Rolling Hitch on Snubber

[JPA Cate]

Evans,

As long as you're running experiments, have you considered using polyester 3-strand line? We used it for a double preventer on our first Insatiable, when the nylon proved too stretchy.

Our snubber, as Jim wrote earlier, is 16 mm nylon double braid, and works well. We stopped using 3 strand because its twist eventually twisted the chain too, in spite of the swivel. So, we quit using it and took the swivel out. No problems. Go figure.

P.S. For the Australians, you can get nylon double braid in Oz, a chandler will order it specially for you.

[s/v Jedi]

Originally Posted by Cotemar

Here is a good video showing just how strong the Soft Shackles are

Indeed, here is another one that shows how it fails at the knot. Also note that the knot is somewhere halfway, in the open between attachment points like it should be regardless of Andrew's theories

rope test 042110(2).wmv - YouTube

[estarzinger]

^^ I run all my soft loops up to 1000kg's (pulling on my 64 winches) just to set the diamond knot. I have never tried to actually break one - not sure I could.

[estarzinger]

Originally Posted by Kettlewell

>>I find that very hard to believe.

Well, I can't help you there. That's what the data says. It is possible that the BoatUS insured sample is somehow skewed, but its a pretty big sample. It's also pretty clear what the loss ratio says (about which type of line has the greater loss propensity), and that is true independent of the sample representativeness.

>> Even the NE Ropes Dyneema ones are supposed to be attached to nylon like this.

You will notice that even there they are not recommending 3 strand or plait, but rather "standard Nylon Double Braid". And it's obvious they are incorporating dyneema into the system (at some significant incremental cost) to try to reduce the inherent chafe vulnerability of the nylon. This sort of hybred . . . dyneema running out over the bow roller then changing to nylon, would also make for an interesting snubber. I can see definite design advantages of it and like it better than the Yale solution (nylon core/Dacron cover). It's the best idea I have see so far for the actual sunbber line.

..........

[Cotemar]

Originally Posted by s/v Jedi

Indeed, here is another one that shows how it fails at the knot. Also note that the knot is somewhere halfway, in the open between attachment points like it should be regardless of Andrew's theories

These Soft Shackles can really take a beating.

I am at my nav station right now making up a few of them.
Purchased some Samson Amsteel 1/8, 5/32, 3/16 and 1/4" and making them using the "Better Soft Shackle" Method
Will post some pictures when they are done.

[Jim Cate]

Re the load testing: were there any numbers given? What was the breaking load and what size and variety was the dyneema used?

Interesting that there were isolated strands failing well before the whole thing failed... might be an early warning of overload in use.

Cheers,

Jim

[estarzinger]

So I think I will make up one of these "Dyneema from the cleat to over the roller and then nylon to the soft shackle" snubber lines.

I have some extra 1/2" amsteel onboard - its 7' from the roller to the cleat. Add 1' to go over the roller, plus 5' to go around the cleat and some extra and it sounds like the dynnema part should be 13'.

I have 5/8" nylon on board but will try to dig up some 1/2" nylon. For this design it seems like max elasticity is correct - that would be nylon brait I guess? I think I might go for 15' of that - splices loops on both ends - cow hitched to the dyneema and stainless thimble for the soft shackle (I know Jedi does not think the thimble is necessary but I like them). The nylon part can always be swapped out later.

Before I make it . . . . any comments . . . . does that sounds about right?

[sabray]

That's prett close to what I did for my mooring penant. All eye spliced. Playing with Amsteel loops and snubber. Best would be like my mooring where Dyneema is at the chafe point and shock is over the side. Think a really long Dyneema loop through the hawser with octoplait running to midship is a good setup.with Dyneema loops as a replacement for chain kook have found it works very well. Easy to set up

[s/v Jedi]

Originally Posted by estarzinger

So I think I will make up one of these "Dyneema from the cleat to over the roller and then nylon to the soft shackle" snubber lines.

I have some extra 1/2" amsteel onboard - its 7' from the roller to the cleat. Add 1' to go over the roller, plus 5' to go around the cleat and some extra and it sounds like the dynnema part should be 13'.

I have 5/8" nylon on board but will try to dig up some 1/2" nylon. For this design it seems like max elasticity is correct - that would be nylon brait I guess? I think I might go for 15' of that - splices loops on both ends - cow hitched to the dyneema and stainless thimble for the soft shackle (I know Jedi does not think the thimble is necessary but I like them). The nylon part can always be swapped out later.

Before I make it . . . . any comments . . . . does that sounds about right?

Why would you cow hitch on one end that never gets submerged and then use a steel thimble on the other end where it's goes in & out salt water all the time is pretty weird yes Make it as simple as can be is what I like. Try it without thimble and you'll find life is good

About the dyneema part of the snubber: this length does not count for stretch so the whole thing will become longer.

I don't think this is a good plan. Lots of money and more trouble with longer snubbers for what? A little more life span? The nylon snubber itself is chafing gear and can be cheaply replaced by a nice new one. Stretching of the part on deck is the bonus. Also, when it breaks there is no problem like on a mooring: this is just a snubber for the anchor rode; for the line to attach to a mooring it's another situation as it is all that is holding the boat in place.

[Cotemar]

Originally Posted by Jim Cate

Re the load testing: were there any numbers given? What was the breaking load and what size and variety was the dyneema used?

Interesting that there were isolated strands failing well before the whole thing failed... might be an early warning of overload in use.

Cheers,

Jim

From all the info I have seen so far, it looks like the breaking strength of these Amsteel / Dyneema 12-strand Soft Shackles is equal to there advertised tensile strength.

1/8" has a tensile strength of 2,500 lbs

5/32" is 4,000 lbs

3/16" is 5,400 lbs

1/4" is 8,600 lbs

5/16" is 13,700 lbs

3/8" is 19,600 lbs

7/16" is 23,900 lbs

1/2" is 34,000 lbs

5/8" is 40,700 lbs

[SVNeko]

I think the question of thimble or not is an important one. It doesn't matter too much for a snubber, but if we could do away with thimbles and just cow hitch a soft shackle to spliced loops, it would make a lot of things easier. Is there anything to indicate this would not be appropriate in a more critical application - eg, connecting lines for a drogue or a regular chain/rope attachment for a secondary anchor? Would the dyneema cut the weaker rope?

[estarzinger]

OK, here is version #1 of my test snubber. I decided to use some of the climbing line I already have on board for the nylon part. I am not sure how to put splices in the climbing line, so I have used knots for now (a figure 8 and a double sheet bend). I have it deployed, but it's not so windy right now.



I was thinking if I want more snubber or more elasticity I could attach a piece of nylon from to the inboard end of the dyneema and take that nylon to a mid-ships cleat. I doubt that will be necessary but it's an option.

[conachair]

Originally Posted by estarzinger

^^ I run all my soft loops up to 1000kg's (pulling on my 64 winches) just to set the diamond knot. I have never tried to actually break one - not sure I could.

I cranked one up to 2500kg, would have went further but that was the biggest load cell there was.



Strong stuff

[conachair]

Originally Posted by estarzinger

Before I make it . . . . any comments . . . . does that sounds about right?

Did you have a look at this link? Recommends joining polyester onto nylon for extra chafe resistance, plus some testing of different methods to join them.

http://pdos.csail.mit.edu/decouto/my...s/seagrant.pdf

[estarzinger]

^^ nice paper . . . . very close to where I have ended up here . . . . except I am now going one better and using dyneema rather than polyester for chafe resistance.

Key quote:

"Following Hurricane Bob, one of the authors (Doelling) wrote a letter to a boat yard operator [lJ with some recommendations concerning ways to reduce damage in future hurricanes. This letter became broadly disseminated. In the letter, we recommended using polyester instead of nylon for rodes because of polyester's superior abrasion resistance when wet (surely its condition in major storms). We have retested that hypothesis and still feel it is appropriate [2, 3]. Since many persons objected to losing the compliance of the nylon, we designed and tested a simple method of joining an (existing) nylon rode with a short polyester line, so that one could enjoy the compliance of a nylon rode and the abrasion resistance of polyester at the chock."