The main reason I doubted this design was the frontal surface, which is increased a lot by going so wide at the roller end and looping the rubber. So I expected the spear to waste all the added power to increased resistance. But then again, you had to make the roller wide because of the chosen material. Steel would allow it to be very slim, but cutting some nylon to shape is far easier for prototyping.
I said you missed by 5cm because you didn't hit that face on the book between the eyes. We all know that's where the fish have their brain.
But I do find this idea quite interesting. Also got me thinking about a pulley handle: twice the speed at half the power. For something light as an aluminium spear this might be interesting. Perhaps it could also enable the use of 14mm speargun rubber, which is far easier to find than <10mm here in south Europe.
Now I have something to start tinkering with during the lockdown here! Thanks!
