Speargun Dynamics

    I saw a speargun fired in a tank in a slow motion video, but I can't find the video. The shaft did behave like one of those arrows bending like hell, except on a vertical plane. The muzzle of the gun would kick up about 6" by the time the shaft was half way out creating an amazing bend in the shaft. The shaft would then continue and slide over top of the kicked up muzzle, amazingly returning to its original plane. Having once before seen a slow motion video of an arrow being shot also behaving in a similar manner, I thought this will always be the case. However watch this series of different arrows being shot, some of them bend a lot and others very little, so I think it does depend on the bow or speargun.


    http://www.youtube.com/watch?v=ZI_17jgEdAI


    http://www.youtube.com/watch?v=xfVonIjirG8


    And a speargun although not in very detailed slow motion.


    http://www.youtube.com/watch?v=-gCJjoZVXXI

    Dan, it's called spline cycle, it about selecting the correct arrow spline for the wt of the bow. The arrow
    bends around the noch and eventually go's into straight flight.
    Cheers, Don

    "Great mother ocean brought forth all life, it is my eternal home'' Don Berry from Blue Water Hunters.


    Spearfishing Store the freediving and spearfishing equipment specialists.

    Edited once, last by Don Paul ().

    In water the spear vibrating has drastic effects. If the gun kicks up 6 inches drag increases minimum 20 times and this doesn't include effects of dragging water in the vortices created.

    Davie Peguero

    Don, I would love to know about the results that you guys came up with in your testing. I assume that you looked at shaft velocity with different diameters.


    What about the impact of a larger diameter tip on the speed of a shaft? Does the mass of the shaft or the diameter of the tip (the amount of water which must be moved) have a bigger impact?


    What factors did you find to be the most important in achieving guns with the best accuracy in terms of handle height, limit of power vs. gun weight, band slot height, etc?


    Impact of enclosed track?


    The list goes on and on. Bottom line anything that you can share would be greatly appreciated.


    Chad


    Hi Chad, I type really slow as I have a broken R hand. I'll share some things but give me some time.
    I have a lot of very close friends in the gun building industry and alot of what I have learned is in the
    personal guns I build for myself. I'll try to get my scanner on line next week most, of my images are pre-digital.
    Gun are a little like religion, many different beliefs to the chosen path.
    All the Best, Don

    "Great mother ocean brought forth all life, it is my eternal home'' Don Berry from Blue Water Hunters.


    Spearfishing Store the freediving and spearfishing equipment specialists.

    Edited once, last by Don Paul ().

    That is gross flexing of the shaft WITH ONLY ONE BAND. I wonder how much it has to do with the huge tip. In my mind shooting with a 1/2" diameter tip is like shooting with a 1/2" diameter shaft.


    My guess is that the force required to overcome the water resistance drastically impacts the flight of smaller shafts when big diameter tips are used.

    what amazes me is the fact that the fish turned broadside in the time it took the spear to get there, that is incredible...Im sure it had to do with the fact it saw the shot first, but that is still crazy.


    cool video

    i like to spear fish

    Quote from LunkerBuster

    what amazes me is the fact that the fish turned broadside in the time it took the spear to get there, that is incredible...Im sure it had to do with the fact it saw the shot first, but that is still crazy.


    cool video


    X2

    Quote from Don Paul

    Gun are a little like religion, many different beliefs to the chosen path.

    :)


    Very good vid Greek, thanks.


    This is one of the reasons I insist on 13" of spear overhang. By the time the muzzle kicks up the spear there's already quite a bit of spear past that point traveling straight, there's a better possibility that the rear of the shaft which has been moved out of position will eventually join the front on the same plane.


    LB, I was so focused on what the shaft was doing that I missed the fish bit until I read your post. It is an amazing thing! But then I've shot fish before where I could see them esquive the spear in the last moment and I'd see one scale stuck on the spear point afterward. I've also seen a fish turn so fast that the spear penetrated it twice, near the head and near the tail. I've heard it said before that you can shoot a fish facing you like that and it will always turn presenting a target for the shaft. But I've never had the confidence to do it, rather I'd wait for the fish to turn, sometimes this was too late. I considered whether it will make a difference if the fish will turned right or left, I concluded that it doesn't make a difference. I will try this kind of shot in the future because of what I saw in this vid. One caveat though is that I think it only applies to fish of certain size, a big fish will be slower to turn and will take the shaft in forehead.

    Quote from griswold

    That is gross flexing of the shaft WITH ONLY ONE BAND. I wonder how much it has to do with the huge tip. In my mind shooting with a 1/2" diameter tip is like shooting with a 1/2" diameter shaft.


    My guess is that the force required to overcome the water resistance drastically impacts the flight of smaller shafts when big diameter tips are used.


    That's an oring on the tip of spear, not a huge speartip.

    My bad, but it doesn't change my overall question.


    What I'm trying to get at is whether the diameter of the object being pushed through the water has the bigger impact on shaft speed, etc. or if the weight of the object has the bigger impact.


    Stated another way, does the diameter of the tip dictate the shaft speed? If so, using a big diameter tip is a huge mistake in most applications. You might as well be shooting a 3/8" shaft if you use a big slip tip.


    To be clear, I'm guessing at this. I would love to know some of the results of what the guys who measured shaft speeds came up with.


    Mass is a good thing once you get it moving, a 3/8 shaft powered by 5 hi modulus bands can do a lot of
    work. If one launches a Ti shaft greater than 15' you will find impact energy values drop off quickly.


    Seawater has a density about 900 times greater than air, yes using a tip with poor hydrodynamic profile
    will have a large effect on speed on a light shaft.


    Off to work. Don

    "Great mother ocean brought forth all life, it is my eternal home'' Don Berry from Blue Water Hunters.


    Spearfishing Store the freediving and spearfishing equipment specialists.


    Totally agree. Makes me shake my head when I see a riffe euro equipped with a 17/64 shaft... and an ice-pick slip-tip. All the negatives of a big cross-section (drag, poor penetration) with none of the benefits (momentum, punch). Like most things in spearguns - it must be balanced.

    I believe most of the shafts companies make shafts that are very poor in hydrodynamics and penetration. They usually have a flopper that sticks out a ton causing drag and poor penetration or huge shark fins or big pin tabs. Flopper, tabs, and sharkfins should all be flushed beneath the surface of spear to get optimum range and speed. It's a tiny bit more work but it would be done right. Tricut is the best spear tip also as it penetrates through fish the best unless you are shooting in the rocky areas.

    Not if you're using an enclosed track gun.


    I don't like tricut, the tip bends too easily and requires constant filing. I find myself hesitating too much when taking shots that could hit the reef bottom. I think it may even affect trajectory the same way a flopper with its lip sticking out does. Getting similar penetration for my purposes from a pencil point is just a matter of sharpening it. The kind of extra penetration provided by a tri cut I think is only necessary with very big fish?

    Quote from greekdiver

    . . . They usually have a flopper that sticks out a ton causing drag and poor penetration or huge shark fins or big pin tabs.


    Lots of factors to consider, and everything is a compromise, right? Recessing the floppers just takes a little extra machining, but that costs money. Some people are probably willing to pay for it, and some are probably not.



    Quote from greekdiver

    . . . tabs, and sharkfins should all be flushed beneath the surface of spear to get optimum range and speed. It's a tiny bit more work but it would be done right.


    But if you reduce the shaft to less than its original diameter, then you weaken it. And how could this be done for an enclosed track gun?

    Quote from Dan≈

    I don't like tricut, the tip bends too easily and requires constant filing. I find myself hesitating too much when taking shots that could hit the reef bottom.


    I love my bowfishing tips for exactly that reason. Considerably harder than a spear shaft, so they resist damage, $2 each and easy to replace if need be. If only they came in a thread that was compatible with standard threaded end spears, things would be easy.


    http://spearfishing.world/spea…dened-tips-close-but.html

    Edited once, last by Guest ().

    Quote from Dan≈

    Not if you're using an enclosed track gun.


    I don't like tricut, the tip bends too easily and requires constant filing. I find myself hesitating too much when taking shots that could hit the reef bottom. I think it may even affect trajectory the same way a flopper with its lip sticking out does. Getting similar penetration for my purposes from a pencil point is just a matter of sharpening it. The kind of extra penetration provided by a tri cut I think is only necessary with very big fish?


    I shoot my RA tricut into all sorts of rocks and have never had an issue with it...maybe different brands dull differently?

    i like to spear fish

    I am not the sharpest tool in the shed, but I would like to contribute what I can.
    1.From past experience a pencil point shaped tip does not CUT through the fish as a tricut tip does, therefore there is less risk of the shaft pulling out of a fish when using a pencil pointed shaft.
    2. As Dan has said, firing a full powered shaft through a reef fish into the reef is hard on shaft tips. My solution to THAT problem is to depower my gun by taking 1 band off to shoot a hog at 12". I swim around with both bands on cocked incase a mac / cuda swims by. The hog will almost always give me time to depower, where you have 2-3 seconds to line up and shoot a mac.
    3. Another factor effecting shaft performance is the Wetted Surface of the shaft. This is a HYDROdynamic only factor, not shared with arrows or other AEROdynamic objects.


    others--I wish I was smart enough to understand the formulas and equasions. Thank you
    All I know is that when I release the shaft on my RA, the muzzle ends up higher then BEFORE I released the shaft.


    seaweed---thanks for this thread:)

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