Home Tournaments Calendar Weather Merchandise Sponsors

Go Back   Spearboard.com - The World's Largest Spearfishing Diving Boating Social Media Forum > Spearfishing Gear > All About Guns

All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here!

Reply
 
Thread Tools Rate Thread Display Modes
Old 01-23-2020, 01:49 PM   #1
renepotvin
Registered User
 
renepotvin's Avatar
 
Join Date: Sep 2006
Location: Montreal
Posts: 735
Question band retraction speed... 14 vs 16 vs 20

Hello, I was watching the slingshot guy and the smarter everyday guy and they were showing on a high speed camera how tapered bands were faster than the non tapered ones... (same material obviously)

This means that a 14mm should retract faster than a 16 mm of the same material. Is that so? Any evidence?
__________________
Rene Potvin
Montreal

Sailing adventures http://miami2montreal.wordpress.com/

Freediving and spearfishing stuff www.renepotvin.com

My spearguns www.renesub.com

On twitter : @living_outdoors
renepotvin is offline   Reply With Quote
Old 01-23-2020, 02:06 PM   #2
popgun pete
Registered User
 
popgun pete's Avatar
 
Join Date: Mar 2006
Posts: 3,493
Re: band retraction speed... 14 vs 16 vs 20

Quote:
Originally Posted by renepotvin View Post
Hello, I was watching the slingshot guy and the smarter everyday guy and they were showing on a high speed camera how tapered bands were faster than the non tapered ones... (same material obviously)

This means that a 14mm should retract faster than a 16 mm of the same material. Is that so? Any evidence?
Depends on what it is pulling.
popgun pete is online now   Reply With Quote
Old 01-23-2020, 03:16 PM   #3
renepotvin
Registered User
 
renepotvin's Avatar
 
Join Date: Sep 2006
Location: Montreal
Posts: 735
Re: band retraction speed... 14 vs 16 vs 20

Right, I mean bands without anything to pull. Only their own weight.


The question becomes, would one single band go as fast as two bands that would have the same amount of material as the single band? Is it better to have multiple smaller bands?
__________________
Rene Potvin
Montreal

Sailing adventures http://miami2montreal.wordpress.com/

Freediving and spearfishing stuff www.renepotvin.com

My spearguns www.renesub.com

On twitter : @living_outdoors
renepotvin is offline   Reply With Quote
Old 01-23-2020, 03:51 PM   #4
popgun pete
Registered User
 
popgun pete's Avatar
 
Join Date: Mar 2006
Posts: 3,493
Re: band retraction speed... 14 vs 16 vs 20

Scubapro's "Big Jim" speargun had band loops on either side of the muzzle that were of a smaller diameter, but that did not seem to work out so well.
Attached Thumbnails
Click image for larger version

Name:	BigJimmuzzle.jpg
Views:	96
Size:	57.5 KB
ID:	244819  
popgun pete is online now   Reply With Quote
Old 01-23-2020, 06:14 PM   #5
renepotvin
Registered User
 
renepotvin's Avatar
 
Join Date: Sep 2006
Location: Montreal
Posts: 735
Re: band retraction speed... 14 vs 16 vs 20

Look at this minute 440. It's a discussion and test of tapered band vs straight band. It's interesting. I know our 14 and 16 are both non tapered, but it got me wondering about retraction speed vs diameter.

__________________
Rene Potvin
Montreal

Sailing adventures http://miami2montreal.wordpress.com/

Freediving and spearfishing stuff www.renepotvin.com

My spearguns www.renesub.com

On twitter : @living_outdoors
renepotvin is offline   Reply With Quote
Old 01-23-2020, 09:42 PM   #6
Marcus
Naval gazer extraordinair
 
Marcus's Avatar
 
Join Date: Jan 2003
Posts: 40,233
Re: band retraction speed... 14 vs 16 vs 20

I'm sure there is some physical model already documented that makes this question perfectly clear. It's not a very simple question...from what I understand. It's not exactly my wheelhouse either. I just know enough to ask the right questions.
__________________
“If the natural tendencies of mankind are so bad that it is not safe to permit people to be free, how is it that the tendencies of these organizers are always good? Do not the legislators and their appointed agents also belong to the human race? Or do they believe that they themselves are made of a finer clay than the rest of mankind?”
― Frederic Bastiat, The Law
Marcus is offline   Reply With Quote
Old 01-24-2020, 12:56 AM   #7
popgun pete
Registered User
 
popgun pete's Avatar
 
Join Date: Mar 2006
Posts: 3,493
Re: band retraction speed... 14 vs 16 vs 20

I watched the video. The statement that "bands lose energy as they cool off" is incorrect. The energy was already lost as it transformed to heat when the band was first stretched as rubber is not a perfectly elastic material and it never stores and releases all the energy put into it. If you drop a ball bearing on a metal plate then it will bounce much higher than a similar weight rubber ball because that collision is more elastic in the technical sense of the word.

Energy stored in the slingshot is determined by the length of the draw and the force applied to get the ball projectile back to the point that you let it go from. Not only does the band propel the ball it also has to move itself. There is less band weight in the tapered band as if you think of it reduced to short segments which contract and pull on each other then at the rear of the slingshot there is less weight to propel. Actually if a speargun was substituted in these slingshot tests then the bottle would been blown to smithereens and ditto for the melon as the energy in a speargun projectile would dwarf that from a slingshot.
popgun pete is online now   Reply With Quote
Old 01-24-2020, 02:35 AM   #8
spearq8
Registered User
 
spearq8's Avatar
 
Join Date: May 2009
Posts: 3,132
Re: band retraction speed... 14 vs 16 vs 20

In a speargun, the bands just provide energy to the shaft. The speed of band contraction definetly must be one of the major factors in play, but it is not the only factor. There is a fine balance between speed contraction and the minimal energy required to move a shaft of a certain mass. As the shaft gets heavier you need more band energy to get the shaft moving. In other words a 5mm diameter band would have better band contraction speed than a 14mm diameter band, but if it has to push a 7mm @150cm shaft, it would not be able to contract at a good speed … while a 14mm band that has more energy would do much better as it has enough energy to get things moving and still get the shaft to its Terminal Velocity. On the same token, a 14mm band would do a much better job than a 20mm band as with the 20mm band you are way over the required energy to get the 7mm shaft moving and thus you would have much energy wasted … and that wasted energy will hurt performance as the extra energy does not go only in shaft speed but also reduces shaft stability. You need to get the minimum amount of band diameter for the shaft mass you are using.

Of course once you sort out the energy requirement for your shaft, there is an even bigger factor that affects performance ... and that is shaft stability. The energy you put in the shaft has to be "controlled" energy that will not cause the shaft to flip up or down. This is where proper speargun design comes in.

I did a video testing different band diameters with different shafts … you can see that with a 7mm shaft that the best results were with 14mm small ID bands. Switching to thicker bands with HIGHER band stretch, the results were actually less even though there was more energy. Things changed when moving up to an 8mm shaft … here is where the thicker bands dramatically improved performance over the 14mm bands.

spearq8 is offline   Reply With Quote
Old 01-24-2020, 06:50 AM   #9
2fishin2
Pacific Spearo
 
Join Date: Jul 2007
Age: 58
Posts: 3,323
Re: band retraction speed... 14 vs 16 vs 20

Why wouldn't bands which are "hotter" not have more energy or force than ones which are cold? Wouldn't the molecules in the "heated/just loaded" band be traveling faster, exerting both more energy and force?

How about the tapered band issue? Interesting that the tapered one applied more force....
2fishin2 is offline   Reply With Quote
Old 01-24-2020, 03:26 PM   #10
popgun pete
Registered User
 
popgun pete's Avatar
 
Join Date: Mar 2006
Posts: 3,493
Re: band retraction speed... 14 vs 16 vs 20

It all has do with the cross-sectional area being stretched. Those slingshot bands are flat rubber, so they are thin in one dimension and wide in another, basically rectangular. Their cross-section is much less compared with speargun rubber which is circular. If you think of a speargun band as being like an onion cut in half it consists of concentric rings of rubber all stacked together. Small ID bands have a larger cross-section than bands of the same OD with a larger hole in the middle, so there is more rubber being stretched in the former. Larger cross-section, more volume of rubber, more weight in the bands, that is all there is to it. The actual shape does not matter. The Japanese wooden rollerguns used flat bands because that was probably all that was available, but they would have been weak compared with modern spearguns as their cross-sectional area was small. Due to the weight of the projectile we require a sufficient cross-section of rubber to store enough energy to accelerate it out of the gun, which is a larger requirement than a ball bearing, especially as we are shooting in water.

Note the bands are not original as they would have been red due to the clay binder used in the rubber.
Attached Thumbnails
Click image for larger version

Name:	Tairyo_rigged1.jpg
Views:	46
Size:	74.3 KB
ID:	244820   Click image for larger version

Name:	Tairyo_rollerBands.jpg
Views:	46
Size:	54.3 KB
ID:	244821   Click image for larger version

Name:	japanese rollergun 3 views.jpg
Views:	46
Size:	145.8 KB
ID:	244822  

Last edited by popgun pete; 01-24-2020 at 03:39 PM. Reason: exra comment
popgun pete is online now   Reply With Quote
Old 01-25-2020, 06:54 PM   #11
popgun pete
Registered User
 
popgun pete's Avatar
 
Join Date: Mar 2006
Posts: 3,493
Re: band retraction speed... 14 vs 16 vs 20

As a matter of interest note the concave surfaces on the brass rollers of the Japanese rollergun. That shape is to keep the flat rubber bands tracking on the rollers as the gun shoots. The bands haul a sliding metal carriage along the twin metal guide rails, the spear being propelled at its tail end. When the sliding carriage slams into the muzzle it runs into rubber sleeves on the rails which act as shock absorbers. Although these guns have been used underwater my guess is that they were originally surface interface shooters for shooting fish, or squid, from a raft or boat. This would enable the band drive to operate in air with only the muzzle sticking into the water and there are modern equivalents that do just that, although in recent years this form of fishing has declined as such guns do not seem to be available now in Japan. The most elaborate of these were the Scope-Arrow guns that had a view box/telescope built into a tubular barrel and were not underwater weapons, even though they looked like they were at first glance.
popgun pete is online now   Reply With Quote
Old 01-27-2020, 03:21 PM   #12
renepotvin
Registered User
 
renepotvin's Avatar
 
Join Date: Sep 2006
Location: Montreal
Posts: 735
Re: band retraction speed... 14 vs 16 vs 20

So... about color....


OMG
__________________
Rene Potvin
Montreal

Sailing adventures http://miami2montreal.wordpress.com/

Freediving and spearfishing stuff www.renepotvin.com

My spearguns www.renesub.com

On twitter : @living_outdoors
renepotvin is offline   Reply With Quote
Old 01-28-2020, 08:20 AM   #13
Mana'squal
Registered User
 
Mana'squal's Avatar
 
Join Date: Jul 2016
Location: North East US
Posts: 366
Re: band retraction speed... 14 vs 16 vs 20

Quote:
Originally Posted by renepotvin View Post
So... about color....

Pink shoots faster than black, simply physics
Mana'squal is offline   Reply With Quote
Old 01-28-2020, 10:35 AM   #14
Marcus
Naval gazer extraordinair
 
Marcus's Avatar
 
Join Date: Jan 2003
Posts: 40,233
Re: band retraction speed... 14 vs 16 vs 20

Quote:
Originally Posted by Mana'squal View Post
Pink shoots faster than black, simply physics
Until you get deep enough where the red spectrum disappears. They then start shooting the same.
__________________
“If the natural tendencies of mankind are so bad that it is not safe to permit people to be free, how is it that the tendencies of these organizers are always good? Do not the legislators and their appointed agents also belong to the human race? Or do they believe that they themselves are made of a finer clay than the rest of mankind?”
― Frederic Bastiat, The Law
Marcus is offline   Reply With Quote
Old 01-28-2020, 11:47 AM   #15
renepotvin
Registered User
 
renepotvin's Avatar
 
Join Date: Sep 2006
Location: Montreal
Posts: 735
Exclamation Re: band retraction speed... 14 vs 16 vs 20

Quote:
Originally Posted by Marcus View Post
Until you get deep enough where the red spectrum disappears. They then start shooting the same.
I thought the same, apparently that's not true... watch this :

Pink remains pink at 150 while red becomes black almost immediately, go figure


Again, red wetsuits would be perfect for security on the surface and not all that visible underwater.
__________________
Rene Potvin
Montreal

Sailing adventures http://miami2montreal.wordpress.com/

Freediving and spearfishing stuff www.renepotvin.com

My spearguns www.renesub.com

On twitter : @living_outdoors
renepotvin is offline   Reply With Quote
Reply

Bookmarks

Tags
bands

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 11:11 AM.


The World's Largest Spearfishing Diving Social Media Forum Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright ©2002 - 2014 Spearboard.com