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Calculation of initial speed and energy of the spear

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Well-Known Member
Aug 13, 2007
Here is an excel file to calculate the initial speed and energy of the spear in pneumatic speargun.

I find this calculation helpful to estimate the expected initial speed of the shaft that influences the performance of an pneumatic speargun.
The initial speed is only the basic condition for shooting performance of an speargun. Other factors like hydrodynamic properties of the spear as whole and the rigging are even more important for overall shoting performanse on target distance!

All Tomba research and design efforts were about to answer those questions:


Calculation make sense on proven speargun designs that are widely use for years, like Mares, Cressi, Asso, LG, Salvimar, Pelengas...
Calculation is not applicable on pneumatic spearguns where there were throttling issues or poor barrel manufacturing or bad assembly.

Calculation is helpful to answer some questions like:
What pressure should be to achieve initial speed of 35 m/s?
What is the influence of the friction of the piston?
How CR affect the performance, loading and shooting?
What is the initial energy of the spear?

Excel in attachment uses compression ratio (CR), as one of the parameters, defined in:
The easiest way to determine CR is to measure it using pressure gauge:
Measure the pressure in a speargun:
  1. for unloaded gun - P1
  2. for loaded gun with the spear ready to shot - P2
Now CR = P2/P1
It might be about 1.1 for Cyrano...depends on the model.

Working course of the piston (L) is the length of the acceleration path of the spear,
or the length of the spear that has to be pushed into the speargun during loading.


  • Speed-Energy.zip
    8.5 KB · Views: 398
Last edited:
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