Anchor question,

[NormanS]

OK Jonathan, I'll bite.
I don't think anyone would suggest carrying 200m of 12mm chain on a 45ft yacht.
My 36ft ketch has a designed displacement of about 8.5t, so in cruising mode, probably about 9.5t.
I carry 65m of 10mm chain, and the boat's fine with that, and I don't think it's excessive. Your situation with a cat, is entirely different, and I completely understand your wish to cut down on unnecessary weight.
Horses for courses.

 

[Neeves]

Thanks Norman,

To me - 10mm chain for a 9.5t yacht is excessive (or unnecessary) its well over strength for the weight of yacht (and a heavy displacement yacht should not yaw (sail at anchor) as much as a flighty AWB). You also reduce yawing by employing a riding sail (great application) and yawing, or the end of the yaw is when snatch loads occur. But in carrying, what I consider, overweight ie 10mm not 8mm, you have 65kg of chain more than I would (with your yacht) - and yes this will extend (in terms of higher windspeed) the usefulness of the catenary. However given that its the square of wind speed - I'm not sure it extends the windspeed very much.

I would have thought 8mm chain would be comfortably satisfactory for a 36', 9.5t yacht and if my thoughts are about right then in many anchorages in F6 I'd guess the chain would look as straight as a die.

The extra weight you carry, that 65kg, is like having a rather wiry man standing on the bow roller, permanently, and surely it is conceivable that performance and comfort, particularly hard on the wind, would be improved without that weight - especially as a decent snubber will do everything and more than the heavier chain. Its this last comment that is the critical statement - smaller chain would be a disaster without the snubber (or mixed rode) - you cannot have the light chain and no snubber (10/15m of nylon).

Definitely horses for courses - and we inevitably inherit what the builder or the previous owner bequeathed to us and changing that bequest can be expensive. If it works its the right horse.

But if someone came to me with your yacht, as is, and needed to replace chain, worn and lacking in gal - I would suggest, new gypsy, 8mm chain G30, and a snubber. The saving in buying the lighter chain should fund the new gypsy. If there was need for a new windlass - then there should be a small saving in the 'lighter' windlass (though I'm keen on over specifying windlass!). I would also suggest the option of 1/4" G70 (around 7mm?) lighter still, well strong enough, reduced towering in the anchor locker - but would not be too dogmatic - I'll be confident in recommending HT chain when we have a few more nights at anchor under our keels with our new 6mm.

Jonathan

 

[noelex]

My philosophy is that a cruising boat should install the largest anchor they can comfortably manage. I do agree with the use of lightweight chain, providing it is strong enough.

The extra weight of an oversized anchor, say one or two sizes over the manufacturer's recommendation, is only small in comparison to the total weight of anchoring gear. Most of the weight is in the chain. 5m of 10mm chain weighs over 10kg.

One of the compelling advantages for oversizing the anchor is enabling the use of anchorages with marginal substrates, or those that demand short scopes.

This example is from last year and features a Kobra which has been mentioned in another current thread. All anchors were doing worse than normal at this anchorage including a Rocna. It was obviously a difficulcult substrate.

This Kobra was doing particuarly poorly. It was slowly dragging as my wife and I watched. You can see the poor set and marks in the sand indicating the long drag.

The Kobra is not a fantastic anchor in hard substrates, but even with the best anchors, staying overnight would have been a gamble. Most if not all of this anchorage had a poor substrate. Larger would have helped provide some additional security.

 

[Neeves]

Its a compelling idea - but if a small anchor cannot be set I find it very difficult to see why a larger one would develop any more hold. Being 'bigger' does not make it able to bury deeper in a hard substrate. Its like a little nail and a big nail - the little one will be easier to hammer in. Or take a big garden spade and small one - the smaller on is easier to dig into hard soil. I suspect given the same effort you dig in the same area - and if its area that provides hold in an anchor - then the hold from the bigger anchor will be identical to the small one.

So compelling, but I am yet to be convinced.

If this was a 5kg Kobra I would concede weight might be an issue - but if a 20kg Kobra does not set I fail to see why a 30kg one would be any better. A different style of anchor might set better but not one of the same design.

Jonathan

 

[GHA]

Its a compelling idea - but if a small anchor cannot be set I find it very difficult to see why a larger one would develop any more hold. Being 'bigger' does not make it able to bury deeper in a hard substrate. Its like a little nail and a big nail - the little one will be easier to hammer in. Or take a big garden spade and small one - the smaller on is easier to dig into hard soil. I suspect given the same effort you dig in the same area - and if its area that provides hold in an anchor - then the hold from the bigger anchor will be identical to the small one.

So do you think very big boats should carry little anchors for seabeds like that?

 

[Neeves]

Its a compelling idea - but if a small anchor cannot be set I find it very difficult to see why a larger one would develop any more hold. Being 'bigger' does not make it able to bury deeper in a hard substrate. Its like a little nail and a big nail - the little one will be easier to hammer in. Or take a big garden spade and small one - the smaller on is easier to dig into hard soil. I suspect given the same effort you dig in the same area - and if its area that provides hold in an anchor - then the hold from the bigger anchor will be identical to the small one.

So compelling, but I am yet to be convinced.

If this was a 5kg Kobra I would concede weight might be an issue - but if a 20kg Kobra does not set I fail to see why a 30kg one would be any better. A different style of anchor might set better but not one of the same design.

Jonathan

Edit,

This is the current collective wisdon

http://www.ybw.com/forums/showthread.php?440143-Dragging-of-anchors&highlight=Anchor+dragging

And for a slightly more up to date comment, see post # 50 above.

close edit

 

[Neeves]

So do you think very big boats should carry little anchors for seabeds like that?

Now that's a novel idea!

Just an anchor of the size recommended by the anchor maker, nothing like two times the weight as advocated by some.

There is no evidence, when using a 'modern' anchor that having a grossly oversized anchor offers any more security that the correctly sized anchor, but there are plenty of people with slightly undersized anchors or anchors of the size recommended by the anchor maker who appear very satisfied.

Buying oversized anchors does benefit anchor makers and might if shouted loud enough appeal to those subject to scare tactics - but there is no evidence to support the contention (that grossly oversized anchors offer any more security). I am ready to be convinced with evidence to support the idea - but so far its all talk and no trousers.

Jonathan

 

[noelex]

Jonathan, I think we will have to agree to disagree on this one.
In my view (assuming an identical design and material):

Larger anchor = greater holding power

This was a difficult substrate. I doubt any of the boats at this anchorage were wishing they had a smaller anchor.

 

[vyv_cox]

Serious question: why did you not save money, weight and effort by buying a 1 ton Rocna?

Serious answer - I bought it before the anchor tests were carried out.

Sadler 34s were originally supplied with a 25 lb CQR. Most owners found these to be insufficient and moved up a size to 35 lb. I did the same but further improved the situation by changing to a Delta. When I decided to change to a Rocna I exchanged quite a few emails with Craig Smith, who recommended the similar weight Rocna. At the time, and probably now, I saw no reason to go to anything else. I suspect that a 25 lb Rocna would do well in the vast majority of cases for me but I have no intention of changing.

 

[GHA]

Buying oversized anchors does benefit anchor makers and might if shouted loud enough appeal to those subject to scare tactics - but there is no evidence to support the contention (that grossly oversized anchors offer any more security). I am ready to be convinced with evidence to support the idea - but so far its all talk and no trousers.

Unless you are long distance cruisers the likes Evans or Dashew with a good chance of needing the extra holding power , end up in questionable substrates or possibly need a short scope.

 

[vyv_cox]

I can't see that people do say that. The other case is also true, I don't feel that anyone seriously thought that catenary worked without limit.
So, when a gale rages at sea, and you have 25kts, or more, through your anchorage the chain will snatch. I doubt you could find anyone to argue with that, or the idea that up to these limits the catenary is doing it's job fine.
A lot of forum dissent seems to hinge on opposition to extreme views which no one really holds

My YM article was somewhat bigger when I wrote it but in the event they only had space for two pages. What was omitted was a very similar case history to my own but in this case a 55 ft USA owned Oyster with 12 mm chain. My photo of their anchor and chain was very similar to my own, i.e. at a scope of around 4:1 in winds gusting F7 the whole of their chain was lifting off the bottom, as was mine. They had a long snubber that no doubt was preventing snatching.

 

[Neeves]

Jonathan, I think we will have to agree to disagree on this one.
In my view (assuming an identical design and material):

Larger anchor = greater holding power

This was a difficult substrate. I doubt any of the boats at this anchorage were wishing they had a smaller anchor.

I have seen 15kg anchors developing 2,000kg of hold, most of the anchor tests of modern anchors report similar levels of hold for 15kg to 20kg anchors, depends on the seabed.

Modern anchors have great potential - I doubt that any are used to their full potential. If you set an anchor, big or small, to 500kg with your engines, they both have 500kg of hold, no more no less. If the wind picks up to 40 knots and allows the yacht to develop a tension on the chain of 700kg then both anchors will be set to 700kg, no more no less. The big anchor might still show a bit of the shank above the seabed, the small one might be completely buried - but they will both have a hold of 700kg, no more, no less. The only time the small anchor will be found wanting is if it reaches its maximum potential - and no-one has reported yet their modern anchor of the right 'sort' of size has dragged.

Edit, Sorry I did not answer the post. it was not suggested they should have had smaller anchors - only that the level of hold will be no more, nor no less, big or correctly sized - for the same design of anchor. The answer was a different style of anchor - or a different anchorage. Maybe rather than grossly oversized maybe different styles might be a better concept, catering for different conditions. close edit

Jonathan

 

[JumbleDuck]

Its a compelling idea - but if a small anchor cannot be set I find it very difficult to see why a larger one would develop any more hold. Being 'bigger' does not make it able to bury deeper in a hard substrate. Its like a little nail and a big nail - the little one will be easier to hammer in.

In this case the hammer is the anchor's weight, which increases as the cube of the dimension. Contact area increases with the square, so the contact stress, which is what matters, increases linearly with the dimension.

 

[JumbleDuck]

Serious answer - I bought it before the anchor tests were carried out.

Sadler 34s were originally supplied with a 25 lb CQR. Most owners found these to be insufficient and moved up a size to 35 lb. I did the same but further improved the situation by changing to a Delta. When I decided to change to a Rocna I exchanged quite a few emails with Craig Smith, who recommended the similar weight Rocna. At the time, and probably now, I saw no reason to go to anything else. I suspect that a 25 lb Rocna would do well in the vast majority of cases for me but I have no intention of changing.

Thanks, Vyv.

 

[Poignard]

My YM article was somewhat bigger when I wrote it but in the event they only had space for two pages. What was omitted was a very similar case history to my own but in this case a 55 ft USA owned Oyster with 12 mm chain. My photo of their anchor and chain was very similar to my own, i.e. at a scope of around 4:1 in winds gusting F7 the whole of their chain was lifting off the bottom, as was mine. They had a long snubber that no doubt was preventing snatching.

If I was anchored in a F7 I'd want a considerably greater scope than 4:1. In fact I rarely use less than 4:1 except in very sheltered locations.

 

[NormanS]

I'm not of the school suggesting that small yachts should carry huge anchors, but my own non-scientific experience indicates that there are times where a heavy anchor will hold, when a lighter one simply won't.

For many years, I sailed around in a 60ft converted Scottish fishing boat. Her anchor was a fabricated plough (no name), weighing 140lbs. By observation, her anchor seemed to work more effectively than those of the AWB, in two different situations.

1. There are some places where the mud on the surface of the seabed is soft, sloppy, and unconsolidated. In these conditions the sheer weight of our anchor ensured that it got down through the sloppy layer, into firmer mud, while the AWB, with its normally adequate anchor, would fail to get a grip. This happened too often to be mere chance.

2. In moderate weed. Again, our anchor immediately penetrated the weed, and got a grip, where a lighter anchor, just by moving back a little, got clogged with weed, and wouldn't grip. In severe weed, no anchor can be relied on. Don't try.

As I say, it's not scientific, and I'm not suggesting that small yachts should carry huge anchors. What I would say, however, is that great care should be taken in choosing the anchorage. Probably much more important than whether the actual anchor is the current flavour of the month or not.

 

[doug748]

......... Bearing in mind the busted flush status of the catenary effect, I'm seriously tempted to replace my 25lb CQR + 8mm chain with something newer and lighter (FX-7?) and rope.

The catenary effect is alive and well in the bosom of Physics.

Unless you are thinking of the weight and perhaps racing, there is little I see to commend long ropes attached to anchors. One of the great pleasures of getting a larger boat is kissing goodbye to lengths of wet, slimy, muddy difficult to stow rope.
Don't do it.

 

[Neeves]

Surely the hammer is the yacht and the nail the anchor? The weight of the anchor is not relevant - most people who use them would say the same sized Spades (talking anchors now, so not the garden variety ), alloy and steel perform similarly. I think our alloy Excel performs similarly to its same sized steel brother. Its not weight but design and area. Or am I confusing the issue?

 

[adwuk]

Most reports I have seen indicate that a steel spade outperforms an alloy one of the same size.

 

[JumbleDuck]

Modern anchors have great potential - I doubt that any are used to their full potential. If you set an anchor, big or small, to 500kg with your engines, they both have 500kg of hold, no more no less.

Counterexample: If in setting they run up against a rock or other underwater obstruction there may well me more than 500kg of holding power there and then. Generalising, the holding power won't be less than 500kg but it may well be more ... it all depends on whether the anchor is still moving up to the 500kg point.