Speargun Band Appropriate Lenght Calculations

[BoltSnap]

What is the method to figure out the proper length for the speargun band please?

I was told for circular (continuous) bands, use 1/3 the length from the spear notch to where the band is connected X 2 (add a couple of centimeters to that length). For two piece bands, same as above but not X2 (use two threaded pieces that are 1/3 the length as above).

Is the above correct or is there a better way to do it?

 

[MAKO Spearguns]

Yes, that is basically the method to deliver 300% elongation. Of course there is no universal agreement on the vocabulary, but here goes.

The unstretched band is at 100%
The band is stretched to two times original length - then stretch is 200%
3 times the original length is 300%

Generally thinner rubber is tied with a little more stretch; 3/4" (20 mm ) is tied with less.

Most people will recommend around 320 to 380% stretch, but it depends on the gun, the person, the thickness of the rubber and even the hardness of the latex. It can vary as well.

You might also want to measure the bridle or wishbone length and then subtract that (or half of it actually) from the distance between the muzzle and the notch.

Should put you in the ballpark.

I think this is the recipe.. but check it first..

Circular band length = 2* (distance from muzzle to notch - 0.5 * bridle length)) / (elongation factor)

For 350% stretch - elongation factor is 3.5.

 

[Hank49]

I agree with Dano.
I prefer 300%, or a stretch of two times the length the band. I like a smoother release and a bit less recoil.
My testosterone loaded sons, on the other hand.....

 

[BoltSnap]

I agree with Dano.
I prefer 300%, or a stretch of two times the length the band. I like a smoother release and a bit less recoil.
My testosterone loaded sons, on the other hand.....

Just so I understand you, if the distance to notch is 90cm, then the band length is:

(90/3)X2= 30X2= 60cm??

 

[100days-a-year]

I use 3/4. / 20mm rubber for one band and 5/8 on the other.

My rubber is cut to 22 to 24 inches for both,the exposed wishbone is 2 inches.My draw length from muzzle to back notch is 43 inches. A little over 300%

 

[Hank49]

Just so I understand you, if the distance to notch is 90cm, then the band length is:

(90/3)X2= 30X2= 60cm??

Yes, a 30 cm band stretches to 90cm

 

[Vicko]

For normal aluminium guns with 1 band get a 18mm at around 2.8-3.2 stretch factor. Twin 16mm at 3.3-3.6 (depending on how stretchy they are) and so on and so forth.
It depends also on the spear, the heavy-er the spear the higher the stretch factor. On my 110 with 6.5 spear i have 3*14.5mm at 3.8 stretch, but in the area I'm fishing I don't expect a lot of big fish, this setup is perfect for snapper or similar mid sized fish in the Adriatic. I would imagine that it's crap for blue water hunting.

The formula to cut them would be L / S where L is the total lenght of the gun from rubber hole to spear notch x2
S is the stretch factor.

If you are cuting to the very edge of the rubbers elasticity make sure to also add 2-3 cm to account for knots.