Anchor thread

[geem]

I think we're all aware that a fouled anchor doesn't work. ? Do you never anchor under sail?

Not often in the Caribbean as anchorages are often quite busy. We wouldd to do it often where space allowed.
Thr point I was trying to make is often engines are not powerful enough to set an oversized anchor. We can easily bury our anchor since we have a 22" prop and a 4.4 litre diesel engine. Similar sized boats to us have far smaller engine with small props and can't power set the anchor. It's not a great time to find out your anchor didn't set when the wind gets up. Also, we find getting an anchor to set here is more difficult than when we used to sail in the UK. A good anchor makes all the difference. When we first came here we had a Bruce. It was awful. It simply wouldn't penetrate the seagrass. We had to look for a patch of white sand and anchor in that. Power setting that anchor was a no no. You would just drag it for miles. It worked perfectly when we were inthe UK. I don't think it would make any difference here if the Bruce had been twice the weight. It still wouldn't have set.

 

[Bouba]

Not often in the Caribbean as anchorages are often quite busy. We wouldd to do it often where space allowed.
Thr point I was trying to make is often engines are not powerful enough to set an oversized anchor. We can easily bury our anchor since we have a 22" prop and a 4.4 litre diesel engine. Similar sized boats to us have far smaller engine with small props and can't power set the anchor. It's not a great time to find out your anchor didn't set when the wind gets up. Also, we find getting an anchor to set here is more difficult than when we used to sail in the UK. A good anchor makes all the difference. When we first came here we had a Bruce. It was awful. It simply wouldn't penetrate the seagrass. We had to look for a patch of white sand and anchor in that. Power setting that anchor was a no no. You would just drag it for miles. It worked perfectly when we were inthe UK. I don't think it would make any difference here if the Bruce had been twice the weight. It still wouldn't have set.

What anchor do you use now ?

 

[geem]

What anchor do you use now ?

30kg Spade. Going rusty after only a year

 

[Tranona]

An anchor doesn't know what size of boat it's holding. It's ludicrous to say that a big anchor won't hold a small boat, because it's not "dug in". It'll soon dig in when the wind gets up.

It will "hold" the boat but when the wind gets up it is the windage of the boat that matters and the pull that it creates on the anchor so it is obvious that a boat with greater windage will exert greater pull and dig the anchor deeper. Smaller boat with anchors bigger than necessary cannot generate the forces to achieve the maximum hold the larger anchor is capable of, nor probably in many cases not even the maximum hold the recommended (smaller) size can achieve). Therefore pointless having an anchor where you cannot exploit its holding power. That is exactly why manufacturers give recommendations and advise against oversizing, recognising of course that there is always an area of overlap where the type of boat and the type of usage means it makes sense to go to the next size up.

This helps understand the loads arising from wind. practical-sailor.com/sails-rigging-deckgear/anchor-testing-and-rode-loads compare those measured loads with the reported maximum holding power of anchors that have been tested.

 

[MathiasW]

For similar geometry anchors it is not usually a good assumption that the holding capacity will vary linearly with the weight of the anchor. It can generally be assumed that for geometrically similar anchors, holding capacity in mud or sand will scale with the area of the anchor, ie with the linear dimension scale factor squared. However, the weight will rise with the cube of the linear dimension scale factor. Hence if one works out the holding capacity as a multiple of the weight of the anchor, one will find that this reduces as the size of the anchor increases.

I used to argue that way myself, but experimental evidence in anchor tests clearly suggests the relation to be more linear than anything else. It seems to be more complicated than simply looking at how the surface area scales with anchor weight.

 

[MathiasW]

An anchor doesn't know what size of boat it's holding. It's ludicrous to say that a big anchor won't hold a small boat, because it's not "dug in". It'll soon dig in when the wind gets up.

Indeed! A bigger than needed anchor does not have to dig in fully to be able to hold a smaller vessel. When you have a very big anchor and a not so powerful engine then yes, the engine may not be able to dig in the anchor completely. But who cares? It will dig it in to the same holding power as a smaller anchor would have, and so the bigger anchor will do the job. What you DO get with the larger anchor is that should the wind pick up beyond the power the engine had, it can dig in even deeper, whilst the smaller anchor will perhaps be already at its maximum holding power.

The only point where this argument starts to fail is when the anchor is SO big that it would not even start to bite the ground a bit and would just lie there. But that would be a massively oversized anchor.

 

[Neeves]

The ability of your engine to develop tension in the rode is a function of horse power and prop characteristics.

A rough rule of thumb is that for every 10hp you can develop about 100kg in a deployed rode. An anchor recommended for a yacht with a 30hp auxiliary engine might be about 15kg and a modem anchor of 15kg would have a tested maximum hold of about 2,000kg.

say, for sake of argument you decide to double the anchor weight. based on scaling you might expect that a 30kg anchor would have a hold of about 3,000kg - your paltry 30hp engine is not going to make much impression on setting that anchor.

Practical Sailor has conducted tests ofn anchors subject to yawing - when the rode, or yacht attached to the rode yaws - holding capacity is diminished. I would expect if you introduced a bit of chop then the hold would be reduced further.. Younalso have a larger lever effect of the shank of a shallow Set anchor.

Suddnely your paltry tension of 300kg for an anchor with a potential hold of 3,000kg is compromised, it is shallow set It’s not buried very deeply, it is constantly being tensioned from each side, the chain is lifting and falling as chop forces the yacht to hobby horse. Pity you did not have an anchor of the correct size which would set more deeply, not have a long lever arm acting on the fluke and it would have been set more deeply (as a proportion of its whole - by virtue of being smaller.)

Shallow set anchors are more sensitive to yawing.

Yawing and Anchor Holding - Practical Sailor

if you rely on the anchor setting more deeply - it might, might not.

Jonathan

 

[[194497]]

Is there any actual evidence or direct experience suggesting that an oversized anchor could drag under circumstances in which a smaller one would set, which is what seems to be being suggested? To my mind, if a boat can drag an anchor, it can set it; if it can't drag it then it's sufficiently set already...

 

[Neeves]

Is there any actual evidence or direct experience suggesting that an oversized anchor could drag under circumstances in which a smaller one would set, which is what seems to be being suggested? To my mind, if a boat can drag an anchor, it can set it; if it can't drag it then it's sufficiently set already...

too simple.

is there any evidence that spending extra money on a large anchor provides any quantitative increase in security..

Anchors do not drag directly because they are oversized but anchors do drag. Anchors drag because of operator error, because of a poor substrate (weed), because the yacht is veering, because the yacht is hobby horsing in chop. Anchors drag in circumstances where the tension in the rode is less than the holding capacity - dragging is thus not inadequate hold - in a straight line. There is no evidence to suggest a larger anchor solves any of these issues .

A poorly set anchor will drag when the yacht is veering, this is part of what the Practical Sailor article illustrates - a shallow set anchor is susceptible to veering (and I’d extrapolate - and susceptible to hobby horsing).

Now you design a test protocol that will stand up to scrutiny for hobby horsing in chop.

anchors and anchoring seem simple - but anchors do still drag. There are still too many unknowns. Devise a test for hobby horsing, or ways of measuring the variables - and the leisure marine world will beat a path to your door.

Jonathan

 

[NormanS]

The ability of your engine to develop tension in the rode is a function of horse power and prop characteristics.

A rough rule of thumb is that for every 10hp you can develop about 100kg in a deployed rode. An anchor recommended for a yacht with a 30hp auxiliary engine might be about 15kg and a modem anchor of 15kg would have a tested maximum hold of about 2,000kg.

say, for sake of argument you decide to double the anchor weight. based on scaling you might expect that a 30kg anchor would have a hold of about 3,000kg - your paltry 30hp engine is not going to make much impression on setting that anchor.

Practical Sailor has conducted tests ofn anchors subject to yawing - when the rode, or yacht attached to the rode yaws - holding capacity is diminished. I would expect if you introduced a bit of chop then the hold would be reduced further.. Younalso have a larger lever effect of the shank of a shallow Set anchor.

Suddnely your paltry tension of 300kg for an anchor with a potential hold of 3,000kg is compromised, it is shallow set It’s not buried very deeply, it is constantly being tensioned from each side, the chain is lifting and falling as chop forces the yacht to hobby horse. Pity you did not have an anchor of the correct size which would set more deeply, not have a long lever arm acting on the fluke and it would have been set more deeply (as a proportion of its whole - by virtue of being smaller.)

Shallow set anchors are more sensitive to yawing.

Yawing and Anchor Holding - Practical Sailor

if you rely on the anchor setting more deeply - it might, might not.

Jonathan

That's a novel idea, Jonathan. Never in my wildest dreams would I select an anchor, based on the horse power of the engine that happens to be installed in the boat.
I have a sailing boat.

 

[Bouba]

The ability of your engine to develop tension in the rode is a function of horse power and prop characteristics.

A rough rule of thumb is that for every 10hp you can develop about 100kg in a deployed rode. An anchor recommended for a yacht with a 30hp auxiliary engine might be about 15kg and a modem anchor of 15kg would have a tested maximum hold of about 2,000kg.

say, for sake of argument you decide to double the anchor weight. based on scaling you might expect that a 30kg anchor would have a hold of about 3,000kg - your paltry 30hp engine is not going to make much impression on setting that anchor.

Practical Sailor has conducted tests ofn anchors subject to yawing - when the rode, or yacht attached to the rode yaws - holding capacity is diminished. I would expect if you introduced a bit of chop then the hold would be reduced further.. Younalso have a larger lever effect of the shank of a shallow Set anchor.

Suddnely your paltry tension of 300kg for an anchor with a potential hold of 3,000kg is compromised, it is shallow set It’s not buried very deeply, it is constantly being tensioned from each side, the chain is lifting and falling as chop forces the yacht to hobby horse. Pity you did not have an anchor of the correct size which would set more deeply, not have a long lever arm acting on the fluke and it would have been set more deeply (as a proportion of its whole - by virtue of being smaller.)

Shallow set anchors are more sensitive to yawing.

Yawing and Anchor Holding - Practical Sailor

if you rely on the anchor setting more deeply - it might, might not.

Jonathan

But if your engine is 30 hp then you not going to red line it just to set an anchor...at best you will use 20 hp (and without taking into account how clean or undamaged or perfectly matched your propeller is to transfer that power into the water)..so now you have a setting of only 200 kgs. So even a tiny anchor will not be fully set.
I rely on the wind to fully set the anchor to match the conditions

 

[Zing]

But if your engine is 30 hp then you not going to red line it just to set an anchor...at best you will use 20 hp (and without taking into account how clean or undamaged or perfectly matched your propeller is to transfer that power into the water)..so now you have a setting of only 200 kgs. So even a tiny anchor will not be fully set.
I rely on the wind to fully set the anchor to match the conditions

I often do that or less; to let it set itself completely. Especially when the wind is strong and where I know the holding is good. Full setting takes time as well as power and a gentle set decreases the chance of an initial drag.

 

[Neeves]

Is there any actual evidence or direct experience suggesting ………

The post made me think a bit more

Many people use a Rocna or Supreme anchor and most suggest they have no issues - but they do drag (and big time)

Morgans Cloud aka AAC removed their recommendation for Rocna because when they drag and are clogged with mud, or weed, they do not reset, or not easily. MC’s action was on the basis of a number of incidences that were drawn to their attention Of big yachts on beaches. (As an aside I spoke to a Greek chandler and he said one of the incidences involved a Supreme but at the time I did not question further). There has never been, of which I am aware of more detail, yachts, locations, conditions etc, and there has never been a suggestion the anchors were too small, nor too big. In fact there has never been mention that none of this would have happened if the anchors had not dragged - and it was the dragging the precipitated the problem.

Modern anchors can drag big time…..

Any anchor of the Recommended size it will not drag as a result of being too small - you will never experience tensions anywhere near as the hold of a correctly sized Delta, Bruce nor CQR. So if the hold of a CQR, Delta or Bruce is adequate - why would you oversize and anchor of twice the hold - you don’t need MORE hold - you need something else……

and as you cannot set a bigger anchor more deeply and resistance to veering etc. needs as much hold as possible

What exactly does a bigger anchor offer.

Now someone will say ah but….. in difficult seabeds ….; but be unable to define which difficult seabeds, harder, softer, less weed…..???

being openly more critical - and it’s very unlike me to defend Rocna - they have been damned and the foundation on which they have been damned is inadequate. More information should have been made available - so that we could draw our own conclusions (which most have done by using a Rocna). More information might also have been educational.

Jonathan

 

[Neeves]

But if your engine is 30 hp then you not going to red line it just to set an anchor...at best you will use 20 hp (and without taking into account how clean or undamaged or perfectly matched your propeller is to transfer that power into the water)..so now you have a setting of only 200 kgs. So even a tiny anchor will not be fully set.
I rely on the wind to fully set the anchor to match the conditions

the 10hp per 100kg of tension is at cruising revs and is roughly equivalent to the tension in your rode at 30 knots. usually we try to anchor where it’s not subject to 30 knot winds.

I‘ve measured all this on the basis of 5:1 scope and 30m of 8mm chain (and a good anchor) - no snubber It is applied later)

Younare correct you will never, ever set a 15kg modern anchor to a point where it will drag - you would need a 2,000kg tension.

So…..given your anchor, in my example, will hold 2,000kg …… what is the objective reason to over size? Why is a bigger anchor, with say a measured hold of 3,000kg more secure….

Jonathan

 

[Bouba]

the 10hp per 100kg of tension is at cruising revs and is roughly equivalent to the tension in your rode at 30 knots. usually we try to anchor where it’s not subject to 30 knot winds.

I‘ve measured all this on the basis of 5:1 scope and 30m of 8mm chain (and a good anchor) - no snubber It is applied later)

Younare correct you will never, ever set a 15kg modern anchor to a point where it will drag - you would need a 2,000kg tension.

So…..given your anchor, in my example, will hold 2,000kg …… what is the objective reason to over size? Why is a bigger anchor, with say a measured hold of 3,000kg more secure….

Jonathan

I think the logic is...as the wind blows stronger and stronger the bigger the anchor the more potential it has to keep digging in...so it turns a dangerous situation (very strong wind) into a safer situation (anchor digs deeper)...whether that works in real life may not be as important as the psychological relief in the knowledge that you have a big piece of iron in the sand

 

[geem]

Indeed! A bigger than needed anchor does not have to dig in fully to be able to hold a smaller vessel. When you have a very big anchor and a not so powerful engine then yes, the engine may not be able to dig in the anchor completely. But who cares? It will dig it in to the same holding power as a smaller anchor would have, and so the bigger anchor will do the job. What you DO get with the larger anchor is that should the wind pick up beyond the power the engine had, it can dig in even deeper, whilst the smaller anchor will perhaps be already at its maximum holding power.

The only point where this argument starts to fail is when the anchor is SO big that it would not even start to bite the ground a bit and would just lie there. But that would be a massively oversized anchor.

On another thread on another forum some sailors were claiming to over size there anchor by 2 or 3 sizes more than recommended by the manufacturer. Going up a size is never likely to cause a problem and on many anchor sizing charts your boat can appear to be between two sizes so going for the larger one makes sense. In addition, you need to select the anchor based on the total wieght of the boat not the manufacturer’s displacement figure. These can be quite different.
I have two sets of original marketing details for my boat. One suggests a displacement of 14.5t. The other suggests 17t. The reality is that we weigh over 18t in cruising trim but we still sit above the original marks. I believe if you take the actual weight of the boat into account and select an anchor according to the manufactures recommendations you won't go far wrong. We see plenty of production boats here in the .Caribbean where there is no bottom paint visible. They are over loaded and likely have a gross weight well in excess of their published displacement. When some of these cruisers say they have an oversized anchor they may actually be closer to the manufacturers recommendation than they think

 

[geem]

I think the logic is...as the wind blows stronger and stronger the bigger the anchor the more potential it has to keep digging in...so it turns a dangerous situation (very strong wind) into a safer situation (anchor digs deeper)...whether that works in real life may not be as important as the psychological relief in the knowledge that you have a big piece of iron in the sand

I think that logic might apply to old anchor designs such as CQRs or Delta anchors that start to plough once they are over loaded. Modern generation anchors just seem to dig deeper in my experience.

 

[RunAgroundHard]

Are displacement and length not just convenient rules of thumb for describing wind drag? What is it about displacement that causes and anchor to drag? Most dragging anchors are caused by wind speed, not water current. Even in an anchorage where wave velocity is significant, is the impact of wind force not more relevant? I am not so sure that overloading a boat is entirely relevant as the stuff that is impacted by wind force, is still the same as the underloaded boat, ignoring the slight differences in hull exposure. Just a thought, happy to have any misunderstanding corrected.

 

[geem]

Are displacement and length not just convenient rules of thumb for describing wind drag? What is it about displacement that causes and anchor to drag? Most dragging anchors are caused by wind speed, not water current. Even in an anchorage where wave velocity is significant, is the impact of wind force not more relevant? I am not so sure that overloading a boat is entirely relevant as the stuff that is impacted by wind force, is still the same as the underloaded boat, ignoring the slight differences in hull exposure. Just a thought, happy to have any misunderstanding corrected.

When a strong gust hits a heavy boat and start it's motion backwards or sideways if the gust was not from straight ahead then the boat has momentum. Momentum is a function of its mass and velocity. The anchor will bring this mass to a stop. More momentum means more load on the anchor as it attempts to bring the velocity of the boat to zero. I have seen this momentum destroy a windlass and an anchor swivel when snubbers were not being used

 

[doug748]

Is there any actual evidence or direct experience suggesting that an oversized anchor could drag under circumstances in which a smaller one would set, which is what seems to be being suggested? To my mind, if a boat can drag an anchor, it can set it; if it can't drag it then it's sufficiently set already...

The usual, no evidence just a lot of conjecture, cobbled up by either taking an extreme case or comparing anchors of different designs as it they were the same.

Even the term "Oversized Anchor" is pejorative nonsense. Most folk either take the manufacturers recommendations at face value or, if on the margin, go up or down in size according to taste. Those seeking more holding power may even go up a full size, and any boat that can wrangle a 15kg anchor will tackle a 20Kg one. The only huge anchors I have ever seen on sailing boats have been Fishermen, for obvious reasons.

For me it's a non debate, tho it will probably dribble on for months and come up like a floater.

.