snubber question

[Mischief Managed]

I have 5/16" HT anchor chain and a single 5/8" 8 plait snubber with a Mantus chain hook. Works fine, but I'm thinking a two line snubber might be an upgrade. I have enough 5/8" 8 plait to make another line with an eye splice that I could attach to the Mantus hook easily enough. Worth it? Should it be made of two 1/2" lines for more stretch?

 

[Mac2]

This information comes from professional cruisers (not me). They found a single line snubber about 35 feet worked best. It has to do with the stretch AND the rebound involved with the stretching. The double line, at 35 feet, looses the perceived benefits. I use the mantus chain grabber as well and love the design and retaining strap

 

[luna]

One has to understand that with a two line snubber as the boat sails around at anchor up to about 50% of the time only one line is loaded, the other is slack. Therefore both lines must be designed to take the full load, but when both lines are taking half of the load each, your bridal has stretched approximately only half as much as a single line snubber and as a result has less of a dampening effect. Yes I know, elongation is not exactly proportional to load in nylon ropes but for these purposes, lets just pretend it is, Ok?

Nylon rope despite its reduced capacity when wet is typically seen as the best overall choice for your snubber.

The other important things are the right sized rope for the load imposed by the boat in the design conditions and the length of the snubber which should likely be about 40 feet in order to get enough stretch (about 5') in the line to dampen the shock loads.

A good read on the subject can be found here: Forces

It's long and involved. Skip to the last page if you want, for the conclusion.

 

[Jc180]

Without getting too scientific, here’s what has worked for me in sustained winds into the 20 to 30 knot range with higher gusts. Single 5/8” nylon snubber with 3/8 ht chain. Approx 45,000 lb boat. Adjust snubber length to keep chain hook off bottom so chain loop loads hook.

Have used double snubber on occasion when boat sails around at anchor to quiet the action. Still use the 5/8” size.

 

[Don L]

I would look at it as a backup snubber line preattached to the chain.

 

[Hippocampus]

Issue is shock loading. So it’s blowing 25kts sustained and gusts are 35kts. 10kt difference. But the force involved is different than if it’s blowing 35kts and gusts to 45kts. Still a 10kt difference but in the second example the shock loading is much greater.

Also line has stretch but also creep. Nylon has a lot of stretch but with prolonged loading also creeps. That’s why people take it out of service if it becomes longer over time. We think of this as a slow gradual process but for the sizes of line we use for the sizes of boats we have in a strong 3 day northeaster it can happened more quickly than we realize. As it creeps the amount of stretch it has decreases.

Even with short times of loading it will stretch to the sustained wind and lose some stretch available to deal with gusts or increased loadings from hunting. When all the stretch is gone it’s no different than chain.

I think you should use a bridle even on a monohull. I think most of us commonly anchor in 10-20’ at around 5:1. Although the physics may suggest 35’ single snubbers are the cat pajamas it’s often not practical. Agree with jc
“Adjust snubber length to keep chain hook off bottom so chain loop loads hook. ”.
Agree you want to temper shock loading to the degree possible but think snubber/no snubber, single/bridle your attachment point, snubber, chain and anchor all need to be stronger than the gusts you might see. I would size accordingly. Few of us have really good Sampson posts so depend on our cleats. I’d rather see those snubber forces divided in two the majority of times knowing that will make my snubbers less likely to fail. Years ago read about a multiplicity of boats having either snubbers or cleats or bows fail. Would like to avoid that. So appreciate the astute thinking in Luna’s post but you end up doing what’s the best you can. Sure storm conditions 35’ of two snubbers go out. Have let out more snubber and chain as forces increase. Otherwise the most that’s reasonable.

 

[mvweebles]

Issue is shock loading. So it’s blowing 25kts sustained and gusts are 35kts. 10kt difference. But the force involved is different than if it’s blowing 35kts and gusts to 45kts. Still a 10kt difference but in the second example the shock loading is much greater.

True. Force is equal to fairly simple equation that includes a drag coefficient multipled by the area of the object multipled by velocity squared. [45 (mph)^2 minus 35^2] is a much bigger number than [35^2 minus 25^2].

Peter

 

[Shrew]

I have 5/16" HT anchor chain and a single 5/8" 8 plait snubber with a Mantus chain hook. Works fine, but I'm thinking a two line snubber might be an upgrade. I have enough 5/8" 8 plait to make another line with an eye splice that I could attach to the Mantus hook easily enough. Worth it? Should it be made of two 1/2" lines for more stretch?

1) Splice a thimble where the snubber will attach to the chain hook. An eye splice is for cleats and pilings. It will endure sawing motion and part if you attempt to attach an eye splice to a shackle.

2) I prefer 2 snubbers. Both for redundancy and because the boat tends to sit yawed to one side and tends to wag weird with just one.

3) I use 5/8" 8-plait for snubbers. Technically 1/2 is fine, but I prefer 5/8. Stretch has more to do with length of snubber than diameter.

 

[Mischief Managed]

1) Splice a thimble where the snubber will attach to the chain hook. An eye splice is for cleats and pilings. It will endure sawing motion and part if you attempt to attach an eye splice to a shackle.

My eye splice would have a thimble. Thanks for the information.

 

[Simi 60]

Wow, two threads same title on same page.

 

[Mischief Managed]

Thanks for all the replies. I definitely learned much more than I expected from this thread. I'm sure my snubber has been subjected to too much stretch over the last 4 years of use and is in need of replacement. I have anchored in some serious blows...


I'll be making two new 5/8" snubbers and testing them to see if I prefer two over one.

 

[Shrew]

My eye splice would have a thimble. Thanks for the information.

Apologies, I misunderstood. I tend to think of a splice with a thimble as a Thimble Splice, and a looped splice without a thimble as an Eye Splice.

Semantics I suppose.

 

[SteveK]

...........

Semantics I suppose.

potatoe potato

 

[rgano]

Because I bought a smaller boat with a combination chain/fiber rode, I went with twisted nylon for the snubber with a six-foot section at the rode end unlaid and then braided. I held either the chain or the plait equally well with a good hitch applied. If it ever failed, there is no danger of a piece of thimble and/or hook slinging back my way. Not liking the issues of corrosion under the splice at the interface and other issues, I dumped the plait in favor of all-chain but kept the braided snubber rather than employ metal out there. I keep a couple of different length snubber aboard because sometimes I just need a shorty to take the load off the windlass during short duration anchorages.