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Old 15-11-2008, 19:01   #1
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Prussic hitch to secure achor bridle

Why not keep a short loop clipped to a ~20' line to provide for bridle adjustment?

www.spadout.com/wiki/index.php/Prussic

This is generally a rock climber knot, but it grips well, is often used in life-or-death situations, and is very well proven. You can tie it with one hand while hanging from a cliff - or a forestay - and can't get it wrong. This seems simpler than a knot (either icicle or rolling hitch) that takes some forming to be reliable.

The negative - or positive - is that it will not release under load. It is required that the prussic line be smaller than the line it is gripping, but it is doubled.
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Old 15-11-2008, 19:40   #2
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Very interesting and potentially useful knot. Thanks for that.
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Old 16-11-2008, 02:46   #3
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Yes, that’s the ‘basic’ Prusik, or what construction riggers used to call a “Double Sliding Hitch”.
I’ve always used - and highly recommend - the “Triple Sliding Hitch”, which requires adding a third turn.



See also the Prusik Knot described under Basic Roped Rescue Knots:
http://www.rescueresponse.com/html/n...technique.html
and
Transferring a Load from Belayer to Anchor via a Prusik Sling

http://www.rescuedynamics.ca/article...nterTieOff.pdf


and my favorite 'knot' site:
“Animated Knots by Grog”
Knot-Tying for Boating, Climbing, Fishing, Scouting, and Arborists

Animated Knots by Grog
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Old 16-11-2008, 04:01   #4
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It is possible to get it wrong when in a hurry. I use it to climb trees for tree surgery. Whilst not critical it can lessen the drag, and increase the difficulty to "ease it" A wonderful knot BUT.....if it is slid through in a hurry it will heat up BIG TIME after all it is only friction. In climbing ropes it is important to move the location where the standing part is. It will melt the surface of the rope if you descend quickly. . In a boating sense I think that the same applies. Use it to work on the mast all the time (with a halyard) . If you are fit the double prussic makes for an easy ascender.
The easiest method is one to the foot and one to the waist(bum). Stand and slide, stand and slide.

cheers
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Old 16-11-2008, 08:52   #5
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To Cooper: Sliding one rope over another under load is very dangerous

You are correct; regardless of the knot type, if the load is there and there is enough motion, one will melt. A few days ago I saw an illustration in a book suggestion that a good way to descend from the masthead is to wrap the lazy end of the rope around the webbing on the bosons chair in such a way as to cause friction, and lower away. I have seen a climber scraped up (he lived) because he lowered off a cliff with his rope sliding through a webbing sling.

Sliding under load is best rope-on-metal. A munter hitch around a separate biner would be very safe. There is rope-to-rope friction with a munter hitch, but the contact point keeps moving so heat does not build.

My real question was how will a prussic hold at a 60 degree angle, cycling and wet? I guess I will do some trials with undersize lines, to see.
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Old 16-11-2008, 13:37   #6
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Red face

There are some interesting devices made to replace prusiks. For about $25 you could get a wild country ascender. It cams down on the rope but fits 10-11mm sized ropes. You could use the ascender and then back it up with a hard not for peace of mind. $25 would buy you a life times worth of prusik material.
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Old 16-11-2008, 15:00   #7
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Hey, climber dude from Colorado; I have climbed in Eldorado and Boulder Canyon - very nice. I am from Virginia, but have been climbing rock and ice all over for 25+ years.

I know for a fact that most camming devices of that sort can slip if loaded other than 180 degrees, and jumars have been known to lever clean off a rope on a diagonal. There are also rope wear issues.

I use Jumars climbing the mast and would use the pictured device as a safety, no question, but I would not use them for this application, I don't think. Which is why I started the thread.
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Old 16-11-2008, 16:04   #8
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Back to the original question

I've used a prussic hitch to attach an anchoring snubber line to both nylon and chain rodes for decades now. It is possible to attach back-up sacrificial snubbers using a boat hook to run them out on an already stretched out rode.

My experience is that the hitch in this application does not slide once you "set" it on rode (snubber dia equal to or less than the rode dia) or chain. It can be attached one-handed in a swell when you need the other hand to hold on to the boat for safety. Practice doing it.

I've ridden out some very heavy swells and wind with the hitch attaching snubber lines and broken some sacrificial snubbers due to chafe on the boat but always had a back-up ready. Since that time I use Dacron at the boat end overboard past fairleads thence attached to nylon the rest of the way to the rode with no failures in heavy swells.
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Old 16-11-2008, 17:25   #9
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No-stretch = less chafe

Thanks Rick, for the practical answer. I still wonder about the angle of a bridle.

Though stretchy material is best for anchor rode, non-stretch is best for bridles and the like. The reason is that stretch encourages chafe. Rock climbers learned years ago - I hope - that ONLY the rope should be stretchy, and that all anchors should be static, lest they cut through on a sharp edge. I always use old mainsheets and halyards for the sacrificial bits. Very low stretch, and I cover wear spots with tubular webbing.
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Old 17-11-2008, 20:33   #10
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we always use a variation with several more turns going away from the standing portion down the anchor line and a couple coming behind. Like the triple except with 5 turns forward and 2 turns aft. Stayed for a total of probably 10 months at anchor in different places and lots of wind and swell. Never a problem.
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