Coiled Leash Freak Accident or Not?

[PonoBill]

I like the looks of the leashes you guys have. The straight section will absolutely act as a damper and reduce the overall effect. Also won't tangle so badly. It will still undoutedly fail in the coiled section if the leash itself breaks, but all leashes have a breaking point.

For anyone that's curious about the springiness of a coiled leash, try what I did last night:

Tie one end of your leash to your garage door frame. Remove the leg cuff allen screw and tie about four feet of string through the swivel on the other end and then tie that to a fifty pound weight. run the string over a broomstick so it can hang down while you stretch the leash enough to lift the weight off the ground. Have your wife overcome her trepidation and cut the string next to the leash.

Whack! Knock a chip off the garage door.

Do the same with a standard straight leash. Convince wife to return.

No whack. Doesn't even make it to the door.

[ehrawn]

Think of the leash as a spring. As you pull on it, there is a required force per unit length of deflection. After releasing it, the stored potential energy will be converted to kinetic energy. When the deflection is zero (i.e. the leash returns to the original unstretched length), the force is zero. The leash now only has its momentum to carry it towards the board. The velocity of the broken end as it hits the board will determine the force of the impact, since it’s the change in that velocity that will determine the force: i.e. F=m*a, or F=m*dv/dt.

For a straight leash, the original deflection is small, even though the force required to stretch it is big. Once it is released, it only accelerates for a short amount of time. Now compare this to the coiled leash. When you first pull it, it deflects a lot as it uncoils. It doesn’t take much force to do this, but, eventually, you reach a point where the leash looks and acts very much like the straight leash. So, the stored potential energy not only includes the component due to stretching the material, but also a component due to stretching the coiled shape. This return force is applied until the leash returns to it original coiled length, which is much closer to the board. That is a lot of time for the broken end to accelerate and thus will result in a much higher velocity at impact.

Compare two cars on a mile long course. One car has a 0-60 time of 3 seconds; the other 10 seconds. You let the first car only use the gas for 0.1 miles, and then coast the rest of the way in. The other accelerates for 0.9 miles. Which will be going faster at the end of the run?

[Nate Burgoyne]

Convince wife to return.

Ha!!!! LOL

[diesel]

From my basic logical skills, after reading what everyone has wrote, I think that the coiled leash could act as a straight leash if, when stretched out, it would turn in the swivel as it is uncoiling.  I don't think it turns in the swivel as it straightens out so it goes straight without untwisting and stores up all that energy.  
It is like those paper/rubberband/paperclip traps we used as pranks when we were kids.  We would put a stiff flap of paper thru a rubberband that was on a paperclip wishbone.  Then twist the flap over and over to coil the rubberband.  Then wrap this contraption in a square of paper like a present and fill it with pencil shavings so when it was opened it would uncoil and scare the crap out of people shooting all the pencil shavings everywhere and making all this noise.  Funny stuff.  Same idea, I think with the storing of energy.
Sorry for the unscientific explanation.  I would not use the coiled leash for surfing.

[PonoBill]

This sounds like a potential Jack O'Neil story. No patches for me, thanks.

[corran]

No way the coiled leash has anything to do with it. In fact, quite the opposite... the coil would tend to store less energy when stretched, and thus have less recoil. A "stretched" straight leash will have far more stored energy. A coiled leash - the "spring" in it  - is very weak. In fact, The damage to this board would have been less because it was coiled, rather than more.

On the other hand, the problem with coiled leashes, while they put less strain on your plugs and ankle, is that after a wipeout you have less idea where your board is on the surface, and you're more likely to surface into it. After the wipeout the leash recoils, pulling the board back towards you. This makes it closer to grab, but also potentially right above you head - fins closest to your upward looking face. After a wipeout I give my foot a little back kick and I know instantly if the board is far away (there is a tug) or right above me (no tug). With the coiled leash I loose all sense of its position.

But this is another debate. I make both coiled and uncoiled leashes and for sure the coiled is safer in the sense that there is less tug on you and less tug on your board, but as I said above, the flip side is...

Corran

[wavehobbit]

I'm impressed with the technical explanations posted.  But to make it real simple, take your coil and stretch it out. Note that when the coils are straightened out, how non-uniform the material is compared to your standard leash.  You'll see the infinite amount of weak points. 

As for the actual velocity when snapping back (coiled vs standard) hmmmm...it would be fun to put them to a bench test (myth busters-like) and see which penetrates the skull (replica) to the greatest extent. 
Ahhh, Viking sword vs Med. Knight sword.   

[maui wave warrior]

I used a coiled leash in surf big and small. Unfortunately, I did not see a disclaimer about not using it in surf. After one week the leash lost much of its coil and constantly got tangled in itself. I can see it as an advantage in downwind runs and racing but not for surf.  

[PonoBill]

No way the coiled leash has anything to do with it. In fact, quite the opposite... the coil would tend to store less energy when stretched, and thus have less recoil. A "stretched" straight leash will have far more stored energy. A coiled leash - the "spring" in it  - is very weak. In fact, The damage to this board would have been less because it was coiled, rather than more.

On the other hand, the problem with coiled leashes, while they put less strain on your plugs and ankle, is that after a wipeout you have less idea where your board is on the surface, and you're more likely to surface into it. After the wipeout the leash recoils, pulling the board back towards you. This makes it closer to grab, but also potentially right above you head - fins closest to your upward looking face. After a wipeout I give my foot a little back kick and I know instantly if the board is far away (there is a tug) or right above me (no tug). With the coiled leash I loose all sense of its position.

But this is another debate. I make both coiled and uncoiled leashes and for sure the coiled is safer in the sense that there is less tug on you and less tug on your board, but as I said above, the flip side is...

Corran

Try my little experiment and see if you still believe that. You don't have to use my wife.

[beaglebuddy]

The O'neil surf guy with the patch over his eye invented the leash, one of his early prototypes snapped back and took his eye, now they are made different, not sure about coiled leashes

[corran]

I like the looks of the leashes you guys have. The straight section will absolutely act as a damper and reduce the overall effect. Also won't tangle so badly. It will still undoutedly fail in the coiled section if the leash itself breaks, but all leashes have a breaking point.

For anyone that's curious about the springiness of a coiled leash, try what I did last night:

Tie one end of your leash to your garage door frame. Remove the leg cuff allen screw and tie about four feet of string through the swivel on the other end and then tie that to a fifty pound weight. run the string over a broomstick so it can hang down while you stretch the leash enough to lift the weight off the ground. Have your wife overcome her trepidation and cut the string next to the leash.

Whack! Knock a chip off the garage door.

Do the same with a standard straight leash. Convince wife to return.

No whack. Doesn't even make it to the door.

Not sure whos coiled leash you're using, but mine has the exact opposite effect... the coil has little if any rebound - its a "pathetic" spring if you like... tension on the straight leash (that causes some minor stretch) results in a whip like return and it flys back at you with some speed. The coiled one pathetically returns to its coiled shape like a wet grape, with less than half the aggressive return whip.

Also, a great deal MORE force than 50lbs is put onto that leash... more like 300 or 400lbs... (your dead weight, dragging under water...). 50lbs is not going to break a leash. 400lbs might very well. In a 50lbs test the straight leash is not stretched, so has no recoil. Now do your test again (use your own wife) with 400lbs on the end of them, and see which one snaps back like a whip! The straight one will be far more lethal.

Basically, in our testing of the two, what we found was that much less "stretching" of the leash occurs as a vast majority of the force is dissipated in the "uncoiling". So once straight, it stretches less, and therefore has less stored energy and less recoil. The straight leash has no "progressive" absorption of the energy, and so all the boards energy goes into stretching the leash, that then whips back at you.

What I'm describing ( the effect of a straight leash - it has spring in it unlike a static rope - there is a reason we don;t use a rope ) is like a climbing rope - or a Bungee... jump off a bridge and it make for less impact on the fall, but then catapults you back into the air. The coiled leash (that we make anyway) slowly uncoils with the tension, absorbing energy, and once extended, so there is less energy left to stretch the leash, and its ability to recoil is so limited that its less than that of the straight, stretched out leash. SUP's are so darn big with massive surface area - even light ones - that they almost always pull and stretch your leash on wipeout.

On the flip side, over time the leash does loose much of its coil.

I've never broken one. Period.  I have also never used anyone elses, so can;t speak for breaking OR recoil of those.

That being said, a coiled leash has its serious downside in that it does retract slowly after the original fall, and so your board often ends up above you as you surface.

Double edged sword for sure. Personally I prefer a straight leash and use a short one (7' most cases, 8' max in giant surf.  I HATE long leashes... and so I think that someone wanting a 9' or 10' leash without all that leash to tangle in your paddle, a coiled leash is a great alternative.

Corran

[lee]

The O'neil surf guy with the patch over his eye invented the leash, one of his early prototypes snapped back and took his eye, now they are made different, not sure about coiled leashes

No Jack didn't invent the lease .Neither did Pat..they thought that a suction cup with with surgical tubing attached to your wrist was better than the 3/8 nylon rope tied to a hole in your fin.
The guys in New Zealand invented it for when they had to many mushrooms.

[DavidJohn]

Yesterday a friend took this pic of me.. well not of me.. I just happen to get in the way as he was taking a pic of my friend Dean as he tested his new board.. anyway.. this pic shows the type of half coiled and half straight leggies that some of us use here in Oz and they're made by Balin and I've had no problem with using them in the surf.. They're also great for flat water paddling and down-winders because they keep the leach on the board and not dragging in the water.. Pulled straight they're about 10' long.

DJ

[jdmotes]

 Thanks DJ... BTW: That's a cool looking board your friend Dean is on. Can you tell us about it?  Thanks,    JD

[DavidJohn]

Thanks DJ... BTW: That's a cool looking board your friend Dean is on. Can you tell us about it?  Thanks,    JD

Sure.. Dean's new board is 8'2" x 30" and the first quad that he's made.. It's increadably light at a little over 4kg (only 9 lbs)

 btw my yellow board in the pic is also one of Dean's but mine's 9' x 32" and a single fin.

Here's a few more pictures.. I think this is the first time I've ever seen Dean fall..  

DJ