by Anthony

I can't think of any immediate reason a D-shaped bow would be a factor of two less efficient....

See page 578-580 of the PDF in link one (note its ony a 38 page document pulled from a collection of Papers).

Nymdok

[Anthony]

Originally Posted by Nymdok

See page 578-580 of the PDF in link one (note its ony a 38 page document pulled from a collection of Papers).

Assuming he's correctly representing the elastic behavior of the wood being used, he's got a point, but I'm suspicious of his efficiency numbers. The fact is, we don't know exactly how efficient a medieval longbow was, because bows don't last hundreds of years. Also, the portion of the wood used to make a longbow didn't have equal strength throughout, so his starting assumptions about compressive and elastic strength are incorrect.

[Mr Frost]

Originally Posted by Nymdok

...Witness the 'power' of tradition. In an apprenticed trade like bowyer, and in the absense of outside influence, that they would do it wrong because thats how they had done it for hundreds of years doesnt suprise me at all...

That does not hold true however if one observes how sword designs for example changed constantly over the same period that that bow design was predominant . They were made by the same Master trains Apprentice tradition .
Even the Romans post Marius whom were obsessed with uniformity were constantly altering their Gladius pattern ; the "Dark Ages" saw much change in swords and Medieval Europe was very fluid in this .

Tradition doesn't halt design for thousands of years when very rich and powerful people are depending on its' products to survive .

Europe was exposed to many different bow designs since antiquity by Cimerians , Scythians , Alans , Syrians {displaced in Roman Service} , Huns , Avars , Arabs , Berbers , Magyar , Cumans , Mongols and I'm really just scratching the surface .
The Roman Empire alone was responsible for a tremendous amount of technology and conceptual transfer due to not only their policy of taking Auxilliary troops from one part of the Empire and stationing them in completely different parts of it where their culture {and its' traditional weaponry} had never before been encountered but also by the simple function of people choosing to travel as well as the effects of internal trade .



Tradition has power , however if one design was clearly superior for battle in the given physical and ecconomic environment it wouldn't have taken very long for some foresightful bower to start producing them and the users to prove it in use and the industry would have followed suit due to market pressure .




Whilst this neither proves nor disproves the specific strengths and weaknesses of the design you were discussing , the design clearly had some strong advantage relative to others {in the environment in which it was built to be used} and your assumption that tradition alone could have maintained its' popularity doesn't stand up as I see it .