My FOC and what it means...

[MEhuntalot]

I just calculated my FOC and it came out negative...is it supposed to be an absolute value or is there something terribly wrong??

I followed the instructions to a T...
balance point = 17 7/16
Total Length = 30 1/16
30 1/16 / 2 = 15 1/32
15 1/32 - 17 7/16 = -2 13/16
-2 13/16 / 30 1/16 = -8%

I am shooting aluminum XX78's (2317)
Shooting 68-70 lbs
100 grain FP's and BH's

Any help would be great!

[Kanga]

Go to www.goldtip.com and use their FOC calculator

[KodiakArcher]

I suspect that you measured your balance point from the wrong end of the arrow. Unless you've got some seriously heavy cresting wraps and large vanes that FOC should actually be +8%.

[MEhuntalot]

I measured from the valley of the nock like the article said...but I will go to that website and use there calculator to see what I get...

Thanks

[ButchA]

I think you got your two figures backwards....

17 7/16 (17.4375 decimal) - 15 1/32 (15.0312 decimal)= 2.4063

2.4063 * "100" = 204.63

204.63 / 30 1/16 (30.0625 decimal) = 6.8068191....

[MEhuntalot]

Determine FOC:

To find the FOC (which is always expressed as a percentage) divide the overall length by two. This should produce the physical center of the shaft. Now subtract this number from the balance point and divide by the overall length. Multiply by 100 to express the fractional value as a percentage.

Most expert archers agree that an FOC value that is between 7 and 10 percent will produce the best compromise between stability and a flat trajectory. The American Society for Testing and Materials, in their specification for measuring balance point, state that a value of 9% is typical. But, they also state that the range can be as wide as 7% to 18% while still producing good arrow flight characteristics.

the way I read it you divide the 2.40625 (+ or -) by the total arrow length then multiply by 100...??

Does anyone know off hand...
GPI of XX78's
weight of 4" duravanes
nock weight of uni-nock's

[ButchA]

Either way.... Multiplying by "100" just turns the sum into a percent, that's all.

[Paul L Mohr]

Assuming you are using unibushings with a 30 inch arrow it should be around 7% with 4 inch vanes and 8.5% with 4 inch feathers.

Paul

[nodog]

17.4375/30.0625=0.58004... Anything over .5 is the foc yours is 8004... Percent. I don't go from the crotch though. The end of the nock doesn't drop off every time why not count it.

[MEhuntalot]

7.5 to 8% is what I calculated too...thanks for the help guys...

I was reading in the bowhunting folder that people were finding 10-12% to work better for them...do you think it would be advantageous to try and go with a heavier head to raise my FOC to that range?