Which is stronger.. ?

[Skindiver]

on a 1.4m RA with 7mm shaft and all rubber lengths the same for comparison purposes:

one 20mm rubber

or

two 16mm rubbers.

I would expect that 16 + 16 = 32mm and that this should throw the spear harder / faster but i have come to realise that what you expect is not always what you get ?

Skin.

 

[SpearSlinger1]

The amount of force stored by a band depends not only on the diameter, but also on the length and the length of stretch. I don't know how many lbs. of force are stored by the diameters you mentioned for a particular length, but the amount is cumulative. For instance, my gun has three 9/16"x24" bands that generate ~80 lbs. each, together this is ~240 lbs. No way could I physically apply this much force to loading a single band. I prefer multiple smaller bands because it not only gives me more total force, but it also allows me to tailor the numbers of bands used to a given situation. I can load one band on the helper tab if I want to shoot 2' into a hole or crack in the reef or I can load all three for longer shots. Along with that, you can apply too much force which causes shaft whip, reducing accuracy with an open track gun. This isn't a problem with an enclosed track.

 

[Shadowkiller]

A rough guide for bands of equal length is cross sectional area where 20mm has a 314mm2 area, a single 16mm has 201mm2 area. So twin 16mm will have roughly 25% more power than a single 20mm band.

Assuming the bands are made of rubber with a similar modulus.

 

[fuzz]

Originally posted by Shadowkiller
A rough guide for bands of equal length is cross sectional area where 20mm has a 314mm2 area, a single 16mm has 201mm2 area. So twin 16mm will have roughly 25% more power than a single 20mm band.

For a dumbed-down version of Shadow's post ... :duh

I just compare the relative strengths as such:

20mm = 100
18mm = 81
16mm = 64
14mm = 49

There are many other factors... for example, in my experience, the difference in power between 18mm bands & 20mm bands is negligible. Maybe the size of the 20 starts to get in the way

Also, traditional 3/4" bands sold as "20mm" bands are really 19's... <<.75*2.54>>

 

[ivan]

hi

My 150 with 2 16mm bands definently has more power than when equipped with a single band, but doesnt mean I like the double bands better

cheers

Ps real men use 1 rubber :t

 

[Shadowkiller]

Originally posted by fuzz
For a dumbed-down version of Shadow's post ... :duh

For those without the mathematical perception of an engineer... and the accompanying lack of social skills, looks and charm...

 

[SpearSlinger1]

Ps real men use 1 rubber

Some of us require more than 1 in a night.

 

[Griff]

there's something that we also have to consider when adding more and more bands to our guns. there must be a terminal velocity of the rubbers. this is the speed that the rubber travels when it is let go freely, ie without the spear's momentum to slow it down. so there will be a point when extra rubbers wont make a difference, performance wise.
hey greg, i read the writeup in divestyle about the fsa champs. its a pity the author missed your dive. he could have mentioned a lot more about it considering you won the event:hmm
nevertheless, congrats on your achievements.