Anchors - Bigger is Better ?

[congo]

Rex, I'll be a bit of a Devil's advocate here. Is there an argument to be made that real-world conditions would be very different from these test-bed conditions, whatever the protocol? Is the strength being tested here relevant or just a number that doesn't really mean much? I know that car manufacturers often tweak many things in order to maximize fuel mileage on the standardized EPA test, but when someone drives the same car in the real world mileage will generally be much less.
__________________
Kettlewell Cruising


Massive difference, saving fuel doesn't save lives, saving lives in the Tsumami requires a well built anchor to a standard, better than one thats strengths is unknown when bracing for such a dissaster.

Regards Rex.

[Kettlewell]

Massive difference, saving fuel doesn't save lives, saving lives in the Tsumami requires a well built anchor to a standard, better than one thats strengths is unknown when bracing for such a dissaster.

I understand that--bad example. It just seems to me that a buried anchor is supported over a much larger area, and might not be subjected to loads in the same way these test jigs do it. Yes, strength is important, but beyond a certain point it seems irrelevant. If the anchor will drag at 6000 lbs. do you need an anchor that can take 15,000 lbs. in the testing machine?

[Andrew Troup]

Originally Posted by Kettlewell

I understand that--bad example. It just seems to me that a buried anchor is supported over a much larger area, and might not be subjected to loads in the same way these test jigs do it. Yes, strength is important, but beyond a certain point it seems irrelevant. If the anchor will drag at 6000 lbs. do you need an anchor that can take 15,000 lbs. in the testing machine?

I'm presuming, from the fact you don't mention it, that you're unimpressed by the line of reasoning that the shank of a jammed anchor (even a newGen which has dug a couple of feet deep, but also the list of situations listed in the BoatUS article and a couple more I instanced) needs to withstand a force potentially far in excess of the rated holding power?

[JonJo]

Originally Posted by DumnMad

It is dead easy to design a grade 500MPa shank to be stronger than a grade 690MPa shank. Increase the thickness & depth each by 12% - its proportional to b x d x d or bending sideways; d x b x b.
The big thing is to make sure its welded right. Another thing is ductility - will it bend or break?? Higher strength steel is less bendy so more likely to break.
It's naive to harp on about steel grades when other factors need to be taken into account. Just sounds like sales talk.

Shank strength is related to the square of thickness of the plate from which it is made. It is easy to design a 500 MPa shank so that it is a strong as ASTM514 - but you need to beef the shank thickness up. Yoy will find width of the shank is restricted, yes you can increase, but not by much or it will not fit on bow rollers. Really the only way to go is shank thickness, both Fortress and Anchor Right use this technique - but thicker shanks provide resistance to diving.

ASTM 514 steel is incredibly elastic,(or springy).

[JonJo]

Originally Posted by Cotemar

No convincing needed.
Here's the facts.

Rocna re-licensing & historical steel quality issues

Cotemar, I think you were saying earlier that all 'new gen' anchors were ASTM 514. And you wanted strong, stronger, strongest. Why do I think you have compromised. Q620 does not meet ASTM 514 which demands a min yield of 690 MPa, However I read Smiths dissertation the steel being used then was only average 690 MPa and the sample tested was 650 MPa ish. I also note that though Smith said they were using Q620 there is no mention of this anywhere else, whether they are using it now? Its certainly not quoted anywhere else and if its good enough why not make it part of promotional material?

[JonJo]

Originally Posted by Kettlewell

I understand that--bad example. It just seems to me that a buried anchor is supported over a much larger area, and might not be subjected to loads in the same way these test jigs do it. Yes, strength is important, but beyond a certain point it seems irrelevant. If the anchor will drag at 6000 lbs. do you need an anchor that can take 15,000 lbs. in the testing machine?

The big problem is that anchors are tested linearly, along the length of the shank. Some loads come at right angles to the shank.

Its bit like testing a carbon fibre tube, great in tension but not much cop at 90 degrees. Or if you have it in America, MDF - difficult to tear it apart linearly but collapses with ease at 90 degrees.

There are plenty examples of anchors bending when loaded at 90 degrees. It costs, in the grand scheme of things, almost nothing to ensure the best materials possible are being used (for an anchor shank ASTM 514) (and to say so) and this ensures that the anchor maker has done as much as possible to ensure the shank of his anchor does not bend when loaded at 90 degrees. Equally Fortress have beefed up their shanks such that compared to a steel anchor for the same sized yacht the Fortress shank is about twice as thick, and its the square of the thickness that is relevant in shank strength (not simple thickness). Spade take a different approach, they have a box section - sadly this defies analysis, or it defies analysis by someone as simple as me!

Really its a question of what the user wants - something that is as indestructible as possible (like a Crosby shackle, strong, stronger, strongest) or do you compromise and buy something that is not as good? Worse do you buy something where the specification is a 'secret'!

It makes no sense to me to read people ranting about bigger is better when they simply do not know what the steel is from which their anchor is made. There are only 3 anchors that unequivocally define steel quality and allow a calculation of shank strength.


I'd follow Kettlewell's suggesting and find a copy of April's Practical Sailor. I'd then wait till the May or June issue which might also be interesting - or at least between them they could keep this thread running for a few more weeks!

[congo]

Quote:
Originally Posted by Kettlewell
I understand that--bad example. It just seems to me that a buried anchor is supported over a much larger area, and might not be subjected to loads in the same way these test jigs do it. Yes, strength is important, but beyond a certain point it seems irrelevant. If the anchor will drag at 6000 lbs. do you need an anchor that can take 15,000 lbs. in the testing machine?

Andrew troup:

I'm presuming, from the fact you don't mention it, that you're unimpressed by the line of reasoning that the shank of a jammed anchor (even a newGen which has dug a couple of feet deep, but also the list of situations listed in the BoatUS article and a couple more I instanced) needs to withstand a force potentially far in excess of the rated holding power?

Rex wrote:
John this is the thing when you are not involved with anchor design, manufacturing and testing, you can only comment from your own experience, I mean no disrespect from that comment. But you say two feet under the mud, the only time an anchor will get that deep is in very soft mud, the shank would be lucky to bury any deeper than 6 inches.
Granted in slop it may go deeper, soft mud will do little to reduce sideways impact on a shank, on the other hand make no mistake, because this anchor has buried so deep, it is the load on the fluke plate that can be enormous with an impact, more reason for a deep setting anchor designs to have a stronger shanks.
Field testing of anchors determines the holding power category of an anchors certification, STD, H/H/Power and S/H/H/Power, this will also will determine an anchors build strength, a H/H/Power anchor will hold more, dig deeper than a standard one, Super High Holding Power will give higher holding power again, more holding power produced by these category’s requires a stronger build to with stand the greater impact loads.
Fore instance, a High holding Power anchor in a good anchorage say, will pull out under extreme impact loads, the super H/H/H/Power one does not pull out so will be subject to greater impacts = stronger build.
A prime example of the higher loads require stronger build strength, was this, the bendy Rocna shanks, more holding power without the build strength to match. Here in Australia anchors are now listed as safety equipment so standards apply regardless, if it is sold as a H/H/Power anchor then ask for proof same if it is sold as S/H/H/Power, this certification gives you piece of mind whether you ever have to test its strength or not, why anyone would purchase an anchor that is not certified, beats me.

[JonJo]

Originally Posted by noelex 77

I don't believe 2x8mm chain (with two anchors) is as strong as 1x10mm chain (with one anchor). The problem is that it is impossible to even out the loads. Particularly when snatch loads are imposed these tend to carried mainly by one rode.
With two anchors I would not advise going below the recommended chain size for your size / displacement boat. This means you end up with double the weight of chain to routinely deploy two anchors.
An extra 75 m length of 10mm chain weighs 176kg (380lb) (even 8 mm chain weighs over 100Kg (220lb)
The anchors are also typically heavier in a two anchor set up (although their contribution is minor).

Yes you can store some of this weight amidships with a two anchor set up, if you don't mind physically carrying the weight to the bow, perhaps at 3am as squall goes through he anchorage.

If the chain is to used regularly, you also need a place amidships to store chain that is likely to be dirty and smelly. The amidships locker will not commonly be self draining.

8mm chain weighs 1.45kg/m; 10mm chain weighs 2.3kg/m

8mm chain has a breaking strain 30% less than that of 10mm chain, depends on the grade. So 2 x 8mm are stronger than 1 x 10mm.

8mm has a breaking strain, G30, of 4t - not sure how many 40' yachts are going to have loads of this level imposed on them and prior - something on the deck will pull out first. People tend to use heavier chain not because they want more strength but because they think the extra weight will help their anchor. A 10mm G30 has a breaking load of 6t, thats as 'heavy' as my yacht! Get real - it might be useful for its weight (catenary) but I'm not a fan - I just use a reliable anchor.

Edit Catamarans carry their chain (and sometimes anchor - as I am sure Cotemar will confirm) under the mast. Snatch loads are removed with snubbers, we've been there, discussed that. But the snubbers (you need snubbers for both rodes) also allow 2 rodes to work together, you should give it a try.

[noelex 77]

Originally Posted by congo

John this is the thing when you are not involved with anchor design, manufacturing and testing, you can only comment from your own experience, I mean no disrespect from that comment. But you say two feet under the mud, the only time an anchor will get that deep is in very soft mud, the shank would be lucky to bury any deeper than 6 inches.

I think the real world experience is better indicator of how anchors perform

Good anchors do bury much deeper than you indicate in many/most substrates when subject to a blow. Even at the moment in medium sand my (oversized) 55kg Rocna shank is 4-5 inches below the surface (I looked yesterday) and it has not been subject to any extraordinary winds. It will go much deeper in the right wrong conditions

Don't take my word for it:
This is a great website for engineering advice, but there are some general comments on anchoring as well.

At anchor
The Rocna is a revelation. It has been buried throughout the three days but now the floating line and buoy attached to its head only protrude about 8 inches from the bottom. The line is 3 feet long!

[Andrew Troup]

Noelex

Good point. I think anchor manufacturers forget that their testing is an idealised proxy (and, in my view, often quite an unrealistic proxy) for reality.

How often does a single anchor get loaded under test for days at a time, under fluctuating loads and directions? It does not surprise me that an anchor tester would not know how an anchor would perform in practice under such circumstances ... but it does bother me.


I was going to gloat about the guy lying to two anchors without a tangle, but when I read more carefully, he did have to untangle the kedge on two occasions when the winds had fallen light.

Still, he took half the time the second time vs the first.
Unless you're planning on leaving the boat unattended, it's seems to me a question of convenience rather than risk.

When the winds were strong, he was sheering a lot less through lying to two anchors: that makes a significant difference to loads on the anchor - now that is a risk factor.

[congo]

Noelex wrote:

think the real world experience is better indicator of how anchors perform

Good anchors do bury much deeper than you indicate in many/most substrates when subject to a blow. Even at the moment in medium sand my (oversized) 55kg Rocna shank is 4-5 inches below the surface (I looked yesterday) and it has not been subject to any extraordinary winds. It will go much deeper in the right wrong conditions

Don't take my word for it:
This is a great website for engineering advice, but there are some general comments on anchoring as well.

At anchor
The Rocna is a revelation. It has been buried throughout the three days but now the floating line and buoy attached to its head only protrude about 8 inches from the bottom. The line is 3 feet long!

Rex wrote:

Sorry Noelex I forget to tell you, I have been boating for over thirty years and have deployed most anchor designs, that is how I became interested in anchor technology, I have seen anchors bury that deep in 60 knots of wind but have not seen ours that deep, yes and no breaking out and resetting, no dragging problems even in Tsuamis, must be just the extra holding power.

We have purposely had boats anchored for months at a time in varying sea bed type’s observing their every move, this plays a large part in any anchors development, and surely you don’t think this is an armchair design similar to that of your analyses of our designs.


Still don’t get it, not a word about that proof test video, whats the go fellers.

Regards Rex.

[downunder]

Originally Posted by noelex 77

I think the real world experience is better indicator of how anchors perform

Good anchors do bury much deeper than you indicate in many/most substrates when subject to a blow. Even at the moment in medium sand my (oversized) 55kg Rocna shank is 4-5 inches below the surface (I looked yesterday) and it has not been subject to any extraordinary winds. It will go much deeper in the right wrong conditions

Don't take my word for it:
This is a great website for engineering advice, but there are some general comments on anchoring as well.

At anchor
The Rocna is a revelation. It has been buried throughout the three days but now the floating line and buoy attached to its head only protrude about 8 inches from the bottom. The line is 3 feet long!

Be a bit cold diving on your anchor at present over there?

[DumnMad]

JonJo you didn't read mine properly. Increase both dimensions by 12% not just thickness to get Gr500 steel shank as strong as a Gr690 shank. Thats a mere 18mm thickness instead of 16mm. No big deal.

Your high tensile steels can't be fully utilized anyway because the risk of fatigue reduces your available strength. Add the difficulty in getting quality welds without residual stresses and then add the risk of crevice corrosion. These risks aren't worth it.

I think Gr500 steel would be better for cruisers. Tensile strength any higher doesn't make sense.

Congo: Designing anchors is no big deal, unless someone sues you. In earthquake engineering its been real world experience and post-failure analysis that leads the technical drive, not the other way round. I'd listen to the most experienced cruisers.

[noelex 77]

Originally Posted by congo

Still don’t get it, not a word about that proof test video, whats the go fellers.

Rex you are far more of an expert on anchor proof load tests than me, but I don't really see your point.
This is a photo of the Rocna and Super sarca attachment points. There does not look to be much difference in the distance from the tip to the attachment point, at least to my eyes.

The Rocna video shows a 55kg anchor that withstands a 17 Tonne force without perminant deformation.
Your website claims a a 185 kg (over 3 times bigger) Super Sarca anchor withstanding a 10 Tonne force.

We consumers are a bit jaded by anchor manufacturers promotional videos so I am not sure it means much.

[congo]

Dumad wrote;
Congo: Designing anchors is no big deal, unless someone sues you. In earthquake engineering its been real world experience and post-failure analysis that leads the technical drive, not the other way round. I'd listen to the most experienced cruisers.

Rex Wrote:
No big deal, well it’s enough to keep you behind the key board, I think 30 years might qualify me as an experienced cruiser, how many you have up your sleeve, your engineering skills must have waned or you simply do not know what you are talking about.

Do your homework on bis 80 before you start spruiking welding procedure and if you cannot come to grips with it then jump in our factory for a week and you will be a lot wiser, the bis is galvanized, further it is scrutinized by the authorities as a suitable steel for S/H/H/Power loads.

As you would know we have been dealing with 300 ton vessels for many years, why not buy an anchor made to strict standards, they don’t cost anymore and you know what you have got, providing the proof testing method is not fudged and you’re not purchasing what you think.

Regards Rex.