Rolling Hitch on Snubber

[Kettlewell]

Judging from that article, I use what is called a "Modified Rolling Hitch" or a "Camel Hitch," though I must admit to never having heard that term before. Looked it up in Ashley's and it is there along with numerous others that might be worth investigating. I often take more turns around the chain if I'm expecting wind.

[estarzinger]

Well, we have a forecast for similar conditions (30 with gusts to 35, with a decent fetch/chop) tonight into tomorrow. I have the mantis hook out now, connected with a spectra sling to the other end of the same piece Of Dacron with a sheet bend. The geometry of the sheet bend is somewhat better than the loaded geometry of the rolling hitch, so it will be interesting to see what happens.

I guess at this point I am not sure if it was the knot or the line (or both) that was wrong.

Dockhead, you keep saying this line was "old" which is factually untrue. I bought it this spring specifically for snubber experimentation. So it's quite new and in quite good condition. I might also mention that last summer I experimented with an even smaller piece of dacron double braid, but I was using it in an experimental "doubled" configuration. I think I posted a photo of this in a prior snubber thread. It worked well, but the specific system design generated more chain noise than I like. And I have years and years of successful experience with the 10mm climbing line. The only time it failed, the cover chafed thru in hurricane Lenny (but the core was still holding when I found it and replaced it). We do carry a "storm snubber", which is an ABI chain plate with dual 5/8" nylon (mega braid) snubbers. I only put it out in storm forecasts.

[Dockhead]

Originally Posted by estarzinger

Well, we have a forecast for similar conditions (30 with gusts to 35, with a decent fetch/chop) tonight into tomorrow. I have the mantis hook out now, connected with a spectra sling to the other end of the same piece Of Dacron with a sheet bend. The geometry of the sheet bend is somewhat better than the loaded geometry of the rolling hitch, so it will be interesting to see what happens.

I guess at this point I am not sure if it was the knot or the line (or both) that was wrong.

Dockhead, you keep saying this line was "old" which is factually untrue. I bought it this spring specifically for snubber experimentation. So it's quite new and in quite good condition. I might also mention that last summer I experimented with an even smaller piece of dacron double braid, but I was using it in an experimental "doubled" configuration. I think I posted a photo of this in a prior snubber thread. It worked well, but the specific system design generated more chain noise than I like. And I have years and years of successful experience with the 10mm climbing line. The only time it failed, the cover chafed thru in hurricane Lenny (but the core was still holding when I found it and replaced it). We do carry a "storm snubber", which is an ABI chain plate with dual 5/8" nylon (mega braid) snubbers. I only put it out in storm forecasts.

Sorry for slandering the age of your rope!

But in any case, the main problem is that Dacron is really entirely unsuitable for a snubber -- it won't do any snubbing at all. The snatch loads will kill it (or your boat, or both) no matter what you do, and no matter how big it is. In order for a snubber to do any snubbing, it must have elasticity, so only nylon will do. Your failure really had nothing to do with the method of attachment.


I've never tried a dynamic climbing rope, but since these are specifically designed to stretch and absorb shocks, I can imagine that this is the best material of all for a snubber. Shame the largest size is 11mm, which is too small for my boat.

They are also made out of nylon by the way.

[Kettlewell]

Evans, you may not want to get into this much hassle, but I have sometimes used two snubbers--one longer than the other. I have done it when failure of the snubber might be a problem in a big storm. One snubber takes the strain, and the other is in place for instant and automatic back up in case the first one goes. You could do that to experiment with a different line or a different knot, keeping the known-quantity snubber on there but loose just in case the experimental one failed.

[estarzinger]

^^DH, well, we will see tonight!

Regarding line type, it is a simple plain fact that after much real world experience (and insurance claims) people running mooring fields have pretty much stopped using nylon for mooring pennants. There are some small differences in the applications (one is that mooring pennants are typically all spliced at both ends) but there are also great similarities to the applications.

K, I have also occasionally done that. These failures seem to all happen at 2am when it is pouring rain, so it's nice to have a 'back up' to catch it until morning.

I am very open minded about all this. We have a solution that is proven to work (like jedi's), and I am just playing around to see if I can find something slightly easier. I am in a situation where snubber failures are not so bad, so it's a good time/place to experiment.

[Kettlewell]

Where the heck are you with that forecast? Hope the holding is good and the shelter is decent and you can get a night's rest. I agree--2 am is when stuff happens, but it often seems to be on the boat directly to windward of me--the one where the crew was up drinking late.

[s/v Jedi]

Originally Posted by Dockhead

A chain stopper is a great solution, of course, provided, however, that you are able to install it in a strong enough spot. I have not yet figured that out on my boat, which has a balsa-cored deck, which is why I use a devil's-claw like technique like on a ship (my arrangement looks quite like the deck of the Royal Navy frigate in the drawing I posted a few pages back). The downside of a chain stopper is that it is probably not possible to make it as strong as a proper chain strop on a boat with a fiberglass deck; the upside is that it is extremely convenient and a cinch to release in an emergency.

Well, my deck is balsa cored and the chain stopper is there and proven stronger than my 6,600lb 3/8", G7 chain. It's a matter of replacing core with solid glass so that it doesn't crush and then adding a stringer and/or partial bulkhead underneath for strength; it is only loaded in shear so it isn't too difficult to accomplish but yes it's more than drilling a couple of holes...

I would disagree, however, that belaying the chain other than by using a stopper is "improper gear".

There is more proper gear than a chain stopper. You recognize it by being able to take it off quickly and without need for tools. I see plenty people creating all steel solutions with shackles and hooks, while a link of Dyneema would enable one to cut it quickly instead of go search for spanners.

When you devise methods for emergency situations, never forget that you also have an engine which can be used to take strain off the anchor chain. It is often the quickest workable solution, but make sure to keep all fingers attached to the hands...

Other questions one should ask: where is the knife? Does the windlass clutch still work good? Where are strong points located? How to mark the chain when letting it slip? How to anchor without engine and how to leave again without engine? How to retrieve the anchor without using the anchor roller? (because it is lost or destroyed, don't ask me ) etc. etc.

[foolishsailor]

Originally Posted by estarzinger

The geometry of the sheet bend is somewhat better than the loaded geometry of the rolling hitch, so it will be interesting to see what happens.

That seems to me to be the main issue and why I don't use a rolling hitch on chain. The line is pulled at over 90degrees where it exits and is under dynamic tensioning. A recipe for trouble.

[Paul Elliott]

To melt a rope doesn't require repeated cyclic loading. At least not with polypropylene line (which I admit we wouldn't be using for a snubber). But I was using some poly between my truck bumper and a tree one day. It was all over within a second: the tree won, the rope lost. Where the rope broke it looked like I had taken a blowtortch to it.

On the other hand, I've had the bad luck to break some dyneema (or similar high-strength) line through over-tensioning, and the break showed no signs of melting at all. This doesn't surprise me, since that particular type of line doesn't even melt when using a butane torch.

I suppose the stretchiness of a line depends on both the intrinsic properties of the material and the geometry of the construction. And heat is more likely generated when the material itself stretches.

[s/v Jedi]

Has nobody experimented with a snubber design that uses different diameter lines all spliced in parallel, with the thicker ones longer so that a thin one first stretches until the next thicker one gets tight and stretches together with the thinner one until the next thicker gets tight etc. You can splice that onto 5/8" Amsteel Blue which then functions as a stop when all the stretch i used up...

I never took the effort because I'm happy with what I have.

[rebel heart]

Originally Posted by foolishsailor

That seems to me to be the main issue and why I don't use a rolling hitch on chain. The line is pulled at over 90degrees where it exits and is under dynamic tensioning. A recipe for trouble.

The recipe doesn't produce much. Rolling hitches have been used for centuries with no track record of snapping at the hitch.

Some three strand and a hitch. It's just that easy.

[colemj]

Originally Posted by s/v Jedi

Sailors that see their hook fall off the chain have either not kept tension on while deploying it,or they didn't put out enough extra chain.

Or they have boats that allow them to anchor in 5' of water, where the hook lays on the bottom...

Mark

[foolishsailor]

Originally Posted by rebel heart

The recipe doesn't produce much. Rolling hitches have been used for centuries with no track record of snapping at the hitch.

Some three strand and a hitch. It's just that easy.

He wasn't using three strand - it was double braid. Different ingredients. One stretches the other not so much. Same as creating a hard point in composites. The rolling hitch was really designed back when they were using really stretchy Manila and the like. I don't feel it is suitable for high tension work using modern synthetic lines.

[rebel heart]

Originally Posted by s/v Jedi

Has nobody experimented with a snubber design that uses different diameter lines all spliced in parallel, with the thicker ones longer so that a thin one first stretches until the next thicker one gets tight and stretches together with the thinner one until the next thicker gets tight etc. You can splice that onto 5/8" Amsteel Blue which then functions as a stop when all the stretch i used up...

I never took the effort because I'm happy with what I have.

I know guys that have done multiples for storms so the could cut away a chaffed one or otherwise have backup.

The only funky thing I started doing lately was hanging a block under my bowsprit for the snubber. I did it for silence, as the line sliding around in the deck chock was noisy in a lot of wind.

It's had the advantage of absorbing most of the movement and having the line at the chock be relatively motionless, but it's only practical if you have a bowsprit.

[noelex 77]

Originally Posted by Dockhead

If your rolling hitch slips -- a very unusual problem -- try tying an extra turn in it, and/or tying off the the tail with a clove hitch or a couple of half-hitches. It should form into the chain and be absolutely secure. You could also try some of the other knots suggested, but keep in mind that few knots compromise the strength of the rope less than a rolling hitch, .

I tried all variation of rolling hitches, extra half hitches etc with no luck. They would only slip a few times a year, so that is less than 1%, but always at the worst time.
I have used a Klemheist knot for the last couple of years and not one slip, so that's one problem solved.

Originally Posted by Dockhead

If your snubbers are breaking, then something is wrong. Is the size ok? Are they breaking somewhere where they might be chafing on something?

I agree, other cruising boats don't seem to break snubbers with anything like the same frequency.
I have tried to eliminate all the chafe possibilities, and there is no sign of chafe on the rope.
I have experimented with different sizes, but I am reluctant to go much thicker due to the lack of stretch.

I think the nylon I am using is just poor quality, but I do wonder about the maths.
Jedi 5//8 inch (16mm) nylon snubber as a typical break load of 6600kg.
However that is new, with no salt abrasion, cyclic loads, splices, and its measured dry.
I wonder if we measured a typical used, but good condition wet nylon snubber would be?. Its only a guess, but somewhere around 3000-4000kg seems reasonable to me.
The anchor tests report the better 35lb anchors will hold better than 2500Kg. Jedi's (or my) 120lb anchor should hold much better than the breaking strain of the snubber.

Its not unreasonable to make the snubber the weak link, but it seems much weaker than the potential holding of the anchor and strength of the chain.

I am not advocating thicker snubbers. Try to go as thin as possible, as long as they don't break.

My new, untried, good quality (Marlow) snubber is 16mm, thinner than I have been using. It will be interesting to see if survives the winter storms.