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Speargun Dynamics Thesis

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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Jesse_Spiller

Active Member
Feb 14, 2020
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Hey Guys,

I've just submitted my Msc Thesis on Modelling Speargun Dynamics that was mentioned here and here.
I was unable to experimentally confirm a lot of findings as COVID-19 shut down my University's labs and workshop; I then had to relocate from the UK back to Australia. Testing to compare the simulator with reality is slated for later this year. The rubber testing is accurate and even the as yet unconfirmed stuff serves to compare different gun designs pretty well.
If you're keen to read 20,000 words on speargun design and tuning: it is linked here or attached below.

JS.

*Edit: the associated website is here: http://www.technicaspearguns.com/
 

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  • R-Thesis-MSC_s323691_Jesse.Spiller_2020.pdf
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Andrew the fish

Well-Known Member
Oct 17, 2010
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Jesse, I am still reading, Posted a question earlier but then I found where I was wrong.
 
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Jesse_Spiller

Active Member
Feb 14, 2020
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Jesse, can you expand on chapter 6.3.3 and especially how did you arrive at equation 6-8?

I am puzzled. Looked through inverted roller schematics, I still can’t see how is it 0.25, unless there is another set of rollers involved. I am still reading, it is a big work of yours.

You're right that doesn't make sense.
I meant to write the velocity of the centre of mass of the rubber, not the rubber itself. The centre of mass is already moving at half the speed of the shaft as one end is fixed to the shaft and the other the speargun. The pully halves the speed again.
I have changed that para to:
'The pulley halves the rubber travel and speed but doubles the tension force; this causes the rubber centre of gravity to travel at a rate four times slower than the spear velocity'
 
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Andrew the fish

Well-Known Member
Oct 17, 2010
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misprint, chapter 10.3 "Recoil and Spear Diameter", table 6. Recoil energy for shaft diameter 9/32 is greater than that for shaft diameter 5/16. It cannot be a legit node, since the gun mass is considered constant.

Chapter 10.8 "effective length". Interesting findings. Let's think about it. It appears mid-handled conventional multi-band gun wins over single band roller or inverted roller. Might require stiff fully extended arm with locked elbow to manage recoil and upend efficiency. Mid-handle offset of greater than 20cm haven't been explored, and this will likely add to the argument for conventional set setup. Great research, Jesse.
 

Jesse_Spiller

Active Member
Feb 14, 2020
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Hi Andrew. Good catch on Table 6; those results are the wrong way round. Fixed for future, thanks. Please let me know if you find any more.

Reference mid-handle dimensions, I like to swim with my guns with a bent elbow. A mid-handle with a butt greater than 20cm stops me from bending my elbow. Have you seen mid-handles with a longer butt?
 

Andrew the fish

Well-Known Member
Oct 17, 2010
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Have you seen mid-handles with a longer butt?
I don't know anything about mid-handle guns, never used one. So my suggestion was simply throwing an idea into the air. I have seen video where someone was holding mid-handled gun with butt hanging free beside the shoulder. For sake of academic discussion, what would stop that butt from being beside the shoulder and a little further behind? I am guessing, if we want to be able to aim looking down the shaft, then perhaps the real limit to the location of mid handle would be the length of arm, from collar joint to wrist.
 

sharkey

Well-Known Member
Nov 22, 2013
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The ones with the blue wing kits certainly are longer than 300 from the butt. These ones are basically just test guns for looking at various spears & rigging. The further forward than normal handle prevents muzzle flip rather than recoil (Im basically the only one to use with the long rear stock as they could smash someone in the face if they weren’t familiar with heavy guns, 200-250 is much safer) & they are also ballasted for “moment of inertia”. These are “extreme” prototypes simply to test all the theories & shoot targets rather than fish. Naturally I have their clones with rear handles, handles at 200 & 250mm. Those blue test guns are super accurate when set up correctly but they are not the fastest to track, there is always a compromise.
The two timber guns in the left are my day to day & Comp guns which I use for about 95% of fishing & the three on the right are my big molded carbon fibre guns for blue water , coral sea, etc. My personal guns are also ballasted to prevent muzzle flip & the mid handle certainly makes a big difference with this as the distance between the axis of rotation is reduced.
AD87BE35-889A-42D2-BE58-5D637F53F806.jpeg
 
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skycatblue

Well-Known Member
Apr 22, 2008
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All I can say is, wow! You've written more here about spearguns than I ever knew existed to be known about spearguns! Just amazing. Congrats on a well-created piece of work. You should be proud of this.
 
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Jesse_Spiller

Active Member
Feb 14, 2020
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All I can say is, wow! You've written more here about spearguns than I ever knew existed to be known about spearguns! Just amazing. Congrats on a well-created piece of work. You should be proud of this.
Thanks SCB, this means more to me than you think it does.
 
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