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Old 10-07-2019, 03:52 AM   #1
Andersp90
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Moving sharkfins further back on spear?

Would there be any problems linked to moving the sharkfins 3,5 cm back on the spear shown in the picture? The gun is a bleutec simple carbon 75.

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Old 10-07-2019, 04:41 AM   #2
Mikel_24
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Re: Moving sharkfins further back on spear?

As long as you can still load it comfortably, there shouldn't be any problem.

How do you plan on doing it? Do you have the tools and skill to cut and shape a sharkfin and tig weld it in place without distorting the shaft or ruining the heat treatment in the process?

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Old 10-07-2019, 06:46 AM   #3
Mana'squal
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Re: Moving sharkfins further back on spear?

Quote:
Originally Posted by Mikel_24 View Post
As long as you can still load it comfortably, there shouldn't be any problem.

How do you plan on doing it? Do you have the tools and skill to cut and shape a sharkfin and tig weld it in place without distorting the shaft or ruining the heat treatment in the process?

Mikel
Wouldnt the easiest way be just to cut the shaft and shape a new notch with a file or paper?
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Old 10-07-2019, 09:30 AM   #4
Andersp90
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Re: Moving sharkfins further back on spear?

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Originally Posted by Mana'squal View Post
Wouldnt the easiest way be just to cut the shaft and shape a new notch with a file or paper?
That would be the easiest DIY fix, but it would also mean a loss of mass.

The spear shown in the picture is from hunt, and I hope they will make me a custom one.
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Old 10-07-2019, 09:31 AM   #5
Mana'squal
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Re: Moving sharkfins further back on spear?

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Originally Posted by Andersp90 View Post
That would be the easiest DIY fix, but it would also mean a loss of mass.



The spear shown in the picture is from hunt, and I hope they will make me a custom one.

If you’re worried about 3cm of half diameter shaft mass loss I would think a custom shaft is the way to go.
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Old 10-07-2019, 09:46 AM   #6
Mikel_24
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Re: Moving sharkfins further back on spear?

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Originally Posted by Mana'squal View Post
Wouldnt the easiest way be just to cut the shaft and shape a new notch with a file or paper?
If the shaft is currently sized so the barb rests on the muzzle (or about to), shortening the shaft by 30mm could be a problem.

I know that in three of my guns I wouldn't be able to do that.

Easier way to add a pin further back would be to file a flat, center drill a divot, drill through with a slight backwards angle, countershink sligthly on the bottom, insert round pin all the way and now you have two choices:
1- Hammer the crap out of the pin on the bottom so as to mushrom it and molde it to the countersunk divot and sand flat.
2.- TIG tack weld and sand flat. This is much easier than trying to weld a sharkfin tab on top and a light tack will not distort the shaft much.

Mikel
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Old 10-07-2019, 09:52 AM   #7
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Re: Moving sharkfins further back on spear?

Depends on your shaft diameter and how your muzzle deals with bands. The lighter the shaft the more problematic it is with these super maxed out back shark fins. By the way I don't consider the Hunt shaft in the picture as "maxed out". If they were maxed out you need to drop your band load to around 310% or 320% ... but certainly no 360%+ ... unless you are using 8.5mm or heavier shaft.
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Old 10-07-2019, 10:00 AM   #8
Andersp90
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Re: Moving sharkfins further back on spear?

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Originally Posted by spearq8 View Post
Depends on your shaft diameter and how your muzzle deals with bands. The lighter the shaft the more problematic it is with these super maxed out back shark fins. By the way I don't consider the Hunt shaft in the picture as "maxed out". If they were maxed out you need to drop your band load to around 310% or 320% ... but certainly no 360%+ ... unless you are using 8.5mm or heavier shaft.
Its a 105 cm 7mm spear. Shouldent it be more resistent to whipping compared to a 150 cm shaft of the same thickness?



My muzzle looks like that. The spear is resting in a shallow track, milled into the carbon.

Last edited by Andersp90; 10-07-2019 at 10:36 AM.
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Old 10-07-2019, 11:23 AM   #9
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Re: Moving sharkfins further back on spear?

Anders,
If there's really that much overhang on the shaft, then chop of the end - it's 3grams loss of mass we are talking...
(The guys were talking about e.g. a stock Pathos setup where the barb is on the underside of the shaft but the shaft is minimal length and the rear tip of the barb lies in a small pocket on the muzzle itself.)

As for the TIG option, it's obviously a great idea if you have someone who can do it well. But... I think Mikel could also be guilty of what I often am, which is a spoiled 1st world thinking where we tend to overthink things. I would have agreed with him until a few months back when I saw an Indonesian home builder move sharkfins on one of my shaft and some of his own. Fancy Euro shafts out of 17-4ph and some home cut SS fins but he used a simple, Chinese stick welder, and some nice grinding and polishing and the end result was stunning. I am fairly sure, he hasn't had one fail and he has done this for years. But maybe with the big fish there, he bends the spears into retirement before a sharkfin would fail.
Yes, you have to straighten the spear afterwards and yes, you probably weaken it a little. And no, personally, I wouldn't do it on a brand new Hunt shaft, haha. He does rinse them out nicely after each dive and tend to keep them oiled as the new fins are not as corrosion resistant as the original ones, I think.
I am not dissing Hunt, GR and the other great shaft builders here - obviously doing it the 'right' TIG way is to be preferred!:-)

Personally, if I don't have a good TIG dude I could ask to do it, I would cut it down and loose the 3g...

Last edited by Diving Gecko; 10-07-2019 at 11:37 AM.
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Old 10-07-2019, 11:31 AM   #10
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Re: Moving sharkfins further back on spear?

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Originally Posted by spearq8 View Post
Depends on your shaft diameter and how your muzzle deals with bands. The lighter the shaft the more problematic it is with these super maxed out back shark fins. By the way I don't consider the Hunt shaft in the picture as "maxed out". If they were maxed out you need to drop your band load to around 310% or 320% ... but certainly no 360%+ ... unless you are using 8.5mm or heavier shaft.

Not sure I got this...? You mean, if the sharkfins were further at the rear, then 360% would overpower the shaft? But as the fins are now, 360 is ok? Not sure that makes sense to me, as 360% on a more rearwards fin should give the same amount of max power - but a longer pull, no? Prolly just me misunderstanding something
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Old 10-07-2019, 01:37 PM   #11
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Re: Moving sharkfins further back on spear?

If you put the shark fin tab back to the leading edge of the sear box then it will be all too easy to bounce the wishbone off the top of the sear box roof and miss the tab when using metal wishbones as the wishbone jerks forwards. Back in the old days wishbone notches were hand cut right back to the sear box mouth, mainly because band rubber was not that great (it tended to not recover), but it was not long before they were positioned further forwards again. If you added a long cocking stock then you could move the drop in position forwards again, but why bother? Spears are made to be interchangeable to some extent and sear box roofs vary in length, so that is why notches/tabs are forwards from the tail end.
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Old 10-07-2019, 04:27 PM   #12
RichT
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Re: Moving sharkfins further back on spear?

You have a picture of a long tang euro shaft in a short tang euro mechanism.
There is a tremendous amount of wasted length of shaft not being utilized which results in much less band stretch.

Some gun makers use long tang mechs and some use short tang mechs.
The trend is moving toward short tang mechs as you gain significant band stretch if the shaft is properly made where sharkfins/notches are placed as far rearward as possible.

Another trend I see that I strongly disagree with is spot welding of sharkfins instead of fully encapsulating the sharkfin.

I suspect these European shaft manufacturers are only spot welding the fins on in order to minimize warping of the sharkfins and warping of the shaft from the heat of the welding.
By doing this they save time straightening the shaft.

Unfortunately you end up with a sharkfin that isn't nearly as strong and one which will trap saltwater under it. I suspect longevity may also be an issue...
I have already seen several of these types of sharkfins broken off btw...

Last edited by RichT; 10-07-2019 at 04:57 PM.
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Old 10-07-2019, 04:43 PM   #13
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Re: Moving sharkfins further back on spear?

Quote:
Originally Posted by Andersp90 View Post
Would there be any problems linked to moving the sharkfins 3,5 cm back on the spear shown in the picture? The gun is a bleutec simple carbon 75.

Hey Anders!
pics below of Hunt 8.5mm shaft with tail chopped so rear tab sits right up snug with mech roof.

Easy job with a hacksaw and round file, and allows you to size the sear slot width precisely so there is zero slop when shaft engaged.

Couple of BIG qualifiers here tho, before chopping down that Hunt shaft!

1. you are messing with the geometry of the sear-shaft interface, and thus potentially the reliability and safety of the mech. I’m using Ermes DR mechs and the big roller sear makes this mod easy, less so with traditional sears that do not engage with the shaft slot so cleanly and thoroughly. Each time i mod a shaft tail i test it exhaustively in the pool before going anywhere near humans or fish
2. by taking the rear band ~30mm closer to the tail of the shaft, you increase the possibility of the shaft tail lifting as it exits the mech, and wrecking your accuracy, particularly as you increase the power with hot small id bands. big thanks to Majd for helping me understand this. 240fps video is really helping me to work out whats happening as that shaft comes out of the mech, and why with some rigs the shot wanders around the target. only one of many factors that need to be tuned in to achieve uber accuracy, but methinks this is a key one
3. bringing the rear tab 30mm closer to the butt pad significantly increases loading strain, and brings different muscles into play. No drama with lighter loads, but with 15mm small ID bands at 380% or more it does take some getting used to. Per your pic, the rear tab on the Bluetec is already quite close to the loading pad, could be hard work with hot 15mm bands, even with such a short gun

love to hear any thoughts on this!

Last edited by kavachi; 10-07-2019 at 05:34 PM.
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Old 10-07-2019, 04:50 PM   #14
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Re: Moving sharkfins further back on spear?

There is nothing new in spearfishing, check out these Wally Potts shaft tails.
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Old 10-07-2019, 04:54 PM   #15
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Re: Moving sharkfins further back on spear?

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Originally Posted by kavachi View Post
Hey Anders!
pics below of Hunt 8.5mm shaft with tail chopped so rear tab sits right up snug with mech roof.
_
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