Snubber sizing for All Chain Ground Tackle

[Jim Cate]

Originally Posted by wrwakefield

Jim,

In the days I used rope rode, I would use a snubber [or bridle] in inclement conditions to transfer any possible chafe points [under load] to the snubber with the intent of sparing the rode.

I can't quantify if it was worthwhile or not as I never was successful ruining a snubber due to good chafe protection...

FWIW

Cheers! Bill

Bill, and all you others who responded to my query... Thanks! I get it now... bridle, huh? Makes sense, and I really like the idea of taking the chafe on something other than the bit connecting the anchor to the boat.

But I still like all chain!

Jim

[thinwater]

Climbing Rope. Dynamic climbing ropes (UIAA single rated) have about 2x the energy absorption capacity of 3-strand nylon. They stretch farther without damage. Their weakness is reduce abrasion resistance due to a thinner cover, but that can be delt with.

Locking Hooks. There are locking hooks out there. Mantus makes 2. Below is a DIY version that has been published in Good Old Boat and in my anchoring book; this excels if you are using a bridle. Finally, you can attach the snubber with either a Dyneema sling used as a prussik or a long soft shackle. These are very strong and secure. Many cruisers confirm chafe is NOT an issue, and there is NOTHING dodgy about using a soft shackle on a snubber. Heck, they stay on flogging jibs just fine.


(this was an early version)


Rolling Hitch. Last year I did some testing with chain and load cell and determined that a rolling hitch generally starts to slip at about 1 - 1.5 times the working load of the line. Several well-known world cruisers confirmed this when I asked them; one had changed to a double rolling hitch, and the other to soft shackles. I would not use a rolling hitch on chain. [It's really weird to watch. Somehow the rope causes the links to shift and shuffle, and that is what allows the rope to slip. The same hitch will hold 2-3 times more on rope! Very weird, but feel free to test it. Curiously, a cow hitch or prussik are not subject to this. Testing published in Practical Sailor.]

Yes, any non-locking hook can fall off if it rests on the bottom in calm winds. I've tested most of them and they can work their way off. The mud lifts the hook and the boat wiggling around does the rest.

No, the hook does NOT need to be as strong as the chain. It needs to match the working load of the snubber, which is about 10% of the snubber strength. In this case, anything over about 2.5 tons BS will not fail. That's not a lot.


Catenary. This horse has been flogged to death, and then flogged to mush. If you have less than 150 feet of chain out and the wind tops 30 knots or so, the catenary is gone. If you have more than 400 feet of chain out, catenary persists well into gale conditions. In between... it depends. The math has been published many places and I'm tired of preaching the gospel. What I know is that I have spent many, many hours on the bow with a load cell, and I use long snubbers. Anything that reduces the load on the anchor and the rest of the anchor chain has got to be a good thing. All chain vs a long snubber can be as much as 3 times different, not based on theory, but based on measurements by multiple researchers. This is established fact.


---

Or at least that is what I think I have learned from a lot of side-by-side testing.

[Paul L]

Originally Posted by GB32

......?
To me there are 3 reasons to use a Snubber:
1. To take the load off the windlass, gypsy and chain stopper.
2. To keep the noise and wear down if yawing while on anchor
3. Allows me to see the stretch and assess how much load is being taken - useful when testing the Anchor - but stretch once anchored tells me 'time to go'.

In no way do I want much stretch - not even 10% of the breaking load. I rely on the catenary of the chain to do the dampening. If the Nylon is working hard that tells me I don't have enough dampening from the chain catenary and pay out more. ......

A snubber is used to dampen the shock load on the anchor in extreme conditions. These are conditions where the wind is strong enough to have the chain bar tight and the waves are creating a shock load.

[Paul L]

Originally Posted by Mike OReilly

Thanks Paul. I may give the soft shackle a try.

If you are using a small chain size one trick to make it easier to feed tbe soft shackle loop through the link is to tie a thin wax thread to the loop. Pass it through first and then pull the loop through.

[CarlF]

I've also gone to soft shackles of dyneema instead of chain hooks as the damn things fall off too often. The soft shackle can be conveniently attached and detached just beyond the windlass and it never falls off while going over the anchor roller.

I use 30ft of 7/16" brait with a 25 ton boat. I believe the brait does a slightly better job than three strand of smoothing out shock loads. And it doesn't heat up with repeated stretching like three strand. The 7/16th hasn't broken in three years through several gales and 60 knot thunderstorms. But for heavy weather I attach a second 5/8" snubber behind the smaller snubber and leave an extra 2ft loop of line. This only come in to play when the primary snubber gets to about 20% of breaking strength.

The one caution I'd have about the OP's setup is whether the anchor roller is strong enough to take the downward force in a real blow. In rough weather it would be better to lead the snubber through a chock to a cleat (with appropriate chafe protection at both chock and cleat).

[Simi 60]

Originally Posted by thinwater

Catenary. This horse has been flogged to death, and then flogged to mush. If you have less than 150 feet of chain out and the wind tops 30 knots or so, the catenary is gone. .

Depends on chain size surely.
100 ft of 10mm has a lot less weight than 100ft of 16mm

FWIW we have been sitting in 30 knot wind for about a week now.
80ft of 13mm chain out in 15ft of water with high windage 65 tonne hanging on it.
Have watched the chain lift and there is still a very visible curve in the chain.

[CaptainDana]

Wakefield, Both of the references you cited in 'your' approach were taken into account in the design of the 7/16 x 35' grabhook snubber. This thread has yielded on bit of true goodness (so far). Aviation and Marine engineers refer to it as 'Service Life'. A snubber with ideal snatch absorption properties is not necessarily ideal from a service life point-of-view. So, Thinwater proposed a recommended 'Remove & Replace' interval of 150 nights at anchor. That is not mentioned anywhere in the literature I've reviewed or you've referenced. Thanks to Thinwater for a truly constructive contribution.

[Mike OReilly]

Originally Posted by thinwater

Climbing Rope. Dynamic climbing ropes (UIAA single rated) have about 2x the energy absorption capacity of 3-strand nylon. They stretch farther without damage. Their weakness is reduce abrasion resistance due to a thinner cover, but that can be delt with.

Thanks Thin, so what diameter climbing rope should I, with my 15 ton boat, be looking at? Or is all climbing rope the same diameter? UIAA….?

OK, never mind. I obviously need to do some basic research. I like the idea though.

Originally Posted by Paul L

If you are using a small chain size one trick to make it easier to feed tbe soft shackle loop through the link is to tie a thin wax thread to the loop. Pass it through first and then pull the loop through.

Thanks Paul. My chain is 3/8”, so not particularly small. I like the idea of soft shackles in general, although to be honest, I really don’t feel the need to improve my snubber setup. I can’t see how this will be any easier than rolling hitches. But live and learn…

[boom23]

Does anyone use a mooring snubber to provide shock absorption?

https://www.amazon.com/Falcon-Safety...ooring+snubber

There are available for up to 1 inch line.

I've been using one and it seems to work so far. I've wrapped the line 4-5 times around the snubber, if I remember correctly.

[Simi 60]

Originally Posted by boom23

Does anyone use a mooring snubber to provide shock absorption?

https://www.amazon.com/Falcon-Safety...ooring+snubber

There are available for up to 1 inch line.

I've been using one and it seems to work so far. I've wrapped the line 4-5 times around the snubber, if I remember correctly.Attachment 181835

Yeah, I don't think a generic one size fits all bought off the shelf device will be worth diddly squat.

[thinwater]

Originally Posted by Simi 60

Depends on chain size surely.
100 ft of 10mm has a lot less weight than 100ft of 16mm

FWIW we have been sitting in 30 knot wind for about a week now.
80ft of 13mm chain out in 15ft of water with high windage 65 tonne hanging on it.
Have watched the chain lift and there is still a very visible curve in the chain.

True. First, the underlying assumption is that the person is using chain no larger than that specified by ABYC. The safety factor has proven sufficient over many, many years. Although this may seem strange, all boats, large and small, using chain rated for the size vessel, will show about the same curve. This is because in every case, the chain is operating at the same % WLL.



Second, 30 knots is moderate wind. Even pop-up summer thunderstorms, for example, commonly bring 60 knots, which is 4 times more force.



Third, just because you can see some curve does NOT men the rode still has measurable capacity to absorb shock. Put another way, stretching the chain just one or two feet may remove that curve, and the force required to move those 2 feet may be more than enough to make the anchor drag.



Finally, rode tension is much more about beam x height (windage) than mass.

[thinwater]

Originally Posted by boom23

Does anyone use a mooring snubber to provide shock absorption?

https://www.amazon.com/Falcon-Safety...ooring+snubber

There are available for up to 1 inch line.

I've been using one and it seems to work so far. I've wrapped the line 4-5 times around the snubber, if I remember correctly.Attachment 181835

They do work, but testing has shown they are no better than making the snubber 5 feet longer. Thus, they are very good for dock lines (which can't be longer) but dubious for snubbers, which can easily be longer.

[thinwater]

Snubber sizing. Climbing rope is proven up to just over 40 feet. UIAA single rope varies from about 10-11 mm. In fact, nearly all of the cruisers actually use used climbing rope, since climbers retire it when it is quite young (not hard to image why).



https://www.practical-sailor.com/iss...e_11951-1.html

[KP44]

Originally Posted by thinwater

A number of well-known and widely traveled sailors have been using climbing rope with that weight and length boat.

Remember also that the snubber is disposable and should be replaced every 100-150 nights, depending on the weather.

There are climbing ropes and they absorb the shock of a fall by stretching. One hard fall may render a rope unusable for climbing, but it has saved the climber from the hard shock of a static line.
Climbing ropes are not suitable for anchor snubbers because they are meant to absorb shock by permanently stretching. If you did use one, you'd want a new one for the next day.

I appreciate hearing about the long snubber. With chafe protection it sounds good.

[thinwater]

Originally Posted by KP44

There are climbing ropes and they absorb the shock of a fall by stretching. One hard fall may render a rope unusable for climbing, but it has saved the climber from the hard shock of a static line.
Climbing ropes are not suitable for anchor snubbers because they are meant to absorb shock by permanently stretching. If you did use one, you'd want a new one for the next day.

I appreciate hearing about the long snubber. With chafe protection it sounds good.

I'm sorry, but the above is incorrect and unsupported by engineering or experience. Climbing gyms ropes catch thousands of falls before retirement, and they are far from worn out at that point. They are retired by industry standard and for liability reasons. As mentioned, they have also been used by cruisers for snubbers for years.



You imply that climbing rope absorbs force by sacrificial failure, but this is untrue. They are just nylon ropes with a weave that allows more stretch. Yes, they can be damaged when loaded to the absolute limit; can't anything? Their is some unrecoverable stretch after severe loading, but this is true of all ropes.