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Go Back   SailNet Community > General Interest > General Discussion (sailing related)
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  #1  
Old 02-15-2005
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Physics of the random overhand

I have long wondered what principle of physics causes a neatly coiled line to spontaneously sprout overhands as it is belayed. Has there ever been a study? Any general thoughts?
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Old 02-16-2005
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Physics of the random overhand

It''s in the technique. When you go to throw your line, you NEVER throw the whole coil. If it has been neatly coiled, take half, or your best estimate of the amount of line you will need to get over to the person at the receiving end, in one hand and and the rest in the other. Using a steady, swinging motion, like a softball underhand pitch, and throw the line, allowing any more needed lengths to come out of your other hand. Amazes your friends and dock boys!

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Old 02-16-2005
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Physics of the random overhand

My Bad. I re-read your post, you were talking about belaying, not heaving.

When you coil a line, you are preparing it for storage. You notice that when you coil a line, you have to add a half-twist to it so the coils lie neatly. That is the problem. A coil is for static storage. When you wish to use a line for active purposes, it should be flaked, not coiled.

When you flake a line, you are not adding any twist, so when the line shakes out, it will not have a tendancy to snake around itself.

This technique should be observed when you are close tacking. The tail of the sheet should be flaked (sort of zig-zagged back and forth on itself) to allow it to run freely through the footblock.

Just remember to flake, and not coil lines, you are sailing with and you won''t have this problem. It''s that twist you add when coiling that causes the problem!
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Old 02-16-2005
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Physics of the random overhand

sneuman,

Your inquiry has to do with the mathematics of topology. First off, here''s a website for you:

http://www.maa.org/mathland/mathtrek_11_3.html

I think it''s helpful to use an analogy to understand what happens to this "neatly coiled rope" as we feed it out. Imagine a chinese yo-yo (a strip of paper coiled about itself and fastened to a stick). It''s analogous to your neatly coiled rope. Imagine you grab the end of the paper strip and pull it as far away from the stick as you can, if the paper doesn''t kink what you will end up with is a twisted strip of paper, looking like an archemedial screw or helical auger bit. Thus the coiled rope has twists incorporated in it when it is coiled in the conventional way.

This is why your handy garden hose neatly coiled at the slip develops kinks when you deploy it to wash your boat or flush your engine. Unless you carefully untwist it when you deploy it you will retain the twist it has in its coiled state.

Flaking is, of course, a way to stow line without twisting it. Another thing you can do is coil a hose or a rope without twist by reversing the twist on every other coil (sort of like adding coils alternately to the back and front side of the stack of coils). You can demonstrate this with a long rubber band or a long strip of paper. Take the long rubber band (or the strip of paper with the ends taped together endwise) and coil it into three smaller coils. If you do it the right way you will have three coils without twist. You will be able to trace your finger along the outside of the coils without encountering a twist. If you pick up these three coils and look at them, you will see that there is a point at which the strip will cross from one side of the coils to the other, crossing over the middle coil. Additional pairs of oppositely twisted coils can be added to form a coiled rope or strip of material with numerous coils, with no net twist in it. Unfortunately, because of the crossing that the coils must do to form this zero "net twist" state, it''s probably not a good way to stow line for quick deployment, as in paying out the line it might get knotted or knuckled. What do you experienced cruisers with rope anchor rodes think about flaking vs. untwisted coiling?

Allen Flanigan
Alexandria, VA
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Old 02-17-2005
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Physics of the random overhand

thanks for the info - and especially for the advice on flaking instead of coiling. I never thought about that, but it makes sense!
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Old 03-12-2005
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Physics of the random overhand

You can pick up a flaked line (shaped like a figure eight) and fold the two loops together to store them like a coil, but first tie up each loop with a piece of twine so you can correctly separate them when you want to deploy it again.
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Old 03-12-2005
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Physics of the random overhand

Okay, after all this instuction, you still flung thirty fathoms of coiled line at the dock and wound up with a boar''s nest. Next time out, tie one end of the mess to the stern, and let the rest stream behind you for a few (or several, depending) miles.
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