Heavy weight equals less efficiency ?

[Crash]

Monterey, I believe the opposite is true.  It takes less material, i.e. less thickness of core and or glass, to make a 40 pound bow versus a 60 pound bow.  The heavier bow will have more material in the limbs, thus making is ever so slightly less efficient in regards to dynamic efficiency compared to stored energy.  It may only go from a dynamic efficiency of 86% to 85%, but some of the stored energy is required to move the additional mass of the limbs. 

[McDave]

I think that has to be true.  A bowyer isn’t going to make limbs that are any more massive than are needed to get the job done, and if lighter weight limbs would get the job done on a 65# bow, then they would be no reason to use heavier weight limbs on a lighter weight bow.  Of course, limbs can be made lighter by using different material or design, but then in order to be comparable, the lighter weight bow would also have to be made out of the same material and design.

[pdk25]

Such a moot point.  There are no good studies to quantify this, and there is no point where the diminishing returns outweigh the significant performance gains of shooting a higher poundage bow of the same design and gpp arrow.  Now if you want to argue about what is necessary to kill something, that is a different story.

[pavan]

Nope

[hvyhitter]

I look at it this way.

A 60# bow will usually toss a 600gr arrow a bit faster than a 45# bow.

A 60# bow is 33% heavier than a 45# bow but the arrow usually is not going 33% faster.

That being said, not all bows of same weight shoot the same. Differences can be more or less or none...……

I will still pick heavy bows to shoot heavy arrows...…..  YMMV

[pdk25]

Nope

Nope what?

[McDave]

I’ll start off by saying that I don’t know what Pavan meant by his “nope.”  That said, enough of us were curious about the issue to want to discuss it.  Curiosity about the way the world works is a basic human characteristic; sometimes it results in useful information, sometimes it doesn’t.  If you’re not curious about what we’re discussing, you’re welcome to browse elsewhere.

[pdk25]

McDave, I would actually be curious if some meaningful data on the subject were to be made available that could point someone in a direction for how heavy of a given bow to shoot game with.  I just don't see how that can be, especially with no good trials, just hypothesis that go against what I have observed .  I am all ears for someone to show the data, and how they used that to decide what bow they would shoot.

If I offended someone by saying it is a moot point, I didn't mean that it wasn't something that can't be discussed.   Just if it isn't a useful tool for deciding which equipment to use, it loses it's value to me.

[Aaron Proffitt 2]

I'll certainly be curious to know about something that , on a basic physics level, doesn't make sense . If a given bow delivers so many pounds of thrust , ie. draw weight , it should deliver 'x'. Now comes the variables such as bow design , string material , etc..

And I find it pretty interesting the diversity of thought that comes through in discussions like these. You hear from guys who are bow builders and others who've studied this stuff to a degree that I dont. I'm a " tune it and shoot it " kinda guy. So I love hearing the 'why's ' from guys who've studied it. 

I shoot 55-65 lbs and am happy with them. I know I could easily go to a 70 or 75 , and I wouldn't hesitate if I saw a used one in that weight in a model I'd love to have. Why ? Cause I'm an American .

[hawkeye n pa]

Don't know if this will help but had a bowyer explain it to me that a 50-55 pound bow will give you the best speed with a 10 Grain per pound arrow.  When you get above this speed doesn't increase proportionately with added arrow weight.  Although the benefit comes shooting a heavier arrow, just not much faster.  He had a graph that plotted this out.

[creekwood]

PDK, you said: "Now if you want to argue about what is necessary to kill something, ...."

and pavan replied: "Nope"

[wingnut]

If you are talking bow efficiency as in stored energy versus momentum or KE, then you are correct that after a point most bows loose efficiency when you get beyond 60 pounds.  The reason is that the amount of material in the limb no longer gains in a linear equation.  Instead of adding say .001" core thickness per pound you end up with .0015 or .002 additional core per pound in the heavier weights.

This adds mass weight to the limb and thus uses more stored energy to move the limb and has a negative effect on efficiency.

This makes it difficult to build the same limb design from lightweight (30) to heavy weight (60+).

This is my experience with building a few thousand sets of limbs.

Mike

[altaberg]

I find this an interesting discussion but also a bit academic. What I mean is, it doesn't matter much for practical applications.

If the definition of "efficiency" above is correct ( and I like it) than heaver bows are almost certainly less efficient. Does of course depend on bow design, arrow weight, correct spine...

BUT, 100# war bow at 60% efficiency (let's assume it is roughly a poundforce of 60) will still be impacting more than a 50# bow at 90% efficiency (pound force 45). Not very efficient for the heavy bow, but definitely more punch.

I think what was said above defines efficiency at the point were the arrow leaves the string.
That doesn't cleanly translate into what happens at the target: arrow design, correct spine and distance come into play.
Also, depends on kinetic energy and momentum, and those are two different things that shouldn't be confused.

Practically, it isn't that important and bow choice is more of a case of what you need ( and what you like shooting).

A 50# bow with good efficiency will go through a deer at 20yard. If you try to penetrate chain mail at 50 or 100 you probably need something a bit heavier, "efficiency" be damned.

[Aaron Proffitt 2]

If you are talking bow efficiency as in stored energy versus momentum or KE, then you are correct that after a point most bows loose efficiency when you get beyond 60 pounds.  The reason is that the amount of material in the limb no longer gains in a linear equation.  Instead of adding say .001" core thickness per pound you end up with .0015 or .002 additional core per pound in the heavier weights.

This adds mass weight to the limb and thus uses more stored energy to move the limb and has a negative effect on efficiency.

This makes it difficult to build the same limb design from lightweight (30) to heavy weight (60+).

This is my experience with building a few thousand sets of limbs.

Mike

Ahhh. I gotcha.

[pavan]

Every design has its own point of of diminishing returns.  In my own testing the fast light limbed bows show the most difference in cast when arrow weight is increased, but they will remain faster than heavy limbed slower bows.  A heavy limb longbow will not show as much of a percentage of speed loss with arrow weight gain, if there is a point where it can pass up a light limbed bow that is faster at 10 gpp, it would be at such a heavy weight arrow that such an arrow would be impractical with either bow.  Now for the big one, some bows that are very fast show more differences with draw length variations and release energy variations, while some bows that are slower do not show as much variations in the energy of the shot.  It all depends what one's own variations are as to which bow will be better for them.  I know that I sometimes I have a half inch variation in the point where the string leaves my fingers, sometimes a quarter inch shortener sometimes a quarter inch longer.  I have seen bows that really come to their own at a specific draw length.  My wife's short and very fast hybrid is good at her standard 26" draw, but at 26.25" the tips have a bit more motion and up that bow really comes on strong, at 25.5" it is no faster on the chronograph than her Hill longbow that is 1 pound lighter with the same arrow pulled to 25.5" draw.   Then the question is how much will that loss of cast affect the arrows cast and which bow can she better adjust to complement  the weaker shot.  So far I have never met a human Hooter Shooter, it is a person by person thing, and impossible to declare precise outcomes.

[madmaxthc]

Wow,

been away a couple of days, found now a lot of interesting posts. Thank you all for sharing your insight and experience.

If you are talking bow efficiency as in stored energy versus momentum or KE, then you are correct that after a point most bows loose efficiency when you get beyond 60 pounds.  The reason is that the amount of material in the limb no longer gains in a linear equation.  Instead of adding say .001" core thickness per pound you end up with .0015 or .002 additional core per pound in the heavier weights.

This adds mass weight to the limb and thus uses more stored energy to move the limb and has a negative effect on efficiency.

This makes it difficult to build the same limb design from lightweight (30) to heavy weight (60+).

This is my experience with building a few thousand sets of limbs.

Mike

Thanks for this answer, Mike, it is very informative 

[Bladepeek]

Seems like saying more horsepower = less efficiency. Sure, the most efficient engine will be the one which is just powerful enough to move the vehicle. A 50 HP motor running at maximum power will use less fuel than a 300 HP motor driving the vehicle the same speed, and you will not get 6 times more speed out of the 300HP motor, but it will be faster by quite a bit.

[McDave]

Seems like saying more horsepower = less efficiency. Sure, the most efficient engine will be the one which is just powerful enough to move the vehicle. A 50 HP motor running at maximum power will use less fuel than a 300 HP motor driving the vehicle the same speed, and you will not get 6 times more speed out of the 300HP motor, but it will be faster by quite a bit.

Interesting anology, but I think WE are engine, while the bow and arrow is the transmission, driveshaft, differential, wheels, etc.