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Old 26-05-2013, 14:46   #166
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Re: Rolling Hitch on Snubber

I've used both rolling hitches (like Kettlewell) and a chain hook (like Jedi.) I found the rolling hitch a bit more reliable, But I can't remember why, I've just stuck with the rolling hitch. It could simply have been my own inexperience back then and the rolling hitch never failed me, so I didn't see a need to change.

It seems both methods have a good track record.

However, like Jedi and kettlewel I used 3 strand nylon line, I think your problem was not using 3 strand NYLON line.

It's the nylons ability to elongate, especially in water that makes nylon, especially 3 strand, ideal as a snubber.
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Old 26-05-2013, 15:12   #167
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Re: Rolling Hitch on Snubber

Quote:
Originally Posted by Andrew Troup View Post
Have you left your boat unattended for a week on a nylon snubber in a windy location?
Not sure I'd leave my boat with any kind of snubber at anchor for a week in a windy location...
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Old 26-05-2013, 15:46   #168
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Re: Rolling Hitch on Snubber

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Originally Posted by conachair View Post
Not sure I'd leave my boat with any kind of snubber at anchor for a week in a windy location...
Things can happen. A guy in the anchorage here had a stroke, ended up in the local area hospital for a month. People have been looking after the boat but it was a good lesson to me that it's a smart idea to set anchor properly, every time, because you don't really know how long you'll be there or what will happen while you're there.
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Old 26-05-2013, 16:20   #169
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Quote:
Originally Posted by conachair View Post

Not sure I'd leave my boat with any kind of snubber at anchor for a week in a windy location...
We leave our boat at anchor when we fly home 7,000 miles for a couple of weeks. Why not? Safer than a marina.
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Old 26-05-2013, 16:34   #170
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Re: Rolling Hitch on Snubber

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FWIW, I saw an article that suggested that the nylon is more likely to overheat if it is inside hose chafing gear; and that frequent changing of softer, water absorbent chafing gear would be much more secure...
Yes, I have read that too, but the evidence is very scant on it happening in the real world. Apparently it has happened a few times, but certainly not very often. I have routinely used clear PVC water tubing over anchor lines in everything from gales to hurricanes and tornadoes, and never had a failure of my chafing gear or the line underneath. In fact, before I splice in the eyes I run a long length of the stuff onto the anchor rode so that it can reach right from the cleat over the bow roller. It is what I routinely use for chafing gear.

And, yes I have left my boat for long periods at anchor, but of course if I do so I try to select a sheltered location. Probably the worst conditions I have seen at anchor were during Hurricane Bob where I estimate the seas peaked at around 6 feet briefly, and the local anemometer ashore blew away after hitting 100 mph. After the storm I examined numerous parted anchor lines and mooring lines as thousands of boats were on the beach all over southern New England. In every case that I looked at the ones that parted were due to chafe due to no or poor chafing gear, inadequate line size, coming off a roller, or knife-edge chocks. However, I was surprised how few boats went ashore due to parted lines. Far more boats simply pulled their moorings out of the bottom due to the storm surge and dragged the whole mess ashore, indicating to me that their mooring painters were certainly adequate. We saw around 10 feet of surge where I was, but further up Buzzards Bay it was closer to 20 feet.
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Old 26-05-2013, 19:13   #171
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When I anchor with a (gasp) rope anchor rode, I still tie a snubber onto it so that the rode does not have to deal with chafing gear at all.
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Old 26-05-2013, 20:36   #172
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Re: Rolling Hitch on Snubber

Firstly thanks to Evans (and in some part to all the contributors like Andrew and Jedi) for the brilliant final solution. I will definitely be using the soft shackle strop system as soon as I can get all the more critical jobs done on the boat. I think this is the best solution I have seen.

Quote:
Originally Posted by thinwater View Post
I posted some calculations on that topic.
Sail Delmarva: Can Nylon Anchor Rope be Melted by a Severe Cycling Load ? Myth Plausible.
I've actually broken ropes on test rigs and looked at the ends. It seems to be about rope diameter and heat dissipation; the rope has to be fat to build heat. Certainly possible and I believe the stories. A risk anytime rope over 3/4-inch is needed.

"Below 5/8-inch rope heating due to cycling is probably not an important factor; failure will be due to something else. Beginning at 3/4-inch moving upwards, it can be very important, since the larger rope can not cool as easily. The myth seems plausible."
Very interesting Thinwater, I was wondering if multiple strands of 6 or 8mm nylon might dissipate the heat better and give a much better capacity for energy absorption due to the much greater surface area/cross section area ratio's. Chafe would be an issue so use chain over the bow roller and shackle them all into one big bow shackle. Or use a soft shackle. Maybe cover the lot with a loose cover of porous webbing.

Quote:
Originally Posted by s/v Jedi View Post
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...
Something along these lines might work as well as long as the long stretchy one didn't overhead and then break before the others took the load.

Quote:
Originally Posted by noelex 77 View Post
Has anyone considered (or used) the 4wd snatchem straps for a snubber.
They are strong elastic and readily available.
This is another good approach, as it should also dissipate heat much better than thick nylon rope, having much greater surface area. chafe could be an issue if the boat shears and the strap runs sideways out the roller. maybe a heavy rope or chain leader running over the roller to take any chafe and then the strap.

Quote:
Originally Posted by wsmurdoch View Post
What spring constant do we want in a snubber? You know, how many pounds force per inch of stretch? Do we want it very low like a big rubber band or bungee cord or do we want it very high like a piece of polyester rope? Too stretchy may be bad because the bow blows off every time a gust strikes the boat presenting the side of the boat to the wind. Not stretchy enough may be bad because shock loads may break gear or tear the anchor out of the bottom. What is the right amount? What is the number? Should there just be a single spring constant, or like Jedi suggests, should the spring constant rise with increasing force? Maybe 100 lb/in for the first 100 lb of load and 500 lb/in for the 100 lb additional load between 1000 and 1100 lb and 1000 lb/in for the 100lb additional load between 2000lb and 2100lb.
I would love to see some technical analysis of what sort of stretch and length are needed. My guess is it would need to factor in displacement and windage. We have a rough idea by reverse engineering what has worked in the past. With some accurate figures we should be able to extrapolate from a normal gale to design a system that can cope with extreme hurricane loads, and also function in more normal conditions.

I still think nylon is the go, but maybe a very long length of polyester could work. Maybe putting a rubber core inside the inner core, that gets compressed as the rope gets loaded up to give it some more elasticity.

Ultimately the best way to dissipate the bigger loads of a swinging boat has to be something like a drag device from the bow, such as a small sea anchor, large buoy or a car tyre.

My ultimate hurricane snubber would have a fair few car tires tied into it for elasticity and drag, sort of like an elastic series drogue deployed from the bow. In a real life threatening hurricane I might even consider breaking out the series drogue and using it as an extra anchor line.
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Old 26-05-2013, 20:48   #173
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Re: Rolling Hitch on Snubber

Quote:
Originally Posted by Andrew Troup View Post
Have you left your boat unattended for a week on a nylon snubber in a windy location?

Regardless of your answer to that: a single person's experience is a small sample to generalise from; I too have not have problems with nylon in the past, but the fact that other people have done is sufficient to make me leery, specifically in the 'abandoned ship' scenario.

In addition to the cumulative effects of cyclical loading on nylon, when there's nobody there to freshen the nip at the first sign of chafe etc etc, the problem is altogether different.
People leave their boats anchored or moored on all-nylon rode for years at a time.

I think it's important to be conscious of this drawback of nylon, but not exaggerate it. It appears at very high loadings, like in hurricanes. I think most of us read about it on Dashew's site. At normal loadings (including occasional storm duty) with reasonably sized gear, nylon is reliable.
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Old 26-05-2013, 21:12   #174
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Re: Rolling Hitch on Snubber

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Originally Posted by Andrew Troup View Post
Maybe I misunderstood; it seemed to me that the logical import of your statement 1 is that lines other than nylon do not have elasticity.

and it further seemed to me that your statement 2, that such lines could not "do any snubbing at all" is absolute and unqualified, and accordingly misleading.

In comparison with chain, ropes other than nylon are still immensely elastic. If the chain is heavy enough to do the lion's share, the snubber can be a lamb ... except of course in "bows going under" conditions, or anything approaching that (or in shallow anchorages, or other special cases)

You describe your "heavy" chain as not providing enough snubbing to get away with a minimal snubber: perhaps that's because, given the size of your boat, in my terms it's actually medium, rather than heavy.

To me, 5/8" / 16mm is "about right" for a boat your size, and therefore qualifies as "heavy". It was pretty standard on the expedition yachts in that size range I've sailed aboard, but admittedly less so in recent times: the fashions have certainly changed.


In the more general case, my feeling is that designers simply put the anchor locker too far forward, particularly on boats intended for the mass market ....
Well even chain has a certain elasticity, but not enough to provide any snubbing effect.

Likewise with Dacron -- an effective snubbing effect will appear only with a very thin (and this dangerously weak) or very, very long snubber.

So yes -- of course both chain and Dacron have some elasticity, but they are not elastic, for practical purposes of being a snubber at reasonable length and diameter.

I still think you are making a mistake, thinking that a heavy chain eliminates the need for any snubbing. Man, the heavier the chain, the more energy there will be in the system when it pulls straight and transfers the shock to your bow roller, possibly ripping it off. Remember that it's not just wind which can cause this, but wave action, so you can get your chain pulled out straight in less than storm conditions, if the shelter is not perfect (or if the wind shifts in the night, which actually happened to me). The primary purpose of snubbers is not to provide comfort (that's a welcome secondary effect), but to dampen these snatch loads, which destroy gear. Someone was talking about the benefits a progressively springier snubber, like a progressive rate spring -- chain catenary is the opposite -- the dampening effect reduces, the higher the load, until it disappears.


You can argue that a piece of wood will be ok for a car's suspension -- because wood has some elasticity. You can argue that the car's tires are already dampening the ride, so are springs really necessary? But if you try it in reality, you will find it's not a good idea at all. Your snubber is like the springs or shock absorbers in your car's suspension -- they need a certain amount of elasticity to be at all fit for purpose, not just some elasticity.



As to chain lockers -- I completely agree. It's not just mass market boats -- practically every sailing yacht built in the last 20 years, whether mass market or the likes of Swan, Oyster, Contest, HR, etc., has the chain locker right up in the bows, where the weight of a substantial chain rode will create trim and ultimately sailing performance problems. The reason is that it is extremely hard to design to a chain locker anywhere else -- you need a naval pipe, etc. You have a big problem how to drain it. So the makers just equip their boats with far too little chain, and sent their clients on their merry way to deal with the design problem later when they upgrade their chain.

The only exception I know about is Dashew's Sundeers, like Nick's, where there is a naval pipe and the chain locker is far aft of the forepeak. Ironically, this same Dashew is a great advocate of light, high-tensile chain, so he doesn't take advantage of this design triumph with the chain locker, to specify a nice, heavy chain I think Nick has 9mm chain for a 65' boat, isn't that right, Nick?

If you're not lucky enough to have a Sundeer, you either have to accept the trim problems, or go to chain/rope rode, or buy a big enough boat that there is enough buoyancy in the bows that you don't notice it too much. But I completely agree -- it's a design flaw.
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Old 26-05-2013, 23:48   #175
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Re: Rolling Hitch on Snubber

I had not been following this thread, I've been out of touch, but have now read the whole thing.

I query a few comments, someone has been suggesting that nylon stretches 100% (prior to failure?). My understanding was that most nylon cordage had an elasticity between 30% and 40% at which point it fails. The variation between 30% and 40% seems to be construction, climbing ropes being the most elastic. Bungy cord, for people jumping of bridges etc, is made with either 100% or 200% elasticity - but I've never checked what its made from.

A comment was passed that a snubber should not be more than 6m long. People have been using mixed rodes for decades, as far as I know always 3 strand nylon but more recently octaplait. There has never been an issue of yachts yo-yoing (or surging) as result of the elasticity of the nylon. Based on this snubbers could be any length, much longer than 6m? There is in fact a whole sub-industry selling chain, say 30m spliced to nylon say 40m - its common and popular (or is in the UK).

Noelex asked about 4X4 snatch tape, I have seen it on one Cat, Soldiers Point, but have no idea how good it is/was. It tends to come in short lengths and might be difficult to attach to a chain, you would need a sewn loop/ to attach the soft shackle? Its about 50mm-70mm wide so not conducive to use. Its also expensive (but that might be mark up for the 4x4 market). I did try to buy some as a roll - without success - could not find a manufacturer (and the 4X4 people here AWB? were less than helpful, for maybe obvious reasons).

We have just tested climbing rope for elasticity. We used bowlines and tore the outer casing at, one single, high load. It seems we should also have tested wet.

We use 11mm climbing rope as our snubbers, 2 off, one down each sidedeck. We attach to the stern cleats and run through turning blocks on each bow. We have used bowlines, but will change to something else? Not sure what. We use a chain hook and really have no major issues, but we can release from the trampoline as our bow roller is aft of the cross beam and I can get my hand in the release the hook. But I could not tie anything, there is only room for one hand/arm. The big downside to climbing rope is that the maximum size is 11mm (and I think 12mm). But one might have thought that using 2 ropes (side by side), one slightly longer than the other would suffice for larger yachts.

We pick ours up free from indoor rock climbing walls. They tend to be short, 14/15m in Oz as a standard wall height is about 10m. There are higher walls, but not nearby, that would have longer rope. The businesses seem to be regulated and retire ropes after a fall or when the outer casing wears or after a period of use, whichever comes the sooner. But they seem, when retired, good enough to use as a sacrificial snubber (as I say we use 2). Climbing rope is not cheap - if its going to chafe, so free rope looks an undeniable bargain?

A question:

Has anyone any idea if it is possible to buy tubular Dyneema to use as a chafe guard. One could slide the snubber though the hollow and position the Dyneema where necessary. Dyneema has good chafe resistance, seems ideal - though maybe too expensive.

Jonathan
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Old 26-05-2013, 23:48   #176
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Quote:
Originally Posted by Dockhead View Post

Well even chain has a certain elasticity, but not enough to provide any snubbing effect.

Likewise with Dacron -- an effective snubbing effect will appear only with a very thin (and this dangerously weak) or very, very long snubber.
Maybe not as big a difference as you might think if you compare similar tensile strengths factoring in a 10 or 15% reduction in strength for nylon when wet.

http://www.exsil.be/#/en/products/nylon-polyester/

It's not quite as black and white as all that.
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Old 27-05-2013, 00:26   #177
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Re: Rolling Hitch on Snubber

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Originally Posted by JonJo View Post
....

A question:

Has anyone any idea if it is possible to buy tubular Dyneema to use as a chafe guard. One could slide the snubber though the hollow and position the Dyneema where necessary. Dyneema has good chafe resistance, seems ideal - though maybe too expensive.

Jonathan
Try these guys; I've found them very obliging in the past.

They'll braid a cover any size you want. (They provide lots of new covers for sheets and halyards where the core is still in good shape but the outer sheathing is worn or damaged)

http://www.nautilusbraids.co.nz/contact.html
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Old 27-05-2013, 00:34   #178
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We leave our boat at anchor when we fly home 7,000 miles for a couple of weeks. Why not? Safer than a marina.
In a place so windy that you worried about the snubber parting?

I've left the boat as well but only in a decent anchorage.
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Old 27-05-2013, 00:36   #179
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Re: Rolling Hitch on Snubber

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Originally Posted by noelex 77 View Post
Has anyone considered (or used) the 4wd snatchem straps for a snubber.
They are strong elastic and readily available.
Thinking on this flutter might be a problem in very strong winds? May need a twist or two induced in it somehow.
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Old 27-05-2013, 00:41   #180
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Re: Rolling Hitch on Snubber

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Originally Posted by JonJo View Post
Has anyone any idea if it is possible to buy tubular Dyneema to use as a chafe guard. One could slide the snubber though the hollow and position the Dyneema where necessary. Dyneema has good chafe resistance, seems ideal - though maybe too expensive.
Try Mike Strong at Strongrope in Sydney, very helpful guy, and I am sure he had some dynex overbraid available.
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