Bluewater Pneumatics - Pros and Limitations

[ECK]

Yes, of course you don’t need to take the 4mm shaft seriously.
Not all fish can be shot with universal weapons that manufacturers offer.
For a 10mm shaft you need a special shotgun. This is the principle of designing all weapons.
First, choose a shell, and then design a gun.

 

[ECK]

Well you could have a 4 mm pump rod in a displacement type pump, but it would take a lot of strokes to push a piston back in say a 13 mm inner barrel. However that would break the loading effort down into smaller chunks. Note that this type of displacement water pump is what is used in the "Alcedo Hydra" hydropump. This type of pump is analogous to filling a glass brimful with water and sticking your finger into it which displaces the same volume of water as your finger displaces.
[/ QUOTE]
Yes, this is obvious, but it greatly simplifies the design of the hydraulic pump.
There is no lever, but there is a compact size Loading handle
Can show the "Alcedo Hydra" hydropump scheme?

 

[popgun pete]

This is the hydropump, the tube with a lot of portholes is the outer handle that slides over the pump body as you operate the pump. The thin rod is the pump rod that slides through a tight fitting seal.

 

[popgun pete]

The pump rod 299 has a tapered tip that pulls free of the seal that it is pushed through when the pump handle 296 is at its most rearward position. That allows water to refill the pump body 288. When the pump handle is pushed forwards by pressing on rubber knob 298 the rod tip enters the seal thus closing it off and then as the rod advances it displaces water inside the pump body. The displaced water injected into the gun with each stroke is the volume of the rod. A check valve where the hydropump attaches to the gun stops water flowing backwards when the pump handle is pulled back for the next stroke. The hydropump's effective bore is the diameter of the rod and thus the force required is as low as possible with such a reduced cross-sectional area.

 

[quakeos]

it's all a tradeoff. a 4mm inner bore means not much force required but slow AF. the 10mm ID is much quicker and the forces required can be provided by most people. Also, its a safety aspect. As gecko mentioned earlier minimum parts or mods required is something that's being vouched for here and I don't want the oleo to go past 45bar as it starts to get a little worrisome without changing a lot- and also there is really no need to take it past that

 

[quakeos]

this leads me to open a can of worms with operating efficiency - before I mentioned sometimes we forget how much stored energy oleos can hold partnered with their incredible efficiency. Doing some calculations a 100% efficient gun with a rectangular energy storage graph at 35kg can provide absolutely sound forces for taking down just about anything in the ocean with respect to the oleos size. For the most part, a rubbers energy storage curve while generally being quite wonky I have measured to approximate that of a fairly equilateral right angle triangle, so assuming a compression ratio of 1.1 which is effectively a rectangle it would have double the stored energy of one rubber band or roughly the same as two as mentioned. I also 100% agree with Pete that is it a quasi perfect constant drive source and another reason why pneumatics can be seen as an ideal speargun.

Pete, or anyone for that matter, do you have insights to the operating efficiency of pneumatics and different types of of rubber spearguns underwater? I really do feel like there is quite a huge gap between them. Assuming no choking points on a vacuum pneumo the loss of friction from the piston is so insignificant compared to the forces involved say at 20bar, and air being almost a perfect spring I imagine their operating efficiency is getting rather close to the impossible triple-digit figure.

 

[quakeos]

whoops my bad, didn't mean equilateral , meant equal

 

[popgun pete]

Pneumatic spearguns are way more efficient than band guns as bands gradually lose some tension after they are cocked. So whatever effort you put into loading does not come out when you shoot, only a part of it. Pneumatic guns lose something to friction both in loading and shooting, plus internal air movement throttling effects and water pumping in a flooded barrel gun, but it is way less than band guns. Pneumovacuum spearguns increase efficiency by getting rid of water pumping during the shot which is slightly offset by some friction with another seal on the spear, but that friction is negligible with thin lip seals. The downside of pneumovacuum guns is potential unreliability of the muzzle vacuum seal.

Efficiency of guns for underwater shooting

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...

forums.deeperblue.com

 

[quakeos]

Fantastic, some nice figures there with that article listed. Modern rubbers are getting very good at not loosing short term performance after being stretched for say an hour however they have their huge efficiency loss in the material itself and also from my testing have seen that they spend a huge chunk of their energy from the friction and drag from displacing water when shot.

 

[popgun pete]

Fantastic, some nice figures there with that article listed. Modern rubbers are getting very good at not loosing short term performance after being stretched for say an hour however they have their huge efficiency loss in the material itself and also from my testing have seen that they spend a huge chunk of their energy from the friction and drag from displacing water when shot.

Band guns in their simplest form are cheap and easy to make, in the sixties and seventies pneumatic spearguns were twice as expensive as any band gun. The sport went through a squeeze point in the eighties when spearfishing was "bad" and many dive gear companies trashed their spearfishing product line or hid it in a subsidiary company out of general sight. When things picked up more effort went into band guns and to stay in business pneumatic guns were made as cheap as possible. Fortunately after about a decade the quality was put back in, but pneumatic guns never recovered to command high prices until the last five years or so.

Many myths surround pneumatic guns which are perpetuated by people declaring what they believe are truthful statements without actually having used one themselves.

 

[Diving Gecko]

Fantastic, some nice figures there with that article listed. Modern rubbers are getting very good at not loosing short term performance after being stretched for say an hour however they have their huge efficiency loss in the material itself and also from my testing have seen that they spend a huge chunk of their energy from the friction and drag from displacing water when shot.

Yep. I actually tested the Primelines and they didn’t loose much at all over time. But... that’s was testing them static on a bench. I am not sure whether the results would be the same for a shot. But Majd tested that by shooting penetration tests. Hardly any loss at all as far as I remember. I’ll try to find a link or post the results later.


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[Diving Gecko]

As for efficiency, I hate to bring our Russian friend into this but his pistonless design is claimed to be 94% efficient. I don’t know how he came up with that number and how far behind a traditional oleo is (with no bulkhead).

Many Ukrainian gun smiths have for a while thought that the standard shooting barrels have too much friction and often guns from there come with polished SS barrels. Again, while it’s fairly easy to measure static friction - which does show a significant advantage - I haven’t seen anyone show how much a difference there is during a dynamic shot.


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[popgun pete]

One way to check a band material is to hang a weight on it and see if stretches more over time. If the rubber relaxes then it should get longer than what it initially stretched out to.

 

[Diving Gecko]

I’m on my phone so can’t post the spreadsheet right now but it’s here:

Spearboard.com - The World's Largest Spearfishing Diving Boating Social Media Forum - View Single Post - How much power do bands lose with time ?

This is a spearfishing discussion forum powered by vBulletin. To find out about vBulletin, go to http://www.vbulletin.com/ .

www.spearboard.com

The bands lost 11% of their static pull force after 45mins. But a lot of that loss happened in the first two mins.
This was at a stretch factor of 4. At x3 the loss was a lot less. Can’t recall how much but it’s in the thread somewhere. Primeline Small ID tend to be rigged at 3.6-3.8. A few people run them super hot at x4.

Also, the very first post in that thread is Majd’s test with a gun that has been sitting loaded for 45mins.


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[Vlanik]

I’m on my phone so can’t post the spreadsheet right now but it’s here:

Spearboard.com - The World's Largest Spearfishing Diving Boating Social Media Forum - View Single Post - How much power do bands lose with time ?

This is a spearfishing discussion forum powered by vBulletin. To find out about vBulletin, go to http://www.vbulletin.com/ .

www.spearboard.com

The bands lost 11% of their static pull force after 45mins. But a lot of that loss happened in the first two mins.
This was at a stretch factor of 4. At x3 the loss was a lot less. Can’t recall how much but it’s in the thread somewhere. Primeline Small ID tend to be rigged at 3.6-3.8. A few people run them super hot at x4.

Also, the very first post in that thread is Majd’s test with a gun that has been sitting loaded for 45mins.


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There is a more interesting work on underwater ballistics ... this is an article by Filippo Anglani

 

[Vlanik]

As for efficiency, I hate to bring our Russian friend into this but his pistonless design is claimed to be 94% efficient. I don’t know how he came up with that number and how far behind a traditional oleo is (with no bulkhead).


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No need to guess ... Just take and count ...

 

[popgun pete]

Bluewater hunting means guns need to be rugged when thrown on occasion into the boat as there is not always someone to hand it to, they being busy elsewhere. Timber band guns are pretty rugged and finishes can be restored in the off season, not so sure about carbon fiber guns. Pneumatics can take a few knocks, but their thin wall tanks can get dented and scratched by people stumbling around on the boat. None of this matters if you don’t baby your gear, but when you have paid two grand for your gun you are less likely to throw it about. When hunting in anything can happen situations I take my timber band guns, if things are more controlled then I take my pneumatic guns as then I don't have to toss my guns around before getting back in the boat. At times you can have drop lines with clips over the side to hang your gun on, but that is not always practical. I don't use my pneumatics on pelagic fish as they (the guns) are not fitted with breakaway rigs.

 

[ECK]

Thank you PETE for the detailed information about "Alcedo Hydra"!
In fact, the time we have at sea is very expensive.
It is very a pity to spend it on unnecessary fuss.
hydropump without leverage will steal a lot of your time.
I saw how Oleg loaded his guns. And it was very fast!

 

[popgun pete]

There is no leverage on the Alcedo "Hydra" hydropump as it was originally an afterthought added onto the gun, the first guns had no hydropump. The idea was you muzzled loaded as usual and then boosted shooting pressure by using the hydropump. Later on it was realised that you could load the gun without much effort by opening a muzzle bypass ring at the base of the front barrel and then once the spear was inserted close that ring and then perform all loading motions using the hydropump. Someone modified the later "Hydra Sprint" model to use a lever system, but this was never offered as standard on production guns.

This gun being demonstrated by Alec Pierce was used as a prop in the Sea Hunt TV show. It has had the lever system fitted by someone who wanted to make hydropumping easier. The gun is the "Hydra Sprint" model.

 

[ECK]

How many interesting designs! It is very clearly visible that pneumatics was rapidly developing and engineering was in full swing. But then the brakes worked, and the world was filled with boring rubber guns.
One can say about this design - it, of course, is not perfect. It seems that engineers brought together many revolutionary solutions, but did not take care of ergonomics.
In this topic, it is very appropriate to show successful guns for hunting for bluefin tuna. And then consider their advantages and disadvantages.