Rob Allan 1500 Carbon Tuna gun!!

[shaneshac]

Hey Rob,

Thanks for your input. It is always more than welcome

I have been chatting to the Euro Master Dapiran who has been testing 8mm spear and 7mm spears for his new MegaJedi. He has also been playing with slighter longer thinner spears comparing them to shorter fatter spears of the same weight.

His results were similar to yours and due to the slimmer profile the shaft carries greater speed and more penetration.

What i think is important is where you hit the fish. I am sure that a 6.5mm spear with enough speed can go through the soft flesh of a whole 300 kilo tuna, but if it touched bone i believe the thicker spear would give you better penetration.

I will currently receive a nice woody which i will mount with 3x16 and a 150cm 7mm spear and compare it to my other woody that has a 3x18 and 140cm 8mm spear (both same length guns and spears weigh roughly the same). I will tell you what does more damage

 

[Rob Allen]

What i think is important is where you hit the fish. I am sure that a 6.5mm spear with enough speed can go through the soft flesh of a whole 300 kilo tuna, but if it touched bone i believe the thicker spear would give you better penetration.


Why should it? Remember their weight is the same but the longer spear is travelling faster? It should go through thicker bone then?

Rob.

 

[shaneshac]

if a thin spear hits a hard spot it will flex. A harder spear will not. This is my theory and have not proven it. The flexing would cause the kinetic energy to be sent sideways and not keep behind the spear.

Again, this is a theory.

 

[Rob Allen]

Good point, quite possible, pity it is not something we could test easily though.

I have a big pool at home where we do testing, all I need now is a large tuna!

Rob.

 

[shaneshac]

Get a thick hard rubber block and shoot it with both spears from same gun.

One that allows penetration but is quite dense.

This should be enough to decide the winner.

 

[Rob Allen]

That will show penetration but not how much the spear will deflect if it hits bone. I can make it easy with a broom stick inside to simulate a spine but to simulate an edge shot at the same angle with both spears will be very difficult.

Rob.

 

[shaneshac]

I am sure that if the rubber is hard enough the thinner spear will flex more than the thicker one. NOt hard enough to dull the spear but enough to only allow a few cm penetration.

Also good to test from a distance as a very high shaft speed will cause more flex and at 4m or so the speed will have dropped and the difference may be negligible

 

[Rob Allen]

I am sure that if the rubber is hard enough the thinner spear will flex more than the thicker one. NOt hard enough to dull the spear but enough to only allow a few cm penetration.

I fully agree, this is why we don't promote thick strong rubbers for 6,6mm spears, I think anything stronger than a 16mm will cause inaccuracies.

Also good to test from a distance as a very high shaft speed will cause more flex and at 4m or so the speed will have dropped and the difference may be negligible

We have done this test, a 6,6mm spear penetrates better than a 7mm spear off the same gun at close range, about 1/2 a spear length away from the gun. As soon as the range is increased the 7mm then penetrates better.

Rob.

 

[Murat]

I am using 6.25mm shaft with omers power 18mm bands and i think its as accurate as speargun could be. The barell length 110, spear length 150, bands length 32cm, wooden body with spear guide.

 

[shaneshac]

Thats the setup i was using when i shot a 30K+ grouper in the head at point blank range

Suffice to say there was very little penetration

 

[Memo]

I dont know really guys, the idea of using same mass with a thinner shaft is logical but also the words of shane about the rigidity of thick shaft is really important. For now i am on the thick side..

 

[Murat]

flexibility is also something due to the content of the steel. E.g Cressi 6mm shaft does flex much more less than omer's 6.5mm.

 

[Rob Allen]

Agreed Murat,

That is why we picked up our steel spec to 2100 MPA.

Rob.

 

[Ted Budion]

Let me add more fuel to this discussion :t Rob and Shaca are in the good path, however, the point I raised relates more to practical use than to the mechanics and ballistic of the shot.

When shooting big pelagics, more so tuna, firstly, one must take the best care of the terminal gear: shooting line/cable, float line/bungees and floats and their connecting points. :duh It may seem obvious, but Rob can attest than at least one marlin world (shot with a regular eurorig) was lost due to faulty or weak terminal gear (and the fish was dead next to the boat!).

On the pratical side itself. Tuna specifically, very few people live near tuna spearfishing grounds or can afford travelling to them. Therefore, the few whom can must maximize their odds in landing a speared fish. Not to mention the ethical side of it. Travel restrictions nowadays are such that an already heavy-loaded passenger, like the travelling spearo, will pay an outrageous surcharge for excess weight. Man, gone are the days of carrying 4 guns and 20 shafts. :waterwork What you'd save buying carbon steel "expendable tuna shafts" you'd pay for excess luggage. :hmm Trust me, I know for personal experience,

I'd love to shoot big tuna with a 6,6 mm shaft and one 16 mm band, not worrying to bend them in a week's trip, for example. But unless someone proves me otherwise, the odds of loosing or bending shafts when using a thicker shaft with sliptip are much smaller than with a regular Tahitian shaft.

If in this equation you change tuna for other big pelagics, the odds are even smaller. OTOH, if I were living and hunting tuna in Cape Town, I wouldn't hesitate in trying Rob's light weight solution, afterall I wouldn't pay excess charge in the bakkie and one carbon steel shaft costs 5 times less than a stainless thicker shaft with slip-tip

 

[Rob Allen]

Agreed Ted,

We found the float and rope system was more critical. We know of 4 marlin believed to be over 1000 pounds lost after being subdued but not able to hold in the water and just sank away, very wasteful.

Rob.

 

[shaneshac]

Ok, so what do you suggest then Rob?

What would be your ultimate pelagic monster setup?

 

[Rob Allen]

That is like asking "what is the best car to use off road?" Every one has their personal preferences and ideas.

Unfortunately for the passed 15 years I seem to only dive with gear that I am experimenting with. I therefore don't get to dive with standard gear any more. I recently used a 1,5m carbon rail gun with a new, high tensile 6,3mm spear, driven with an 18mm rubber. It was extremely light and in pool tests showed it needed 85 grams of lead in the muzzle to get it to be neutral in the water.

I only had 3 hours in the water and was hoping to see dog tooth. I still needed to test the rig so shot cuta (Spanish mackerel) and wahoo with no problem. As I got out the water with a wahoo, a 44kg doggie was shot. I had planned to go back with a bigger set up, double 16mm rubber, 7,5mm spear but the trip was cancelled.

Rob.

 

[shaneshac]

What rig were you using.

I mean, bungee, floats, line and sliptip used.

Which would you use if you had to shoot a 300k tuna. I want your personal option if you dont mind

 

[Rob Allen]

We were lucky where we were diving, the reef comes up to 10m and has a very gradual slope out into the deep. We were diving in 25 to 30m using float lines about 25m with a short boingie and an 11 lt float.

The wahoo and cuta were not a problem but the dog tooth took the float for +- 2 km before it surfaced. Where it stopped it was only in about 40 m and the float pulled it up no problem. On any normal dog tooth drop off type spot I doubt we would have seen it or the gear again but here, being shallow and with no sharks to speak of was easy.

The boogie board system Tommy is using seems to be the way to go. Many large fish including a 100 kg marlin have been taken using it. The problem I believe with these big tuna is the lifting of the fish once it has died. The board has a lock system allowing you to pull in line and then rest up. My only crit of the board is the drag if it gets pulled under. This can cause a bad shot to pull out more easily.

We have been setting guys up with multiple floats and break away lines. The amount of floats and lines are up to the customer to decide, each have their own idea. Guys have been successful with 30m float line from the gun, 5m boingie to an 11 lt foam filled float followed by a 35 lt inflatable with one of our speed pouches. This has a 40 m line in it that breaks out at about 10 kg of pull. The boingie stretches to 25 m at around 10 kg. The 11 lt will go under at just above that force and the break the away line will deploy straight after.

This set up is not much drag and just over 30 m long. It is possible to include another 40 m break away in front of the 11 lt, behind the boingie. This will give over 150 m of line to play with.

The only difference I'd personally do is, use a 15m float line with a 2 m boingie straight behind the gun with a 10 m boingie on the other end of the 15 m line. Then the 11 lt with speed pouch and 35 lt float after.

Pre the making of the 35 lt floats we had one customer who wanted and used a set up with 3 x 11 lt with 2 x 30 m pouches breaking away on each. He used a 40 m line and a 5m boingie. this was a total of around 240 stretched!

Rob.

 

[shaneshac]

AWESOME!!!

Thanks.

Yeah, tommy and miles seem to have it all down to a fine art these days, although a 300k atlantic bluefin might require an even more robust setup