Anchors - Bigger is Better ?

[Hudson Force]

Anchors are for holding........ anchors are for marketing......... It's a floor wax......no, it's a dessert topping........ it's both! Watch out!

[Jim Cate]

Originally Posted by Hydra

I took the time to read the part of USLC section 13 about anchors. It says:

"The masses given are for Admiralty Pattern Stockless anchors with an assumed holding power of 3 times their own mass.

The Authority may allow approved high-holding-power anchors to be carried at the owner's request, and shl allow a reduction of 30 percent of the specified anchor mass, where such anchors are used. Approved high-holding-power anchors shall be those anchors having a holding power at least double that of Admiralty Pattern Stockless anchors, ie. high- holding-power anchors must have holding power at least 6 times their own mass."

All average-to-good quality anchors used on yachts have holding power much greater than 6 times their mass. For example, in Yachting Monthly Nov 09 test, the Britany 16kg (35lb) anchor held 446kg (982lb) in muddy sand. That's more than 27 times its mass and the result was considered rather poor by comparison with other anchors.

IMO, the authors of USLC had a very pessimistic opinion of anchor performance. Perhaps is it not necessary any more to follow it closely.

Alain

G'Day all,

Alain, I also read that section of the code and was perplexed yet again!

As I mentioned previously, the code recommendation for our boat was a 45 Kg "regular" anchor. Using their formula, that would provide 135 Kg of "holding power". I don't own a strain gage or load cell, but I have watched our 16 mm double braid nylon snubber stretch like a rubber band (oh, ok, that's hyperbole, but it does stretch a couple of feet) when anchored in gusty 45 knot winds. I firmly believe that our boat can and does exceed 135 kg loads on the ground tackle at well below the code's 60 knot standard.

How, then am I to put much credence in these standards ? Either they grossly underestimate the anchor loads or they actually believe that the holding power of a stockless anchor is far greater than three times its mass.

For Conger (and I find many of your comments about anchor design to be interesting and informative BTW): You suggest that if I was to approach an expert from the classification societies he would figure out my requirements for an anchor. I'm curious as to what he would use to do so when the code itself fails to provide guidance for sailing yachts and their particular windage situation. Would he (if I were to be applying for survey approval) use an unapproved method?

In actual fact, these questions are hypothetical. I'm happy with my (more or less) normal sized MS anchor and don't really care what the official code is. But my native curiosity is tweaked when folks start extolling the code as an ultimate authority.

Thanks to all for an interesting and relatively dispassionate anchor thread!

Cheers,

Jim

[DumnMad]

Originally Posted by JonJo

What science?

Geotechnic or soil science, comparing different soil densities, soil cohesion, soil friction and the angle between line of pull and the blades - diggability & extractability. The variabilities are infinite.
Ya can't use a small experiment to convince people you have the answer. Hence my advice; listen to the most experienced cruisers.

[downunder]

Jim,

I wouldn't be too hung up on the USL codes as the ultimate guides. Just look at the EC reqts as another minimum standard. Not sure what they say about anchors but their requirements for throughulls/seacocks is the subject of considerable debate.

I guess their primary purpose is as a minimum for commercial vessels and if there were big deficiencies they would show up quickly.

Certainly many cruising vessels have greater windage than standard and as long as you are happy with your system from your great experience all is well.

cheers

[Kettlewell]

JonJo has done some interesting anchoring tests, and I will be very interested in what he comes up with on this new one.

JonJo: Can you post some links to some of your earlier tests?

[Snowpetrel]

Originally Posted by Jim Cate

How, then am I to put much credence in these standards ? Either they grossly underestimate the anchor loads or they actually believe that the holding power of a stockless anchor is far greater than three times its mass.

Found this RIS statement interesting, page 13 or so discusses the issues of the usl code, so it seems the regulators know the system is flawed but it also kind of works... They are now trying to move from the prescriptive usl code to the more performance and outcome based NSCV, which allow you to find and justify an alternative equivalent solutions.

This means that if you can show evidence that your proposed method meets the same basic safety requirements. Eg Anchors are needed in case of engine failure. Therefore a vessel with twin independent engines and rudders on short haul trips might justify having no anchor because the risk analysis shows that the chances of both engines failing together are negligible. So the need for an anchor is gone..

A mate of mine is involved with all this and finds himself much of the time, juggling all sorts of industry and state lobby's. Not easy to get consensus on any change.

Cheers

Ben

[JonJo]

Originally Posted by DumnMad

Geotechnic or soil science, comparing different soil densities, soil cohesion, soil friction and the angle between line of pull and the blades - diggability & extractability. The variabilities are infinite.
Ya can't use a small experiment to convince people you have the answer. Hence my advice; listen to the most experienced cruisers.

Sorry, I thought you were referring to some science quote earlier, that I had missed

[JonJo]

Originally Posted by Kettlewell

JonJo has done some interesting anchoring tests, and I will be very interested in what he comes up with on this new one.

JonJo: Can you post some links to some of your earlier tests?

Do you subscribe to Practical Sailor?

[Kettlewell]

I've seen that article in Practical Sailor, but I thought some others here would be interested too. I believe there is an Australian version on the Web somewhere too.

[Snowpetrel]

Originally Posted by Kettlewell

JonJo has done some interesting anchoring tests, and I will be very interested in what he comes up with on this new one.

I am also interested to see how jonjo's theory stacks up, he might have a good point, In some bottom types it might be that a well set smaller anchor could be more reliable than a poorly set bigger one. I can see the chain getting wrapped under a poorly set large anchor and then pulling it out in a windshift, where a deeply set smaller one might not suffer?

As a group we should be interested in finding the lower limits of these new anchors capability. Even if we choose to upsize for our main, we might want to use a much smaller anchor as a spare, second anchor, kedge, or for when that massive power windlass dies and we have to complete a cruise hauling the lot up by hand!

I still feel that one size up (or rounding up) is a pretty good basic rule, two sizes up worries me slightly due to the massive loads the anchoring gear could be regularly subjected to when raising it from a sticky bottom, unless it is all also massively oversize.

The bigger your boat the more you need one large anchor, hence Morgans cloud and the dashews logic is correct, messing about with dinghy's and extra anchors is not a safe option, but under the 40 foot mark second anchors, and changing anchors to suit the bottom type is far more practical, hence Jonjo's setup.

I am also trying to get some idea of the relative effects of displacement on anchor loads, vs windage. Maybe some of jonjo's and jims success with their correctly sized (rather than oversized) anchors is due to the lighter weights of their boats. I recall the 60 footer I ran in Antarctica having pretty light anchor loads due to only being about 16 tonnes. Jump up to your average 50 foot cruiser at around 20 tonnes, I am guessing you need twice the anchor size to hold it than you would on a 10 tonne 40 footer. It might be that the more windage based anchor selection tables don't take this properly into account. Double the length of a boat, 4 times the windage, 8 times the displacement, while at the same timedoubling the weight of the anchor doesn't double the surface area of the anchor.

Finally all anchoring is a lottery, there is far to many variables. It wouldn't do to get to complacent, in the wrong bottom type any anchor, even a massively oversize one can fail (though probably not as often).

cheers

Ben

[Cotemar]

None of the anchor sizing charts from any of the anchor manufacturer are specific to catamarans.
They may have a foot note saying you should consider going larger, but that’s it.

That may be one of the reason that most cat owners go up a size or two.
No catamaran data out there. I went through three anchors before I felt comfortable

Cats have more windage and are getting bigger and heavier every year.
Smaller anchors would not be a good move for some of these boats

[JonJo]

Originally Posted by Kettlewell

I've seen that article in Practical Sailor, but I thought some others here would be interested too. I believe there is an Australian version on the Web somewhere too.

Nothing I have had published in Oz is on the Web, that I am aware of. Cruising Helmsman (Oz) has published articles which tend to be more digestable or populist versions of information contained in PS. CH were talking of going electronic this year, but I have not had an update recently. Sadly I do not get pdfs, publishers here are trying to protect their income from their paper publications simultaneously trying to cope with the electronic age.

Really the best source for anyone with an enquiring or questioning mind would be PS, who have a large enough readership (based on N Ams bigger population) and can manage to publish without pandering to advertisers. There might be better sources in general or for specifics - but I am not aware.

[Kettlewell]

JonJo, isn't this your test?

[Snowpetrel]

Originally Posted by Cotemar

No catamaran data out there. I went through three anchors before I felt comfortable

What three anchors did you try?

Also considering windage, the more and more common practice of keeping solents jibs on furlers behind a light genoa has got to be worth going up an extra anchor size, whereas cockpit awnings, dodgers, arches etc might actually act as a riding sail reducing peak anchor loads?

[JonJo]

Snowpetral,

Ben

You raise a number of interesting issues, and I think Jim is onto something similar.

In addition to length (and on the basis beam is roughly proportional to length for most monohulls) we have underwater profile, fin keel, long keel (the high rise development on the transom) etc and we also have displacement. Loads on anchors tend to be caused by snatching (rather than the yacht steadily sitting and imposing a load caused only by windage). If loads are caused by yachts yawing and sailing 'momentum' comes into the equation, which introduces displacement. But heavy yachts for a given size tend to be less skittish so though they weigh more they accelerate less - and maybe the momentum is the same (for light and heavy yachts of the same length)?

Catamarans are a different issue. We compared our profile, we are basically a 35', with a 3' transom extension, and our windage is the same as a Bavaria 45 from about 2 years ago. Windage being based on front and side areas. But we weigh in at 6t and the Bav maybe 12t (both in cruising mode). We have mini keels, draw 1m, and the Bav a full depth fin, draw 2m. I'm not sure that our skittishness is much different - but that is very subjective.