Cow Hitch vs Spliced Loop

[Dockhead]

My sheet leads for my blade jib (which I use more than the 120% yankee) employ low friction rings and dyneema loops attached to strong through-bolted padeyes.

This system has to carry tons of forces, and the dyneema of my loops seems to be squashed where it is cow-hitched to the padeyes.

The padeye loops are similar to the diameter of the dyneema (8mm I believe). So I would have thought that it is not that much weakened by this method of attachment.

Yet I seem to recall that someone on here (SWL?) was carrying on about how much a cow hitch weakens a piece of rope.

Would it be better to simply splice it in a simple loop?

Or maybe there is some kind of hardware I could use -- a kind of grommet -- to increase the diameter of the turn?

Anyone have any experience or ideas about this?

[Seaworthy Lass]

Originally Posted by Dockhead

My sheet leads for my blade jib (which I use more than the 120% yankee) employ low friction rings and dyneema loops attached to strong through-bolted padeyes.

This system has to carry tons of forces, and the dyneema of my loops seems to be squashed where it is cow-hitched to the padeyes.

The padeye loops are similar to the diameter of the dyneema (8mm I believe). So I would have thought that it is not that much weakened by this method of attachment.

Yet I seem to recall that someone on here (SWL?) was carrying on about how much a cow hitch weakens a piece of rope.

Would it be better to simply splice it in a simple loop?

Or maybe there is some kind of hardware I could use -- a kind of grommet -- to increase the diameter of the turn?

Anyone have any experience or ideas about this?

Yes, a cow hitch will apparently weaken the loop by about 50% when used on a padeye of similar diameter.
Edited to add: I checked the figures Evan's Starzinger and system strength is apparently down to 42% for a loop attached with a cow hitch going around a 1:1 bend ie system strength is down to 85% of line strength instead of a potential 200%.

The problem with splicing the loop onto the padeye is that it is then not removeable and replacement is slow. Also, your work needs to be done outside.

Dockhead, the Bullseye soft shackle is ideal for this purpose with an estimated significant increase in strength over a loop made using the same thickness dyneema.

SWL

[Dockhead]

Originally Posted by Seaworthy Lass

Yes, a cow hitch will apparently weaken the loop by about 50% when used on a padeye of similar diameter.

The problem with splicing the loop onto the padeye is that it is then not removeable and replacement is slow. Also, your work needs to be done outside.

Dockhead, the Bullseye soft shackle is ideal for this purpose with an estimated significant increase in strength over a loop made using the same thickness dyneema.

SWL

OK, thanks. Maybe I'll try that. But does that address the problem? I think the extra strength would be useless if the body of the shackle is itself weakened to such an extent by having to make such a sharp bend around the shackle (its own diameter).


When I wrote "grommet" above; I meant "thimble". Brain fart.

Like one of these:



Not sure I'd want all that hard stuff flopping around up there, though.

[Seaworthy Lass]

Originally Posted by Dockhead

OK, thanks. Maybe I'll try that. But does that address the problem? I think the extra strength would be useless if the body of the shackle is itself weakened to such an extent by having to make such a sharp bend around the shackle (its own diameter).


When I wrote "grommet" above; I meant "thimble". Brain fart.

Like one of these:

Not sure I'd want all that hard stuff flopping around up there, though.

A thick shackle would work as well if you wanted to secure a loop and make it removable, but the problem again is that you have a hard fitting banging on the deck. Something you really want to avoid. You could make it a thick soft shackle, but that is adding unnecessary complexity and length.

-----

The issue of strength being reduced as the dyneema is passing around an object is less of a concern for a soft shackle than a loop made with the same dyneema, as the maximum "potential strength" is much greater for a soft shackle than a loop to start with.

For a 1:1 padeye:dyneema diameter, the overriding loss in strength with a Bulleye soft shackle using a diamond knot is from the knot, not the 1:1 turn.

SWL

[Dockhead]

Originally Posted by Seaworthy Lass

A thick shackle would work as well if you wanted to secure a loop and make it removable, but the problem again is that you have a hard fitting banging on the deck. Something you really want to avoid. You could make it a thick soft shackle, but that is adding unnecessary complexity and length.

-----

The issue of strength being reduced as the dyneema is passing around an object is less of a concern for a soft shackle than a loop made with the same dyneema, as the maximum "potential strength" is much greater for a soft shackle than a loop to start with.

For a 1:1 padeye:dyneema diameter, the overriding loss in strength with a Bulleye soft shackle using a diamond knot is from the knot, not the 1:1 turn.

SWL

You're a very good and very persistent saleswoman

That sounds pretty persuasive, actually. What are the strength calculations according to your reckoning?

[Seaworthy Lass]

Originally Posted by Dockhead

You're a very good and very persistent saleswoman

That sounds pretty persuasive, actually. What are the strength calculations according to your reckoning?

I have been very quiet for 6 months, but you did ask .

1.75 x line strength is estimated (Evans Starzinger concurred) if passing around something with a similar diameter.

A loop will only have a bit less than 1 x. Cowhitched, even less.

SWL

[Dockhead]

Originally Posted by Seaworthy Lass

I have been very quiet for 6 months, but you did ask .

1.75 x line strength is estimated (Evans Starzinger concurred) if passing around something with a similar diameter.

A loop will only have a bit less than 1 x.

SWL

OK, I am persuaded

When I change the current tethers, I'll switch over to your shackles.

By the way, what do we think about UV deterioration of these dyneema shackles and loops? Some of mine are looking faded and feel different -- kind of fluffy and friable, as if. I think that must be deterioration of the resin or whatever they put into the fibers, and not the fibers themselves, but what do you think? I don't actually fancy one of these letting go while I'm sailing hard in rough sea conditions.

[Stumble]

Originally Posted by Dockhead

OK, I am persuaded

When I change the current tethers, I'll switch over to your shackles.

By the way, what do we think about UV deterioration of these dyneema shackles and loops? Some of mine are looking faded and feel different -- kind of fluffy and friable, as if. I think that must be deterioration of the resin or whatever they put into the fibers, and not the fibers themselves, but what do you think? I don't actually fancy one of these letting go while I'm sailing hard in rough sea conditions.

It really depends on how far gone they are, but luckily Samson has a nice pocket guide for dyneema inspections. It's on a continuum so as it gets progressive you worse you more seriously need to think of replacement. http://www.samsonrope.com/Documents/..._Guide_WEB.pdf

The one thing to keep in mind is that the guide they publish is for tugs based on a 5:1 safety margin. If you specced your line fore stretch, then you are initially operating at closer to 10:1, so a little line strength loss isn't quite the issue it is for towing.

[Bor the Wolf]

Maybe I've hit a language barrier here but what is wrong with using simple bowline and tie the sheet directly to the sail. Fast and easy. I've been doing it like that for almost 40 years but maybe I'm old fashioned?

[Dockhead]

Originally Posted by Bor the Wolf

Maybe I've hit a language barrier here but what is wrong with using simple bowline and tie the sheet directly to the sail. Fast and easy. I've been doing it like that for almost 40 years but maybe I'm old fashioned?

We weren't talking about the attachment to the clew -- we were talking about sheet leads using low friction eyes, as an alternative to jib cars, a system used on racing boats and very nice on cruisers as well.


Changing the subject to clew attachments -- I also attach normal polyester sheets with bowlines. But Dyneema sheets don't like knots -- Dyneema is too slippery for good knots, and knots weaken Dyneema too much. For Dyneema sheets, you need to splice an eye at the end and use a soft shackle.

[Seaworthy Lass]

Originally Posted by Bor the Wolf

Maybe I've hit a language barrier here but what is wrong with using simple bowline and tie the sheet directly to the sail. Fast and easy. I've been doing it like that for almost 40 years but maybe I'm old fashioned?

With a cutter rig the bowlines can catch on the staysail when tacking, so eliminating this without adding solid hardware is good.

If the ends of the sheets have an eye splice a soft shackle will easily, quickly and strongly connect the sheets to the clew. Disconnecting the sheets can be done quickly and easily as well.

Dockhead is enquiring about the best way of attaching low friction rings to the deck though to enable the clew to be easily manouvered up and down and in and out.

SWL

[Oceanride007]

Suggest you do away with the cow hitch,
Reason being is that cowhitches concentrate the load unevenly, whereas a loop will rotate.
My experience in this matter is related to Harbour Tugboats. There loops use to be triple cowhitched but now they lash the dyneema thimble to make the end loops. Then they retie the lashings to rotate the thimble, so that the wear is not concentrated.

[TheThunderbird]

Whatever said, bending a rope on a 1:1 diameter ratio is too severe a setting.

The section gets fully flexed.

ALSO, as with bollards, l turn a rope 360°, not 180°, for lower chafing.

PS l use Wichard thimbles on halyards. Each season, l have to shorten/reverse the line, sk78 gets whirled and squeezed as i never saw on PE ropes. Just the view is miserable, hopefully !?

[sailcrazy]

We had the same issue, with the headsail clew attach/sheet catching on the staysail. About 6 yrs ago we bought a new sheet twice as long as each side, doubled the sheet and put that middle loop through the clew, and then put both ends thru that loop. No knot, and nothing to catch on....works well! We do undo the connection each end of season, and wash the sheet and let it relax.....but so far no evidence of any issue with the sheet.

[UNCIVILIZED]

For chafe & UV resistance, Maxi Jacket II or RP25 will help things a bit. And why not add a short section of chafe sleeve over the Dyneema where it makes sharp turns around fittings? Enough so that the Dyneema itself is covered where it would touch the metal. But not for 100% of the length of the cordage used. Though you'll probably need to stitch it in place, & perhaps paint it with Maxi Jacket II/RP25 as well, so that it stays put.