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Best rubber´s lenght for speargun

Best rubber´s lenght for speargun

This is a normal question when we are changing our rubbers. Maybe we don´t remember the size, maybe we are trying a new brand or changing into rubbers by meter and dyneema wishbone.

Most of the times my customers asked me about a rubbers for their speargun. A 75cm, 85cm, 90cm… But it´s a wrong question because it depends on the brand and model and even the shaft.

Some brands call 75cm a speargun which is bigger than 85cm in other ones. And some shafts have the shark fins closer to the muzzle than other ones. So won´t be the same rubber.

To choose the right rubber there are only a few important things.

The distance from where the rubbers are located in the muzzle (parallel rubbers) or where they pass through (circular rubbers) to the shark fin (where the wishbone fits in the shaft) Must be careful because not all the shafts are the same, some of them have it closer to the muzzle or a bit far away.

Wishbone´s length. It´s important. As bigger is the wishbone we will use a bit shorter rubber. That´s why it´s so important using short wishbones.

So to calculate our rubber´s length we must know:

So we need to do an easy calculation.

We are going to see an example. We have an 85cm speargun. And the length from the muzzle to the first shark fin is 82cm. To the second one is 90cm. The wishbone is 2cm (short one) We are going to use a 17,5mm rubber. And we are looking for a 300% in the first shark fin.

82cm (total length) – 2cm ( wishbone) = 80cm

Total length/Percentage = 80/3 = 26.6cm

So we would need a 26-27cm rubber. This is for a parallel rubber. If it´s circular we will need the double (both sides) so we would need a 52-54cm.

And if we load it in the second shark fin we would have: (90-2)/26.6cm = 3.3

So the stretching in the second rubber would be the 330%

Now we are going to see the most used in normal spearguns in a 350%. To have an idea.

75cm parallel: 20cm

75cm Circular: 40-42cm

85cm reverse trigger or 90cm normal trigger in parallel rubbers: 22-23cm

85cm reverse trigger or 90cm normal trigger in circular rubbers: 44-46cm

95cm reverse trigger or 100cm normal trigger in parallel rubbers:  25-26cm

95cm reverse trigger or 100cm normal trigger in circular rubbers: 50-52cm

But we see that it´s very easy know the perfect length for our spearguns.

You can ask he or in the forum if you have any question or doubt. And you will find the best equipment at www.subandcast.com

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