Tomba - All in One barrel sealing

[Don Paul]

f I had the picture of it with measures I could maybe make one tomba for you. I would like you to try tomba. I just make it for fun, anyway.
Cheers, tromic

Thanks tromic, I'll try to order that part from Omer and send it to you if you PM me. I would like to pay you for your time and materials as well. (PM a add)
I had the Nitrobalete in the sea again on Mon shooting it at 30 bar with a 7mm shaft and two full wraps of black 300 # outrigger mono. Even though I
had the drag on the reel set to medium ( I'll test lbs pull with scale wet)
a shot at a 4'' top smelt pulled 4' from the reel. I am very happy with the guns performance but I will still like to tinker a bit with power this winter
after my game fish season ends. No I did not hit the skinny bait fish 15'' of the tip, but that was the shooters fault.
All the best, Don

 

[tromic]

This is a knot for the line slider for tomba:

The Nail Knot

 

[Don Paul]

Great link tomic, I'll try that knot after work tonight. I will be talking to my Omer dealer Fri to order some Airbalete parts that I will ship to you.
I plan on getting a few extra 7mm microspeed sliders to re-engineer with a 17/4 sleeve/ line anchor of less mass. The stock cast microspeed with the
front mounted dimple/hump puts the line in a prime location for cuts by bones when making head shots on big fish. Not that big fish can't be landed as is. I plan on designing a more hydrodynamic approach than has been shown on the Airbalete thread by Mark labocceta.
Three of the Microspeed sliders I have inspected are a big improvement over the big cross sections of the old plastic type, but they were never designed to support the 300 lb mono I am rigging with currently. The inner machining of the Microspeed slider bores i have inspected show a less then ''Micro'' metal finish. The part is most likely cost efficient to investment cast rather the machine from 17/4 and heat treat.
Cheers, Don

 

[tromic]

A DB member asked me if it is worthy to have vacuum barrel (Tomba) on the pneumatic gun (Cyrano).

I asked him:
Is it worthy to have about 45% better performance: vacuum barrel (min 25%) + more hydrodinamic parts on the shaft (min 20%)?

This is true for the majority of pneumatic guns. For Airbalete performance could be better "only" 25% in shallow water. In deeper water more.

 

[foxfish]

25% is a very worthy increase indeed but 45% is amazing!
Everybody should own a Tomba...

 

[tromic]

25% is a very worthy increase indeed but 45% is amazing!
Everybody should own a Tomba...

Other kits are good too: tovarich, karayo, karamba, STC, mamba is not so hydrodinamic on the shaft.

 

[tromic]

This is a Croatian link. Tomba in action on Seac sub Hunter 50!
[ame="http://podvodni.com/forum/showthread.php?t=6515"]Podvodni ribolov i ronjenje na dah[/ame]

Seac Hunter 50 with tomba on 15 Bars. Shaft 7 mm. Shooting distance 2 m.

 

[Don Paul]

Thanks, Don.
I could make a replacement for this part of the Airbalete muzzle:

If I had the picture of it with measures I could maybe make one tomba for you. I would like you to try tomba. I just make it for fun, anyway.
Cheers, tromic

Just a update, still waiting for the part from Omer tromic.
Cheers, Don

 

[tromic]

I did a new comparison: Tovarich to Tomba.
Same harpoon (Cyrano factory), shaft (Devoto 7 mm), line (mono 1,7 mm), distance (5,2 m), pressure (25 bars):


I made Tovarich max hydrodynamic with this harpoon.


I lost the picutre of the tomba setup. It was without the metal taper ring.

And the result was same for both. I used Devoto slider with the Tomba because I had 1,7 mm mono line.

I also compared the factory set of the Cyrano 850 (original Mares slider, original black line) to the tomba set. The difference was huge: 36 x higher energy at 5 m distance from the gun and on 25 Bars, 6 x higher speed of the shaft. Not all thanks to tomba vacuum barrel but the all setup made the difference.

 

[tromic]

I also measured the influence of mono line thickness on the energy of the shaft.

Gun on 25 bar (Cyrano 850 - Tomba)
Distance from top of the muzzle to the front end of the shaft: 5.2 m.
Airbalete shaft: 7 mm/100 cm

With mono line 1.7 mm I had 3.6 J on 5.42 m
(0.22 m is additional stretching of the mono line and the rubber tubing used for measurement)

With mono line 0.8 mm I had 9.6 J on 5.75 m
(0.55 m additional stretching)

With mono line 0.8 mm I had 2.68 x more energy (168% more) of the shaft than with the 1.7 mm mono line!

So, if possible one should use thinner line on his gun.

 

[tromic]

Same gun, with vacuum barrel (tomba), the gun is noticeable more quiet than with water barrel? I am not sure how to explain this.

 

[popgun pete]

For there to be less noise from a pneumatic speargun the piston has to strike the shock absorber anvil or stopper with a lower impact speed. But if the speed of the shaft from the vacuum barrel gun is equal to that from a wet barrel gun operating at a higher chamber pressure compared to that of the vacuum barrel gun then you would expect the respective pistons to hit the stopper at the same terminal velocity. I think that if the noise reduction is real then the answer may lie in the final moments before the piston hits the shock absorber stopper. Initially the inner barrel of a "Mamba" modified gun has a relative vacuum inside it after the gun is muzzle loaded, but as the piston advances along the barrel during the shot the vacuum condition lessens as the barrel volume in front of the piston rapidly reduces. At some point the vacuum may fall off enough that the sealed slider is dragged by the shaft out of the muzzle causing a backflow of water into the gun. This water entering the muzzle may reduce the piston impact if it occurs over the last few centimeters of barrel travel, particularly if the water traveling rearwards has some velocity due to suction. This is about the only mechanism that I can think of to explain any degree of noise reduction with these guns. With no slider this mechanism cannot occur unless the seal on the shaft is broken at some point in the spear's travel along the barrel. It would be interesting to video in slow motion a vacuum barrel gun firing and determining at what point the sealed slider leaves the muzzle compared to how much of the shaft length has emerged from the gun.

A wet barrel gun that has had the water tipped out is quite noisy, especially if fired when pointed straight down. I have noticed it when for some reason I have had to lift the loaded gun from the water, but kept the muzzle inclined downwards for obvious safety reasons, while traversing over a very shallow section before re-entering deeper water.

 

[tromic]

I had got an answer that the main reason was closing the holes in the muzzle which are very close to the shock absorber where the noise is generated. Also there is no water turbulence from water escaping the muzzle. Rubber tubing also reduces the noise.

 

[foxfish]

It appears to me the rush of aerated water exiting the barrel of a conventional gun is responsible for at least some of the noise - my mambas are definitely a lot quieter to fire.
I guess it could be an illusion to some extent, mambas are so much smoother to fire anyway it might just be it seems quieter?

 

[tromic]

This is idea for my new Tomba - MiniTomba:



Uploaded with ImageShack.us

This will work without the plastic ring on the shaft. The o-ring in contact with the taper metal ring lies on the taper part of the adapter.

I expect lower friction during loading - easier, smooth loading, better sealing, still more hydrodynamic ...

 

[popgun pete]

The abatement of noise from the vacuum barrel system may also be due to the absence of the muzzle relief ports which act as windows in a standard muzzle. These ports allow a direct transmission path of sound waves from the piston to shock absorber stopper impact zone out into the surrounding water through these windows. Sound also transfers through the body of the muzzle and the rest of the gun, but by closing the muzzle ports off the transmission of higher frequencies may be inhibited compared to lower frequencies, so the character of the perceived noise will change even if the impact energy is exactly the same. This would result in a more subdued noise from the gun. Often a sound will appear louder when in fact it is just the changed nature of the spread of frequencies in that noise compared to those in another noise of the same sound level.


The size of the muzzle relief ports does not seem to be a factor, the small relief ports in my original model "Sten" do not stop it from making a lot of noise, however it does have a metal piston which may have some effect as well. I have never conducted a shoot off with a number of guns to compare them directly on one dive, so have no direct comparisons to draw from, I am usually too busy looking for fish to load up a second gun if I am carrying one.

 

[popgun pete]

This is idea for my new Tomba - MiniTomba:


This will work without the plastic ring on the shaft. The o-ring in contact with the taper metal ring lies on the taper part of the adapter.

I expect lower friction during loading - easier, smooth loading, better sealing, still more hydrodynamic ...

If this new arrangement is muzzle loaded in one motion then the "O" ring will tend to stay against the tapered adaptor sitting in the muzzle as the shaft slides through the both of them, but will the "O" ring stay against the adaptor if the shaft moves forwards at all during loading? There is not much of a cross sectional (annular) area for a pressure differential to act over and hold the essentially free floating "O" ring in place before a sufficiently high vacuum develops in the inner barrel. A larger diameter sealed slider offers a greater annular area for the pressure differential to work over and is more likely to stay in position in the muzzle during loading. Ideally you need to hold the "O" ring captive against the adaptor so that the shaft has to travel through it even if the shaft moves forwards slightly. The adaptor that I am referring to is the rear tapered slider (darker green or teal colour), not the muzzle adaptor "nose" that screws into the muzzle.

 

[tromic]

If this new arrangement is muzzle loaded in one motion then the "O" ring will tend to stay against the tapered adaptor sitting in the muzzle as the shaft slides through the both of them, but will the "O" ring stay against the adaptor if the shaft moves forwards at all during loading? There is not much of a cross sectional (annular) area for a pressure differential to act over and hold the essentially free floating "O" ring in place before a sufficiently high vacuum develops in the inner barrel. A larger diameter sealed slider offers a greater annular area for the pressure differential to work over and is more likely to stay in position in the muzzle during loading. Ideally you need to hold the "O" ring captive against the adaptor so that the shaft has to travel through it even if the shaft moves forwards slightly. The adaptor that I am referring to is the rear tapered slider (darker green or teal colour), not the muzzle adaptor "nose" that screws into the muzzle.

Right Peter!
The boring in the adapter to the muzzle, before the taper, is such in ID that also seals the O-ring sufficient for short term sealing. Final sealing is in contact with the taper and the metal sliding ring.

 

[tromic]

New MiniMicroTomba:



Uploaded with ImageShack.us

 

[tromic]

This is a new type line slider for use with the Tomba (lower image):



It could be used with the fishing wire when fishing big, strong fishes.