Calculate draw weight?

[Aksel]

Hi.

I am working on a bow which now draws 45 lb at 13,5". Is there a way to calculate what its draw weight would be if I pulled it to 27"?

[paulsemp]

Approx 2 to 3 lbs per inch. Usually comes out to 2.5 lbs.

[Pat B]

I agree with Paul. 

[Aksel]

Thanks!

[Pat B]

If you draw to your intended weight as you are tillering you should come in at your intended draw weight at full draw.

[Aksel]

Pat, I am making a replica of a stone age bow so I donīt know what weight I am aiming for...! Thatīs one of the things I am looking to find out, aswell the full draw profile. I am following the measurements with a caliper and doing a bit evening out of the tiller as I am working my way to full draw.

[Badger]

Put a very long string on the bow so it hangs loose to about 24" and see what it weighs at that point. That will give you a fair idea.

[Del the cat]

45# divided by 13.5" gives you the pounds per inch. Multiply that by the draw length you want gives a good approximation.
So 45/13.5 = 3.33 multiply by 27  gives 90#
Del

[willie]

Pat, I am making a replica of a stone age bow so I donīt know what weight I am aiming for...! Thatīs one of the things I am looking to find out, .

if you share more specs about length and width and species and something about the handle, and anything about arrow length of historical era which might  help set a target draw  length.....

you might get some good estimates of reasonable draw weights to tiller for.

[sleek]

If I know the surface area of the bows working limb, and what wood, or the specific gravity of the wood, I can tell you what the draw weight can be with minimal set, depending on tiller.

[Aksel]

Thanks for all interesting ways of calculate the draw weight. It turned out to be apr. #83 at 27" so #2 per inch was right in this case.

willie, I am not a specialist in arrows but my understanding is they all shot looong arrows which makes it difficult to say anything about draw length or shooting style.

Original bow was a very narrow and thick elm bow with shoulders/ levers half way out the limb and only 3,6 cm / 1,4" wide. 61,5" long. I stretched the length by 10% otherwise faithful to the measurements. Grip area is short, a little narrowed and barely thickened so it is not stiff.

This is the FD at 27" profile i came to after I evened out the tiller the original measurements gave me. Any thoughts or comments appreciated!

[willie]

Unusual design for a bow,

I am curious if the find you are replicating has been dated?  If old enough could the design be considered a transition between the age of the atlatl and the age of the bow? you mentioned longer arrows associated either the find or era.
 I can see where more "atlatl like" darts would work better for such a bow than shorter "arrows".

[Aksel]

Hi Willie, yes the bows for this site (Tybrind Vig, Denmark) is dated to 4-5000 BC, so itīs later part of the early stone age -but still 3000 years younger than the famous bows from Holmegård. Not many intact arrows exist from mesolithic times, but the ones Iīve read about are 90-120 cm (3-4 feet) long, long by todayīs standard but quite typical for primitive archery. With some exceptions are bows from that time typically 150-165 cm long. Mean height for mesolithic european men were 166cm (65"). Bow design is a lever tipped bow with bendy handle