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post #11 of 45 Old 08-17-2008
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G forces are one thing... being held against the hull by a tether and 6+ knots of water is entirely another. Buy strong. Also consider chafe and UV degradation. The stronger material will have a longer useful life.

As for the material itself, I am a fan of the polyester webbing. It lays nice and flat on the deck. When it is wet it almost sticks to the deck nearly eliminating the tripping hazard. breaking strength is 7000 lbs according to WM.

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post #12 of 45 Old 08-17-2008 Thread Starter
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My question was based on going to a climbing & mountaineering store. That was poopoo'ed. I guess falling 100' off a cliff while the safety line is being abraded on sharp rock is not nearly as bad as falling 5 or 10 feet off a boat. Looks like the mountaineering folks don't know anything about line strength or safety. Thanks for the warning.
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post #13 of 45 Old 08-17-2008
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xort,

aving been on my share of rocks, with the potential for a 3000' one way or 2000' free fall the other.......I personally do not think it matters "WHICH" place you buy the material at. In the end, it is quite possible the webbing is made at the same factory in "timbuktoo"! Just packaged accordingly.

So as to not poopoo the other posts, I do believe the strength parts are going to be the same either way. BUT, if falling while climbing, one is usually looking for a bit more potential stretch than a jackline on a boat. Only because you will usually fall at minimum 10-20' to upwards of 150' or what ever the rope length is you are tied to. Again, not really answering your question, just why the two webbings may have different ratings and needs.

In all honesty, I would probably hit my favorite outdoor place BEFORE a marine shop as the prices are generally cheaper. BUT< I have seen marine places with jacklines premake with loops to tie one end from the get go. so potentially worth the slight extra in cost.

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post #14 of 45 Old 08-17-2008
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Xort,

Relax, your post raised a great question and I don't see anyone attacking you. Many folks reading this thread will not have much of an idea about the forces involved and so far I think the conversation has been helpful.. At least it has for me.

For what it's worth, I bought the 4700# rated nylon webbing from Sailrite along with a pair of Wichard hooks for one end of each of the two jacklines I made up. I run them from the forward sampson post down each side and secure the aft end to my aft deck cleats located about 4' forward of the stern.

I tension them as tight as I can make them by hand and secure them to the cleat using the standard hitch for such a cleat. I note they have considerable stretch when they get wet. We have been fortunate to date to not have pressed them into extreme service so I can't offer any insights on failure mode of my home built jacklines.

I also have SS cable lifelines down each side of the deck at 15 and 30" above the deck. THe bronze stanchions are bolted thru the deck with backing plates.


Good luck in your research.

Best Regards, John

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Last edited by Whampoa; 08-17-2008 at 03:24 PM. Reason: Spelling Correction
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post #15 of 45 Old 08-17-2008
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The G forces in the fall are proportional not only to height of fall (acceleration part), but also to the distance allowed to come to total stop (decelerating part). In the Dog's example if the steel ball would compress only 0.1 mm the G force would be extremely large. If on the other hand it could compress 10mm (or fall to a flexible surface like 10mm neoprene pad) the G force would be relatively small.
So, having SOME stretch is desirable in theaters and jacklines.
If you used steel wire for jackline and theater and harness you could stay on the deck, but with broken spine.
Too much stretch is bad as it would allow you to fall overboard. The idea is to stay ON the boat if at all possible.
The forces on jacklines are very large also because you can pull perpendicular to the line stretched between two points. creating a large purchase.
Therefore - low stretch and strong is good.

The forces of dragging a body in the water at 6+ knots are not that great - not more then 2 or 3 times your weight - still more then you can pull - so do not go over.


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post #16 of 45 Old 08-17-2008
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By the way - we often have some fun when sailing in warm waters by tying a docking line on stern cleat, leaving the other end dragging in the water and jumping into the water (not all crew of course) catching the line and drag yourself behind a boat.
Observations:
Almost anyone can hold easy at 2 knots and also climb a boarding ladder.

At 3 knots you can hold easy as long you are retaining hydrodynamic shape. Be prepared to get some water in your mouth if you are not careful. Climbing a ladder becomes difficult (hard to overcome the force of water to bring your leg forward

4 knots is the limit for most people. you can hold, but you have difficulties advancing towards the boat, you must be careful not to drink too much water, getting aboard is only possible by pulling yourself up with your arms, not using the legs at all until the legs are out of water.

5 knots - only for people in good physical condition

6 knots - water over your head most of the time, you must turn backwards to breathe, once you arm gets downstream it is very hard to bring it forward under the water. you can not make advances toward the boat.

All this was always conducted wearing only a swim suit (lo life jacket) in warm water, for fun.
If I imagine any clothing + life jacket getting back aboard at 5 knots is not an option. OK, adrenalin could help to gain additional strength, but do not count on it.


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post #17 of 45 Old 08-17-2008
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Quote:
Originally Posted by xort View Post
My question was based on going to a climbing & mountaineering store. That was poopoo'ed.
I don't recall anybody pooh-poohing your idea of going to a mountaineering store--just alterative suggestions. I assumed you were looking for such by the nature of your OP.

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post #18 of 45 Old 08-17-2008
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G-forces measure the approximate acceleration or deceleration of a body. Acceleration/deceleration at 9.8 m/s^2 is equal to 1 G.

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post #19 of 45 Old 08-18-2008
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My jacklines, and harness saved my life while single-handing. I used flat webbing with SS buckles on the ends. Ran them through the stern cleats, and also through the bow cleat. I kept them a wee bit tight, so they wouldn't bunch up when dragging my harness clip. When it was wet it would stretch, and bunch up a bit. They still managed to yank me back onto the boat when I was thrown from Frolic.
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post #20 of 45 Old 08-18-2008
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Also remember that the jackline is not the only component whose strength and stretch is involved. The tether also has some stretch and that is important to avoid the injury possible with a high-g stop. So when you are considering appropriate stretch and loading, consider the system, not just one component.
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