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Old 01-05-2017, 08:31   #1
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Chain snubber - do I need some elasticity?

I have a six-foot long nylon anchor chain snubber/mooring ball rode connected to the waterline chainplate for my bobstay. I am considering replacing it with chain. Should I be concerned with the loss of elasticity that will occur when I have an all chain rode connected fast to the chainplate?
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Old 01-05-2017, 08:36   #2
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Re: Chain snubber - do I need some elasticity?

If the entire connection from the anchor to the boat will be of the metal to metal sort, then yes, shock loads will be a problem. And could possibly; break out the anchor, tear out a fitting, or part your rode.

A trick way to rig up a snubber, is to shackle & safety wire a block to the bobstay fitting by the WL. Then run your snubber over your bow roller, through the block, & then connect it to the chain. It lets you adjust the length of the snubber, or amount of rode you're using, without having to pull in your rode enough to be able to first unhook your snubber from it.
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Old 01-05-2017, 10:47   #3
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Re: Chain snubber - do I need some elasticity?

if you use enough chain it is not an issue. enough means more than the alleged recommendations.
friends use water line snubbing, which is what you describe, and find their issues are nil. they use , as i do, 120 ft on ground in short water. (25 ft or less)
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Old 01-05-2017, 12:42   #4
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Re: Chain snubber - do I need some elasticity?

I normally make the whole connection in chain only THEN add a snubber so that some length of chain is slack while the snubber takes up the job. Should the snubber go (it never did) the chain is there.

A snubber makes it a whole lot quieter onboard.

I use light snubbers and replace them when they show some chafe. Nylon is great and polyester is not bad either. Polyester lives longer BUT it tends to pre-stretch over time and stay that way (=bad). Nylon dies sooner but it seems to retain its ability to stretch and contract over all life.

Keep yours, imho.

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Old 01-05-2017, 12:59   #5
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Re: Chain snubber - do I need some elasticity?

Quote:
Originally Posted by YellowcakeMan View Post
I have a six-foot long nylon anchor chain snubber/mooring ball rode connected to the waterline chainplate for my bobstay. I am considering replacing it with chain. Should I be concerned with the loss of elasticity that will occur when I have an all chain rode connected fast to the chainplate?
To properly calculate, we need to know...
  • water depth
  • length of chain
  • chain size
  • fetch
  • size of ball (yes, it actually matters)
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Old 01-05-2017, 17:59   #6
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Re: Chain snubber - do I need some elasticity?

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Should I be concerned with the loss of elasticity that will occur when I have an all chain rode connected fast to the chainplate?
Of course, yes.
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Old 01-05-2017, 18:23   #7
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Re: Chain snubber - do I need some elasticity?

Hello, Yellowcakeman,

I'm in the you need the shock absorbing capabilities. One option not mentioned on the line is nylon double braid, which is what we use for our snubber.

Something previously mentioned on another thread is that one can have the cleat-to-snubber portion that goes over the roller be of dyneema, or some other line less susceptible to chafe than nylon, with the dyneema shackled to the nylon, at an eye you splice in, around an s/s thimble. This type of thinking came out of people using s/s cable for the purpose for hurricane moorings.

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Old 01-05-2017, 18:29   #8
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Re: Chain snubber - do I need some elasticity?

The chain would get out of sync with the boat in small/moderate waves at anchor. Felt like a giant had grabbed hold of the bowsprit and was shaking the boat. Added a 20' long 5/8" rope snubber attached to the bobstay fitting and all was fine. Would always go for elasticity.
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Old 01-05-2017, 18:54   #9
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Re: Chain snubber - do I need some elasticity?

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Originally Posted by UNCIVILIZED View Post
A trick way to rig up a snubber, is to shackle & safety wire a block to the bobstay fitting by the WL. Then run your snubber over your bow roller, through the block, & then connect it to the chain. It lets you adjust the length of the snubber, or amount of rode you're using, without having to pull in your rode enough to be able to first unhook your snubber from it.
This was the way I was going to rig up my system until I could not locate the backing plate to my bobstay fitting. It may be in there buried in the wood, but unless I could locate it, I was not willing to put a loading on that fitting in a different direction than what it was designed for.
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Old 01-05-2017, 20:09   #10
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Re: Chain snubber - do I need some elasticity?

Let us all remember that 6 feet of conservatively-sized nylon (loaded below the WLL) will only stretch 72 x 9% x 12/20 = 3.8 inches total, and only ~ 2 inches of this will be in response to surges (the rest is steady load). Just 2 inches in the worst case. Most of the shock absorption will come from the catanary and from the mooring ball being tugged under.

Check the math. Short snubbers aren't really for energy absorption, and given nylons weakness to chafe when wet and low WLL, the argument for it is not overwhelming. That is why we are seeing more polyester and Dyneema pendants. Much depends on the mooring design.
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Old 02-05-2017, 15:43   #11
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Re: Chain snubber - do I need some elasticity?

yes /snubber/shockabsorber
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Old 03-05-2017, 00:34   #12
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Re: Chain snubber - do I need some elasticity?

Yes, that's the main purpose in having one.

6' is way too short. I would look at 15-20' minimum. We used a 50' line with each end led back to a bow (catamaran).

All chain works in moderate conditions but in a heavy storm, the cantenary is gone before the shock loads hit.
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Old 03-05-2017, 02:07   #13
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Re: Chain snubber - do I need some elasticity?

150 feet of chain in 20 feet of water,
Allows the boat to float up and over the waves,
So even if the chain was tight from the wind forces, the strain would be constant and no or very little shock if at all,
Short chain or rodes are what create shock impacts from the chain,
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Old 03-05-2017, 02:37   #14
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Re: Chain snubber - do I need some elasticity?

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150 feet of chain in 20 feet of water,
Allows the boat to float up and over the waves,
So even if the chain was tight from the wind forces, the strain would be constant and no or very little shock if at all,
Short chain or rodes are what create shock impacts from the chain,
Not if it gets *really* bad. Nothing left for any dynamic loads like when the boat sheers around just in the wind or big gusts from completely different directions like you sometimes get in island bays, 60Kn gusts from all directions can and do happen.

Fairly simple physics will show the force on the anchor will be reduced with another 10m or so of nylon snubber.
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Old 03-05-2017, 02:40   #15
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Re: Chain snubber - do I need some elasticity?

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Allows the boat to float up and over the waves,
So even if the chain was tight from the wind forces, the strain would be constant and no or very little shock if at all,
n,
In a storm, a steep wave face hitting the bow will apply a force pushing the boat back. The shock load will be passed before the boat rises up on the wave. If the cantenary in the chain is already used up resisting relatively steady wind loads, the wave hitting the bow becomes a shock load and the chain will have no appreciable give to absorb that load.

In more moderate conditions, it works because the cantenary (ie: sag) allows for some give when a wave face hits the bow. Nothing magical about 150' and the effectiveness of 150' will vary greatly depending on the water depth.

Of course, there is always the extrme that will leave the chain bar tight and snap the snubber but short of extreme amounts of chain an elastic snubber is a good idea and doesn't negate the value of cantenary in the chain.

The other problem is if there are other boats in the anchorage, 150' may not be practical as you will be swinging into your neighbors.
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