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Question about the Hydro - dynamics of the spear

Menny1975

New Member
Jul 8, 2018
4
1
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44
Iarsel
Hi guys,
I need your help.
I'm using the 125 Merlin Beuchat speargun, with two 5/8 speargun rubber tubing, and a 6.5 m"m spear.
Recently, there is a strange noise during the shot and the shots are not accurate.
I have two questions:
1. what could be the problem?
2. Are there any basic rules for a clean and a hydrodynamic shot In terms of the mechanism of the speargun?
Thanks, Menny.
 
Last edited by a moderator:

Mr. X

Forum Mentor
Staff member
Forum Mentor
Jul 14, 2005
7,310
1,385
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Sunny Britain
Beuchat Marlin speargun?
Is the spear straight? It the flopper/barb straight, properly seated and freely pivoting?
Metal wishbone?

 
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Menny1975

Menny1975

New Member
Jul 8, 2018
4
1
3
44
Iarsel
Hi Mr. X,
Yes it's a beuchat Merlin speargun, the spear is straight ( a brand new one I just bought ) and the wishbone is from Dynema, not metal. Sorry for my ignorance... but what is the flopper/barb?
 
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Mr. X

Forum Mentor
Staff member
Forum Mentor
Jul 14, 2005
7,310
1,385
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Sunny Britain
Have you tried using just one band? Perhaps the 2x16mm bands are over-powering it, causing it to flex/whiplash?

For example, the Rob Allen railguns equipped with 2x16mm bands have thicker spears (e.g. Tuna model has a 7.5mm spear, ref. https://www.spearfishing.co.uk/shop/spearguns/rob-allen-spearguns-tuna-railgun/ ). Their Sparid model has a 6.6mm spear with 2 notches and a double-rubber muzzle but it is only equipped with 1x16mm rubber.

e.g. This chap is using a Beuchat Marlin with 2x16mm but a 7mm spear:

e.g. This Beuchat marlin with "2x17mm" (17mm :D) comes equipped with a 7mm spear as standard:
 

SubSub

Well-Known Member
Aug 26, 2015
487
183
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Stockholm
Yes. To me a 6,5mm spear on such a long gun seem on the lower side.

If you try to hook it up with 14mm small ID bands and start off with a lesser stretch on the bands and work your way up so to say, to see how far there is a increase in accuracy and where the decrease starts.

The flopper is the thing that sits close to the top of your spear, the thingy that flops out and keep the fish on the spear.

 
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Menny1975

Menny1975

New Member
Jul 8, 2018
4
1
3
44
Iarsel
Aha...so now I know what the flopper is :) . Well I'm using a new shaft so it's not the cause of the recoil and the inaccuracy.
Yes the matter of the over power make a lot of sense to me, I could definitely feel it when I shot.
So first, I'll try a 7m"m shaft for those two 16 m"m rubber bands and update you how it went :giggle:.
Thank you very much!
 
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Menny1975

Menny1975

New Member
Jul 8, 2018
4
1
3
44
Iarsel
Hi guys.
I dove todays morning.
Fixed my speargun with 2 rubber bands 5/8 and a new 7 m"m stainless steel shaft.
I shortened the rubber bands according to this formula: Distance between the rubber hole and the notch divide by 1.5.
So the longer one is: 124 : 1.5 = 82.7 c"m
And the shorter one is: 118.5 : 1.5 = 79 c"m
The shots were quite accurate and the sound or recoil were not presented. Now my question is, should I shorten them even more to get a greater power?
I'de love to try Subsubs suggestion with the 14 bands as well, but what their length shoud be? Is it same as the 16 bands? My logic tells me they should be shorter.
 
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