Dragging of anchors

[JumbleDuck]

I think you are quoting Hooke's Law but you are ignoring the concept that as the snubber stretches it (and the chain) are absorbing the kinetic energy of the moving yacht and the force imposed on the short snubber and that on the long one are not constant nor the same (they start the same). But the short snubber is used with less chain and to deploy more snubber you, in the way we use it, must deploy more chain. This is because the longer snubber, (with chain) results in the need to extend more chain and you need to introduce the additional benefit of the longer chain catenary. Frankly the maths is far beyond me (but JD possibly has the answers at his finger tips) but in practice the longer snubber of 2 x length, with commensurate increase in chain deployed (extra snubber length + stretch), stretches much less than the shorter one 1 x length).

You called, sir? Happy to oblige ...

To stretch a spring of length L, area A and Young's Modules E by an amount l needs a force of F = EA (l/L). The energy stored Q = 1/2 F l = 1/2 EA l²/L.

If the energy stays the same and the length (but no A or E) is changed then it follows that l²/L is constant and the extension l is proportional to the square root of L. In other words, doubling the rope length will increase the stretch by about 40%; to double the stretch needs a rope four times as long.

But ...

As you say, snubbers do not work in isolation, so it's never going to be that simple. For a start, whatever is accelerating the boat (wind and/or waves) will have 40% further to do it with the double-length snubber, so the energy won't be the same. There may also, I imagine, be a slingshot effect which results in the boat moving further forward during lulls if the snubber is long - that too will result in more energy to be soaked up. I think we can discount the effect of chain lifting off the sea bed, because Vyv Cox has shown pretty conclusively that all the chain is off the sea bed in any sort of a blow. However, there may well be additional dynamic effects in the chain.

So on the whole I don't think theory has a huge amount to contribute, and it's probably best just to use something that works for your situation. As I have written before, I don't use a snubber because I have never felt any need to. I think that's because a relatively boat with a very curved stem has plenty of energy absorption built in - as the anchor chain goes tight she just pitches down a little in any conditions I have yet experienced. I don't remember the interest - and occasional angst - about snubbers 30 years ago, so I suspect they have become much more of a necessity with vertical stems and flattish bow sections.

 

[NormanS]

I am a simple person, and am capable of, for instance, switching on the TV to watch something, without having the slightest clue as to how it works. I tend to anchor in the same trusting way, and after many decades, I am seldom disappointed.

I must say that I find the idea of diving down to see the anchor every time I drop it, quite hilarious. If not OCD, certainly OTT.

 

[AntarcticPilot]

Many years ago studying physics in school I learned about some strange obsessive chap. Rutherford I think. Who spent his life drip drops of oil through a hole and measuring the deflection caused by a magnetic field. To determine the charge on 1 electron. One of the most important scientific advancements of his day.

My thought at the time "Bloody hell" there got to be more to life than that. Like beer and girls. What an edgit?

No doubt the anchor watchers are making a very significant contribution to yachting.
However. Watching videos of my anchor give me the same impression.

Well, his experiments determined that charge was quantized (don't worry about it), and was part of the evidence which led to Quantum Physics, which underpins quite a lot of the electronic devices we use in ever part of our lives!

The quantization of charge was actually one of the major discoveries of the 20th century, alongside Relativity, DNA and other major Nobel Prize winning discoveries

 

[Neeves]

Thank you JD, I knew it was all beyond my simple mind.

There is another effect to the extra long snubbers (sorry bridle, and use of a bridle might be critical) veering seemed reduced. But this might well be more of an effect of less wind variation - and you need a lot of data to offer any conclusions (and then you need to lean on a decent Scots education to decipher it all).

I do note that in the same anchorage some yachts are much more stable than others. Relatively heavy yachts, long keel yacht, older yachts (maybe one and the same) are more stable - and if you have stability - why use a snubber (to engender stability). I have wondered if this ability is a fixed characteristic - does this stability reduce at higher wind speeds? But there are many yachts that are not docile (and that's what volume producers seem to be building) at anchor and snubbers, riding sails (so 20th Century - but not to be dismissed) are all options.

I do wonder if, JD, part of the answer is in current yacht design, very high topsides, maximum accomodation, lots of headroom, biminis, weight (being cost) squeezed out, fin keels, plumb bow, etc - maybe the idea of being at anchor in any wind is not part of the design equation (and I include catamarans in this)

I don't have many of the answers, I keep asking the questions, to the annoyance of some, in the hope something sparks off some dim lights at the end of the tunnels.

We have come a long way from dragging of anchors - which is maybe a good thing as 'dragging' was not a very fruitful question. No reflection on those that answered - but I did not see any conclusive patterns.

Jonathan

 

[RupertW]

I am a simple person, and am capable of, for instance, switching on the TV to watch something, without having the slightest clue as to how it works. I tend to anchor in the same trusting way, and after many decades, I am seldom disappointed.

I must say that I find the idea of diving down to see the anchor every time I drop it, quite hilarious. If not OCD, certainly OTT.

It's part of the ritual of anchoring - has the added benefit that you can see exactly how your anchor is performing and exactly what the seabed is like and whether it's truly dug in or just caught on something. The anchor seems to work equally well in the early part of the season when the sea is too cold for me to dive in, but after a hot day's sail there is nothing better than to dive into the water, check the anchor and be showered off as the beer and nibbles appear on the cockpit table.

 

[noelex]

diving on anchors

Issues in Australian waters with regard to being eaten are in keeping on an anchor thread where the idea of casting doubts on safety are commonplace.

I have published a lot of photos of anchors taken mostly in Mediterranean, but I have actually done far more diving on anchors in Australia and in the South Pacific.

The danger of sharks to snorkelers who are not spearfishing in most of Australia is small, if you have just a little common sense. There are some isolated areas in northern Australia with Saltwater crocodiles and I would not get into the water in these locations.

There are more significant concerns related related to currents, other vessels (especially jet skis), and medical problems while diving. These issues exist worldwide.

Despite these risks diving is a relatively safe sport and great fun. However, with the advent of cheap underwater cameras you can see what your anchor is doing quite easily without ever getting wet. You can strap the camera to anchor as Steve has done with his great videos, or simply lower the camera from the tender. I made this contraption from a junk piece of aluminium to keep my camera steady and pointing in the right direction when lowered from the tender, but you don't need anything so elaborate if you are starting out.

It is not necessary to observe your anchor to anchor safely, but if you are interested in anchors it is great way to learn how they behave. What the anchor manufacturers want us to believe and what actually happens on the seabed are two quite different things.

The biggest risk is once you have seen with your own eyes the enormous difference between good and not so good anchors you may want to upgrade your primary anchor, so ultimately it can be an expensive hobby.

 

[jordanbasset]

On a nice warm day in clear water I often dive down onto my anchor, gives me something to do and cools me off. Have even dived down when it is being set by my wife. Glad to report it works as well as I feel it does, digs in really well and buries itself. Okay not scientific proof but I must have done this a hundred plus times in different sea bed conditions and feel very confident about it. Certainly out performs the other two anchors I had on the boat.
Having said all that if I had never dived down at all I suppose I would have been no worse off.
Will not mention the anchor or the ones it replaced as that is not the purpose of the post

 

[Neeves]

On a nice warm day in clear water I often dive down onto my anchor, gives me something to do and cools me off. Have even dived down when it is being set by my wife. Glad to report it works as well as I feel it does, digs in really well and buries itself. Okay not scientific proof but I must have done this a hundred plus times in different sea bed conditions and feel very confident about it. Certainly out performs the other two anchors I had on the boat.
Having said all that if I had never dived down at all I suppose I would have been no worse off.
Will not mention the anchor or the ones it replaced as that is not the purpose of the post

Nor the purpose of the thread!

Jonathan

 

[NormanS]

Judging by the amount of mud adhering to the anchor and chain, when heaving up, any diving on my anchors would be a cold waste of time. But then, I trust my anchor to do the job it's supposed to do, without spying on it.

 

[Artic Warrior]

Normally when waves form and snatching occurs. ......then you get problems......or the dredded weed

 

[noelex]

Judging by the amount of mud adhering to the anchor and chain, when heaving up, any diving on my anchors would be a cold waste of time. But then, I trust my anchor to do the job it's supposed to do, without spying on it.

Medium mud is the easiest substrate. Most anchor designs set and bury well in this sort of substrate so there is less to learn about how different anchor designs will behave.

The visibility in mud can also be very poor but with modern typically very wide angle underwater cameras you can still often see the anchor in murky water. It is worth adding an underwater float to the anchor so you can still find the anchor and estimate its depth even if completely buried. This is especially important if the anchor has no high features such as a roll bar to indicate the position even when reasonably buried.

But mud is such an easy substrate for an anchor to set you have to be very keen (like me) to bother taking a look. You will learn much more about anchor performance looking at difficult substrates.

If the goal is check the anchor rather than learn about anchor performance weed or where there is a risk of rock are probably the most important substrates where a visual check of your anchor is not essential, but is beneficial. In both of these bottom types the anchor can give the impression it is holding well, but visualising the anchor can show otherwise. Unfortunately, in weed you sometimes have to part the weed and feel if the toe of the anchor has penertrated to the substrate below the weed to see how well the anchor is gripping.

There is not much to be learned about comparative anchor performance in rock, but weed is very important substrate that is the Achilles heal of many otherwise good anchor designs. So be sure and share your results.

This is a photo our anchor in poorish visibility, deep water and in the middle of winter, just before it buried the roll bar in some stronger wind.

It did not mind being spied on.

 

[NormanS]

Aw! I like the Christmas decorations on the anchor.

I find that with the use of either No 1 eyeball, if the water is clear, and/or the use of a fishfinder, I can usually avoid dropping my anchor where there is weed or rock. OK, sometimes it's unavoidable, but I simply will not anchor overnight, or leave the boat unattended if anchored thus. Where I sail, there is usually enough choice of suitable good anchorages, in either mud or sand. I strongly recommend using a good fishfinder to help find a good clear, clean bottom for anchoring.

 

[noelex]

Aw! I like the Christmas decorations on the anchor.

I find that with the use of either No 1 eyeball, if the water is clear, and/or the use of a fishfinder

Thanks Norman .

The substrate is vital. We have a fishfinder both on the main chartplotter and a small unit that I made for the tender. I do my best to try an interpret the bottom type based on the return, but I don't think I do a very good job.

Surprisingly, there seem very few threads on this subject on sailing/anchor forums. It deserves a lot more attention.

Have you any tips, or links you would recommend?

 

[zoidberg]

This thread has a fascination stretching beyond the 'geeky', but I sense a limit may be close. To give it just a little more dynamic, albeit slightly obliquely, I'm hoping this will stretch the interest a little further.....

It is not only the situation while anchoring which is of occasional concern. My own club, the Tamar River SC, has a floating landing pontoon ( in several moored sections ) which is mightily disturbed by the wash of passing Royal Marine Landing Craft ( training ), harbour tugs, and tripper boats. Not an issue, if an occasional nuisance, while one is out on the trot moorings - but it is a menace when moored alongside the pontoon, and much more so when several are rafted alongside, as is often the case before the start of the 'Jesters' events hosted here.

The boats bounce, the other boats bounce, and so do the pontoons - all in different cycles and degrees of violence. That has ripped cleats from decks and done other damage to hulls, toerails and spreaders. There's an obvious answer, but visitors don't always listen.

Spotting these items in a 'recycle outlet' going free, I had me a dozen. They're effectively large rubber bands, about 12" across and 7/8"/22mm thick. I'm quite sure their energy absorbing characteristics will prove useful in mitigating damaging surge and scend, but I'm still in the process of puzzling out 'how'.....

 

[NormanS]

Thanks Norman .

The substrate is vital. We have a fishfinder both on the main chartplotter and a small unit that I made for the tender. I do my best to try an interpret the bottom type based on the return, but I don't think I do a very good job.

Surprisingly, there seem very few threads on this subject on sailing/anchor forums. It deserves a lot more attention.

Have you any tips, or links you would recommend?

When I started "cruising" in an 18' gaff rigged converted ship's lifeboat, I used a lead line. (I still have it, and use it occasionally with the dinghy.

The first echo sounder that I had was one of these whirly Seafarer things, with the flashing LEDs. With careful use of the "gain" control, one could refine the reading and tell if there was weed reaching up from the bottom. This was a huge advance from the lead line.

When most people moved on to the more "modern" digital sounder, which only showed a number, I kept with the Seafarer, simply because it gave me more information. (This with several boats).

Fast forward to the present day, with a plotter at the helm, with the facility to have a split screen with chart/fishfinder.
With the colour sounder, I feel as if I can practically "see" the bottom. It's a bit like deciphering what you see on a radar screen, and practice makes perfect. It is easy to see if there are weedy patches, or an uneven bottom probably indicating a stony or rocky bottom.

Our transducer is fairly far forward, and with my wife up forward, ready to let go, I can "read" the bottom not that far back from the bow roller, and when we come to a clear bit, give her the nod to let go.

I would far rather know that I am dropping the anchor in a good place, than just drop it in, and then have to jump in after it to confirm.

 

[thinwater]

This thread has a fascination stretching beyond the 'geeky', but I sense a limit may be close. To give it just a little more dynamic, albeit slightly obliquely, I'm hoping this will stretch the interest a little further.....

It is not only the situation while anchoring which is of occasional concern. My own club, the Tamar River SC, has a floating landing pontoon ( in several moored sections ) which is mightily disturbed by the wash of passing Royal Marine Landing Craft ( training ), harbour tugs, and tripper boats. Not an issue, if an occasional nuisance, while one is out on the trot moorings - but it is a menace when moored alongside the pontoon, and much more so when several are rafted alongside, as is often the case before the start of the 'Jesters' events hosted here.

The boats bounce, the other boats bounce, and so do the pontoons - all in different cycles and degrees of violence. That has ripped cleats from decks and done other damage to hulls, toerails and spreaders. There's an obvious answer, but visitors don't always listen.

Spotting these items in a 'recycle outlet' going free, I had me a dozen. They're effectively large rubber bands, about 12" across and 7/8"/22mm thick. I'm quite sure their energy absorbing characteristics will prove useful in mitigating damaging surge and scend, but I'm still in the process of puzzling out 'how'.....

I'd try a prusik sling on one side and a rope to a cleat on the other. Use them to take slack out of the lines. You probably only need 2. I've always felt it wansn't the impact per se, but the bouncing or whip lash at the other end that did the damage.

I've got a 24-foot try in a 45-foot slip and it's a funny fit (I still have to enter from the side because of my 19-foot beam). What works to elimante shock is using Shockles to eliminate the slack. They are actually on the bulkhead side. That's how lots of the guys do it here.

 

[zoidberg]

I'd try a prusik sling on one side and a rope to a cleat on the other. Use them to take slack out of the lines. You probably only need 2. I've always felt it wansn't the impact per se, but the bouncing or whip lash at the other end that did the damage.

I've got a 24-foot try in a 45-foot slip and it's a funny fit (I still have to enter from the side because of my 19-foot beam). What works to elimante shock is using Shockles to eliminate the slack. They are actually on the bulkhead side. That's how lots of the guys do it here.

It's part of my thing to learn from others' experience - in tales and pics and illustrations - and I'm well aware that many of the issues we face today have been addressed by seamen down the centuries. We have the advantage of better materials, but the limitation that we are not all that practised in learning from those who went before.

Here's an example, which would have been common knowledge in the days of working sail. Having this kind of awareness tucked away in 'the dim recesses' might save a costly yard job should I ( you? ) ever need a tow from someone not well skilled - or past caring.

I'm also intrigued by the inventive minds of modern race-boat riggers, who bring new materials and thinking to old rigging problems, such as the guys at Colligo Marine and those who work on the AC 45 and 75s. I was able to wander through the 'prep sheds', asking questions, when the '45s were here in Plymouth. Yachting World has some fine pics.....

 

[NormanS]

I'd try a prusik sling on one side and a rope to a cleat on the other. Use them to take slack out of the lines. You probably only need 2. I've always felt it wansn't the impact per se, but the bouncing or whip lash at the other end that did the damage.

I've got a 24-foot try in a 45-foot slip and it's a funny fit (I still have to enter from the side because of my 19-foot beam). What works to elimante shock is using Shockles to eliminate the slack. They are actually on the bulkhead side. That's how lots of the guys do it here.

That sounds a very dangerous way to use these things. Rigged that way, if I understand you correctly, if the rubber fails, the line fails. It's much more normal and safer to rig so that the rubber takes up stretch, but ultimately the line is still in one piece.

 

[Neeves]

That sounds a very dangerous way to use these things. Rigged that way, if I understand you correctly, if the rubber fails, the line fails. It's much more normal and safer to rig so that the rubber takes up stretch, but ultimately the line is still in one piece.

Which is how those dogbone rubber things work, and it is surprising how many you see still attached, but broken - underlining Norman's point. Shockles are somewhat similar as the outer cover is meant to be able to take whatever load, should the rubber fail. I'm with Norman - use them with a bight of the mooring line as part of the assembly and if you measure it correctly you can limit the amount of stretch of the giant 'O' ring.

The other option, completely different, is to use those shorter lengths, 15m, of climbing rope - maximising length as much as possible. So - use the full 15m, don't use them for a 2m length.

Jonathan

Zoidberg, I think you are correct as most if not all the issues we address today are the same issues of 50 or 100 years ago but the solutions we have available can be vastly different to the solutions then. Our access to cordage like dyneema and modern climbing ropes is one example, certainly an improvement on manilla! Our access to aluminium (that can be anodised) and cheap steel (either galvanised or stainless) in a large cross section of strengths and toughness is another. The development of the CQR was hampered by an inability, then, to weld. We have come a long way and are still learning. Its applying this new material and technology to that old problem - and having the toughness of skin to ignore the doomsayers (who would never even look outside the box).

Roughly on the theme of the thread - think of welded anchors, anchors with high tensile components (usually the shank), aluminium anchors, some with high tensile aluminium shanks, HT shackles and HT chain. What is interesting is that HT aluminium was developed, I think in 1937, and the first use in anchors was around 2010 and I'm not sure that it is the one application in yachts - but common place in commercial marine and aeronautics.

New technology and material take a very long time to be accepted.

Its amazing those that simply say, 'it won't work' (because I did not think about it and certainly have never tried it.)

 

[Neeves]

We find that if the water is clear(ish) and its not overcast and dark (nighttime) then simply looking offers the most accurate way of determining weed - on a sand seabed. The sand is white, or at least pale, and the weed black. The person on the bow can have the anchor hanging ready and drop into the sand patches - you really want the sand patch to be a decent size.

Most, even very cheap, or basic, fish finder/depth sounds offer an ability to identify weed - its not difficult. The instructions usually include detail on how to enhance the images of bottom type.

Jonathan