Intro: Jesse Spiller (Research Student - United Kingdom)

[Jesse_Spiller]

Good afternoon All,

I’m an avid Spearfisher and postgraduate Gun Systems Design student at Cranfield University in the United Kingdom. My thesis, which will be released in August, is based around speargun dynamics and building a better scientific consensus on their function. I have use of a dedicated pool facility, an underwater high-speed camera, machining workshop and 6 months labour.

[ Details deleted. Please see full details at: https://forums.deeperblue.com/threads/speargun-dynamics-research-help-sought.116479/ ]



I need whatever material support can be offered - the things I still need are listed here (hyperlink). I'm in dire need of rubber (different diameters and from as many different manufacturers as possible). Rob Allen, Jeremy from DiveFactory, Marco from Ermes Sub and Carlos from Picasso have expressed interest in helping with this research. Radio silence from other manufacturers so far.
If you can help, or now anyone who could, could you please get in touch with me on this forum, else jesse.spiller@cranfield.ac.uk?

Else, just keen to hear what the peanut gallery thinks of these ideas, and if there's any areas of interest that might be worth further research?

Regards,

Jesse.

 

[Mr. X]

Sounds cool Jesse but please don't make duplicate posts in different areas, it is against forum rules. But you can link to your main post.

 

[Jesse_Spiller]

Cool, it is just the sort of thing we spearos have loved to discuss over the years. So this is just theoretical currently?

I think I see a couple of dubious assumptions. In the rubber comparison you say something about if you can stretch a 16mm rubber to double it's length but it is quite normal to stretch a rubber to about 3.5x it's original length. Also, it is normal to stretch thinner bands more than thicker bands e.g 14mm > 16mm > 18mm-20mm. Rubber diameter can vary as well e.g. 3/4" rubbers could be 18-20mm. The inside hole size varies too (e.g. US bulk rubber tend to have much smaller holes than traditional European bands).

I am sceptical that an inverted roller would be more efficient in practice. That extra roller is a moving part. Also the shorter rubbers (assuming 2x the number used on the regular roller) would , I suspect, not work as well. But prove me wrong in the pool!

I'm surprised that you did not standardize on one length of speargun, e.g. 100cm, to simplify calculations and side-by-side comparisons. Does that reflect your personal speargun arsenal?

Good luck. This is information that should prove useful to spearos and manufacturers, and could form the basis for future research.

Hi Mr. X,


Thanks for the engagement. It is currently just theoretical but I am in the process of acquiring materials for pool testing. The testing data will be incorporated into the model to make it more accurate.

In the 14/16mm example, the point I'm trying to illustrate is that a shorter 14mm rubber will produce more energy with less effort than a longer 16mm rubber, as long as that force is below 27 kg. There are windows like this between all band diameters.

Similarly, why is it normal to stretch thinner bands more, and thicker bands less? Is it because people find it too difficult to stretch a thicker band to 350%? or some other reason? I question this conventional wisdom. Like the example above, it might be better for people using 18mm bands to switch to 16mm and cut them shorter. Numbers and testing will provide the detail as to when and how much.

Rubber differences shouldn't matter much; I'm not trying to develop a universal model for rubber. Brands and their advertised dimensions will be used as options for people using the future calculator.

An invert roller should be more efficient as the rubbers are moving the opposite way to the spear (their momentum is in opposite directions), whereas a conventional speargun the momentum is in the same direction, and a roller is somewhere in between. It'll be interesting to see whether the mechanical losses in rollers offset this, and to what degree?

No, the spearguns don't reflect a persona arsenal. The spearguns in the example all shoot approx 350 Joules of energy, so if they had the same length and diameter spear they would shoot it the same velocity. I wanted to compare spearguns with a similar terminal effect.

Thanks for your questions,

JS.

 

[Mr. X]

Hi Jesse, I have responded to your post on your main thread in the technical area of the forum. Suggest that you use this thread for more general, social, business type discussion, rather than splitting the technical data