Tether Length

[Harry Black]

Can anyone suggest the best length for a tether?

I am going to make one out of regular rope from the marina. I have a harness.

Is the idea to keep you from falling out of the boat or to attach you to it so that you have a chance of getting back into the boat from the water?

[estarzinger]

Tethers are generally other 1m or 2m. Some tethers have two legs, one 1m and the other 2m. Go as short as you can and still do the Work you need to do.

The idea is primarily to keep you on the boat, secondarily to keep you attached if you do go over.

[thinwater]

I really prefer webbing, since visually I associate webbing with safety lines and rope with running rigging. When I have used rope for tethers--typically an expedient when they were forgten at home or we have additional crew that forgot theirs--it always seems to cause more visual confusion.

I would only add to estarzinger's comment that the correct lengths are boat-specific. I would try knotted tethers first (fair weather) and adjust untill they fullfill estarzinger's requirements. For example, I have a cat with a wide beam but narrow side decks, so the short tether is shorter and the long tether is longer.

[svHyLyte]

Originally Posted by Harry Black

Can anyone suggest the best length for a tether?

I am going to make one out of regular rope from the marina. I have a harness.

Is the idea to keep you from falling out of the boat or to attach you to it so that you have a chance of getting back into the boat from the water?

Harry--

By it's nature, common rope is not ideal for tethers as it is surprisingly easily broken under sudden shock loads. In the '79 Fastnet, many rope tethers failed when crew relying upon them were flung by the violent rolls of the yachts in heavy seas (for more see Mate's book, Fastnet Force 10). The two legged--one short, one longer--tether made of tubular webbing is much preferable, with leg lengths sized for your particular application. A further improvement is to encase a length of shock-cord, roughly 75% of the length of the legs within the cores of webbing tubes, secured at each end of the leg. The shock-cord will allow the legs of the tether to retract somewhat keeping them from under foot when moving about on deck but allowing one to extend them full length, when necessary. A sizable shock-cord with also buffer, to a limited extent, the sudden shock if one is thrown or falls to the end of ones tether length.

Ideally, a tether should keep one on the boat. A jack line amid-ships with a tether length that will not allow one to go over the side is preferred tho' sometimes impracticable.

FWIW...

[estarzinger]

Article: Jacklines and tethers

[Randy]

This whole concept of tethers and jacklines is in common practice poorly implemented.
The entire system to work properly, has to keep an individual not only onboard but safe. A person being thrown a distance of 6' will generate a force 3000 lbs and a tether/harness and jackline not only has to be able to withstand that force but also distribute and dissipate that impact on the body. A person can only withstand a force of 900lbs before physical injuries start to be experienced.
Getting a piece of line or webbing and making your own tether while possible ought to be proof tested to 5000 lbs as is the case in commercial fall protection gear.

[estarzinger]

Originally Posted by Randy

This whole concept of tethers and jacklines is in common practice poorly implemented.
The entire system to work properly, has to keep an individual not only onboard but safe.

A person being thrown a distance of 6' will generate a force 3000 lbs and a tether/harness and jackline not only has to be able to withstand that force but also distribute and dissipate that impact on the body.

Randy, I agree with the first part. Sailors are generally not implementing the best practice system.

However I disagree with the second part (the 3000lb load case). There are almost zero cases of sailors hurt when falling onto their tethers, and almost zero cases of jacklines or tethers breaking due to shock loading. This strongly suggests the real world loads are much less than that. I have details of a bit more than 200 real workd cases of sailors thrown at their tethers, and there are some drownings (when they go overboard and are dragged) and in that sample there are some failed stitching (DIY or UV damage), but zero cases of injury or webbing breakage due to shock loading.

[Randy]

Evans,
I appreciate your experience and contributions to this forum as well as elsewhere. The numbers that I threw out there are taken (I believe accurately) from the ANSI Z359 code which addresses fall protection code. I've had a fair amount of training in fall protection but wouldn't call myself an expert in the field. The physics are well established but poorly understood in the yachting world nor is the hardware well adapted to the yachting environment. I believe in your paper on tethers you refer to a European version of the ANSI code which will be very similar.

[estarzinger]

^^

I understand the physics of a 6 ft fall (I used to rock climb when I was young) . . . But my point was that empirically those sorts of fall loads don't seem to happen in "the real world" on a yacht deck. Empirically it seems much more a case of "stumble and slide with stuff grabbing you along the way" rather than " free fall 6ft". The situation is not exactly like high rise window washing or working up a ladder. To get useful information from load models you need to match your physics model with the actual real world situation and confirm the output with the empirically observed loads. All I am saying is that the data I have do not support 3000 lbs loads on human bodies (or on the webbing) actually occurring (at any measurable statustucally valid frequency) on sail boats. As I have said about some other calculations (like on snubbers) . . . . If the observed real world loads don't match the model calculated output . . . It's probably the model that's wrong.

[estarzinger]

Just as a specific example is the recent Uncontrollable Urge incident. A violent capsize. Three crew ejected overboard while tethered and two more thrown across the deck but stayed on board while tethered. About as strong a "fall" situation as you can get on a yacht. . . . But None of the crew suffered any injuries due to the fall/harness. None of the tethers or jacklines broke.

One of the crew that was ejected overboard died because the rig fell on him and he was trapped under/in it and could not get free from his tether. But he did not have any "fall" related injuries.

[Rakuflames]

Originally Posted by svHyLyte

Harry--

By it's nature, common rope is not ideal for tethers as it is surprisingly easily broken under sudden shock loads. In the '79 Fastnet, many rope tethers failed when crew relying upon them were flung by the violent rolls of the yachts in heavy seas (for more see Mate's book, Fastnet Force 10). The two legged--one short, one longer--tether made of tubular webbing is much preferable, with leg lengths sized for your particular application. A further improvement is to encase a length of shock-cord, roughly 75% of the length of the legs within the cores of webbing tubes, secured at each end of the leg. The shock-cord will allow the legs of the tether to retract somewhat keeping them from under foot when moving about on deck but allowing one to extend them full length, when necessary. A sizable shock-cord with also buffer, to a limited extent, the sudden shock if one is thrown or falls to the end of ones tether length.

Ideally, a tether should keep one on the boat. A jack line amid-ships with a tether length that will not allow one to go over the side is preferred tho' sometimes impracticable.

FWIW...

Yes if you have it short (and IMO you should), you should have two, so you can clip one on before taking the other off, just as you would in mountain climbing. In fact, I think about rock-climbing when I move around the boat, especially in heavy seas.

I know someone who was saved by his tether. He was standing on the cabin by the mast putting reefs in because of a sudden and very strong storm. He clipped one end to him, wrapped it around the mast twice, and then clipped the other end on to him. So when the boat got knocked down and he was thrown off the deck and through the lifelines, the tether stopped him when his waist was at the edge of the boat, and then tugged him back. The boat sat up again, and he was on, not off, the boat. He then had a really wild ride -- but he was alive, and not being dragged behind his boat.

If the tether is too long and you go over, the best you can say is that they'll find your body with the boat. IMO a tether badly used is very dangerous.

[Rakuflames]

Originally Posted by Randy

Evans,
I appreciate your experience and contributions to this forum as well as elsewhere. The numbers that I threw out there are taken (I believe accurately) from the ANSI Z359 code which addresses fall protection code. I've had a fair amount of training in fall protection but wouldn't call myself an expert in the field. The physics are well established but poorly understood in the yachting world nor is the hardware well adapted to the yachting environment. I believe in your paper on tethers you refer to a European version of the ANSI code which will be very similar.

One thing I haven't seen mentioned yet is the need for a crotch strap so the chest doesn't take all the forces. I know someone whose opinion I respect who says that harnesses without crotch straps can result in broken ribs, and if he's right -- you really don't stand a chance of saving yourself if you're being dragged by your boat with broken ribs. He has a whole neck to thigh suit he wears that attaches to a tether (he does some really serious single-handing). Next time I see him, I'm going to ask to see it.

(I hope he didn't get it for his birthday -- har-dee har har!)

[builder dan]

boat specific but I reckon as short as you can manage and still reef down etc,nothing worse than tripping over long tethers.

[conachair]

I use a grigri.

Works great for me, tether whatever length you want.


http://en.m.wikipedia.org/wiki/Grigri_(climbing)

[Miniyot]

Years ago in construction, our "fall protection" was a piece of rope and a safety belt. There were alot of injuries from the safety belt when someone fell.

Now, we have to use a 5 point harness and a specially designed webbing that will absorb the shock load of a fall.

You might think I'm talking about a 20 foot fall.....you are wrong, it's only six feet. Can you imagine falling, but your safety gear catches you at 6 feet but your back gets broken because you only had a belt and rope? It used to happen.

Will I take that chance because I am on a boat and not building a high rise? In one word NO. in two words....HE** NO.....
This isn't the 18th century where sailors were tuff old coots and didn't need no bloody safety sh!t......
When I get the boat I want and get of this stinking island, you can bet I will have a 5 point harness, and 2 web straps designed for fall protection. Each web will be attach to a jackline (one on each side of boat) so incase I do fall during a storm, I will not fall far and the jacklines will be spaced far enough apart so I can perform the duties i will need to do without being able to fall overboard.
Laugh if you want but its better to be safe than dead.