A couple of my mates who went to the dark side have had bad experiences with leg ropes, the bleeding head kind! So they don't use them anymore, that's fine, but a few guys here have lost their boards thru not having legropes.
Automatic release could save this, but then you've still got the problem of detached board, getting the tension right would be important.
What about a different material for the rope, ideally something that doesn't stretch, that should allow much more tension without the flying back problem.

Nebian, trouble with getting too complicated, is the mixture of saltwater and sand!! Any reel system will probably have problems with that mix

Verdo, why don't you investigate elastomeric materials that can be stretched quickly but have a slow acting memory. I might be imagining it but I seem to remember little rubber-like figures you'd probably get at a toy shop that you stretch its arms out, and they gradually shrink back to shape, rather than springing back immediately. There's probably a range of polymers available that would have those properties yet have a sufficient tensile strength to still act as a legrope. You are trying to avoid the rubbery elastomers that will store (as potential energy) the kinetic energy of a board flying away from you, which energy is released as it smacks you in the face when the elastomer rapidly "remembers" its shape.
In my work I see a lot of innovation. The more complicated your design is, or the more exotic materials you use, the higher the manufacturing costs will be and the greater the market resistance to buy your product. I'm assuming that part of your project involves the manufacturing, marketing and and cost issues, not just the design. You might like to look at the US Patent Office database (Google it) to search for what others might have done on legropes in the past. Good luck.

I would have thought that there is quite a bit of force on a leg rope to stretch it enough so as it's elastic propeties can rifle the board back at you, remebre we have all been in the situation where we have physically been dragged through the water by our boards still caught in the whitewater.

Myself I would never use a auto detach leg rope as it kind of defeats the purpose of the leg rope. I have on a number of occasions down south had the pleasure(?) of wiping out on sizeable surf and having to do the painfull climb back up the legrope.

The only problems I've seen with surfing legropes was a mate who when sitting ing the lineup snagged his on a shallow reef, when a wave went past he went under like he was on an elevator, it was difficult to undo the ankle strap on that one. I have also been Tied up in legg ropes which is not a fun experience, a bit panicy but can be resolved fairly easy.

I have seen what you have described but I think you are greatly underestimating the forces applied here.

A mate of mine was surfing at Old Cobbles down south on a 5 foot day, bailed in a close out section and hios momentum projected his 90+kg body close to 10 feet above the wave, his board caught under the lip slowed his flight to an almost halt fairly quickly then was pulled through the wave to come flying after him. It takes a lot of energy to through 90kg verticaly as well as quickly decelerate it.

Same applies with Kiters the kite has enough energy to loft an 80kg kiter but leave the board stuck in the water and then lauch the board rather rapidly after the kiter.

The problem is in the materials, you have to use an elastic material else if you used a non elastic rope (ie rope) then serious injury is likely to occur once the load is applied.

What is really needed in this case is an elastic material which has a high break strength whilst having a Slow energy release, that is it returns to its original length slowly, the down side of this is after being dumped by a wave your 6 foot leggy may be 7 foot when you paddle out.

It's a fun thing which your trying to do, I think you will learn a hell of a lot if you take it further, Enjoy

All the best.

Alby

I think I'm getting closer to the materials you need. Try investigating visco-elastic urethanes, like the ones referred to at gallaghercorp.com/hysteresis-in-urethane/
Start talking about hysteresis curves, fatigue, stress/strain, cut propagation, breaking strength etc in your assignment and you're bound to get top marks.
You should be looking for a material with a high viscosity/low resilience. When being stretched, the high viscosity material converts the force (or more accurately, kinetic energy) of a board flying into heat. As mentioned at the webpage, the enemy of urethanes is heat. You have the perfect solution to this- oceans of beautiful cooling medium, namely sea water. Ideal way to dissipate that heat!

plasma rope..i recently changed my winch line on my trailer boat from a wire rope to plasma rope.I did so because it is safer. Less likely to decapitate you if it breaks or a shackle breaks.Its lighter too. Plasma rope is remarkable. It is incredibly strong, but the interesting characteristic that might interest to you is that it has virtually no elasticity. It is the stored kinetic energy of a stretched elastic leash or board rope that is the problem.

jeremy