There is an excel file attachment based on my real measurements in water in years 2011. and 2012. I suppose it might be useful to calculate the real speed of the shaft on some distance in water for several cases: for 7/1003 mm 301 g shaft and for 8/1280 mm - 483,5 g shaft. Both shaft using two mono line thickness 1 mm and 1.5 mm. For 7/1003 mm 301 g shaft, there is also calculation/measurement for 2 mm original black Mares rope (I suppose it is maybe similar to 2 mm Dyneema)

Calculation in https://forums.deeperblue.com/threads/calculation-of-initial-speed-and-energy-of-the-spear.114778/ can be used to determine the Initial speed of the shaft.

That initial speed v0 is then multiplied with normalised speed v/v0 from given tables or using formula for v/v0 = y from the graph as on image. "x" in formula is a distance in (m) for which you want to calculate the speed. The graph starts with distance 0 m. That distance is actually measured from the shaft tip after the shaft is inserted into the spearguns muzzle before loading the speargun.

One more thing, also very important, that influences the performance is the kind of slider on the shaft. This measurement were taken using Tomba10 slider. It was 10 mm OD slider for 7 mm shaft.

If using free shaft, mode of tying the line to the shaft also makes significant difference. Measuring 8 mm shaft performance was as "free shaft" (I was using Cyrano 1100 for shooting the spear https://forums.deeperblue.com/threads/measuring-speed-of-the-shaft.91007/page-5#post-887541 ).

I have to say, to be quite correct, I have not really tested the performance of 8 mm shaft in water using that black nylon rope because I knew it would be very poor and that I would be never using it. Formula on a graph y=e(-0,3x) for that case is result of some mathematical extrapolation combining data from 7 mm and 8 mm shaft measurement. So it should be taken having that on mind! I had really tested that black nylon line only with 7 mm shaft so that data must be correct.

Calculation in https://forums.deeperblue.com/threads/calculation-of-initial-speed-and-energy-of-the-spear.114778/ can be used to determine the Initial speed of the shaft.

That initial speed v0 is then multiplied with normalised speed v/v0 from given tables or using formula for v/v0 = y from the graph as on image. "x" in formula is a distance in (m) for which you want to calculate the speed. The graph starts with distance 0 m. That distance is actually measured from the shaft tip after the shaft is inserted into the spearguns muzzle before loading the speargun.

One more thing, also very important, that influences the performance is the kind of slider on the shaft. This measurement were taken using Tomba10 slider. It was 10 mm OD slider for 7 mm shaft.

If using free shaft, mode of tying the line to the shaft also makes significant difference. Measuring 8 mm shaft performance was as "free shaft" (I was using Cyrano 1100 for shooting the spear https://forums.deeperblue.com/threads/measuring-speed-of-the-shaft.91007/page-5#post-887541 ).

I have to say, to be quite correct, I have not really tested the performance of 8 mm shaft in water using that black nylon rope because I knew it would be very poor and that I would be never using it. Formula on a graph y=e(-0,3x) for that case is result of some mathematical extrapolation combining data from 7 mm and 8 mm shaft measurement. So it should be taken having that on mind! I had really tested that black nylon line only with 7 mm shaft so that data must be correct.

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