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Old 27-05-2013, 06:09   #196
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Re: Rolling Hitch on Snubber

So, on rodes . . . .

First related to the specific breakage in the OP. . . I am as sure as I can be that it is NOT related to the line being Dacron. #1 the Hall guy looking at the break said that, and #2 the same line held up in essentially the same conditions with a different knot. I fully understand the general elasticity argument, but the details of my specific case don't seem at all to fit that hypothetical cause.

Dockhead, what I mean by 'the icicle might be better' was that the geometry of the icicle provides for a much less sharp final loaded turn than the rolling hitch. In a cyclic load this 'should' provide less cutting/wear (in addition to less raw strength reduction - although that's not the key point here). So, I full agree the icicle hitch has more 'grip' (And my practical sailor testing supported that), but I also think (without testing) it should have less wear (and more strength). This winter I might do a bit of break and cycle load testing of these knots, but I can't do that on the boat, and I have not seen any real good tests of these gripper type knots..

One potential cause of my breakage that would have nothing to do with either the line OR the knot, is if that rolling hitch just happened to be tied around a specific chain link that had some sharp welding or galvanizing flash on it, that could have eaten the line. The Hall guy said it did not particularly look like a metal cut, but he could not be sure about that.

But I see no specific facts to indicate that this specific case is 'Dacron related'.

Related to snubber material more generally. . . .

Regarding test results . . . you need to be pretty careful you are testing the exact right thing. I am quite familiar with the chafe and cyclic testing that has been done (I worked for North and Southern Spars for a while, and was involved in their QA program). The data that Dockhead provided (nylon 'more resistant' than dacron) comes (I believe) from a test conducted with dry line and the same length of stretch (they used an eccentric wheel to stretch the two lines). However, if you test the lines using the same cyclic load (and the nylon then stretches further), the nylon will chafe much faster (as it also will if it is wet).

It is a plain fact he most statistical large sample real world experience comes from mooring pennants (which I now have access to thru BoatUS's insurance history). There is a lot detailed experience with all sorts of line construction. The strong conclusion of all this real world data is that nylon is one of the poorer choices for that application (only behind polypropylene), because it is both more UV sensitive (which is also why it is recommended you use polyester jacklines rather than nylon) than Dacron and more vulnerable to chafe. Now I will acknowledge that the mooring pennant application has one major difference to the snubber application - if a mooring pennant breaks your boat is on the rocks, while if a snubber breaks you still have the chain to hold the boat. So the snubber application is a little less fatal to chafe.

Finally, there is a question about 'how much elasticity is ideal'? That I don't think anyone has answered. One school is 'more is always better', but I am skeptical about that. I have wondered both in para-anchor rodes and snubbers if there is an anmount of stretch that is 'too much' and which can cause the 'sling shot effect', increasing the amount of 'sailing back and forth' motion and resulting cyclic loads. If someone really think 'more is always better', there are ways to get more that most people are in fact not using (long nylon, using big bungee cord, adding the rubber stretchy pieces, etc) . . . so people don't in fact seem to act as if they strongly feel that 'more is always better'.

Please note that I am NOT saying that Dacron is a better material for snubbers. All I am saying that I think it worth a little time and experimentation on my part, as I don't know what is the best material, and there is evidence to support both nylon and Dacron.

And I continue to think that it is worth some experimentation, and that my first failure was not primarily 'Dacron' related. I will say that from my experimentation to date, that for the same diameter and length(I typically have used relatively short and relatively skinny snubbers), I so far I prefer the 'motion' of nylon. I am now going to try double the length of dacron and see how I think that 'feels'.
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Old 27-05-2013, 06:17   #197
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Re: Rolling Hitch on Snubber

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Originally Posted by estarzinger View Post
snip

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.

Snip.
Evans, I think you are mistaken. My experience is limited compared to yours, but the ONLY mooring pendants in use (or sold by chandlers such as Defender or Hamilton Marine) are nylon core (for stretch) covered by polyester or PET braid for chafe and UV resistance. The braid is a construction that allows stretch. Often they have a rubberized coating on top of that. This is all I see in use in New England.

Edit: examples would be the Yale Maxi-Moor, the New England Ropes Nylon Mooring Pendants, the Yale Polydyne
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Old 27-05-2013, 06:19   #198
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Re: Rolling Hitch on Snubber

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I would be worried about the dyneema getting nipped between the slack link of the chain and either chaffed or caught so it's hard to release.
Agreed that's one of two things that I will watch closely.

But my strong guess at this point is that it will not be a problem. Last summer I experimented with taking a Dacron line thru the chain, and 'nipping' was not a problem, so I guess the spectra will be even better.

Here's what I was trying last summer (see the white line running from one cleat up thru a chain link and back to the other cleat) . . . worked pretty well, except more chain noise on the roller and side cheeks than I liked. (PS don't show this pic to the "traditional snubber" crowd as they will say that it cannot possible work )

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Old 27-05-2013, 06:26   #199
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Re: Rolling Hitch on Snubber

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nylon core (for stretch) covered by polyester or PET braid for chafe and UV resistance. .
That's the Yale rope. They make one double braid with a standard polyester cover (polydyne) and another with a special tighter weave cover (Maxi-moor).

So, yes, I probably was being too simple and imprecise in my language - when I said "Nylon" I meant the 3 strand and braits that everyone in this thread is generally referring to, and when I said 'dacron' I meant the standard Dacron double braid (not there are brait dacrons that in fact do have more stretch than the double braids). I think you will agree that basically no-one is using 3 strand nylon or braid nylon for mooring pennants.

The MAxi-moor might in fact make an very interesting sunbber line - expensive though.
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Old 27-05-2013, 07:04   #200
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Re: Rolling Hitch on Snubber

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That's the Yale rope. They make one double braid with a standard polyester cover (polydyne) and another with a special tighter weave cover (Maxi-moor).

So, yes, I probably was being too simple and imprecise in my language - when I said "Nylon" I meant the 3 strand and braits that everyone in this thread is generally referring to, and when I said 'dacron' I meant the standard Dacron double braid (not there are brait dacrons that in fact do have more stretch than the double braids). I think you will agree that basically no-one is using 3 strand nylon or braid nylon for mooring pennants.

The MAxi-moor might in fact make an very interesting sunbber line - expensive though.
I don't agree that ANYONE is using "standard Dacron double braid" for mooring lines. The cores are always nylon, in my experience.

The use of 3-strand for snubbers and bridles is quite common, and I've been using it on my mooring bridle for about 12 years with no issue. My trimaran bridle uses a standard pennant (such as Polydyne or similar) for the center hull, and 5/8 3-strand nylon for the bridle attached to the amas. The whole setup is adjusted so the center attachment is slightly looser, as backup, and will never be loaded unless one of the outer 3-strand attachments were to fail. My mooring has a ~70-mile fetch exposure to the east, and I have seen waves in the 7+ foot range under rare storm conditions. Never a failure or even a sign of weakness. (I do change the bridle lines every 3 years due to UV or sooner if I see chafe from a wrap on the mooring chain. I buy standard 3-strand anchor line and splice the thimbles myself. I always have a spare bridle made up at home, and also carry one on the boat for anchoring that can be attached to a guest mooring when we cruise.)
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Old 27-05-2013, 07:21   #201
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Originally Posted by SailFastTri View Post

I don't agree that ANYONE is using "standard Dacron double braid" for mooring lines. The cores are always nylon, in my experience.

The use of 3-strand for snubbers and bridles is quite common, and I've been using it on my mooring bridle for about 12 years with no issue. My trimaran bridle uses a standard pennant (such as Polydyne or similar) for the center hull, and 5/8 3-strand nylon for the bridle attached to the amas. The whole setup is adjusted so the center attachment is slightly looser, as backup, and will never be loaded unless one of the outer 3-strand attachments were to fail. My mooring has a ~70-mile fetch exposure to the east, and I have seen waves in the 7+ foot range under rare storm conditions. Never a failure or even a sign of weakness. (I do change the bridle lines every 3 years due to UV or sooner if I see chafe from a wrap on the mooring chain. I buy standard 3-strand anchor line and splice the thimbles myself. I always have a spare bridle made up at home, and also carry one on the boat for anchoring that can be attached to a guest mooring when we cruise.)
You sure? I see this all the time and these are considered the world cruisers that transit the Panama canal!

Also, to state nylon is used so much more is very US centric; low price nylon is much more popular in the US than in Europe. A good rope anchor rode in Europe can be polyester 8 plait with lead weight in the center and what have you; much more elaborate than the 3-strand nylon that is most often seen in the US. I don't even see regular 8-plait that often on US yachts.
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Old 27-05-2013, 07:46   #202
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Re: Rolling Hitch on Snubber

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You sure? I see this all the time and these are considered the world cruisers that transit the Panama canal!

Also, to state nylon is used so much more is very US centric; low price nylon is much more popular in the US than in Europe. A good rope anchor rode in Europe can be polyester 8 plait with lead weight in the center and what have you; much more elaborate than the 3-strand nylon that is most often seen in the US. I don't even see regular 8-plait that often on US yachts.
He meant mooring pennants; not dock lines (I agree "mooring lines" is ambiguous).

I have seen polyester rope used for anchor rode in the US as well as in Europe. I am persuaded by Dashew's arguments for it versus nylon for that application, and, as I wrote, I use polyester myself for me all-rope second anchor rode.

I do agree with SailFastTri that all the mooring pennants I know of have at least a nylon core.

For dock lines, I use a bit of everything -- my favorites are polyester octoplait, but I have also have nylon dock lines for rougher weather. I have a special love for two long lines I inherited from my boat's PO -- 100 feet long each x 1", three-strand nylon. They're just pretty pieces of cordage -- I am conscious of all the disadvantages of three-strand. They are for tying up to non-floating quays in places with a large tidal range, or for shore lines when rafted up. I use them a lot
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Old 27-05-2013, 08:10   #203
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Re: Rolling Hitch on Snubber

FWIW,

In Australia (admittedly a backwards place) there are lots of moorings and all that I have seen utilize either three strand nylon or polypropylene or what is locally known as "silver rope", a really sleazy fibre made (I think) from recycled grocery bags. Typically used in 25 to 32 mm diameters. I have never seen any type of braid used for a pennant here, let alone some fancy composite stuff.

They seem to work, but I have no experience personally.

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Old 27-05-2013, 08:17   #204
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Re: Rolling Hitch on Snubber

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I don't agree that ANYONE is using "standard Dacron double braid" for mooring lines. The cores are always nylon, in my experience.
Well lets address that with some data . . . In the NE of the USA approximately 60% of the mooring pennants are Dacron double braid, according to boat US insurance data. Approximately 5% are nylon 3strand or brait.

It's pretty hard to tell from the outside if a double braid with a Dacron cover has nylon or Dacron inside. The Boatus data suggests more have Dacron than you think. The Dacron double braid is way less expensive than the hybrid lines, and the loss history (%lost/%used) is not much different.

Do you know anyone other than Yale making a hybrid (nylon core, lower chafe cover)? Serious question, as I am interested in doing some testing. I doubt that Yale has 100% market share of mooring pennants.

Interestingly New England Ropes specialty mooring pennant line is 100% dyneema! Eg they have focused almost exclusively on chafe, and have decided on almost zero stretch as the correct engineering!

Samson has 7 ropes listed for the mooring pennant application. Five of them have no nylon in them. Two have nylon, but neither are 3 strand or 8strand brait.
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Old 27-05-2013, 08:20   #205
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Re: Rolling Hitch on Snubber

And while we are at it, why are we arguing about which line's stretching characteristics are best when we have not determined how much stretch is optimal?

I have to wonder just how much stretch is needed to remove the dreaded "shock load" from anchor and deck fittings. There is a big difference between a chain coming up tight and even a couple of feet of stretch... what is really needed?

And the "rubber band" or "slingshot" effect seems real to me. Don't have any objective data, but experientially it seems that my boat sails around more with a longer and stretchier snubber. Also seems logical that if the snubber stretches, say fifteen feet, the bow will go much further before fetching up than if it only stretched three feet. The deceleration would be slower with the longer stretch, but the boat would be nearer to beam on... so, which is best?

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Old 27-05-2013, 08:35   #206
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Re: Rolling Hitch on Snubber

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So, on rodes . . . .

First related to the specific breakage in the OP. . . I am as sure as I can be that it is NOT related to the line being Dacron. #1 the Hall guy looking at the break said that, and #2 the same line held up in essentially the same conditions with a different knot. I fully understand the general elasticity argument, but the details of my specific case don't seem at all to fit that hypothetical cause.

Dockhead, what I mean by 'the icicle might be better' was that the geometry of the icicle provides for a much less sharp final loaded turn than the rolling hitch. In a cyclic load this 'should' provide less cutting/wear (in addition to less raw strength reduction - although that's not the key point here). So, I full agree the icicle hitch has more 'grip' (And my practical sailor testing supported that), but I also think (without testing) it should have less wear (and more strength). This winter I might do a bit of break and cycle load testing of these knots, but I can't do that on the boat, and I have not seen any real good tests of these gripper type knots..

One potential cause of my breakage that would have nothing to do with either the line OR the knot, is if that rolling hitch just happened to be tied around a specific chain link that had some sharp welding or galvanizing flash on it, that could have eaten the line. The Hall guy said it did not particularly look like a metal cut, but he could not be sure about that.

But I see no specific facts to indicate that this specific case is 'Dacron related'.

Related to snubber material more generally. . . .

Regarding test results . . . you need to be pretty careful you are testing the exact right thing. I am quite familiar with the chafe and cyclic testing that has been done (I worked for North and Southern Spars for a while, and was involved in their QA program). The data that Dockhead provided (nylon 'more resistant' than dacron) comes (I believe) from a test conducted with dry line and the same length of stretch (they used an eccentric wheel to stretch the two lines). However, if you test the lines using the same cyclic load (and the nylon then stretches further), the nylon will chafe much faster (as it also will if it is wet).

It is a plain fact he most statistical large sample real world experience comes from mooring pennants (which I now have access to thru BoatUS's insurance history). There is a lot detailed experience with all sorts of line construction. The strong conclusion of all this real world data is that nylon is one of the poorer choices for that application (only behind polypropylene), because it is both more UV sensitive (which is also why it is recommended you use polyester jacklines rather than nylon) than Dacron and more vulnerable to chafe. Now I will acknowledge that the mooring pennant application has one major difference to the snubber application - if a mooring pennant breaks your boat is on the rocks, while if a snubber breaks you still have the chain to hold the boat. So the snubber application is a little less fatal to chafe.

Finally, there is a question about 'how much elasticity is ideal'? That I don't think anyone has answered. One school is 'more is always better', but I am skeptical about that. I have wondered both in para-anchor rodes and snubbers if there is an anmount of stretch that is 'too much' and which can cause the 'sling shot effect', increasing the amount of 'sailing back and forth' motion and resulting cyclic loads. If someone really think 'more is always better', there are ways to get more that most people are in fact not using (long nylon, using big bungee cord, adding the rubber stretchy pieces, etc) . . . so people don't in fact seem to act as if they strongly feel that 'more is always better'.

Please note that I am NOT saying that Dacron is a better material for snubbers. All I am saying that I think it worth a little time and experimentation on my part, as I don't know what is the best material, and there is evidence to support both nylon and Dacron.

And I continue to think that it is worth some experimentation, and that my first failure was not primarily 'Dacron' related. I will say that from my experimentation to date, that for the same diameter and length(I typically have used relatively short and relatively skinny snubbers), I so far I prefer the 'motion' of nylon. I am now going to try double the length of dacron and see how I think that 'feels'.

This is a very thoughtful and interesting post with a lot of points to think about and engage.

I am fiercely prejudiced against polyester for snubbers (it's just wrong!), as I guess I have not been able to conceal well enough, but I will follow Evans' experiments with great interest, and will be happy to be proven wrong. I've already learned a lot I didn't know prior to this thread. Of course it's worth further experimentation -- here I'm sure everyone agrees with Evans.

One test which I think would be very telling would be to take a weight, tie it onto a piece of rope, tie the other end to a bridge rail, and drop it off until it breaks. Dollars to donuts -- a polyester rope of the same strength will break far sooner than the nylon one will. The stretch of polyester rope absorbs the energy; in a shock loading situation the energy in a polyester rope has no where to go, and will break something, often the rope itself. This is very relevant to snubber duty, since that is exactly the kind of load you will get on the snubber when the chain pulls tight in a situation like Evans' the other night. If you Google "polyester rope shock load" you get a lot of interesting things on this ("snaps like a twig" is one phrase I came up with; and frequently things like "Unlike nylon, polyester stretches very little and therefore cannot absorb shock loads").

So if you use an unconventionally (for this application) inelastic rope to rig something which is designed to absorb and dampen shock loads, and it breaks, would you be surprised? Hmmm. Neither the fact that the snubber broke on the inside, rather than outside of the bend in the rope not the fact that it didn't break on another night with another knot contradicts the proposition that the root cause of the failure was inability of the material to absorb the shock loads from a rough night at anchor. A nylon snubber, I argue, would have easily absorbed the same shock loads without needing a different knot.


I certainly agree with Evans that elasticity in the snubber is not a case of more is better. Otherwise, we'd use bungie cords. I think the best we can do is tune our snubbers so that they feel right. But I also think we should beware of using thin and short snubbers which "feel right" in reasonable weather--they will not protect the boat in rougher weather. In my opinion, a polyester snubber which has any palpable elasticity at all will be so weak in a shock loading situation that it will provide almost no protection in case of weather where the chain snaps tight, and it seems obvious to me that that's what happened to Evans.

If someone would do an experiment to show how many foot-pounds or whatever of energy a given rope can absorb in a short period of time (some fraction of a second) without breaking, I'm sure you'd see a dramatic difference between nylon and polyester -- I wouldn't be surprised if it's 5x or 6x or more. That would be the pushing the weight off the bridge test, or something similar. And the shorter the period of time, the bigger the difference.

As to the Coast Guard abrasion test showing that nylon is much more abrasion resistant than polyester -- this contradicts everything I ever learned, so like Evans, I am skeptical. However, I can't find any flaws in the test, which seems to have been very well designed indeed. The samples were not indeed dry -- they were immersed in water (see Appendix E). They were not tensioned to constant elongation-- on the contrary, they specifically included a turnbuckle to take up slack caused by elongation of the samples. It's all a puzzle to me, as there is so much information to the contrary.
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Old 27-05-2013, 09:23   #207
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And while we are at it, why are we arguing about which line's stretching characteristics are best when we have not determined how much stretch is optimal?

I have to wonder just how much stretch is needed to remove the dreaded "shock load" from anchor and deck fittings. There is a big difference between a chain coming up tight and even a couple of feet of stretch... what is really needed?

And the "rubber band" or "slingshot" effect seems real to me. Don't have any objective data, but experientially it seems that my boat sails around more with a longer and stretchier snubber. Also seems logical that if the snubber stretches, say fifteen feet, the bow will go much further before fetching up than if it only stretched three feet. The deceleration would be slower with the longer stretch, but the boat would be nearer to beam on... so, which is best?

Cheers,

JIm
Indeed. Based upon my everlasting experimenting, I have found the following to be the best approach:

Let's say you have a 3/8" BBB chain and/or a 3/4" 3-strand rope rode. This is the majority of 30-40' cruisers I think. Simply start by getting 24' of 3-strand 3/8" nylon and splice a loop with your chain hook (or just a loop if you want to use a soft shackle). Deploy it with a loop of slack chain that is well below the water surface so that it has plenty room to stretch. Now let some squalls hit you. You should clearly see it stretch a bunch. I normally see my chain get turned around the snubber 5-6 wraps as the nylon torques when it stretches. If it doesn't stretch enough to your liking, go down a size (5/16"); when it breaks, go up a size. I am 27 tons US (25 tons metric) and I break 1/2" but am good with 5/8". Your snubber is too thick until you prove that by breaking one size smaller.

When you use a chain hook make sure you can retrieve it when the snubber breaks you will find that the snubber breaks somewhere in the middle and shows evidence if melting. If it breaks where it goes over the toe-rail, you need to device a way to prevent chafing instead of going in size.

About the rubber band / jojo effect: I let that go but see it all the time. Mono's almost beam to the wind and cats jumping forward all the way to where the anchor is.
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Old 27-05-2013, 09:38   #208
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Re: Rolling Hitch on Snubber

^^ That was a model post Dockhead.

One 'engineering factor' to consider is that people like Dashew and us, with metal boats & welded cleats and massive bow rollers and massive anchors, may be less concerned with shock loads (And thus relatively more concerned with chafe) than people with weaker gear and smaller anchors. So, as with so many cruising topics, there may not be an optimal 'one size fits all' solution.

That testing pdf you posted is very interesting, one I had not seen before, and I will have to read it more carefully . . . however looking at the appendix E test, if I understand it correctly, the elongation/stretch length is the same for all the tested ropes ("driven by the crank of a 44rpm motor" as I suggested it might be). While in 'real world' applications the nylon will actually stretch back and forth several times longer in distance than the Dacron (if the lines are the same breaking strength). They do have that turnbuckle in the system to adjust the tension, but it does not (appear to) vary the 'throw' of the crank.

Its actually not so easy to make a machine that will do 1000's of cycles with a constant peak load but variable throw - the best way is with a very very long and quite fast and quite strong hydraulic ram, but those are not so common - although if anyone could build one it would certainly be the US Navy.
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Old 27-05-2013, 10:02   #209
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Re: Rolling Hitch on Snubber

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I think you will agree that basically no-one is using 3 strand nylon or braid nylon for mooring pennants.
Quote:
Well lets address that with some data . . . In the NE of the USA approximately 60% of the mooring pennants are Dacron double braid, according to boat US insurance data. Approximately 5% are nylon 3strand or brait.
I find that very hard to believe. I keep my boat in the area, and I see nylon rodes on most moorings, including numerous 3-strand ones. Commercial vendors of mooring painters make them variously out of 3-strand or double-braid nylon, sometimes with a polyester cover, but I can't recall ever seeing a commercial vendor selling a Dacron braid mooring painter. Even the NE Ropes Dyneema ones are supposed to be attached to nylon like this.

R&W Rope:
Quote:
Stock mooring pendants are straight pendants made from our Protector Series Nylon Double Braid with a heavy duty galvanized steel thimble on one end, 12" whipped eye other end, two feet of chafe protection, and urethane coated for added protection.
New England Ropes:
Quote:
Mooring Pendants are designed to withstand chafe and absorb energy associated with a mooring system. Available in either 3-strand nylon or durable polyester/nylon double braid.
Yale Ropes:
Quote:
Maxi-Moor II double-braided rope is improved from our original polyster/nylon construction with twice the high-tenacity PET fiber, so it maintains integrity for up to eight times more loading cycles.
West Marine Advisor:
Quote:
Large-diameter three-strand nylon line is used because its inherent elasticity (stretching about 10 percent under a load equaling 20 percent of its tensile strength) allows it to act as a shock absorber. Polyester line, Dyneema line or stainless steel wire is preferred by some for better chafe resistance. Length should be about 2 1/2 times freeboard. Diameter should be as large as is practical—it must be able to fit through bow chocks and around a bow cleat.
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Old 27-05-2013, 10:38   #210
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Re: Rolling Hitch on Snubber

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