Why has the market not embraced alloy anchors?

[CAPTAIN FANTASTIC]

I'd be very happy to use an alloy anchor, but there are 2 things they need to get tight before I do:

1) cost ... way too expensive at the moment.

2) weight. Needs to be at least as heavy as the steel one it is replacing. Heavier the better.

The design of the Anchor is the critical determining factor rather than the weight. With the advancement of modelling, anchors design can be optimised to deliver maximum holding power to minimum weight and optimum strenght of material.

I look forward seeing an Anchor manufactured using Additive Manufacturing (3D printing) technology to reduce production costs and to achieve deterministic design.

 

[bedouin]

The two most important jobs for an anchor are to set well and then hold when it is set.

In most bottom conditions weight (in fact I would guess pressure) is an important factor in digging in. So a heavier anchor will always set better than a lighter anchor that is otherwise identical.

Steel is also stronger and cheaper so the only advantage of aluminium is that it allows you to carry a larger anchor for the same weight. Once set a larger anchor will hold better than a smaller one of the same design, but won't necessarily set any better initially.

 

[JumbleDuck]

Why do people call aluminium 'alloy'?

A contraction of the old "light alloy", I suspect.

 

[JumbleDuck]

I wonder if the idea that 'heavier is better' comes from the bad old days of CQR's, fisherman's, etc, where you might actually be relying on sheer weight instead of grip?

I think that it's generally size that's better (a Fortress holds about as well as a much heavier Danforth of the same size) and unless you change materials weight is a handy proxy for size.

 

[Zing]

Why do people call aluminium 'alloy'?

I think it is a corruption of and confusion with the word ally as in ‘An ally ladder is light weight’.

 

[Egbod]

Pure aluminium is very weak. It is used to make cooking foil that crumples easily. To make aluminium more usable small amounts of other metals are added to make it stronger or less bendable. There are lots of different mixtures or alloys. Adding 3% copper to aluminium roughly doubles its strength. If aircraft wings were made of pure aluminium they would just fold up. As well as strength the different alloys have different corrosion resistance which is very important when they are exposed to sea water.

 

[KINGFISHER 9]

You're a very naughty boy, sitting there in Australia and starting an anchor thread! … You should know that there's nothing that will bring on an attack of the vapours more than an anchor thread suggesting change! You should also know that the British are anal about everything in general and anchors in particular! ……. :encouragement:

 

[CAPTAIN FANTASTIC]

You're a very naughty boy, sitting there in Australia and starting an anchor thread! … You should know that there's nothing that will bring on an attack of the vapours more than an anchor thread suggesting change! You should also know that the British are anal about everything in general and anchors in particular! ……. :encouragement:

January is a very boring month; so, we must have something to excite us and to disagree with; haha.

 

[rszemeti]

Why?

Why, because the weight helps it set. rather than just skid along the surface.

Additionally, aluminium has a low fatigue life ... it fractures where as steel is more malleable and elongates, with a much higher fatigue life ...

I just see no purpose whatsoever in an aluminiun anchor, they strike me as about as useful as chocolate teapots and polystyrene fishing weights.

 

[rszemeti]

Why?

Pure aluminium is very weak. It is used to make cooking foil that crumples easily. To make aluminium more usable small amounts of other metals are added to make it stronger or less bendable. There are lots of different mixtures or alloys. Adding 3% copper to aluminium roughly doubles its strength. If aircraft wings were made of pure aluminium they would just fold up. As well as strength the different alloys have different corrosion resistance which is very important when they are exposed to sea water.

True, but pure aluminium is also less prone to fractures, and will elongate rather than crack ... the harder grades (typically 5083 for Marine use) tend to crack when repeatedly stressed.

 

[langstonelayabout]

I look forward seeing an Anchor manufactured using Additive Manufacturing (3D printing) technology to reduce production costs and to achieve deternimistic design.

Whilst using 3D printing will enable the verification & validation of anchor design it certainly won't decrease unit cost and is unlikely to yield the best ultimate strength characteristics.

3D is a great fast prototyping method but is slow and costly for volume manufacturing, especially if you are using metals which will require sintering afterwards (furnace or laser). Also, the grain structure of the metal (notice I didn't mention alloys of steel, aluminium or other metals ) won't be present. The presence and direction of the grain structure of metals is often key to design and their strength/characteristics in use.

 

[dunedin]

The two most important jobs for an anchor are to set well and then hold when it is set.

In most bottom conditions weight (in fact I would guess pressure) is an important factor in digging in. So a heavier anchor will always set better than a lighter anchor that is otherwise identical.

Steel is also stronger and cheaper so the only advantage of aluminium is that it allows you to carry a larger anchor for the same weight. Once set a larger anchor will hold better than a smaller one of the same design, but won't necessarily set any better initially.

And the third thing is to stow easily and not project out too many sharp bits. For most boats using a bow roller, the Fortress style has too many sharp bits sticking out the sides. This is not a feature of the metal chosen, but the design shape.

If Rocna or Sapde etc were sold in Aluminium Alloy version then the advantage might be to have a larger surface area for similar weight to a steel one. But space on the bow roller could again be an issue.

 

[CAPTAIN FANTASTIC]

Why, because the weight helps it set. rather than just skid along the surface.

Additionally, aluminium has a low fatigue life ... it fractures where as steel is more malleable and elongates, with a much higher fatigue life ...

I just see no purpose whatsoever in an aluminiun anchor, they strike me as about as useful as chocolate teapots and polystyrene fishing weights.

The Aluminium alloy used for anchors can be designed to have specified ductility and other design characteristics; this is why is called "aluminium alloy". They are half the weight of the steel anchors with a larger surface area to assist holding. I use a steel Kobra 16 kg and an expensive aluminium Fortress.

 

[JumbleDuck]

Why, because the weight helps it set. rather than just skid along the surface.

Evidence? There seem to be no complaints about Fortresses setting.

Additionally, aluminium has a low fatigue life ... it fractures where as steel is more malleable and elongates, with a much higher fatigue life ...

Only relevant if you exceed the yield stress (low cycle fatigue) or apply at least hundreds of thousands of loads (high cycle fatigue). Why do you think is likely to be a problem in an anchor?

I just see no purpose whatsoever in an aluminiun anchor, they strike me as about as useful as chocolate teapots and polystyrene fishing weights.

You'll note that this thread was started by someone who uses exclusively aluminium alloy anchors and has no problem with them.

 

[zoidberg]

They are half the weight of the steel anchors with a larger surface area to assist holding. I use a steel Kobra 16 kg and an expensice aluminium Fortress.

I note that Cap'n Fantasy 'inhabits' the Brizl Channel and South Wales. That's 'mud, mud, glorious mud'......

However, I agree, having also a steel 16kg Kobra and a 'cheap' Fortress of similar or better holding power. I say cheap, as it was purchased here, at a very considerable discount.....

 

[vyv_cox]

Nowadays the main use for my Fortress is as the second anchor in a fork moor. It is inevitably laid in a far from ideal manner: not selecting a sandy patch amongst the weed, always in lots of wind, chucked over the side of either the boat or tender, hopefully with a good scope but quite often less than ideal. Despite all of these potential fails the Fortress has set every time, first time, and held strongly in gale force winds with scopes as little as 3:1. The only problem has been getting it out of the seabed when we departed.

The only genuine problems we have had with it was setting or resetting in very light wind in probably a fairly hard seabed. We would now avoid this combination.

 

[noelex]

The aluminium Fortress is a great secondary anchor. In this role the lighter weight is especially a bonus because the anchor can be carried easily in the dinghy or even swum out with the help of a fender. However, in my view, it is not a great primary anchor. It does not respond as well as many other designs to a change in direction of pull and while it is exceptionally good in softer substrates, it struggles in others such as very hard substrates and weed.

The aluminium Spade is a good anchor. It is a useful option where weight is an overwhelming consideration, such as those boats without a windlass, yachts primarily racing, or lightweight catamarans, but unfortunately in my view it does not have as good performance as the steel Spade, especially in harder substrates (although the steel Spade is excellent, so this a high benchmark).

At least the above have been my observations when diving and looking at anchor performance. This has also been confirmed by the independent anchor tests (see below) and user reports. MaineSail (Compass Marine) who is a great commentator on all things nautical, even produced a nice video showing the steel Spade and the aluminium Spade setting (or not setting, which was case for the aluminium Spade) side by side, but unfortunately I do not have a link. Following the video, Spade swapped his aluminium model for a steel version. It should also be noted Spade themselves specifically recommend the aluminium version is not to be used as a primary anchor:

"it is important to note that we do not recommend the use of an aluminium anchor as a main anchor."

They also acknowledge that the aluminium version does set as well as the steel version:

“This is true; the model in steel will dig in slightly more readily than the equivalent aluminium version. “

I think Spade should be congratulated for this honestly when advertising their products although for obvious reasons they downplay the differences. See here:

http://www.spade-anchor.co.uk/sd_further_info1.htm

There are other aluminium anchors: the Manson Racer, Guardian, FOB Light, the Lewmar LFX anchor and aluminium Excel. I have probably left a few out .

I think there is a gap in the anchor market for an excellent aluminium primary anchor, although for those boats with all chain, or even predominantly chain rode, the weight reduction in terms of the percentage of the total ground tackle weight is not great. For many cruising yachts (not all) most of the ground tackle weight is in the chain not the anchor.

This link shows the measured reduction in holding power between the steel and aluminium Spade:

https://www.georgekniest.nl/pdf/manuals/kobra.pdf

 

[rszemeti]

You'll note that this thread was started by someone who uses exclusively aluminium alloy anchors and has no problem with them.

No, that is incorrect. It was started by someone who has an aluminium anchor and has not had a problem with it yet.

As others have noted, at least one manufacturer is honest enough to note that it should not be used as a main anchor and could have trouble setting in harder ground.

Fatigue cracking in Aluminium is a major problem, so is corrosion. on a rough night in a big sea, the last thing I want to be worrying about is "will the anchor snap" ...

 

[Birdseye]

The issue Neeves is that many sailors are very conservative traditionlists with little or no engineering / scientific knowledge. Many still hanker after heavy dispacement long keel boats using designs that were forced on boat builders when the only material available was wood. Others like steel, quietly forgetting rust and weight issues. And its the same with anchors and anchor rodes.

Many sailors chose all chain rodes - fine if the catenary is till there but likely to jerk the ancor out of the sea bed or the cleat out of the grp if the wind and sea really get going. They like manhandling heavy steel anchor despite the risk of medical problems both handling and recovering.

But it would be a poor situation if we all thought the same way wouldnt it.

 

[JumbleDuck]

Fatigue cracking in Aluminium is a major problem ...

SO are you worried about low-cycle fatigue or high-cycle fatigue? I'll mention in passing that I spent two years of my life sharing a tensile testing machine with someone researching fatigue in aluminium alloys.