Efficiency of guns for underwater shooting

[popgun pete]

I recently tried to post an English translation of the important article by Valerie Vasilyevich Evtushenko on this topic because I believe it deserves a wider readership here than it would receive if left in the Russian language original, but unfortunately it is not posting for some reason. The article is a great report on the results of experimental testing undertaken to ascertain the operating efficiency of spearguns using different propulsion methods and is of most interest to those who follow the "dark side", although in my biased view this really should be the enlightened side.

There is much to reflect on in this article as it sets some bounds on efficiency levels that can be reached with various design choices. Rubber powered guns show efficiencies from 15% to 37%, the lowest figure probably being some less than top notch Russian speargun (poor band quality?), while spring guns, the metal coil type, have an efficiency of 25%. Moving on to hydropneumatic spearguns there is the quirky RPS-3, which just shows that you can make any strange operating principle work if you put enough engineering effort into it, but do not expect good results as it achieves only a lowly 35%. Other hydropneumatic spearguns, all home-made and thus superior to what the various State factories were producing back then (the report was published in 1991) offer between 50% and 60% efficiency.

Pneumatic guns produce the best figures, except for the RPB-2 speargun's lacklustre 35%, of between 65% and 83%. Significantly the report mentions that a dry barrel gun, as in tipping water out of the inner barrel before firing the gun, raises the efficiency to 87%. That will be what you would expect from a vacuum barrel gun, only none were tested at that time. Significantly extra seals on the piston worsen efficiency by 3% to 4% due to the extra drag imposed on the inner barrel, a result that other testers have independently confirmed since then.

 

[popgun pete]

Here is the article, hopefully it goes OK this time.

 

[tromic]

...
There is much to reflect on in this article as it sets some bounds on efficiency levels that can be reached with various design choices. Rubber powered guns show efficiencies from 15% to 37%, the lowest figure probably being some less than top notch Russian speargun (poor band quality?), while spring guns, the metal coil type, have an efficiency of 25%. Moving on to hydropneumatic spearguns there is the quirky RPS-3, which just shows that you can make any strange operating principle work if you put enough engineering effort into it, but do not expect good results as it achieves only a lowly 35%. Other hydropneumatic spearguns, all home-made and thus superior to what the various State factories were producing back then (the report was published in 1991) offer between 50% and 60% efficiency.

Pneumatic guns produce the best figures, except for the RPB-2 speargun's lacklustre 35%, of between 65% and 83%. Significantly the report mentions that a dry barrel gun, as in tipping water out of the inner barrel before firing the gun, raises the efficiency to 87%. That will be what you would expect from a vacuum barrel gun, only none were tested at that time. Significantly extra seals on the piston worsen efficiency by 3% to 4% due to the extra drag imposed on the inner barrel, a result that other testers have independently confirmed since then.

I suppose nowdays rubber guns should have higher efficiency than 37 %. It would be interesting to find out what was the reason for such low efficiency.
87% - 65% = 22% This is similar to my result. I find that the vacuum barrel gun is about 25 % better than the water barrel gun.
I am not sure if the author of the article had used a line for the shaft because it is very important to know, also how was the line connected to the shaft: head, back, with/without slider.
I was expecting that the hydro-pneumatic gun would have lower efficiency that pneumatic gun.

 

[popgun pete]

I would expect that rubber relaxation may contribute to some loss of efficiency in band guns, you do not get out all that you put in when drawing the bands back unless the gun is fired virtually immediately.

 

[tromic]

I would expect that rubber relaxation may contribute to some loss of efficiency in band guns, you do not get out all that you put in when drawing the bands back unless the gun is fired virtually immediately.

I would say that the major reason is the drag of rubbers, maybe some parachute effect, and the drag of the line tied to the end of the spear. Pneumatic had a slider I suppose, so there was not drag of the line but only after leaving the gun. In 10 cm for measuring the speed it was not significant influence.

 

[tromic]

This is the main reason for lower efficiency of band gun:

 

[popgun pete]

The rubber bands and the wishbones that temporarily attach them to the spear have to be dragged through the water as they are rapidly advanced towards the muzzle during spear propulsion from the gun. Water is much denser than air and the water moved aside by the band system has to remove energy from the gun that would otherwise have been available to accelerate the spear. There will also be cavitation effects behind the circular cross-section band ends, the wishbones as well, as they rip through the water. The inefficiency of the band gun is offset by its effectiveness and the very simple design which is forgiving of lack of any maintenance by owners. The pneumatic gun has none of these parasitic drag elements, but in its wet barrel form has the undesirable function of a water pump, that too takes away energy from the shot. Once the spear exits the muzzle it is irrelevant what type of gun is propelling the spear.

An example of the water drag effects on the bands is what happens when a band unexpectedly snaps as the wishbone is just being dropped into the slot (or tab) on the spear shaft. On land this is a much more violent action than it is in the water, I can tell you this from direct experience! Loading any speargun in the air is bad practice, but nearly everyone has done it at some time and when something goes wrong you quickly learn not to do it again.

 

[tromic]

The rubber bands and the wishbones that temporarily attach them to the spear have to be dragged through the water as they are rapidly advanced towards the muzzle during spear propulsion from the gun. Water is much denser than air and the water moved aside by the band system has to remove energy from the gun that would otherwise have been available to accelerate the spear. There will also be cavitation effects behind the circular cross-section band ends, the wishbones as well, as they rip through the water. The inefficiency of the band gun is offset by its effectiveness and the very simple design which is forgiving of lack of any maintenance by owners. The pneumatic gun has none of these parasitic drag elements, but in its wet barrel form has the undesirable function of a water pump, that too takes away energy from the shot. Once the spear exits the muzzle it is irrelevant what type of gun is propelling the spear.

An example of the water drag effects on the bands is what happens when a band unexpectedly snaps as the wishbone is just being dropped into the slot (or tab) on the spear shaft. On land this is a much more violent action than it is in the water, I can tell you this from direct experience! Loading any speargun in the air is bad practice, but nearly everyone has done it at some time and when something goes wrong you quickly learn not to do it again.

Peter, I agree. That is all true, plus what I sketched.

 

[tromic]

This one could be much more efficient than the regular band guns and could have more that 80 % higher energy of the shaft. It has slider on the shaft!


PSMCAFE, toute l'info sur la Chasse sous marine, l'Apnée, Snorkeling & Photo subaquatique - Tests-2

 

[foxfish]

Pretty serious piece of kit!!

 

[tromic]

This one could be much more efficient than the regular band guns and could have more that 80 % higher energy of the shaft. It has slider on the shaft!


PSMCAFE, toute l'info sur la Chasse sous marine, l'Apnée, Snorkeling & Photo subaquatique - Tests-2

80% is due to construction of the gun with rollers.
Actually it could have about 280 % higher energy of the shaft because it has no parachute effect of the line attached to the back of the arrow. I believe that using some good slider could increase the energy of regular guns by 100%. This is from some measuremens I did in the water. Really it is not big problem to try your gun with slider.

This is very similar to the above video.

 

[settingsteel]

Very interesting as always PP

 

[jtkwest]

isnt that like comparing apples to oranges? how can you rate the energy used to cock a band(which is mostly leverage,) to the energy to push the rod into a pneumatic barrell. and even if you used a meter to test for it, it wouldnt be accurate since we use combination of leverage and muscle to pull band back, which makes it paramount to impossible to rate .power is what i'm after. why is efficiency such an issue? all the pneumatic guns i have tried simply lack power period. i can see for the euro guys, who shoot short guns because of low vis conditions. maybe would want a popgun for the simpler loading(is it simpler?)but all my friends dont shoot air guns because they simply dont have enough range for florida. it seems that whatever your choice is ,(concerning air or bands) is efficiency ever considered as criteria? if they are so efficient, then why do they produce such slow shots? and unless you are freeshafting, the line slider HAS to be drastically reducing accuracy. i dont know of any studies to quote on this, but my personal experiance is that slide rings reduce accuracy. i have always thought spearguns were "cool" and probably the airguns are even "cooler" ,(in that sense) but in reality, they seem more complicated with less NET results. plus all the rebuilding. and what about the huge POP when they go off?

 

[foxfish]

I think if you could get hold of an dry barrel air gun, you would then understand the "darkside" & never look back!

 

[Don Paul]

Or shoot my Stein 140. I've lined 30# yellowtail 10' of the tip.
I'm Catholic in my gun choices, band gun or air gun what ever puts food on
my table.

Cheers, Don

 

[jtkwest]

I think if you could get hold of an dry barrel air gun, you would then understand the "darkside" & never look back!

they definately sound cool. i will check it out someday. but what about the boom when they go off. do you think they might scare fish off, i mean the fish you are shooting at, is usually scared byt the shot, no matter what. but others may hang around , not realizing the danger. but once you set off one of those pop guns, it seems it may scare everything off. i dont KNOW this for sure, since i dont have a popgun, but i hunted with setting steel once and he had one. it was loud! but, come to think of it, he did shoot some good fish that day. have you had any experience with this? or am i just wrong? i dont know. it sounds good.

 

[popgun pete]

Efficiency is used to help assess incremental improvements to individual spearguns and differentiate which of the factors being varied are more important than others (i.e. first, second and third order effects). It is therefore a handy quantitative measure for controlled experiments where the energy stored in the gun after loading is compared to the energy delivered to the spear and the gun when the trigger is pulled, although the latter (gun recoil) is not usually measured. So we are talking about the efficiency of shooting rather than the efficiency of loading/cocking the gun. Possibly the energy expended by the diver is not totally stored in the gun at the completion of the loading/cocking task (I would be very surprised if it was), but as we are interested in shooting fish rather than how tired the diver gets the efficiency of loading is not generally considered.

If you were shooting fish for hours on end and reloading with only your own resources then you would soon appreciate a more efficient speargun from both aspects, i.e. loading and shooting, however most divers take a relatively low number of shots per dive outing, so speargun efficiency is less important in an everyday sense unless the speargun used is highly inefficient. For example inefficiency plus intensive maintenance requirements got rid of the spring gun which once held top dog position in the speargun world with 2 metre long spearguns, extension spring guns using the full length of the barrel for propulsion unlike their compression spring counterparts which only used half that length.

 

[popgun pete]

they definately sound cool. i will check it out someday. but what about the boom when they go off. do you think they might scare fish off, i mean the fish you are shooting at, is usually scared byt the shot, no matter what. but others may hang around , not realizing the danger. but once you set off one of those pop guns, it seems it may scare everything off. i dont KNOW this for sure, since i dont have a popgun, but i hunted with setting steel once and he had one. it was loud! but, come to think of it, he did shoot some good fish that day. have you had any experience with this? or am i just wrong? i dont know. it sounds good.

Some fish species will be alerted by the noise of a pneumatic speargun firing, but the one in front of the gun will be dead before it thinks too much about it. Sometimes other fish come in to investigate and provide even more opportunities, while others flee for their lives. If it was really a problem, as non-users often say, then the manufacturers would never sell a pneumatic speargun. As a problem it is way overstated. Ditto for the maintenance aspects, pneumatic spearguns are made to use, usually all that is required is to rinse the gun off after a saltwater dive.

 

[jtkwest]

why are pneumatics so small? very few that i have seen are much longerthan about 24" to 36" which, at that size, simply isnt big enough to shoot most of the fish we have in my area. the problem with using little guns in my area is: you never know when you may come across something nice swimming by (even in shallow water) more than a few times, i have been lucky enough to have a big grouper who wont rock up and only presents a 15' shot. if i were to even consider a pneum. it would have to be atleast 5' long minimum. they dont sell em in the stores down here that big. and making alot of noise in the water seems like a bad idea. it is a fundamental fact , that you be as quiet as possible when hunting anything anywhere. this is not a myth, i asssure you. animals and fish are wary of noises. if you think about it, when you POP off that gun, you dont think, maybe a grouper hanging out on his doorstep around the corner, might rock up,(way up) and you never got to even see that fish. thus could keep on assuming you werent scaring them away,(since you didnt SEE them leave) when you consider the lateral line and its sensitivity to vibrations,(noises) seems like it must have some effect. now, honestly, i think they are pretty cool idea, and i have seen one guy who uses on well,(setting steel) i just like throwing my 3 cents in, and i enjoy a light hearted debate now and again. why arent lost gas systems more common? those can be very powerful. and if its gonna POP, why not add some bubbls and get some REAL power? why not a pump up gun, like a pellet rifle? these guns(air powered spearguns) have been around forever, virtually unchanged. with all the new materials and innovations,(computers and such) why are we still looking at the same designs, with the same problems? since they invented pop guns, the rest of the world now has microcomputers, carbon fiber, space travel, etc. yet our spearguns havent improved almost at all? my feeling is that popguns are a cool idea, they just need some technology to make them quieter and more powerful

 

[foxfish]

you can get long air guns but something like a mamba kitted 115 will kill virtually any fish.
Check out Harry's post DeeperBlue Forums - View Profile: GreekDiver as he fishes in your area.
watch a vid of a dry barrel airgun being fired & you will see just how smooth & quiet the shot is.