Chain snubber - do I need some elasticity?

[Dockhead]

Originally Posted by Mr B

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,

Put enough force on it, and the catenary will disappear, and you will get shock loads. Waves don't just make the boat go up and down, but also back and forth, and worst of all, pitch the bow up and down. I would never anchor in really bad conditions, without a stout and long snubber, or a couple of them.

That being said, long enough and heavy enough chain, in deep enough water, will absorb a remarkable amount of energy. After some experiments, I have basically stopped using a snubber at all in anything less than F7, provided I have enough room to put out at least half of my 100 meters of 12mm chain.

[SeaSon]

Yes, you should be concerned. Not a good idea.

[thinwater]

There are lots of non-stretch pendants out there and they work. I thinks we are missing a few key facts:

1. A 6' nylon pendant is only going to stretch 2-3" to absorb loads. Stretch is a myth unless the pendant is long.
2. Although chain catenary is diminished in high winds, it does not vanish. Assuming the chain is grade 30 and up one size (which it almost certainly is) the chain will still have 2' of "stretch" left in the catenary at 40 knots and 8" at 60 knots. This is more than the pendant.
3. This is a mooring. We are not concerned about the chain coming off the bottom.
4. The chain does stretch, about 4" at the tension we are considering. Though it stretches much less than rope, there is 25 times as much or it out.
5. The mooring ball will be tugged under, absorbing stress.

I would want a long, strong snubber if the location was very exposed, but assuming some protection from waves, show me the math. Valhalla is right--it is shallow water that is the killer. Also waves, but if there are waves, the OP's short pendant will also fail. I've done a lot of testing with load cells, so I'm pretty sure of the numbers. A 30' snubber (probably thinner than the pendant) will stretch 3' at high load, and will not last as long. A totally different situation.

[Kahala]

The problem with most snubbers is they are too short to provide any elasticity. During a storm in Swarrow (look this up) one year, we used 2 X 40ft nylon snubbers and rode the storm out in great comfort and safety. Other boats with 6-8ft snubbers were snapping them continuously.

[Rebar_Caruso]

it's not only for the shock on the boat, but the Gypsy isn't going to love you either unless you give it some relief. My snubber goes from the sampson post behind my windlass, through the anchor roller & down about a foot into the water. the bow of the chain from snub knot to the bottom does alot to absorb some shock as well. I use 16 mil 8 strand & just use a snubber knot / rolling hitch on the chain.

[Dockhead]

Originally Posted by Rebar_Caruso

it's not only for the shock on the boat, but the Gypsy isn't going to love you either unless you give it some relief. My snubber goes from the sampson post behind my windlass, through the anchor roller & down about a foot into the water. the bow of the chain from snub knot to the bottom does alot to absorb some shock as well. I use 16 mil 8 strand & just use a snubber knot / rolling hitch on the chain.

Don't rely on the snubber to belay the chain and take the load off the gypsy! By design it is much weaker than the chain and much more subject to failure from chafing. Belaying the chain is a separate function which should be done with something at least as strong as the chain itself. Either a stout chain lock or a strong strop.

You can lose your boat if you rely on a snubber to keep the chain attached to the boat!!