Rolling Hitch on Snubber

[Kettlewell]

My bottom line is that if I am getting significant wave action, I get out of there, hopefully before it gets too hard to leave. Re: the Cabo San Lucas disaster. It is almost always more comfortable underway, even if you just go a short distance and heave-to. There is no good combination of rode and snubber for shallow water with big seas.

[Andrew Troup]

If I was trapped in a shallow water/exposed to big seas from open waters situation, I would if possible rig a zig-zag (alternating floats and kellets) rode, and possibly leave the boat to fend for itself

[Andrew Troup]

The beneficial influence of chain catenary on the upangle of the anchor shank, to my way of thinking, is restricted to two cases

1) Setting or resetting: a heavy chain does a good job of automating this process, especially with certain styles of 'fussy' anchor

2) Difficult bottoms, where a drag might otherwise happen at quite low rode tensions: heavy chain can be greatly beneficial here, IMO

My observations and experience suggest to me that experienced cruisers hardly ever drag in strong winds, and if they do, they take immediate and effective action.

The more common scenario which can occasionally catch them unawares is the combination of light or moderate wind with undetected bottom problems .

[Kettlewell]

If I was trapped in a shallow water/exposed to big seas from open waters situation, I would if possible rig a zig-zag (alternating floats and kellets) rode, and possibly leave the boat to fend for itself.

I've been on some moorings in fairly high waves (up to 6 feet) and high winds during a hurricane, and having that big mooring float out there makes a huge difference. I have read that some people rig something similar to cushion their ride at anchor. In other words, the float, maybe 20-30 feet out, takes the load of the anchor chain off the bow of the boat, and before you can straigten the chain you have to pull that float way under water, which requires quite a bit of force. So, the float both acts as a cushion and allows the boat to rise to the waves more easily.

[Watercolor]

Just a point to consider -

Nylon is hydroscopic and adsorbs moisture that's why it elongates, also the moisture provides a lubricant. Nylon is semi-crystaline, like a rock crystal it has plates. The moisture is adsorbed into those plates and the amount of moisture varies with the ambient moisture.

This is great on fresh water, but there is some discussion in the plastics world as to the effect of the salt water moisture adsorption in warm heavily salt laden waters. Each time the moisture level decreases water evacuates the nylon. It is believed that some of the salt remains in the nylon and can cause friction or abrasion to the rode. This may be why nylon seems to get stiff over time , more so in the south.

The other point, I've know of quite a few people who soak their rode stiffened with clorox and water. It seems to make the rode softer, possibly leaching out the salt. The downside is that chlorine does have an small impact on nylon. So I'm not sure if the "softness" is due to the removal of salt or degradation of the nylon.

[Kettlewell]

The other point, I've know of quite a few people who soak their rode stiffened with clorox and water. It seems to make the rode softer, possibly leaching out the salt. The downside is that chlorine does have an small impact on nylon. So I'm not sure if the "softness" is due to the removal of salt or degradation of the nylon.

It can help to soak and wash old nylon rope in a tub with fresh water and detergent, but I usually just ignore it and replace it every ten years or so. High quality nylon like the stuff made by New England Ropes or Yale comes with special treatments and lubricants that helps to keep it relatively soft and performing for many years of hard use. I have been amazed by how long some of the New England stuff I own has maintained a good "hand," as they say.

[JonJo]

On rubber snubbers, I'm thinking of the long ones, 1.5 long, like a soggy police batton.

There seem to be a number of manufacturers but they all seem similar in form. They tend, here, to be expensive (for what they are). They are heavy. If used as recommended they have 3 turns round the shaft and based on their own performance data each rubber snubber will absorb around 250 joules, though this excludes any energy absorption of the rope wrapped round them. 250 joules is, basically, a waste of time. It is not recommended to stretch them beyond the point where they have absorbed the 250 joules as they snap (I have not tested when they fail - but have heard of failures). A 10mm nylon line will absorb 250 joules at something slightly over 130kg of load. We have tried rubber snubbers using 2 in line on each bridle rope, they seem to have a long life span, but they are not much use in stronger winds and seas.

Rubber snubbers are good for mooring in a marina, not much else. Though if you used 4 in a line they would be about the same as a 10mm nylon line loaded by 300kg.

For our 11.5m cat, 6t I'm thinking I need to be considering 600kg snatch loads, 3,500joules - but accept that under hurricane force winds this will be low, but I would then hope to have had time to deploy other anchors (with their own snubbers). Recall - I'm not to be reliant on one anchor.

On nylon in water - the only information I have seen is in fresh water (its actually described simply as water and I assume fresh). Degradation of strength, no-one mentions elastcitity seems to be 10%-20%. Some ropes are treated, to reduce this degradation, but I have seen no data on how good the treatment is - but you pay extra for the treatment. But as I'm subjectively thinking the loads are much less than the strength of the nylon, or dacron, I personally do not think it an issue (though longevity must be compromised - but as my snubbers are free and I treat as consumables I accept this.

I too do not like knots and climbing rope seems to demand knots, though maybe Evans can try splicing Dynamic climbing rope (remembering that kermantle covers many ropes other than climbing ropes). There are splicing instructions for kermantle but as climbing rope makes specifically warn against splicing I had lazily assumed not to bother (Evans you have shown me up). Bowlines are notoriously weak and the recommended knot is the double figure of 8, which is really ugly! Currently, for our snubbers, we are using a scaffold knot at the chain hook end (might swap hook to soft shackle - but difficult in our configuration to install) at the other end, horn cleats, we use bowlines. But having torn the cover under load at the bowlines we need something else.

Jonathan

[Andrew Troup]

Yikes

Re using a bleach containing chlorine to treat nylon cordage: this is a 'Severe Effect: Not Recommended' combination, according to chemical resistance charts from the likes of

Nylon Chemical Resistance Chart

I'm a believer in washing lines regularly in warm water to free them of their salt load, but would never use anything more agressive than the gentlest soap or detergent I had to hand which was able to raise a lather in salt water.

[Andrew Troup]

I think the reason climbers shun splices is that they like the workmanship of any life-critical item to be out in the open where they can see it, even if they did it themselves.

Generally they would prefer something less strong but reliable over something stronger but less verifiably so.

Slings are a case in point: these are almost always knotted rather than sewn, even though sewing is clearly superior in every respect other than verifiability.

[Delfin]

Originally Posted by Andrew Troup

I personally think that the slack should not be based on how much the snubber can stretch, but on how much you NEED it to stretch.

And the latter will preferably be a smallish proportion of the former.

Unless conditions were likely to get rapidly worse and/or the boat would be unattended, I would personally err on the side of less slack, and pay out a bit more every time there was a severe snub.

Whether correct or not beats me, but I use the total stretch of the snubber length prior to breaking that I'm using as the length of the additional chain deployed over the snubber. For the 30' snubber I use, that's an extra 10 feet, with the snubber's breaking strength approximately equal to the wll of the chain. What I don't know for sure is whether nylon 3 strand will break beyond 30% stretch. I vaguely remember hearing/reading that, but confirmation from someone more knowlegeable would be appreciated.

[JonJo]

Energy absorption,

I have been quoting joules in terms of the performance of nylon and rubber snubbers.

It was quoted earlier, but to keep it topical and relevant:

a 5t yacht moving at 1 knot needs to have 1,250 joules absorbed - this is a bit lighter than our cat at 6t.

What the relevant speed is, I really do not know.

So to compensate for the energy of the 5t yacht one would need 5 rubber snubbers (assuming no benefit from the rope wrapped round the snubbers - too complicated to work out!).

To compensate for the energy of the 5t yacht one would need, say a 10m snubber - which would be working at 20% of the breaking load of the snubber and about 15% of the working load of the climbing rope. Recalling that working at 60/70% of the breaking load of a climbing rope gives it a life of about 10 cycles, 30/35% of the working load gives it a life of 100 cycles and 15/20% - presumably a lot of cycles. This is all in the dry.

Jonathan

[JonJo]

Originally Posted by Delfin

Whether correct or not beats me, but I use the total stretch of the snubber length prior to breaking that I'm using as the length of the additional chain deployed over the snubber. For the 30' snubber I use, that's an extra 10 feet, with the snubber's breaking strength approximately equal to the wll of the chain. What I don't know for sure is whether nylon 3 strand will break beyond 30% stretch. I vaguely remember hearing/reading that, but confirmation from someone more knowlegeable would be appreciated.

My understanding is that nylon breaks at 30%. However there seems ambiguity on the amount of stretch of both octaplait and 3 strand nylon. For apparently the same product manufacturers quote from slightly less than to slightly more than 30%.

Jonathan

[Delfin]

Originally Posted by JonJo

Energy absorption,

I have been quoting joules in terms of the performance of nylon and rubber snubbers.

It was quoted earlier, but to keep it topical and relevant:

a 5t yacht moving at 1 knot needs to have 1,250 joules absorbed - this is a bit lighter than our cat at 6t.

What the relevant speed is, I really do not know.

So to compensate for the energy of the 5t yacht one would need 5 rubber snubbers (assuming no benefit from the rope wrapped round the snubbers - too complicated to work out!).

To compensate for the energy of the 5t yacht one would need, say a 10m snubber - which would be working at 20% of the breaking load of the snubber and about 15% of the working load of the climbing rope. Recalling that working at 60/70% of the breaking load of a climbing rope gives it a life of about 10 cycles, 30/35% of the working load gives it a life of 100 cycles and 15/20% - presumably a lot of cycles. This is all in the dry.

Jonathan

Jonathan, going back to the formula posted by Marine Safety (http://www.marinesafety.com/research...ynamicload.pdf), if the vessel weighs 5 tons, and the speed is 1 knot, and further if the vessel were brought up hard in 6 inches (pretty much a physical impossibility), you'd have a peak load of 1,000 # to deal with, which is close to the value of joules you reference converted to English units. Using the snubber you describe and assuming 15% stretch, the total energy to be absorbed would only be 1000#/5, or 200#, which would mean you could use a fairly thin snub line. As noted before, the distance over which the energy is absorbed is critical to calculating loads, which is why tankers may go into neutral a very long way before their destination so the energy of that much mass can be dissipated. I think this is the reason why as you suggest rubber snubbers are by themselves not all that useful - they can only stretch a few inches. This is also why a short snubber may be just fine most all of the time, but the more energy you have to unload, the longer the distance you want to unload it over, which would justify having a fairly long snubber for hurricane conditions. Does this make sense, or have I hashed the math?

[Snowpetrel]

Originally Posted by Delfin

...This is also why a short snubber may be just fine most all of the time, but the more energy you have to unload, the longer the distance you want to unload it over, which would justify having a fairly long snubber for hurricane conditions.

I am not sure it is just as simple as changing the length of a snubber for extreme conditions. Often there is a steady wind loading that in extreme conditions (that are moderately steady ie not just extreme gusts and calms) that would use up most of elasticity in a skinny standard snubber, pushing it from the 5-15% elongation that is probably safe, into the 15-25% elongation starting to get into dangerous territory for a snubber to take long term. lengthening the snubber might reduce the stretch down to 15-20% but it still might not stop it heating up and snapping.

The longer snubber reduces the peak elongation, but not the base elongation.

The only cure I can think of is to go to a much heavier stronger storm snubber, this would drop the stretch down to say 5-15%, which may survive hurricane conditions.

In Andrews case, for leaving a boat unattended, two or even three snubbers set up might work. The skinny standard snubber is long and set to only extend out to a max of 10% before the heavy shorter one takes over preventing the light one from over extending. In extreme loads the storm snubber might extend out to 10-15% with the normal snubber also extending only 15%. A very very strong backup snubber can be left to protect the windlass and chain in the event of a failure of both snubbers.

The storm snubber needs to be shorter to prevent the standard snubber overextending. Working out how to achieve this would be tricky. Maybe using spectra leaders on the storm snubber might work, with both attached to the chain at the same point , or careful measurement of the attachment points on the chain, with the storm snubber attached a few meters closer to the boat.

[Delfin]

Originally Posted by Snowpetrel

I am not sure it is just as simple as changing the length of a snubber for extreme conditions. Often there is a steady wind loading that in extreme conditions (that are moderately steady ie not just extreme gusts and calms) that would use up most of elasticity in a skinny standard snubber, pushing it from the 5-15% elongation that is probably safe, into the 15-25% elongation starting to get into dangerous territory for a snubber to take long term. lengthening the snubber might reduce the stretch down to 15-20% but it still might not stop it heating up and snapping.

The longer snubber reduces the peak elongation, but not the base elongation.

The only cure I can think of is to go to a much heavier stronger storm snubber, this would drop the stretch down to say 5-15%, which may survive hurricane conditions.

In Andrews case, for leaving a boat unattended, two or even three snubbers set up might work. The skinny standard snubber is long and set to only extend out to a max of 10% before the heavy shorter one takes over preventing the light one from over extending. In extreme loads the storm snubber might extend out to 10-15% with the normal snubber also extending only 15%. A very very strong backup snubber can be left to protect the windlass and chain in the event of a failure of both snubbers.

The storm snubber needs to be shorter to prevent the standard snubber overextending. Working out how to achieve this would be tricky. Maybe using spectra leaders on the storm snubber might work, with both attached to the chain at the same point , or careful measurement of the attachment points on the chain, with the storm snubber attached a few meters closer to the boat.

Thanks, SP. As noted above I think sizing the snubber so that its breaking strength is close to the working strength of the primary rode makes sense. But you raise a good point. If the wind is steady and strong, whatever length you have will elongate. If gusty, the longer snub line would seem to be preferable, but you're right, when it gets really hairy is when you encounter sustained high wind and under those circumstances, doubling up with a strong backup to the 'daily use' snubber that can still provide some shock loading but which has equivalent breaking strength to the chain is probably ideal.