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Old 03-08-2016, 03:05   #61
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Re: whipping - antal method - low friction ring

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Originally Posted by nigel1 View Post
Regarding shaping the LF ring more in the shape of the traditional pear shaped thimble.
My thoughts are that the LF rings are probably machined, turned up on a lathe, which would reduce the time needed to smooth the ring.
I wonder if a separate rounded top wedge shaped piece could be molded, and then fitted on the ring.
If the top of the wedge was made with a convex top, and the two sides concave, a snug fit could be achieved and then held in place with a suitable whipping or seizing.

When I did my apprenticeship, we had to be competent in the making of pilot ladders. Above and below the each step, where the ropes passed through, wooden wedges were fitted and then a seizing made around the ropes to hold the wedges in place.



For some reason, in the UK, these wedges were known as winnets, I never discovered how they got this name, (I do know the other meaning for winnet), but the term is still used.
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That is a brilliant idea regarding the wedge shaped piece, Nigel.

The two pieces needn't even be stuck together. You could just have a wedge that was curved at the top to sit snuggly against the inside curve of the ring tucked under the flange and throw a loop of dyneema over and secure it. The wedge could never come out unless your method of securing the loop failed.

If you wanted to whip it, the force at the throat is dramatically less then if you do this at the edge of the ring itself.
My opinion is that if you want a strop, then a better solution (still not ideal, but a lot better) is to make Brummel lock then 2 long bury splices as CF member Benz is doing. Very simple, secure and nothing needs to be "added" to the loops.
If you want a soft shackle type of strop that can be made up about a third as long as a loop strop, there are all sorts of options there as well for securing it.

For a perfect fit, you would need to have a "wedge" available per ring. One size could be used less snuggly on several rings maybe? They could simply be sold as accessory parts. The shape of them is complicated, but they don't have to be aluminium. A moulded plastic wedge would work extremely well I think. Cheap and easy to produce. The doubt the stress on them would be high, as they are just used to "fill" the gap in the throat.

We are starting to use these rings more and more and simple, decent solutions need to be found for securing them.

SWL
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Old 03-08-2016, 03:53   #62
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Re: whipping - antal method - low friction ring

I agree with Nigel that a pear-shaped low friction ring would definitely be much more difficult and expensive to make.

I also don't think that these rings are any problem. I have been sailing hard on an almost daily basis, with rings laced up per SWL's original design, and also according to my own more primitive invention, and they are holding up perfectly. This is under tonnes of force -- jib sheet leads (twings).

I can't comment on SWL's table*, but I would like to opine that compromise of strength is not the only, and perhaps not even the main problem here. The throat angle will improve under load as the slack in the system is taken out.

In my opinion the bigger problem is the seizing working loose as the construction "pants" under load -- something I experienced with a couple of generations of strops I made with seizing.

The lacing totally eliminates this and is actually really satisfactory. SWL's lacing cleverly puts bulk between the strop legs (no dirty jokes please) to keep them apart and reduce the throat angle. This greatly reduces or eliminates the "panting" which destroys seizing in my experience.

I guess SWL's diamond-woven strops will also be fine. I'll make a couple of them when I have a chance.




* I'm not sure that 33% of the system load, acting on the seizing, is a problem, with regard to strength of the system, if there are many loops of seizing spreading the load. Maybe it is a problem, but it's not obvious to me, anyway.
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Old 04-08-2016, 14:06   #63
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Re: whipping - antal method - low friction ring

SWL

I suspect you are over-thinking the side load at the throat. The side load does not add a ton of stress on the fibers. It adds compressive force on the fibers but that is not "tearing" anything apart. Small angles in the direction of the pull just increase the load as a sin/cos function. For small angles the increase in load is not a lot. I think for 10 degrees deflection the side forces are <5% of the applied load. This is why people "sweat" lines to add tension. The side load is on the order of one tenth of the main load.
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Old 14-08-2016, 04:55   #64
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Re: whipping - antal method - low friction ring

I used to be a mechanical engineer....


The stress on whipping is 50%.

Yes, it is pulling 100% along the axis of pull, and there is a lateral component of 50 (compression ) each sides (statically fixed, and still) and of 75 %along the throat line of Dyneema, to close the triangle of forces.

Dyneema has two lines, each taking up half of 150% of nominal pull, on the increase due to the bending up to 150%

Same for the thread of whipping. They avoid the release of loops horizontally, therefore they match the 50% component of stress perpendicular to the pulling line.

Point is another one: first loop will absorb say 65% INITIALLY of the total nominal stress (50%) and will, though minimally, stretch and loosen, giving out some stress, going down to say (??) 50% of nominal stress.

Second closest loop will absorb say 30% of nominal stress, with trivial deformation, for our purposes.
Third pull carries up another 15%,.. 4th and 5th the residual 5%, assuming the 6th loop (at 1 diameter distance, better of 1,5X) unstressed.

That said, I knew of these rings being used for 3D regulation of clew-points...only... what ELSE??

Should I be concerned at having none on my cruiser?? :-)
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