Power enough? Two 16mm bands at 2.5 elongation...

[spearmantw]

Hi there,

I am a spearo from Taiwan.
Need advise on my gun set and am wondering if my guns are power enough.
I know that euro guns normally are equipped with single 20mm band at 3 times or more elongation.
I got three guns, which are 90, 120, 140cm for different spearfishing spots.
The elongation for my bands is only about 2.5 times. My shafts are made of 7mm steel.
Two 16mm bands at 2.5 elongation for 7 mm steel shaft is power enough?

Thanks.
Spearmantw

 

[GALADION]

Hey Spearman,

You have to be more specific about the band, shaft, and barrel length in order to get a proper answer.

 

[spearmantw]

Thanks Galadion and sorry for my fist post.

I have three spearguns and the specification of them as below.
Barrels (made of wood) length Small: 90cm, Medium: 120cm, Large: 140cm
Length of rubber(a loop): Small: 66cm, Medium: 92cm, Large: 102cm
Band: 16mm natural latex rubber
Handle: Undersee Manta Grips (Australia speargun company)
Shaft (made of Steel) length: Small: 135cm, Medium: 165cm, Large: 185cm

The rubber is set to be lengthened to approx. 2.5 times of original length and I always put on two loops of 16mm rubbers for my guns.
From the posts here, I know that most of you will recommend just put on a single 20mm band lengthened to 3 or more times of original rubber length.

I am only 5’6 tall and pretty skinny and have difficulty in loading 20 mm rubber, especially for my large gun. I have tried it before and it really kills me. :waterwork

What do you think about two loops of 16mm band lengthened to 2.5 times, is it power enough? Especially compare to one single 20mm?

Thanks.

Spearmantw

 

[Bill]

Spearman
The math is prety simple, area=radius squared times PI. Two 16's should have about 50% more power than a 20 if they're the same length and stretched the same. For years I used three 16 mm rubbers on the big gun. When I switched to four 14's, there was no noticeable difference in power but, it was easier and only a little slower, to load. You can juggle the lengths for different shooting characteristics too.
Aloha
Bill

 

[defofthecrown]

The power gain from bands is not linear. Think of earthquake scales which are logrithmic, a 6 on the richter scales is twice as powerful as 5. By stretching your bands 2.5 times vs. 3 your not getting ~82% of the power, your getting less. There's a graph with powerband elongation statistics somewhere in www.rocknfish.com I believe.

The question is why are you going for 2.5 when you know the ideal stretch is 3+. The answer is all technique. I always have fun giving my guns to people that don't spearfish and ask them to load the gun. The always pull the band about 2" and give you a quizical look. If you search this site or the internet you'll find loading technigues for longer euro guns. The trick is to get the loading pad high on your chest and using your back muscels. You'll be shooting a shortned 20mm in no time.

Don't worry about longer bands. Just practice your technique and start w/ normal length 16mm bands. Good luck! Welcome to the site.

-Chris

 

[spearmantw]

Hi Chris and Bill,

Thanks a lot for your explainations and advises.
I would try to shorten my bands to at least 2.75 or 3 and then try the loading technique.

Thanks again.

Spearmantw