More power please!

[Badger]

Just converted my 1.4 rail gun to a gun that is hopefully capable of landing a bigger fish like Tuna or Doggie. I replaced the 7 mm spear with an 8 mm shaft, a Daryll Wong slip tip, locally made by the way, and a breakaway rig. Pool testing shows that the spear is remarkably accurate but does drop slightly when shooting from distances greater than 4 metres. Currently using a 20 mm rubber 870 mm length(total) Was thinking of going 2 x 20 mm but that may be too strong and cause the spear to damage the trigger release mech. which would not end well. Would 2 x 16 mm rubbers provide more power? 2 X 18 mm? Can only go to max. of two bands. Planning on using a 2 metre bungy onto a surf lifesaving foam filled float followed by a 5 metre bungy and a 35 litre air filled float, hope that this will provide enough resistance.

 

[Jegwan]

Yes. The stored energy with 2 X 16 mm will be more than with 1 X 20 mm. Theoretically; you can compare the square section of the bands. A = phi X sq r
1 X A20 = (phi X sq10) - (phi X sq2) = 302 mm2
2 X A16 = 2 X ((phi X sq8) - (phi X sq2)) = 377 mm2
Provided that the length, hole inside and the material of the slings are the same 2 X 16 mm would theoretically be 377/302 = 1,25 = 25% more powerful.
Jégwan

 

[Badger]

Yes. The stored energy with 2 X 16 mm will be more than with 1 X 20 mm. Theoretically; you can compare the square section of the bands. A = phi X sq r
1 X A20 = (phi X sq10) - (phi X sq2) = 302 mm2
2 X A16 = 2 X ((phi X sq8) - (phi X sq2)) = 377 mm2
Provided that the length, hole inside and the material of the slings are the same 2 X 16 mm would theoretically be 377/302 = 1,25 = 25% more powerful.
Jégwan

Thanks Jegwan, appreciate the time you have taken.

 

[Jegwan]

You're welcome.
Please note, that if you change to a smaller diameter band, you will be able to pull one that is shorter than the 20 mm you use now. A 18 mm band will perform it's best at a stretch around 270 - 340% a 16 mm band around 290-370%. What you can pull is normally the upper limit. I can't stretch a 16 mm band to anything near 370%!
Jégwan

 

[sharkey]

Just converted my 1.4 rail gun to a gun that is hopefully capable of landing a bigger fish like Tuna or Doggie. I replaced the 7 mm spear with an 8 mm shaft, a Daryll Wong slip tip, locally made by the way, and a breakaway rig. Pool testing shows that the spear is remarkably accurate but does drop slightly when shooting from distances greater than 4 metres. Currently using a 20 mm rubber 870 mm length(total) Was thinking of going 2 x 20 mm but that may be too strong and cause the spear to damage the trigger release mech. which would not end well. Would 2 x 16 mm rubbers provide more power? 2 X 18 mm? Can only go to max. of two bands. Planning on using a 2 metre bungy onto a surf lifesaving foam filled float followed by a 5 metre bungy and a 35 litre air filled float, hope that this will provide enough resistance.

If youre going to target doggie's over 50kg a 3/8 6ft ( 10mm 1.8m) shaft will give you the most consistent results. Sure fish have been landed with lighter gear, but many lost too. I wouldn't consider anything less than the above if I was targeting fish in the weight class from 30kg to 100kg. I like using three bungy's straight off the back of the gun (no breakaway rig). The riffe bungys revolutionised the landing of doggies in the mid 90's, & we saw our record rise from 55kg

 

[sharkey]

Sorry about above post ,it cut short & I don't see how to edit.
Yes, bungy's are great & the more the better . I use three with a small egg shaped float between each as this lets you pull up & clip off your rig at these points without the fear of the fish running & breaking the bungy if you clipped off in the middle of a section. I like to apply a 3:1 ratio of fish to float ( don't remember why but it hasn't failed yet), so a float with 35 litre displacement should land a 105 kg pelagic.

I use 3 5/8 rubbers to launch the above shaft & use a 4:1 ratio on these. I've got bigger guns with more power but its always a compromise & I've had the best luck with this above combination.

Cheers Sharkey