Who Needs a Snubber, Anyway?

[tomfl]

Originally Posted by boatman61

Having owned cats in the past one learns pretty quickly that a bridle is the way to go with a cat at anchor.. it gets the bows facing square into the wind which in turn stops the sailing around and reduces loads on one or the other hulls deck cleats.

SNIP

When anchoring in places like the Bahamas and Florida Keys the shallow water and tides going to and from deeper water and the Gulf Stream pouring out of the Gulf into the Florida Straights can often result in the wind direction being different than the wind direction. Sometimes it can be more comfortable to get the bows facing square into the waves instead of the wind. A significant current can, but not always will, overcome any sailing around.

My bridle is made of two lines attached to a hook to secure on the chain. The bitter end of the bridle is secured on cleats on the bows of each hull. While I have used a Magic Marker to indicate just where the first turn on the cleats is taken for even lengths of both sides of the bridle at times I have adjusted one side or the other to get the bows square to the waves/current instead of square to the wind.

Part of my anchoring dance (which probably takes half an hour to complete) includes securing the bridle to the cleats, looking to the sides for land marks to check for dragging later, and then walking directly behind the bowsprit and checking if the chain/hook is obscured by the bowsprit or to one side or the other. If the current/wind/what ever is causing the chain/hook to be visible I know something needs to be done to obscure it.

Of course this is a dynamic situation and after an hour or two or three or more I have probably checked to see if there is a need to adjust the bridle length on one side or the other. It just makes sense to me to have a bridle with adjustable length; even if most of the time the bridle is the same length on both sides.

YMMV

[thinwater]

Originally Posted by Dockhead

I'm not sure why you wouldn't have any shock absorbing ability with chain on the bottom -- of course you will. More scope increases the energy absorbing capacity of the chain, just like heavier chain does.

I'm not saying it does not give some absorption, but I anchor a lot in very shallow water, often less than 5', and I can tell you that at 10:1 scope I can have chain on the bottom and still have massive jerks. What is critical is the difference in length between very slight curve and bar tight. It will only be 1-2 inches in such shallow water, which makes it practically rigid. Check my math. I broke a 1200-pound load cell testing in shallow water in 12 knots. All it took was a small wake. Bam.

My comment was for those digging into the math, that there are 2 related but slightly separate subjects.

[sy_gilana]

To answer Dockhead. I don't. Never have, never will, never had a problem. I will continue snubberless as long as I am sailing because that's the way I learned it on ships, and thats the way I have been doing it for, oh, 6000+ nights on anchor.

[evm1024]

Just a summary of my snubber understanding.

Wind and waves transfer energy to the boat which moves. Snubbers bring the boat to a halt and thus the energy is transferred to the snubber. Snubbers dissipate this energy in 2 primary ways. The first is that they transfer some of the energy back to the boat (lets call it rebound) which transfers it back to the water. The other way is through heating the snubber.

This heat is in the form of molecular motion (that is what heat is after all) that can be dispersed in the form of heat radiation, conduction to the water that may be in contact with the snubber and to rest of the line or convection in the form of heating the air around the line. Basic physics.

For any given snubber diameter the snubber will elongate further as the energy it needs to dissipate increases. More force more stretch. So a short, small diameter snubber needs to stretch a lot to handle any given force. A long, small diameter snubber stretches less percentage wise to handle the same force. i.e. short (oh say 10'), small diameter snubber may stretch 10% to give us 11' at full extention where a long (say 30') small diameter snubber may stretch 5% to give 1.5' of stretch (elongation) for a total length of 31.5'. The longer snubber stretched more but at a lower percent of the length.

A large diameter snubber of short length will have a greater capacity to handle the force but because of the strength will do so over less time and put greater stresses on the boat and anchor. A long snubber of larger diameter will have a much greater length to dissipate the forces along.

It is known that the cyclic load failure rate of nylon is directly related to the elongation (in terms of the elongation as a % of the elongation at breaking).

Thus a line that is cycled to a larger % of it maximum elongation will fail sooner than a line that is cycled less. (darn where did I put that study, I cited it somewhere on CF)

If I recall (and don't quote me, look at the study) if you cycle the snubber to 50% of the elongation % at the breaking strength of the line it will fail in just a few hundred cycles.

There is an elongation (some % of breaking elongation) where the failure rate is nil. So if your snubber never exceeds this elongation then it will last a long time.

Short, small diameter snubbers have to elongate a lot to absorb the energy and will fail quickly (when the forces are great enough of course)

Long, small diameter snubbers can last a lot longer. But are more subject to abrasion.

Short, large diameter snubbers also can last longer but have higher peak forces at the connection to the boat.

Long, large diameter snubbers last a long time and limit the peak forces transmitted to the boat. Plus they are more resistant to abrasion.

This is why I have a large, long snubber on my boat.

============

I do not recommend using climbing ropes for any anchoring use. Climbing ropes are designed to have individual fibers break as they absorb the energy of a fall. This is done to limit the impact force that the climber (faller?) is subject to. No need to break the climbers hips.

As such climbing ropes are rated in the number of falls they take before being retired. 4 to 8 is a normal range of falls. After that number of falls the ropes ability to limit the impact force is decreased with the UIAA tests actually showing the rope breaking.

Image surge tossing the boat with 1000 pounds of force 100's of times.

The old adage is that climbing ropes do not break, they are cut. This is true as the weak point of a rope will be where the rope goes over a rock edge or where some earlier injury to the rope cut some fibers and created a weak point. I have seen a climbing rope that was snapped in the middle. It did break where there was some weak point. This was at a blace between 2 climbers who were caught in an avalanche and one of the climbers came to a standstill in the snow (which set up of course) and the other climber was still entrained.

[Cotemar]

Originally Posted by thinwater

I'm not saying it does not give some absorption, but I anchor a lot in very shallow water, often less than 5', and I can tell you that at 10:1 scope I can have chain on the bottom and still have massive jerks. What is critical is the difference in length between very slight curve and bar tight. It will only be 1-2 inches in such shallow water, which makes it practically rigid. Check my math. I broke a 1200-pound load cell testing in shallow water in 12 knots. All it took was a small wake. Bam.

My comment was for those digging into the math, that there are 2 related but slightly separate subjects.

I agree. In shallow water you need a snubber.

In deep water with lots of scope out, have at it.

My snubbers are automatic, so they are deployed no matter what the scope is.

We never think about them as they are working all the time at anchor.

Its nice to know that when your in town and the wind picks up that your boat is not getting jerked around, because you forgot to setup your snubbers.

[evm1024]

Hey, look at this, PS has an article on snubber sizing... I've not read it yet.

What is Ideal Snubber Size? - Practical Sailor Print Edition Article

[evm1024]

One more pdf on climbing and sailing ropes

http://personal.strath.ac.uk/andrew.mclaren/JMDA75.pdf

[Cadence]

Originally Posted by a64pilot

You know I have never heard any noise from the chain, but seems I'm always in sand or mud or a mix.
I use a bridle of dual 25' three strand, cause it's cheap and stretchy, using both cleats seems to help some with sailing about at anchor. I keep meaning to try attaching to a midship cleat on one side to see if that makes sailing any better.


Sent from my iPad Pro using Cruisers Sailing Forum

A 25' bridle of three stand makes sense.

[Dockhead]

Originally Posted by thinwater

I'm not saying it does not give some absorption, but I anchor a lot in very shallow water, often less than 5', and I can tell you that at 10:1 scope I can have chain on the bottom and still have massive jerks. What is critical is the difference in length between very slight curve and bar tight. It will only be 1-2 inches in such shallow water, which makes it practically rigid. Check my math. I broke a 1200-pound load cell testing in shallow water in 12 knots. All it took was a small wake. Bam.

My comment was for those digging into the math, that there are 2 related but slightly separate subjects.

OK, that makes sense. That's the effect of that part of the catenary range being cut off.

[Kenomac]

Originally Posted by evm1024

Just a summary of my snubber understanding.

Wind and waves transfer energy to the boat which moves. Snubbers bring the boat to a halt and thus the energy is transferred to the snubber. Snubbers dissipate this energy in 2 primary ways. The first is that they transfer some of the energy back to the boat (lets call it rebound) which transfers it back to the water. The other way is through heating the snubber.

This heat is in the form of molecular motion (that is what heat is after all) that can be dispersed in the form of heat radiation, conduction to the water that may be in contact with the snubber and to rest of the line or convection in the form of heating the air around the line. Basic physics.

For any given snubber diameter the snubber will elongate further as the energy it needs to dissipate increases. More force more stretch. So a short, small diameter snubber needs to stretch a lot to handle any given force. A long, small diameter snubber stretches less percentage wise to handle the same force. i.e. short (oh say 10'), small diameter snubber may stretch 10% to give us 11' at full extention where a long (say 30') small diameter snubber may stretch 5% to give 1.5' of stretch (elongation) for a total length of 31.5'. The longer snubber stretched more but at a lower percent of the length.

A large diameter snubber of short length will have a greater capacity to handle the force but because of the strength will do so over less time and put greater stresses on the boat and anchor. A long snubber of larger diameter will have a much greater length to dissipate the forces along.

It is known that the cyclic load failure rate of nylon is directly related to the elongation (in terms of the elongation as a % of the elongation at breaking).

Thus a line that is cycled to a larger % of it maximum elongation will fail sooner than a line that is cycled less. (darn where did I put that study, I cited it somewhere on CF)

If I recall (and don't quote me, look at the study) if you cycle the snubber to 50% of the elongation % at the breaking strength of the line it will fail in just a few hundred cycles.

There is an elongation (some % of breaking elongation) where the failure rate is nil. So if your snubber never exceeds this elongation then it will last a long time.

Short, small diameter snubbers have to elongate a lot to absorb the energy and will fail quickly (when the forces are great enough of course)

Long, small diameter snubbers can last a lot longer. But are more subject to abrasion.

Short, large diameter snubbers also can last longer but have higher peak forces at the connection to the boat.

Long, large diameter snubbers last a long time and limit the peak forces transmitted to the boat. Plus they are more resistant to abrasion.

This is why I have a large, long snubber on my boat.

============

I do not recommend using climbing ropes for any anchoring use. Climbing ropes are designed to have individual fibers break as they absorb the energy of a fall. This is done to limit the impact force that the climber (faller?) is subject to. No need to break the climbers hips.

As such climbing ropes are rated in the number of falls they take before being retired. 4 to 8 is a normal range of falls. After that number of falls the ropes ability to limit the impact force is decreased with the UIAA tests actually showing the rope breaking.

Image surge tossing the boat with 1000 pounds of force 100's of times.

The old adage is that climbing ropes do not break, they are cut. This is true as the weak point of a rope will be where the rope goes over a rock edge or where some earlier injury to the rope cut some fibers and created a weak point. I have seen a climbing rope that was snapped in the middle. It did break where there was some weak point. This was at a blace between 2 climbers who were caught in an avalanche and one of the climbers came to a standstill in the snow (which set up of course) and the other climber was still entrained.

It's a shock absorber.

[Cadence]

Originally Posted by Kenomac

It's a shock absorber.

I guess those that don't get that should just go dah.

[evm1024]

Originally Posted by Kenomac

It's a shock absorber.

Exactly - we are discussing the failure modes of different shock absorbers.
.

[thinwater]

Originally Posted by evm1024

... I do not recommend using climbing ropes for any anchoring use. Climbing ropes are designed to have individual fibers break as they absorb the energy of a fall. This is done to limit the impact force that the climber (faller?) is subject to. No need to break the climbers hips.

As such climbing ropes are rated in the number of falls they take before being retired. 4 to 8 is a normal range of falls. After that number of falls the ropes ability to limit the impact force is decreased with the UIAA tests actually showing the rope breaking.

Image surge tossing the boat with 1000 pounds of force 100's of times.

The old adage is that climbing ropes do not break, they are cut. This is true as the weak point of a rope will be where the rope goes over a rock edge or where some earlier injury to the rope cut some fibers and created a weak point. I have seen a climbing rope that was snapped in the middle. It did break where there was some weak point. This was at a blace between 2 climbers who were caught in an avalanche and one of the climbers came to a standstill in the snow (which set up of course) and the other climber was still entrained.

I find this sort of definitive statement interesting for 2 reasons:

1. A climbing rope is only suitable up to a certain boat size. What works very well on my 8500-pound cat will not work as well on a XXX ton mono. Few thing in life are one size fits all. In fact, I use a 7.8mm climbing rope bridle, because 11mm was more than engineering design called for for my boat up to 70 knots. But for a larger boat I would spec something larger, in proportion to wind load.

2. I'm not guessing or theorizing. A good number of regular cruisers have adopted climbing rope for this use, including at least one circumnavigator on a rather heavy boat. It does require attention to chafe, but climbing ropes, in real practice, have VERY long fatigue lives in shock absorber duty, no doubt related to the same design features that allow them to withstand enormous whippers a few times.

The PS guidelines were based on calculation, instrumented testing, and comparison with the experience of numerous cruisers. And all three methods agreed. This is for shallow waters of course. The same study pointed out that deeper water changes everything, and at some point (depends on numerous variables) chain cannot snatch load.

No, you don't need a snubber. The testing also concluded that if everything is built to ABYC standards (Is it? Does your bowsprit and roller have a SWL measured in tons? Would you hang a car from it?) it should endure without it. It barely matters unless you are caught in the open in a blow. But the odds of dragging an anchor go up if the water is at all shallow.

[evm1024]

Originally Posted by thinwater

I find this sort of definitive statement interesting for 2 reasons:

1. A climbing rope is only suitable up to a certain boat size. What works very well on my 8500-pound cat will not work as well on a XXX ton mono. Few thing in life are one size fits all. In fact, I use a 7.8mm climbing rope bridle, because 11mm was more than engineering design called for for my boat up to 70 knots. But for a larger boat I would spec something larger, in proportion to wind load.

2. I'm not guessing or theorizing. A good number of regular cruisers have adopted climbing rope for this use, including at least one circumnavigator on a rather heavy boat. It does require attention to chafe, but climbing ropes, in real practice, have VERY long fatigue lives in shock absorber duty, no doubt related to the same design features that allow them to withstand enormous whippers a few times.

The PS guidelines were based on calculation, instrumented testing, and comparison with the experience of numerous cruisers. And all three methods agreed. This is for shallow waters of course. The same study pointed out that deeper water changes everything, and at some point (depends on numerous variables) chain cannot snatch load.

No, you don't need a snubber. The testing also concluded that if everything is built to ABYC standards (Is it? Does your bowsprit and roller have a SWL measured in tons? Would you hang a car from it?) it should endure without it. It barely matters unless you are caught in the open in a blow. But the odds of dragging an anchor go up if the water is at all shallow.

And of course you should take it as my own opinion and use your own judgement.

I am sure that there are many experienced cruisers who do use climbing ropes for their sailing needs. And have not experienced a failure. I would say yet but that would be misleading as that all systems fail sooner or later.

Here is a short video of the UIAA climbing rope test. The test is designed to simulate a quite severe (fall factor 1.7) leader fall over a biner. The ropes typically fail in 6-8 "falls"

https://www.youtube.com/watch?v=_J_Eu6IO6DE

Fall factor is used as that it removes the length of the rope as a factor in the stress that the rope is subjected to. Peak impact forces are in the 1500 pound region.

Of course on a boat you most likely will not be doing a 180 degree turn over a 5mm radius but you will have some other stress point that will be the point of failure.

The question for me with any snubber is: How many peak loads (storm surge) do you expect the snubber to withstand during the course of the storm?

And again (hey thanks for calling my definitive statement interesting, rather than attacking) it is my opinion that a climbing rope is not suitable to be used as a snubber - during a storm or other robust weather. Other can do as they feel is best.

[seahag]

I'm wondering if anyone has more information about anchoring in deeper water. In Peter Smith's nice essay he bordered on it, though the first graph regarding deep water was something like 30 feet. In Alaska where we cruise, there is no anchoring in 30 feet. We typically are setting anchor in 80-120 feet of water. It is so very different--we almost never have 3:1 scope out, and we get hammered by katabatic winds often, some with gusts up to 100 mph but MANY hitting 60. 40 MPH is possible on practically any night without warning. Our tides vary from significant (12+ feet) to Enormous, but we avoid anchoring in really big tidal areas and don't generally anchor in areas of much current. Many days we have unavoidable swells from exposure to the Gulf of Alaska, which can be pretty massive, and the holding ground is quite often very rocky.

With all of that, we have dragged twice in the last two seasons. The first was a brutal Katabatic wind that first blew a large fishing vessel past us, then a smaller sailboat. We held for another hour but when the wind hit (I am guessing 75 mph, possibly more, I was in the cabin) we started to take off. The second time was different. We were anchored facing the ocean swell in lighter winds but in the night, a powerful wind shifted to the opposite direction, coming down off of a glacier and ripping across about a mile of fetch, and blowing from different points on the bow, giving us a really unsteady and constantly changing angle to the wind and the waves as we sailed, pulling repeatedly on the anchor rode in a more jerky fashion.

During all this, our rode consisted of 125 feet of chain, backed by 200 feet of 3 strand nylon with a 22KG Bruce anchor. This year we switched to a 55 lb Mantus and have noticed a difference with no dragging and it gives us a feeling of confidence.

Since our windlass setup is really a pain in the butt to use with the nylon (I have to feed it foot by foot as it comes through the windlass into the locker or it binds up due to some missing parts on the windlass) I have been considering going with all chain, as I'm not too concerned about adding the weight of another say hundred feet of chain to the bow in this case.

When we bought the anchor I had intended that, so we ordered a 25' snubber from Mantus which is still in the bag because we've never been in shallow enough water to use it with our chain setup.

Alternatively, we have an extra length of 150' of the nylon line we could add to what is on there now. In either case, I would be concerned about the connection--I am just "okay" with my splicing skills and when I've done three stand splicing, I have had decent results and can make it look "okay" but not professional. That concerns me. I have also read on this forum about a particular chain splicing bit that is far and away the best (chain is 5/16") but I don't recall what that type was.

Anyone with some advice especially tied in with real deep water anchoring experience that could help with some further direction would get my sincere appreciation as to me, the shallow water anchoring most people are doing does not really seem congruent to what we experience here.

Thanks!