Maths to check pressure?

[okamotoa]

new or used as long as its in good working condition

 

[Mongrel454]

I think he paid $140 aus for it.
So roughly $100us??

 

[onefish]

Mine cost $120USD from Divers Supply - Discount Scuba Gear - Serious About Your Fun, and Your Savings! (+ shipping within the USA). They matched the price of another online seller (that was out of stock, but I didn't tell them that). I had it shipped to my Mum in the USA who brought it out to me on her recent visit to Australia. The exchange rate is pretty good for us in OZ at the moment : ) Same gun is >$260 here.

This leaves me some $$$$ for pimping.

Cheers,
TJ

 

[Corsican diver]

Hello Onefish,

I see some potential problems about using a Tovarish kit on your gun, and a standard length shaft too.

First, I am not not sure the muzzle will resist to the combination of high pressure +
light shaft. With a dry barrel, more than 32/33 bars seem a bit risky..

Second, if the shaft has the same length as the 8mm shaft, it could be a bit light. If my Ministen has at a range of 2.5 m with 30 bars, I suspect it's because my shaft has some mass, and it's thin. I tried a 6.5 mm, standard length shaft : faster, but water was like an handbrake : no range. (1m 50 at best). And please, use a thin line too, to reduce the drag : 0.90 mm could be optimum. Then, you should replace it frequently, but on this kind of line, you can use simple knots instead of sleeves.

Third, if I understand things correctly, the Tovarich kit needs a binding of the line in the frontal part of the shaft. I fear you could have powerful shots, but no precision : this kind of binding tends to deviate the shaft, and it's worse with a short gun. You should try first on fixed targets first, IMHO.

Regards.

PS. Is there anybody kind enough to give me a link for Karamba/Tovarish kits ? I could not find one.

 

[onefish]

Corsican Diver,

You raise some good points. I have just done some checking online for mass of 17-4 SS, weighed my current spear and did some more maths. Stainless steel is heavier than other steels so it turns out that the 7.14mm SS spear in the same length as the standard 8mm spear is only 30g lighter. Including the slide ring and spring that I won't be using with the Tovarich. To get the same weight I need to add 90mm to the length. That's not too much so I may do this or use longer tips with more mass.

I also had concerns about the line connection at the front of the shaft pulling and reducing accuracy so I came up with a method that will be very hydrodynamic and pull from the rear of the spear with the Tovarich. I will use 1.6mm diameter dyneema kite cord that I already have (400lb test). There won't be any loops or knots to create extra drag, just straight line along the plane of flight. I'll post pics when I finally get it all together.

This is a link to a thread on the medfish forum that has some info on the Kara-yo and Tovarich kits.
http://www.medfish.com/forum/viewtopic.php?t=2577&sid=7ebac42ab9b1b45c4a8e11e54c05627b

Alternatively, Ramon has emailed me a catalogue. PM me with your email address and I can forward it to you.

Cheers,
TJ

 

[Groupermadness]

40 Bar... thats some feat, as far as i know the only limit the cressi has is its weak point at the trigger pin o ring, i had mine fly out with holding screw and a crap load of bubbles and it was not at 40 Bar, the gun itself is designed to self seal at high pressure, ie the more you put in the tighter it gets and then it will just literally go pop... Be carefull with them,

Peter.

 

[ulysses]

You fellas are correct, my gun is only SL55 currently with standard 8mm cressi spear. I have just ordered the Tovarich kit in 13 x 7.14mm (9/32) and I'm in the process of getting some custom spears made with line attachment as hydronamic as possible. SS spears in imperial measurements from the USA are much cheaper than metric ones in Australia.

I use the gun primarily for crayfish but still have to be able to nail a decent fish when I peak around a bombie and there's a big coral trout staring at me. It was a bit of a compromise, getting a gun short enough to reach around in holes and up under bombies, yet have enough grunt to nail a fish when required. The gun puts the spear straight through a trout out to about 2.5m but they have soft skin and small scales. The spear won't go through a parrotfish or bluebone at that range though. They have big tough scales. Mind you my tip is a bit blunt from shooting crays in the rocks.

I went for the SL55 because I figured that i could get it to be effective out to about 3m by using a dry barrel (am I wrong?). This is plenty of range for the type of hunting I do. The visibility is never too good anyway. If I want to catch big pelagics I troll a line out behind my boat. Likewise if I want to fill my big esky with reef fish I through in a handline.

But if I want crayfish...........................

The diving is also quite adictive. Last weekend my 8 year old daughter and I had a huge manta ray hang out with us for about 20 minutes. It got close enough to brush my daughter's leg. She was a little frightened until she found out it was nemo's teacher : )

I'm sure the Tovarich and smaller spear without slide rings will increase speed. I'll probably drop the pressure back to about 30-35bar after.

Cheers,
TJ

Sorry, onefish but IMO you bought a good kit (Tovarich) for the wrong gun (SL55). A 55cm airgun is good for cave hunting (I'd prefer a 70cm) and close range shoots only. This 'pistol' type of airgun is not versatile and regardless of the power you put in it will never be any good even for intermediate distance shots (erratic targeting guaranteed).
The Tovarish is something to upgrade a 90cm and longer airgun, but totally wasted and even detrimental to the potentially good use of your SL55 for cave hunting.

Cheers
ulysses

P.S. I am just curious: Did Ramon understand that you ordered the Tovarich kit for a 55cm gun??

 

[ulysses]

I am still dumbfounded from learning that the airgun in question is a SL55! 40 bar? / Tovarich? :naughty

To relay some advice as to the proper use of this type of gun: Fabio Antonini once won the Italian National Spearfishing Championship hunting exclusively with an Omer Tempest 50. However, he had it at 15 bar and (apparently, not so needless to say) he used a multiprong.

Cheers

 

[Old Man Dave]

Just guessing here but I think you may have the wrong gun for the job and no amount of pumping up the pressure will make it do what it's not in its nature to do.

Dave

I think I was right.

Dave

 

[Corsican diver]

Hello Ulysses.

My opininion is a bit like yours, about the length of the gun, but not completely , for some different reasons.

First, you are right, "barrel-sealing-kits' are more efficient on longer guns. Just because, I think, the column of water to expell is longer for the same diameter, on long weapons. But this doesn't mean there will be no improvement, but just less improvement.

Second : There is a test on the Maori site, and a test by the engineer I spoke above, (again in Italian, sorry, but after all, they are the makers.) that shows that the speed of the shaft, with a 70cm gun, is good at 4 meters. Precision seems nice too. And all this with a 6.5mm shaft, speed conservation will be better with a 7 mm one.

Third : on bandguns, a 1m shaft is propelled by the latex tubes on a length of 50 cm or less... Don't forget that when the bands are almost retracted, their energy falls dramatically.

So, I think a 55 cm gun, which will push strongly the shaft on 50 cm, could be tested with an 80 cm shaft or even a bit longer.

It will become front-heavy : a small wooden horizontal stabilizer can improve this. I think this kind of gun can be less visually impressive for the fish, but effective.

Last thing : the arrow must be guided by the line-drag. When the shaft goes out of the gun, the line must be installed properly, to act as an axial stabilizer. It must be just behind the shaft, not laterally positioned.

Regards.

 

[Corsican diver]

Oh, I forget to tell you : the tests on the 70 cm gun are conducted with pressures from 18 to 25 bars, with a sealed barrel.

Cheers.

 

[Corsican diver]

I forget two important points : the 70 cm guns tested were "sealed-barrel" types, and the test pressures were comprised behind 18 and 25 bars.

Cheers.

 

[Corsican diver]

Ok, double message.. bugs ?

 

[ulysses]

Hello Ulysses.

My opininion is a bit like yours, about the length of the gun, but not completely , for some different reasons.

First, you are right, "barrel-sealing-kits' are more efficient on longer guns. Just because, I think, the column of water to expell is longer for the same diameter, on long weapons. But this doesn't mean there will be no improvement, but just less improvement..

Hello CD,

Efficient in what way? If you are into this sport for some time and have ever used a 55cm airgun you will appreciate that this type of gun is designed for shots in caves at point blank range. Any increase in power either by installing a sealing kit or simply be increasing the pressure is absolutely counterproductive! If your style of hunting requires more range, get another gun.

BTW: Talking about the efficiency and the designated purpose of a 55cm airgun ... with a standard 8mm threaded shaft, a multiprong and pressurized at 15-18 bar this is probably the most efficient gun for cave hunting. It is actually the terrible efficiency of this set-up that persuaded me to abandon this type of airgun altogether. If you are into competitions this may be a winner, however, a true sportmans will give the fish a chance.

Second : There is a test on the Maori site, and a test by the engineer I spoke above, (again in Italian, sorry, but after all, they are the makers.) that shows that the speed of the shaft, with a 70cm gun, is good at 4 meters. Precision seems nice too. And all this with a 6.5mm shaft, speed conservation will be better with a 7 mm one.

It is quite some time since I read the article/report by Anglani which was published in 'PescaSub' last year. However, I don't recall any reference to the accuracy of the Mambas, Mamba-kited and standard airguns tested for the report.

Furthermore, you do recall two things: i. no airgun below 70cm was tested; ii. no Mamba-kitted gun (max pressure 25 bar) will be more powerful than a standard gun at 40bars.

Third : I think a 55 cm gun, which will push strongly the shaft on 50 cm, could be tested with an 80 cm shaft or even a bit longer. It will become front-heavy : a small wooden horizontal stabilizer can improve this.

rofl A small wooden stablizer on a SL55 in order to counterbalance an extra-long tathian shaft ... Sorry, rofl please confirm if you have ever used this type of gun ...

Last thing : the arrow must be guided by the line-drag. When the shaft goes out of the gun, the line must be installed properly, to act as an axial stabilizer. It must be just behind the shaft, not laterally positioned.

Again, off the mark for a 55cm gun (same as the 0.9 mono advice earlier). The Italian champ I referred to earlier uses a single wrap of 2-3mm braided line on his Tempest 50, and so did I when I was more into cave hunting than nowadays. Don't worry about balistics on a hole gun (in French: 'rageur'), chaving and fraying of the line and quick shaft/fish retrieval is the cave hunter's main concern - and shaft retrieval will be problematic on a Tovarich kitted gun (due to the line attachment in the front tier of the shaft).

Amicalement
ulysses

 

[azapa]

i can kinda see the use/need for that Corsican explains, and I have the same need:

poke around caves all morning, pop up, nice fish 2M away. I have asked them to wait until I fetch and load my Cayman 90, but they never seem to listen..

I love my Asso 65 for caves and weedy areas, i use with three loops and have taken fish 2 to 3M away. Long guns are so clumsy and counterproductive in these situations.

I must state that as standard my gun seems very powerful and easy to load, I have taken 7Kg grouper with it, i really don't feel the need to go to a sealed barrel conversion.

 

[Corsican diver]

Ulysses,

the length of your answer, and some clues in it can make me think you took my message as a kind of insult. I sincerely apologize, this was not what I wanted to do. Anyway, if I don't answer your last post, I'll be seen as perfectly ridiculous. Let it be. Perhaps this was the purpose of it, perhaps not. Anyway I could continue the discussion, but I prefer to pronounce a self-inflicted banishment from the forum. For life, needless to say.

Cheers.

 

[Old Man Dave]

You made some good points Corsican and have nothing to be ashamed of. These forums are generally friendly places but they would be pretty boring if everyone held the same views, so don't go - we'd miss you .

Dave

 

[onefish]

Well looks like I started some contraversy here. I researched a fair bit prior to getting the 55 gun. As mentioned it was a compromise, on both sides. It's already proven too long to get at some crays but I can get to most. And it's never going to be a longer range cannon. As mentioned I am only hoping to be able to shoot out to about 3m maximum and the majority of shots at fish are much closer. If that's not possible then I will use the gun within its limitations.

My logic is as Corsican's. The Tovarich will improve performance, albeit not as much as it would improve the performance of a longer gun.

On the question of accuracy, I am no expert but I believe I have come up with a system of line attachment that will allow the best speed and accuracy possible with the Tovarich and shorter spear. Exactly how good that is, I will have to test when it's all together. I will add ballast if needed. I don't shoot little fish anyway and fairly close range so I don't need pinpoint accuracy (I do need to hit them though : )

Now testing at the town pool might be a bit tricky................. (plenty of targets though)

Cheers,
TJ

 

[onefish]

This thread is getting off topic a bit but there have been some interesting questions raised and I, for one, would like to explore them a bit further. I'll start a new thread if anyones interested.

Cheers,
TJ

 

[okamotoa]

i am...4 1 at least