Anchor Wars - In Search of the Lost Truth. - Page 11 - SailNet Community
Old 05-08-2011
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Quote:
Originally Posted by LinekinBayCD View Post
I was not talking about strength to weight. In my example I was disregarding weight other than to generalize that a bar of steel would be heavier than a bar of aluminium of the same dimensions. So a 2 foot (in length) 1" x 1" bar/rod of aluminium will support more than 2 foot 1" x 1" bar of steel? That's news to me.

Aluminum sheet vs steel sheet

The following table gives a quick point of reference when you need the approximate thickness of aluminum sheet to use in replacing steel sheet. The designated aluminum thickness will give you about the same stiffness. Or, putting it another way, the deflection will be about equal. As a rule of thumb, plan on using an aluminum sheet about 40% thicker than steel. Since aluminum weighs only 1/3 as much as steel, this means that the equivalent aluminum sheet will weigh only half as much as the steel sheet it replaces.

Approximate stiffness equivalence:

Steel LB/SF Steel Thick Alu Thick Alu LB/SF
.975 .024 .032 .452
1.22 .029 .040 .564
1.47 .035 .050 .705
1.80 .044 .063 .890
2.44 .059 .080 1.13
2.56 .062 .090 1.27
2.86 .070 .100 1.41
3.66 .089 .125 1.76
4.88 .119 .160 2.25
5.49 .134 .190 2.68
7.33 .179 .250 3.53
So theoretically for an aluminium anchor to behave in the same way as a steel anchor. The thickness of the metal would have to be 40% bigger with the internal dimensions (the holding Dimensions) the same. If this is approximately correct (I say approximately purposely to take care of the pedantics amongst us) what would the approximate weight ratio be between two anchors with the same internal dimension (design) and the same manufacturer. 40%????

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Capitain Mike
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Old 05-08-2011
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Quote:
Originally Posted by WDfrmTN View Post
Not taking sides on the anchor issue, but I will against incorrect information. The strength-to-weight capabilities of aluminum and other allows over steel is well documented and time proven.
Of course but you seem not to know that the recommended anchors for a given size of a boat, in aluminum and Steel have not the same weight but approximatively the same size. And that's what counts: On same sized anchors, a well made steel one will be stronger than an aluminum one. That's why on the anchor tests they almost always bent Aluminum Anchors (not only the Fortress) and rarely bent steel anchors.

When I have said well made steel anchor that includes a proper grade of steel.

Regards

Paulo

Last edited by PCP; 05-08-2011 at 04:19 PM.
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Old 05-08-2011
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Quote:
Originally Posted by PCP View Post
Of course but you seem not to know that the recommended anchors for a given size of a boat, in aluminum and Steel have not the same weight but approximatively the same size. And that's what counts: On same sized anchors, a well made steel one will be stronger than an aluminum one. That's why on the anchor tests they almost always bent Aluminum Anchors (not only the Fortress) and rarely bent steel anchors.

When I have said well made steel anchor that includes a proper grade of steel.

Regards

Paulo
Hmmmmmmmmm!!!!!! In Reply to your statement/question I was not making a point I was discussing the relative strengths of an anchor made from Aluminium with a 40% increased in material not size than the same anchor made in steel.

An anchor rode entirely of chain with a rope snubber will hold just as well as a larger anchor on rope so weight also matters.

I would be very interested to know if you have a boat of your own now and if so please tell us the anchors you are using.

You don't seem to know or ignore the fact that there are different sizes recommended by different manufactures for the same size boat or there size tables do not equate weight of vessel to length of vessel in relation to their anchor size choice. This means pushing you to purchase a larger anchor than is needed for their profit margin or maybe not if its to big a reconstruction job to make it fit. Do what I did when I was looking for an anchor collate all the recommended sizes on one sheet. Spade, Manson, Rocna, Buegel, Ultra, etc then make a statement.

Am I right in believing that you are the gentleman who used to work in the aussie anchor market and then set up a business in Latin America if so I looked at your design which was pretty good but unfortunately you had ceased production I think because of carriage costs.

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Capitain Mike
Mediterranean Sea
Cobra 850
1978
8.68m
"Money won't buy you happiness but it will allow you to buy a yacht big enough to pull up along side it"
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Old 05-08-2011
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Quote:
Originally Posted by PCP View Post
Of course but you seem not to know that the recommended anchors for a given size of a boat, in aluminum and Steel have not the same weight but approximatively the same size. And that's what counts: On same sized anchors, a well made steel one will be stronger than an aluminum one. That's why on the anchor tests they almost always bent Aluminum Anchors (not only the Fortress) and rarely bent steel anchors.

When I have said well made steel anchor that includes a proper grade of steel.

Regards

Paulo
Sorry to post again but I just re read your post and I have another comment/question.
Paulo you state.

On same sized anchors, a well made steel one will be stronger than an aluminum one. That's why on the anchor tests they almost always bent Aluminum Anchors (not only the Fortress) and rarely bent steel anchors.

When I have said well made steel anchor that includes a proper grade of steel.
1. A well made steel one.
This infers that the aluminium anchor is not well made.
On some sized anchors. What almost always bent.
Take all you have said put it in a bag shake it put your hand in and take one out.
That one seems to be the winner

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Capitain Mike
Mediterranean Sea
Cobra 850
1978
8.68m
"Money won't buy you happiness but it will allow you to buy a yacht big enough to pull up along side it"
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Old 05-08-2011
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Quote:
Originally Posted by PCP View Post
That's why on the anchor tests they almost always bent Aluminum Anchors (not only the Fortress) and rarely bent steel anchors.

When I have said well made steel anchor that includes a proper grade of steel.

Regards

Paulo
In the case of the Fortress anchor bending during an anchor test, it is almost ALWAYS under a load that occurs long after the steel anchors have pulled out of the sea bottom.

Or put in a different way, the steel anchors don't often bend in the anchor tests because they will pull out of a sea bottom first.

And Paulo, I will see if I can locate pictures of the high grade steel anchors that were destroyed in the US Navy tests, while the Fortress anchors tested had minimal damage.

These tests proved beyond a doubt that just because an anchor is manufactured from a high grade of steel does not guarantee that they will be able to withstand heavy loads, or even provide good holding power for that matter.

Structural strength can be achieved by properly thickening and machining the metal at it's critical stress points.
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Old 05-08-2011
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If anyone could provide the strength to weight ratio data for a cider block tied off with clothesline that would be a great help to me.

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Old 05-08-2011
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Quote:
Originally Posted by CapitainMike View Post
Sorry to post again but I just re read your post and I have another comment/question.
Paulo you state.

On same sized anchors, a well made steel one will be stronger than an aluminum one. That's why on the anchor tests they almost always bent Aluminum Anchors (not only the Fortress) and rarely bent steel anchors.

When I have said well made steel anchor that includes a proper grade of steel.
1. A well made steel one.
This infers that the aluminium anchor is not well made.
On some sized anchors. What almost always bent.
Take all you have said put it in a bag shake it put your hand in and take one out.
That one seems to be the winner
Nothing than I have said permits you to infer that I think aluminum anchors are not well made or not made with the best possible alloy but only that for a recommended given size of boat they are less resistant in extreme conditions.

That is for example the opinion of Spade that makes steel an aluminum anchors. On the tests I have saw that compare the Aluminum Spade and the Fortress I have no reason to believe that the Spade is less resistant than the Fortress and I don't think that neither the Fortress or the Aluminum Spade are made with low grade aluminum alloys, quite the contrary.

Spade commenting on his aluminum Anchor versus its Steel Anchor (same design):

What type of aluminium are you using? Is it more prone to bending than steel?

We use a marine aluminium alloy, and as its resistance is less than that of steel, we use heavier grades to compensate. But for use in very rough conditions, we will suggest our steel model as a main anchor and the aluminium one as a secondary to stern anchor.

Following your recommendation, what would be the best use of your aluminium model?

We will suggest our aluminium model as a secondary or stern anchor; or as a main anchor if your boat is a ULDB; or light weight catamaran; or if you are frequently racing; or if you have a large boat and no electric windlass.

FAQs

Regards

Paulo

Last edited by PCP; 05-08-2011 at 07:44 PM.
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Quote:
Originally Posted by CapitainMike View Post

I would be very interested to know if you have a boat of your own now and if so please tell us the anchors you are using.

Am I right in believing that you are the gentleman who used to work in the aussie anchor market and then set up a business in Latin America if so I looked at your design which was pretty good but unfortunately you had ceased production I think because of carriage costs.
I'm going to let Paulo answer this in full but you are way off beam here.

Andrew B (Malö 39 Classic)

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― Terry Pratchett.
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Old 05-08-2011
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Quote:
Originally Posted by CapitainMike View Post
..

I would be very interested to know if you have a boat of your own now and if so please tell us the anchors you are using.
I have used extensively a 15K Spade on a 6.5T 36ft with an all chain rod (for 7 years). Never dragged not even when most boats around me were dragging (+35K wind). However on very strong wind I have noticed that the anchor moved slightly during several hours ( a meter or two) without losing grip. Probably as they say on the chart that boat was on the limit for that anchor.

I have used occasionally a Kobra and a Delta (with a lot less confidence) and never in a blow (+25k).

Quote:
Originally Posted by CapitainMike View Post
You don't seem to know or ignore the fact that there are different sizes recommended by different manufactures for the same size boat or there size tables do not equate weight of vessel to length of vessel in relation to their anchor size choice. This means pushing you to purchase a larger anchor than is needed for their profit margin or maybe not if its to big a reconstruction job to make it fit. Do what I did when I was looking for an anchor collate all the recommended sizes on one sheet. Spade, Manson, Rocna, Buegel, Ultra, etc then make a statement.
Can you explain what you mean ? the recommended charts are very similar. Here you have the one from Spade (click on details), from Rocna and from Mason. Note that the one from Mason don't specify the weight of the boat, an important factor and they say:

Anchor sizing should be interpreted as a guide only. Many factors influence anchor size selection ie, whether the boat is a heavy displacement or a light displacement craft and how much windage the vessel has. T... Finally the vessel usage should also be factored in ie whether the anchor will only be used as a "lunch pick" in fair weather for day outings or indeed whether the vessel will be going on extended coastal or offshore cruising. If in any doubt about anchor selection always use a bigger anchor, ..

Range Overview

Mason:

Manson Supreme recommended sizing chart

Rocna:

http://www.rocna.com/themes/rocna/pd...ric_tonnes.pdf

Quote:
Originally Posted by CapitainMike View Post
Am I right in believing that you are the gentleman who used to work in the aussie anchor market and then set up a business in Latin America if so I looked at your design which was pretty good but unfortunately you had ceased production I think because of carriage costs.
No, you are not right.

Regards

Paulo
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Old 05-09-2011
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Quote:
Originally Posted by BrianFortress View Post
In the case of the Fortress anchor bending during an anchor test, it is almost ALWAYS under a load that occurs long after the steel anchors have pulled out of the sea bottom.

Or put in a different way, the steel anchors don't often bend in the anchor tests because they will pull out of a sea bottom first.
That is a generalization that not only is true but yes I can accept that. At least it happened in some tests with some bottoms but that regards only badly bent flukes.

The problem with aluminum anchors has not to do with bent flukes but with the forces on the long shank in a veering moment. Regarding that, what you say is not accurate. About the test carried out by west marine Yachtingmonthly say :

" we subjected it to a further test at 3/1 scope and it cave an amaising 4.500 lb plus resistance though the shank bent slightly during our veering test." . They don't say at what force the shank bent but their conclusion is "This is a lightweight anchor wich should prove dependable in an emergency".

This seems to me like a recommendation as a secondary anchor and a not recommendation as a primary anchor and I believe it has to do with the inferior resistance showed on the tests comparing with steel anchors. For instance they say about the Spade : At 5/1 it repeatedly held at the maximum 5,000 lb and on the veering test we recorded up to 5,400 lb! and about the Mason: "Even 3:1 scope it held to an astonishing 4,612 lb. It was unfased by the veering tests – refusing to budge at 5,000 lb from all angles".

Neither the Mason or the Spade were affected (bent) by the veering test even if they hold as much or more on a veering test than what the Fortress on a forward pull. Again, they don't say at what force the Fortress shank bent, they say only : "though the shank bent slightly during our veering test"

Regarding the French test that also had a veering test they could not test on that regard the Fortress because it was been destroyed already by a frontal pull (with a huge holding force, I agree) but they had tested several other aluminum anchors and also bent the Spade shank on the veering test. They finally opted not to test the aluminum anchors on the veering test anymore and they opted to recommend on their conclusion the use of Aluminum anchors only as secondary anchors and that is after all also the use that Spade recommends for their aluminum anchors.

Quote:
Originally Posted by BrianFortress View Post
And Paulo, I will see if I can locate pictures of the high grade steel anchors that were destroyed in the US Navy tests, while the Fortress anchors tested had minimal damage.

These tests proved beyond a doubt that just because an anchor is manufactured from a high grade of steel does not guarantee that they will be able to withstand heavy loads, or even provide good holding power for that matter.
As you pointed out with the bent Rocna made with an inappropriate steel grade, if a Steel anchor is not well designed and made with a proper steel grade it can bent as easily as an aluminum anchor and has no guarantee of being stronger than an aluminum one. However a proper grade steel in a similar sized and designed anchor will make it stronger than if you apply an identically appropriate aluminum high grade as it is showed on the Spade that has two similar anchors, one made of steel another from aluminum.

Show me on that navy tests a Steel Spade or a Mason supreme destroyed by a force that a Fortress could sustain without damage and you prove your point. Show that happened with any other different designed or made with lower steel grade steel grade anchor and that proves nothing regarding the superior steel resistance, except that you should not buy any of those destroyed anchors .

The opposite is true. It was proven that the Fortress would be rendered useless and bent its shank by veering forces inferior to the ones that had no effect on steel anchors, namely the Spade and the Mason.

Regards

Paulo

Last edited by PCP; 05-09-2011 at 06:22 AM.
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