Compressing Bow ST into a smaller range

When I wrote The Deadly Spring, I pegged the strongest bow that humans pulled at about 200 pounds draw. I saw lots of bows in history in the 170-190# range, but not much more than about 200#. Mongol composite bows of as much as 165#, the strongest bow on the Mary Rose was about 185#.

OK, that was the strongest bow. Great. Well, if we tag bow draw weight to basic lift, putting a 200# bow drawn to about 30-32″ at (Lifting) ST 20 made some degree of sense. Well, if we do that, it naturally puts a ST 10 bow at a factor of 4x less, so a ST 10 bow would be a 50-lb. bow, that is, something eminently suitable for hunting animals.

That all seemed to fall out quite nicely, even putting a 20-lb. kid’s bow at ST 6 or so (and ST 8 bow at about 32 lbs, which would be the women’s Olympic norm).

Still, that has the interesting and unwanted side effect that to draw what seems to be a moderate power warbow judging (perhaps wrongly) by the samples reconstructed from the Mary Rose (the average was what by this scale would be a ST 17 bow), one has to be extremely strong. ST 17 is 1d+2 thrust and 3d-1 swing as raw damage, so our hero would do 1d+3 imp with a “regular” bow and 3d+1 cut with an axe, or 3d with a broadsword.

That’s serious hurt.

Really? ST 17?

Well, not entirely. The Strongbow perk lets you draw that bow with “only” ST 15 if you have your Bow skill at DX+2. You can also justify 2-3 levels of the perk “Special Exercises: Arm ST” as a dedicated archer. That brings your overall ST requirement down to 4-5 levels below the draw requirement, or ST 12-13.

Not unreasonable, but if we assume that a 175# bow (about ST 19) isn’t that rare, it means there were a whole lot of ST 14-15 (plus Strongbow plus special exercises) people were kickin’ around England in Ye Merrieye Oldee Tymes.


There are a couple ways to go about this one, though, if you don’t care for this outcome.


Not everyone that is good with a bow is good with a really powerful bow. You could be relatively weak but not practiced in the art of, well, pulling really strong springs. It should be possible to be DX+Lots in bow skill but not necessarily be able to pull a hugely powerful bow.

Note: the following options are a bit stream of consciousness, and not ordered by preference. They’re just coming out as I type. If this were a published article, I’d pick the best options and cull the rest. 

One possibility is to allow multiple levels of Strongbow. Each point doubles the bonus for getting to DX+2 in Bow. So 5 points would give you +5 to the ST of the bow you can draw at DX+1, and +10 at DX+2. So a ST 10 archer with DX+1 skill could draw a ST 15 (113#) bow, and DX+2 could draw a 200# bow (!).

The downside of this is that for a relatively low cost (DX+2 is 8 points, and 5 points for Strongbow 5) you put a 2d-1 base damage bow in the hands of just about anyone (2d regular bow, 2d+1 longbow).

Of course, that’s 2d+1 imp every second or third round. For the same 10 points, your ST 11 guy does 1d+1 cut every round by swinging a shortsword, and 1d+3 cut with an axe. That’s not hugely imbalanced, considering ranged attacks require a much higher skill for equal effectiveness.

I suspect allowing just this won’t break anything.

Drawing Powerful Bows

There are two mentions of this in the Basic Set, as mentioned here by +Cole Jenkins, and one in Low-Tech on p. 75. This seems to supersede p. B270 but frankly does so in a confusing way due to the problems talked about in Inefficient Springs, below.

So let’s use the usual rules for doing things at lower ST than required: -1 skill per -1 ST and a fatigue penalty at the end of the battle. So a ST 12 (reasonable) archer pulling a ST 17 bow will act at -5. But they’ll be aiming (+2 or +3 to hit) for at least 2 seconds (an extra +1) and shooting at an area, not a point target. While you might traditionally go for +4 to hit a hex, you might also say that a battle line might be +10 to hit, if you’re just launching into a 50yd x 100yd box. So even someone using a bow at DX+2 (call it Bow-12) at 250yds (-13) would be at a net flat skill. Sure, you’re not Robin Hood, but Henry V is thought to have had a million arrows on hand with his forces at Agincourt.

Shoot all you want, miss some, no problem. Just drop an arrow into the box 75% of the time every six seconds or so.

Inefficient Springs

Drawing an overstrength bow seems like a good idea in GURPS, and if you assume that you can simply pull the thing back to full draw and you just get inaccurate and a bit tired, you’re good.

But I suspect that’s not how it works. You’re as strong as you are, and if you can’t exert 145# of force come hell or high water, you can’t pull the bow back to full draw. For a basically linear bow, like many self-bows (but not recurves, reflex bows, or compound bows), the linear spring assumption where draw force is a constant times draw length isn’t spectacularly awful, and is close to correct.

That means that if F = K x D (K is constnant, D is draw length), then normally you’d put energy into the bow equal to roughly half of F x D, assuming that F is the max force at the full draw.Or F squared divided by K.

But if you’re only strong enough to draw the bow halfway back (D/2 and F/2) then you’re putting energy into the bow equal to F-squared / 4 K.

So drawing a full-strength bow halfway back is not the same as drawing a bow of appropriate poundage the entire way back. In fact, it’s got half the energy, or roughly 70% of the penetrating power (b/c GURPS does penetration with guns as sqrt(KE)).

So if you do (say) 1d+3 with a ST 17 bow at full draw, and 1d+1 with a ST 14 bow at full draw, you will not do 1d+1 with a ST 17 bow being drawn by someone of ST 14 – it should be more like ST 12, for 1d. Probably a nice -1 per die damage penalty would work here. So if you take a very strong bow that you can only pull as ST 12 (1d for a regular bow), you’ll hit for 1d-1 instead.

Strongbow II

Another way to go with Strongbow is to treat it like a Technique. You normally take a -1 penalty to skill for every -1 ST you have. Use Strongbow to buy this off.

This would allow a ST 10 person to draw a ST 20 bow at full skill for 10 points, because you’re buying off a -10 to skill. This is a restated variation on an idea presented here.

That nicely uses the Technique rules (used for buying off penalties to skill), doesn’t require a huge investment in ST other than that required for character concept, but gives a minor cost to pulling a powerful bow. It also decouples skill at hitting point targets with the ability to pull powerful bows – maybe a feature, maybe a bug. If you have ST 12 and 5 points in the Strongbow Technique, you can fire at full skill a bow up to ST 17. Not extra skill, but full skill.

Going Non-Linear on ya

Another way to go would be to consciously couple skill and the ability to draw a powerful bow, such that you could keep archers’ ST in the 10-14 range but still hit a ST 18 bow. That would basically allow Strongbow to scale more. +1 to ST for each point of relative skill from DX to DX+3 (say), so that at ST 14 (2x in basic lift) and DX+3 (12 points expended, or +4 lifting ST for bows only) plus the Strongbow perk to represent pulling powerful bows (and what you might get for spending the points in Bow and ST to pull it to begin with) you could basically have a strong guy pulling a 160# bow, or an average one pulling a ST 14 (100#) bow, generally considered an entry-level warbow.

Trained ST

I’d be remiss if I didn’t just say “treat Strongbow like Trained ST,” which would allow up to +5 to the ST for pulling a bow at DX+10 – but that has the undesirable side-effect that you have to get to DX+10 to pull a heavy bow.

So anyone that can pull a ST 15 bow with only ST 10 raw has Bow-20? Really?

No. Much as I loves me my Trained ST, this one doesn’t work. Or rather, doesn’t work as the only solution. This couples well with Strongbow as a perk (see what I did?) for spending the 40 points in skill for getting to DX+10, but not as the only way to get there.

Parting Shot

I think overall I prefer Strongbow II and the extra damage penalty of -1 per die for shooting a bow in excess of what you can draw.  It plays well with the rules, gives an incentive to meet or exceed the ST of a bow you’re pulling, and doesn’t make archers even yet more painful to play than they already are.

2 thoughts on “Compressing Bow ST into a smaller range

  1. That's a VERY interesting breakdown. I've only been the occasional GURPS fantasy player (GURPS makes a better superheroes game IMHO and there are plenty of systems for swords and sorcery) but I'm also a recreational historic archer with a 58lb English War Bow and also a mechanical engineer.

    A) You got the math right. (Yay math!)
    B) It's nice seeing someone use historic data to number-crunch a game for realism. (Yay game realism!)
    C) I'm not a terribly strong person being a desk-jockey with arm-chair spread but it takes a fair amount of conditioning for me to maintain strength to draw my bow consistently.
    D) Very few other recreational archer I meet can consistently draw my bow even if they are very good shots with lighter bows. (They also think I'm nuts) and the ones who can already shoot ELB or self-bows.
    E) Having read the accounts from Crece, Agincort, Poitiers and the Mary rose find along with others I don't think that the Mary rose held an atypical selection of archers.
    F) If the Mary Rose held typical archers and the typical archer could pull in the 160-180 lb range then we as modern men are WEAKLINGS! I only know 1 or 2 modern archers who can draw in that range consistently and they aren't really that strong at other tasks. Meanwhile the people I know who are generally strong can span my bow a few times but not hold it without shaking and they aren't capable of drawing the historic draw weights.
    G) It seems the only way to draw and shoot bows in that poundage is to develop a special dedicated set of muscles (not just generally strong) and that set of dedicated muscles comes from a lifetime of bow training.

    Which leaves us with: Historically the solution may be 'trained strength' even if that does not fit with game mechanics and game balance as easily… BUT you might consider access to certain regional/society/racial perks (Born Welsh or Raised in Mongolia)that could reduce that cost or provide a cumulative bonus if maintaining historical accuracy was very important to you.

    Thanks for the analysis!

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