snubber chafe and melting

[Andrew Troup]

<< I've come to believe that snubbers are perhaps best viewed as a nicety in normal and moderately windy conditions but that for severe storms, one must expect that they will chafe/explode and that the rode's attachment to the yacht must stand on its own in the absence of a snubber.>>

I think there's a deal of truth in this. I certainly wouldn't want to have to anchor in bad conditions in a boat where the chain and fittings and foredeck were not up to anchoring without a snubber.

Most workboats don't feel the need for them, and forty or fifty years ago, neither did most substantial yachts (sailboats) which were using all chain. It has to be said their chain was typically up to twice the diameter which is now fashionable, with bollards and mooring bitts to match.

Hiscock mentioned the possibility of using snubbers where they might help reduce snatch in some of his later writings, but I think even he would be surprised at how they have become the foredeck 'accoutrement du jour'. I suspect his recommendation had as much to do with comfort, and keeping the noise from the grumble of the chain out of the sleeping quarters, as it did with saving the gear.

It's become a circular reasoning proposition, it seems to me: almost everyone is now using light chain, which means they have to use snubbers, and the extent to which heavy chain eliminates the problem is not evident to the majority who have not tried heavy chain.

Instead the argument which is repeatedly used against heavy chain is that at high loads, it becomes virtually straight.

Which completely misses the point: the snubbing capability is a function of the area under the graph for load vs horizontal displacement as the chain loads up. This represents the work done to straighten the chain, measured in watt-seconds or kWh or whatever energy unit you prefer.

This crucial difference between light and heavy chain is considerable, in theory and in practice, and the notion that it makes no difference makes no sense to me.

[carstenb]

I keep wondering about chafe. Firehose as a chafe protector is frequently mentions, but why not just use a 1 wire braid rubber hydraulic or thermoplastic hose?

These types of hoses have tremendous chafe resistance, are temperature resistant and flexible.

Anybody try it?

[Jim Cate]

Well, IMO the place for the dyneema is as a strop between the snubber and the bollard/cleat/sampson post. That is, the dyneema goes from the attachment through the chock or roller or whatever the source of the chafe might be and thence to the end of the snubber, however long it may be. Thus the stretch and relative movement all happen outside of the boat and its chafe points. One could as well use wire rope for that matter!
No weak points involved...

And FWIW, I agree that the advantage of heavier chain as an energy absorber as it straightens out is often overlooked. Folks are always yammering about "bar taught" chain rodes, but they are only looking at the bits near the boat and have no means of determining whether there is appreciable catenary remaining.

Cheers,

Jim

[DumnMad]

Originally Posted by Jim Cate

Well, IMO the place for the dyneema is as a strop between the snubber and the bollard/cleat/sampson post. That is, the dyneema goes from the attachment through the chock or roller or whatever the source of the chafe might be and thence to the end of the snubber, however long it may be. Thus the stretch and relative movement all happen outside of the boat and its chafe points. One could as well use wire rope for that matter!
No weak points involved...
Cheers,
Jim

Make sense, same as oil tanker wire mooring lines with their 11m stretchy tails to the bollard.

[Andrew Troup]

Originally Posted by Jim Cate

.... a strop between the snubber and the bollard/cleat/sampson post. ....One could as well use wire rope for that matter!

or chain .... <G>

Originally Posted by Jim Cate

And FWIW, I agree that the advantage of heavier chain as an energy absorber as it straightens out is often overlooked. Folks are always yammering about "bar taught" chain rodes, but they are only looking at the bits near the boat and have no means of determining whether there is appreciable catenary remaining.

Thanks Jim, I sometimes wonder if there's a bunch of people who are under-persuaded by the new teachings, but keep their heads down when those teachings are being disseminated...

I think it goes further than whether there's catenary remaining. Ideally with an elastic snubber, it's rigged so that it is not exposed to infinite force, by the chain coming tight. So at that point, we are back to the situation of a bar-taut chain. Oddly, that doesn't seem to be considered a deal breaker.

The important question is this: Firstly: how progressively is the restraining force applied? (with a light chain, it happens more suddenly: the graph looks like a hockey stick)

Secondly: how much energy has the system converted from kinetic to stored form (gravitational potential energy, or elastic strain in the case of a snubber) in getting to that condition. (The gentler slope of the heavy chain has more area under it = more work done lifting the chain)

And, in the case of an elastic snubber, how long can it dissipate energy at that rate (measured in, say, kW) before it can no longer function. And how do you change it safely, when that point is reached?

One of the leading proponents of "light chain/heavy anchor" does not conspicuously follow his own advice: which proved fortunate when he struck conditions in Sth Georgia which meant that, in his judgement, it was not viable to fit a snubber.

(insufficient searoom to leeward to deal with it, if the anchor were to drag and the cable had to be retrieved under emergency circumstances)

[HappyMdRSailor]

Originally Posted by Andrew Troup

Hiscock mentioned the possibility of using snubbers where they might help reduce snatch in some of his later writings, but I think even he would be surprised at how they have become the foredeck 'accoutrement du jour'. I suspect his recommendation had as much to do with comfort, and keeping the noise from the grumble of the chain out of the sleeping quarters, as it did with saving the gear.

It's become a circular reasoning proposition, it seems to me: almost everyone is now using light chain, which means they have to use snubbers, and the extent to which heavy chain eliminates the problem is not evident to the majority who have not tried heavy chain.

Instead the argument which is repeatedly used against heavy chain is that at high loads, it becomes virtually straight.

Which completely misses the point: the snubbing capability is a function of the area under the graph for load vs horizontal displacement as the chain loads up. This represents the work done to straighten the chain, measured in watt-seconds or kWh or whatever energy unit you prefer.

This crucial difference between light and heavy chain is considerable, in theory and in practice, and the notion that it makes no difference makes no sense to me.

+100

I've also seen the practice of hanging a secondary at 1/3-1/2 the length of the rode from the pointy end...

PS: can you convert kWh to Horsepower-Minutes for me??? I'm a little fuzzy on the math...

[s/v Jedi]

What you want to prevent losing the boat is a chain stopper. The snubber is an attempt to prevent needing it but, as demonstrated, you still need it. Heavy chain was to make it strong enough. Taking twice the weight with you fo a snubber while a piece of nylon can do the same is just silly.

Chafing gear around the snubber does not help because we're talking about internal chafing.

[zeehag]

rh--i havent had any problem here in swellville with my snubber bridle chafing--we have constant swells of 1-2 meters here...i am using a 3 strand line of 5/8 with a chainhook. so far, so good. even withstood a tormenta with some excellent winds in december.
my snubber protects my sprit from wear and erosion from stress on it from anchor chain on the rollers...

[Kettlewell]

In the worst conditions my main snubber goes to a bow eye I have installed that is just above the waterline. Therefore no chafe on the line, and most of it will be nearly continuously in the water, so it is water cooled. However, I've never busted a snubber of any sort in bad conditions, and that includes a few hurricanes up to 100 and over. I have read reports that claimed melted nylon was found in some mooring lines that snapped after Hurricane Bob, but I was anchored nearby where the highest winds were experienced and we did not suffer such things. The mooring lines I saw that were parted appeared to all be from ordinary chafe. As I said in the other thread about chain hooks, in hurricanes and such I use multiple snubbers tied on at various lengths and secured on the boat in various places, so that if one goes there is a back up in place and working instantly, though I have never had the primary let go.

[Liam Wald]

Really great discussion! Thanks everyone. I have never anchored in conditions beyond 40 knots with small to moderate swell. I also am set up with two snubbers that attach to different locations. One snubber has single 1/2 3-strand nylon (primarily used), the other has dual 5/8 braided nylon (back-up). I like the idea of installing a bow eye near the waterline and will put that on the project list.
Here's hoping I never have to anchor in conditions worse than I have in the past!!

[Sandero]

A good solution for a snubber is to use a EDPM rubber mooring compensator with 3 wraps. This will help a bit.

[zeehag]

defjef--thse do not function out here in swellville...i broke 2 super heavy ones in la cruz in the marina. they popped in less than 20 kt winds and less than 2 ft swell.....