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

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Old 06-19-2017, 04:16 PM   #1
spearq8
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How much power do bands lose with time ?

I have been asked many times if band power drops with time. I do my testing with quick loadings and some were telling me they think this does not give accurate data as during hunting situations there is a long soak between shots. And that especially when using smaller diameter bands like 14mm and 14.5mm small ID stretched at 360% or 380% ... there would be a drastic loss in power with time. I never noticed a drop in power or change in impact point due to a time wait ... so it was time to test this. My guess was that bands must drop in power ... and my estimate was that they lose about 20%. So when I setup a gun I always tried to push the bands at a little higher than Terminal Velocity ... the idea being that even if there is a slight power drop, it will not affect my impact point or my power. I think I was wrong about the 20% and it is probably much less.

Here is the test. I initially wanted to wait 1 hour ... but then the kids were getting impatient and I sort of had to rush things and made it 45 minutes. I think that is good enough.

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Old 06-19-2017, 07:27 PM   #2
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Re: How much power do bands lose with time ?

It is not just time but also water temps. Rubber will start collapsing at high stretch and it will get less reactive at lower temps. 45 minutes is not enough time.
My bands got elongated 4 inches during a weekend of tuna hunting. I cut them at 32 inches on Thursday when I setup my Oceanborn and on Monday they were 36 inches long. They lost well over 10% of their power. I did not check though to see how much power they lost exactly.

There is no need to shoot the gun to figure that out. All you need to do is elongate a band attaching a scale on one side and see how the power in lb gets reduced in connection with time.
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Old 06-19-2017, 08:01 PM   #3
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Re: How much power do bands lose with time ?

How much does rubber lose its power from being old? I've had rubber sitting in a trash bag that I take on dive trips, leave in my car, out in the sun, etc. Aesthetically, it looks as good as new, but it is probably a year old..
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Old 06-20-2017, 12:18 AM   #4
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Re: How much power do bands lose with time ?

I think bands stretch out when they are brand new ... then they stabilize. As for time between shots ... if it does make a difference it is not much. I doubt there will be a big difference if I had waited another half hour. 4 inches of stretch is a lot of stretch ... I have never noticed that ... but then again I never measured before and after. In the end you want your shot on target to not be affected by either impact point or power at impact. This is what I wanted to test here. That is why I used 8 meter test ... I actually did not expect the gun to pass ... but it did quite easily with room to spare. As for temperature ... for sure that would have an affect ... as does the shore hardness of bands from batch to batch. How much ?? Really not sure ... someone else needs to test that.

To store bands the best way is to use a vacuum sealer and put the bands in a freezer. Another great way is to to put a layer of silicone grease all over them and then put them in a zip loc bag with as little air inside as possible. I once went on a spearfishing trip and kept my used bands in this silicone grease method and another set just was on the gun with no protection... came back 2 years later and the silicone greased bands were as fresh as I left them ... while the other band was totally unusable. I heard of people also using Vaseline ... but I would not recommend using that as it might react with the rubber. Best is the silicone grease that is used on "O" rings. And don't worry ... the stuff comes off very easily with just a wipe of a tissue or towel.
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Old 06-20-2017, 03:46 AM   #5
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Re: How much power do bands lose with time ?

I cut the new band shorter than my calculation and put long wishbone , once it elongated after a week or month I just change wishbone length and make it shorter don't need to re-cut again the rubber .

Last edited by doyenofcastle; 06-21-2017 at 04:02 PM.
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Old 06-20-2017, 09:07 AM   #6
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Re: How much power do bands lose with time ?

Majd, how old are your kids?

There's been a few tests on Speargun Rubber Force over time. In one test which I thought was very simple and very telling, the guy set up the bands on a Scale and showed the Force of the bands over time increments. It was actually quite a dramatic loss of power over time and if I recall correctly it was a relationship between % stretch and Force lost over time ie higher the stretch, higher the force lost over time. Water Temp is another Force Killer.

Here's a Link. Band Hysteresis (Power Loss over time) https://www.youtube.com/watch?v=A1SOW_93MsA

Last edited by Behslayer; 06-20-2017 at 12:40 PM.
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Old 06-20-2017, 01:25 PM   #7
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Re: How much power do bands lose with time ?

I just did exactly this with a pair of Pathos 16mm bands I pulled off my Pathos gun when installing Small ID bands.
Put them on my test bench, pulled them by a factor of 3 and let them sit for 45 mins. I ran this test twice.

They lost 9% of force in 45 mins

Whether that's a lot or a little, I don't know.
This was in 24C room temp.
One thing that could play in is that these bands are brand new.

In case you care to know the numbers, the scale said 35.8kg at 200% strecth (what spearos normally call 300% but no matter what, it is a factor of 3). After the soak of 45 mins, the scale read 32.6kg.
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Old 06-20-2017, 01:48 PM   #8
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Re: How much power do bands lose with time ?

Good data. 9% at 300% over 45 minutes. Got to wonder what 380% at 45 minutes would be. One more reason to unpower guns in the boat.
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Old 06-20-2017, 02:00 PM   #9
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Re: How much power do bands lose with time ?

Quote:
Originally Posted by Behslayer View Post
Majd, how old are your kids?

There's been a few tests on Speargun Rubber Force over time. In one test which I thought was very simple and very telling, the guy set up the bands on a Scale and showed the Force of the bands over time increments. It was actually quite a dramatic loss of power over time and if I recall correctly it was a relationship between % stretch and Force lost over time ie higher the stretch, higher the force lost over time. Water Temp is another Force Killer.

Here's a Link. Band Hysteresis (Power Loss over time) https://www.youtube.com/watch?v=A1SOW_93MsA
I just checked out that video. Nice and simple setup. If his analogue scale can be trusted, then he has even less loss than I did. His old bands lost 6.2% over 45mins and the brand new ones only 3.4% (my math based on the numbers he reads out).
Maybe then loss over time is indeed not as pronounced as a lot of people tend to think.
I have definitely heard spearos from Denmark complaining about substantial loss of power in the colder months.
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Old 06-20-2017, 02:03 PM   #10
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Re: How much power do bands lose with time ?

Quote:
Originally Posted by Behslayer View Post
Good data. 9% at 300% over 45 minutes. Got to wonder what 380% at 45 minutes would be. One more reason to unpower guns in the boat.
I have some small ID here, I can cut a piece and test it in a few days. That will be brand new rubber though. I wanna test how much force it will take me to pull out a plastic wishbone insert anyways.
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Old 06-20-2017, 03:22 PM   #11
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Re: How much power do bands lose with time ?

Here is the test:
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Old 06-20-2017, 03:27 PM   #12
phil herranen
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Re: How much power do bands lose with time ?

More important than the overall load Loss is the loss of elasticity and rebound speed , when tuna hunting and haveing a gun loaded for long periods on the boat I have seen substantial changes in gun power
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Old 06-20-2017, 03:53 PM   #13
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Re: How much power do bands lose with time ?

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Originally Posted by phil herranen View Post
More important than the overall load Loss is the loss of elasticity and rebound speed , when tuna hunting and haveing a gun loaded for long periods on the boat I have seen substantial changes in gun power
Ah, so we are back at the penetration test then, I reckon. I mean I only have a scale and a way to pull the bands here. I can't think of a way to test the "delivery" of the power in my apartment, I think;-).
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Old 06-20-2017, 04:48 PM   #14
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Re: How much power do bands lose with time ?

Now my 5 cents about that questions.I define that loss like a loss of elasticity and lower contraction speed.The band power loss is two types-short term and permanent.I thing that the discussion is mainly about the short-term,but the permanent is more serious problem and they go together usually
I see some statements with percents,but to calculate the losses is not so simple and they are functions of many values.
The first and most important value for both kinds of losses is the band material.It could cange dramaticly the results.Thats why I have my strict preferences about bands.
So briefly said,the short term and the permanent loss-they are functions of the band material,water temperature,number of loads,duration of the strech and one of most important-the strech factor.Bands get tired verry quickly when they stay streched at high coef. over 3.3-3.5.Every single loading causes invisible braking of internal elastomer conections,wich is irreversible-like dieing of the brain sells.As higher is the strech,its more.
Actually the easiest way for me to compare the quality of the bands is the cold water-then the contrast is biggest and good elastomers are doing much better.These are the bands with the smallest deformation,best memory and elasticity.
Changing all these values may cause up to 50% power losses,and this could be even more than the power differences in different speargun systems.So-do not underestimate that!

Last edited by seal77; 06-20-2017 at 05:01 PM.
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Old 06-20-2017, 07:22 PM   #15
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Re: How much power do bands lose with time ?

My brain doesn't wrap around all that fancy jargon. Does that mean it might be better to have more bands with less stretch?
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