Anchor Scope

Andrew G said:
KellysEye - please read all that I say below. This is a serious subject and I would not want less experienced readers to get on the wrong track. BUT some of your basic premises are wrong.
What I attempt to explain is based on the theoretical and experimental work by many others, reviewed by peers, is well documented and is supported by 99% of mariners – I’m afraid you are in the 1%.
If you disagree please cite your calculations, experiments and documentation. Mine are listed on posts 18 and 49 above.
Anchoring is a system, with a number of components playing a role. Each has to be strong enough to support the others and need not be so strong as to be wasteful:
1) The anchor transfers the load from the vessel to the ground, it needs to be matched to the ground conditions and be large enough and be designed and constructed to hold the load. (Its design includes the need to re-set, be able to be handled, fit the bow etc).
We agree that it must be set properly to work.
2) At the bow the load needs to be transferred to the vessel by a snubber, chain lock, cleat etc.
3) The rode transfers the load from the vessel to the anchor.

What 1% do not realise is:
a) THE ONLY ROLE FOR THE RODE IS TO TRANSFER THE LOAD FROM THE VESSEL TO THE ANCHOR. IT PLAYS NO MATERIAL PART IN TRANSFERRING LOAD TO THE GROUND. (Sorry for shouting but this is where you are wrong). Different types of rode do behave differently, eg rope vs chain, but their role is the same – to transfer the load between the vessel and the anchor.
b) In extreme conditions there is essentially NO CATENERY. The rode is in a straight line from the bow to the anchor with little or no rode on the ground. (If the anchor digs in there will be some where it exits the hole and if it is not yet extreme there may be a meter or so at the anchor. In lighter conditions there will be quite a lot on the ground).
c) Since a chain (or rope) is a series of hinged joints it transfers no vertical force TO the anchor (it just cannot!) – ITS WEIGHT DOES NOTHING FOR THE ANCHOR. It does transfer a vertical component of the load vector to the anchor but that is UP, NOT DOWN. That is why the angle to horizontal needs to be minimised.
d) If you could dive on an anchor and lift the chain it was NOT EXTREME.
e) The reason one pays out more rode in stronger winds/tides is to reduce the angle of the rode to horizontal AT THE ANCHOR – this is vital for improving holding.
f) I agree that, having payed out rode, if the anchor is not coping one needs another anchor, preferably in-line (and when you do get ashore get a better/bigger anchor for next time).
g) One doesn’t see piano wire in use as a rode because it is NOT strong enough, it can’t be handled without kinking or cutting hands, can’t be winched in or stowed etc. BUT IF IT WERE STRONG ENOUGH IT WOULD BE JUST AS EFFECTIVE AS CHAIN IN TRANSFERRING THE LOAD TO THE ANCHOR.
For those within the 1%, or teetering please:
- read the references cited in posts 18 and 49 above; and
- not anchor up-wind of Brut.
Cheers, Andrew
Click to expand...

I feel you are taking a very simplified view of things.
In a dynamic situation, many more subtle effects may become significant, such as the damping of the rode moving through the water.
Moving the rode through the water takes out energy.
Moving the rode through the silt or whatever will take out more energy, and probably makes a difference to how quickly the force at the anchor moves from side to side, so I don't fancy the piano wire irrelevance.
A fatter chain will be slower to bury, but also slower to veer or un-bury.
A catenary is never zero, it always makes a difference. That difference may be very small, but it can matter.

Also, I feel that people banging on about 11:1 rodes and 4:1 rodes or whatever is not ever so helpful, since the stretch in a rope or the catenary of a chain, and the dynamics of a yacht vary with the length of the rode and the depth of the water in a non-linear way. 4:1 in 30m is a very different animal to 4:1 in 3 metres.
A danforth will hold quite well at 1.5 to 1, in 70m of water, using polyprop for the rode, as we found out in a race, kedging against the tide.

Personally, in the UK, I don't want to be sailing with the weight of an all-chain rode in the bow, so I've tended towards plenty of nylon.
From experience I'm a fan of the kellet, but that may be related to me being a fan of anchoring in sunshine and fickle breezes (and moored to something stout in a gale).
Their is some useful stuff in this thread, but it goes bad when people oversimplify things to prove their point.
 
NormanS said:
So thanks to all for all the fascinating information in this thread. I just wonder how we all survived before the "new generation" anchors arrived on the scene. Maybe we used anchors and gear sized to suit our boats rather than sized for easy handling by the crew.
.
Click to expand...
The vast majority of the time people didn't explode when using petrol engines on yachts in the olden days. Enough people did explode, however, that modern yachts only ever have diesel inboards. In a similar vein, enough people dragged with a CQR that most reasonable people see new generation anchors as a good thing and don't try to argue that they are unnecessary by quoting anecdotal evidence.
 
lustyd said:
In a similar vein, enough people dragged with a CQR that most reasonable people see new generation anchors as a good thing and don't try to argue that they are unnecessary by quoting anecdotal evidence.
Click to expand...

Do you have any non-anecdotal evidence to support that statement? :D
 
lustyd said:
The vast majority of the time people didn't explode when using petrol engines on yachts in the olden days. Enough people did explode, however, that modern yachts only ever have diesel inboards. In a similar vein, enough people dragged with a CQR that most reasonable people see new generation anchors as a good thing and don't try to argue that they are unnecessary by quoting anecdotal evidence.
Click to expand...

Ah well, if we're going to talk about "exploding people", I'm afraid you've got me there. I admit to knowing nothing on that subject.:)
 
NormanS said:
Well, I was anchored in 74 knots of wind (sustained), with a fabricated plough anchor, based on a CQR, but with a shorter shank. It wasn't a particularly pleasant experience, particularly as most of the time was overnight. We didn't drag.
I'm glad that at the time I didn't know that I was doomed if I didn't have a snubber, because I wasn't using one.
I'm glad that I didn't know that my heavy chain would stop my anchor from burying. It didn't, indeed it was very difficult to break out.
I'm glad that I didn't know that my system wasn't getting relief from the chain's catenary, because it obviously was.

So thanks to all for all the fascinating information in this thread. I just wonder how we all survived before the "new generation" anchors arrived on the scene. Maybe we used anchors and gear sized to suit our boats rather than sized for easy handling by the crew.

I should perhaps add, that although the 74 knot occasion was a one-off, we have frequently had gales in the mid 60s.
Click to expand...

Have you ever considered sailing somewhere nicer?
 
KellyE. I do not wish to cause offence but your answer to my question caused me great concern:

Q "Are you saying that the chain is providing holding power (for example via friction with the seabed) and that the anchor is a backup to the chain (that is, provides less holding power)?"

A "Yes it is providing holding power but not friction it is the weight of chain in the catenary, if the wind slowly picks up and the boat moves back more chain will rise off the bottom increasing the weight of the catenary. Eventually the catenary will reach the anchor and that's when it's time to do something, as mentioned more chain or a second anchor. If the chain goes straight there is no catenary to hold the boat so you will drag very soon. Hope the explains it. "

Please explain:
- how the weight of the chain in the catenary contributes to the holding power?
- why the anchor will drag very soon after the catenary approaching zero?

LW395. I'm sorry if I appear to over-simplified things but I am concerned that there is some serious unsupported stuff being bandied around.
I agree that there are many second-order effects (and that is why I used weasel words such as "essentially").
I am trying to get across the first-order principles such as anchor holding power, angle to the seabed (ie scope) and snubbing - and re-buff some points that I saw as being wrong such as, in extreme conditions catenerary assisting anchor holding (the small catenerary remaining is not first-order - the length of the rode is).
For anyone confused please read the references cited in post 18 above.
Cheers, Andrew.
 
For those relying on the rubber snubbers - they provide only about 50mm ( 2" ) stretch.
Take one, thread a say 12mm rope through it, briefly pull it tightish to bed it in, mark the rope where it goes in and out, unthread it, measure between the marks. Only about 50mm more than the length of the snubber - that is the maximum help they can give.
I still use two, they help get the chain hook on and off the chain, but rely on the rope to do the work.
Andrew
 
vyv_cox said:
In fact the article I linked does suggest 180 degree yawing. I didn't want to frighten people so I said 140 degrees in the post;)
Click to expand...

Sorry Vyv,

I read the post not the link, lazy (I know) And it is a bit off-putting to go into a sheltered anchorage to discover a new set of parameters - instead of strong wind in one direction, bullets in directions apparently totally unrelated to the wind outside.

Jonathan
 
NormanS said:
Well, I was anchored in 74 knots of wind (sustained), with a fabricated plough anchor, based on a CQR, but with a shorter shank. It wasn't a particularly pleasant experience, particularly as most of the time was overnight. We didn't drag.
I'm glad that at the time I didn't know that I was doomed if I didn't have a snubber, because I wasn't using one.
I'm glad that I didn't know that my heavy chain would stop my anchor from burying. It didn't, indeed it was very difficult to break out.
I'm glad that I didn't know that my system wasn't getting relief from the chain's catenary, because it obviously was.

So thanks to all for all the fascinating information in this thread. I just wonder how we all survived before the "new generation" anchors arrived on the scene. Maybe we used anchors and gear sized to suit our boats rather than sized for easy handling by the crew.

I should perhaps add, that although the 74 knot occasion was a one-off, we have frequently had gales in the mid 60s.
Click to expand...

Entirely logical,

People used to travel to Australia quite safely in square rigged ships and we all managed quite comfortably and happily before we had ever heard of Bill Gates. Join the luddites and you will need not need, fibreglass, chartplotters, nylon nor modern new fangled anchors. it would be simpler - but lack forum threads.

Jonathan
 
Neeves said:
Entirely logical,

People used to travel to Australia quite safely in square rigged ships and we all managed quite comfortably and happily before we had ever heard of Bill Gates. Join the luddites and you will need not need, fibreglass, chartplotters, nylon nor modern new fangled anchors. it would be simpler - but lack forum threads.

Jonathan
Click to expand...

How true. I used a CQR when I first began cruising many years ago. It didn't set every time and dragged on a couple of occasions but this was put down to our inexperience. Then a club member recommended changing to a Delta, which brought noticeable improvements. We used all chain and had never heard of a snubber. Once introduced to them it is now standard procedure to set one on almost every occasion.
 
lw395 said:
That's fine, provided you can cruise under scientifically controlled conditions.
Click to expand...

No, the scientific conditions are used to prove that one is better than another by excluding sufficient variables to accuratly compare the two things. Once the better thing or method has been determined the controlled conditions can end and the smart people read the research and use the better method or thing. The rest post mindless rubbish on forums with only anecdotal evidence to back them up. Quite a few times on this thread people have linked to research papers which show quite clearly the improvements that can be made yet still others come back (presumably having not read the linked research) and offer an anecdote. As has been said many times, there is no evidence whatever that catenary helps, or that CQR anchors are even remotely as reliable as modern anchors, or even that heavier chain helps. There is, however, a huge body of evidence and many, many research papers based on properly conducted experiments to confirm the contrary.
Before someone says it and needs a slap, the controlled conditions are things like ensuring the bottom is consistent for anchor tests, ensuring the force pulling the rode is consistent between tests (even if the force is variable within a test, simulating waves and/or wind), and ensuring that the measurements taken are consistent. It is entirely possible to record the varying force in the rode on a real anchored yacht over a period of time and then "replay" those forces in a controlled test, so these tests, although controlled, can be very realistic.
 
If you're all so worried about your anchors dragging, why not do something to reduce the force on it. Rig an anchor sail to stop your boats yawing about so much. That will dramatically reduce the load. Another good thing is to invest in a good Fishfinder. It can tell you whether it's a good, clean, weed-free bottom. There are lots of ways to improve your anchoring, apart from having the latest flavour-of-the-month anchor.
 
Norman,

Just out of interest - do you still use a short shanked, copy, CQR, no snubber, no anchor alarm? And a decent fishfinder, needs another hole in the hull, a bit fiddly to install, costs more than a modern anchor from a reliable manufacturer, (some of which work in weed). You can, usually, see the sand from the weed - look over the bow - not at the screen? Not knocking modern fisfinders but I'd buy a decent anchor and 10m of 10mm nylon first (because then I could fish and relax)

Actually some of us are not worried about dragging our anchors. We plan on the basis they might - and when we think about it we are relieved that it never happens, maybe proving we are not in the '60s anymore:)


Lustyd

+1

Jonathan
 
Broadminded,

In defense, well - sort of, of Kelly + assorted others.

I thought, its an anchor thread - needs a bit of controversy:)

There is no basis in fact for any belief in the security of catenary (everyone agrees). Anchor chains are too heavy.

No-one, never say no-one - almost no-one has ever heard of anyone breaking a new(ish) brand name, quality,anchor chain - they last for ever. Anchor chains last for ever and are grossly overspecified.

Anchor lockers are too small - our chains tower up inside (if we had less (smaller volume) chain this problem would go away)

Big(ger) anchor chain needs a bigger windlass, which means more money (and I have not thought about it and assume it needs more power) (and more reinforcing of the deck).


There is a strong case for smaller (smaller link size) anchor chains (given that anchor chains are specified (seem to be specified) by people that believe in catenary.

Anyone know anyone who has jettisoned the specified anchor chain and gone smaller? If not - why?

Jonathan
 
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Neeves said:
Norman,

Just out of interest - do you still use a short shanked, copy, CQR, no snubber, no anchor alarm? And a decent fishfinder, needs another hole in the hull, a bit fiddly to install, costs more than a modern anchor from a reliable manufacturer, (some of which work in weed). You can, usually, see the sand from the weed - look over the bow - not at the screen? Not knocking modern fisfinders but I'd buy a decent anchor and 10m of 10mm nylon first (because then I could fish and relax)

Actually some of us are not worried about dragging our anchors. We plan on the basis they might - and when we think about it we are relieved that it never happens, maybe proving we are not in the '60s anymore:)


Lustyd

+1

Jonathan
Click to expand...

No, for your information, I don't now use the short shanked plough anchor. That was with my previous boat. By the way, it was 140lb, matched with 85m of 16mm chain. Not a toy. My main everyday anchor for my present boat is a genuine Bruce. I also carry a Fortress, and a Fisherman.

I don't use an anchor alarm.

I use a snubber, as and when I think appropriate. (Seldom, to be honest)

The transducer for the fishfinder is installed inside the hull, so no extra hole required.

You cannot always see the bottom. Sometimes, in shallow water, on a sandy bottom, we can, but if it's deep, or there's a lot of plankton, or it's dark, we can't. I do not, for choice, anchor in weed.

The reference to the 60s was wind speed in knots, and not to a decade. (I'm sure you realised this).

I think that covers most of your points. Just remember that anchoring is not an exact science, and as they say, "There's more than one way to skin a cat".
 
Norman,

Thanks :)

If anchoring was an exact science anchors would look more similar, many of the articles in yachting magazines and an equal number of forum threads would disappear and we would all agree with each other:(

Jonathan
 
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