Lon nan Gruagach
Well-Known Member
Those with aluminium boats are quite keen on them...
Why has the market not embraced alloy anchors?
- Thread starter Neeves
- Start date
Those with aluminium boats are quite keen on them...
alan_d
Well-Known Member
That would be my guess too. Entering "Light Alloy" into wikipedia redirects you to "Aluminium Alloy" but does not further mention the term. My impression is that "light alloy" was the common name for aluminium alloys (in Britain at least) in the 1940s and 50s, but I have been unable to find a history of that usage.
thinwater
Well-Known Member
luminium and stainless steel together also appears to be a bi-metallic corrosion risk, from the 'nobility' table.
With this combination the affect of relative surface area on corrosion is important.
A large area of 'cathode' relative to 'anode' will accelerate the anodic corrosion. Although aluminium is anodic to stainless steel, large relative surface areas of aluminium to stainless steel can be acceptable, dependant on local conditions.
To complete the cell, a conductive liquid must bridge the contact metals.
The more electrically conductive the liquid is, the greater the danger of corrosion. Seawater or salt laden moist air is more of a risk than contact with rain water or towns water.
In testing I agree that Aluminium and Stainless steel would be ok , but we are dealing with Salt water , and salinity in Water varies around the world ,The deep salinity within the Mediterranean Sea is between 38 and 39 psu and in the North sea The salinity averages between 34 to 35, so does the composition of the water with other chemicals present, Just saying
People like to test in nice dry environments wit hall the best tech .
I'm guessing you don't accept that Fortress anchors have been quite popular and widely used in the US for about 20 years.
Why the ax to grind? I'm confused. I'll bet we're all confused.
rszemeti
Well-Known Member
Whilst it is indeed possible to get 7000 series alloys with similar tensile strengths to steel, there is a crucial difference: they are brittle.
In rocky holding, a steel anchor may possibly get a bent shaft ... try bending a piece of forged steel, you'll be able to bend it into a U shape with enough force, no cracking.
Bend a piece of thick plate 7082 and .. you'll have two pieces ... it simply is not malleable. It cracks and fails.
I'll stick with tried and tested heavy steel anchors, ta very much though.
In rocky holding, a steel anchor may possibly get a bent shaft ... try bending a piece of forged steel, you'll be able to bend it into a U shape with enough force, no cracking.
Bend a piece of thick plate 7082 and .. you'll have two pieces ... it simply is not malleable. It cracks and fails.
I'll stick with tried and tested heavy steel anchors, ta very much though.
Neeves
Well-Known Member
You are quite correct, though I have never tested 7082 but have tested 7075. It, 7075, breaks like glass unlike steel which tends to more visibly yield. However to break it, 7075, you do need to apply considerable tension, more than would be possible with an anchor sized to fit the yacht. Your point is well made, but hardly valid. Its about engineering and ensuring the various components cannot be stressed to a point where they fail. I'm not aware that 7082 is used in any alloy anchor, though 7075 is used.
Of Fortress failures - I have never heard of anyone cracking any part of their anchor - they bend. If Anchor Right 7075 shaft had cracked and failed - I am sure Noelex would make sure I heard about it!
I have seen a bent alloy Spade shank, it looked a bit like a cork screw - it bent but did not crack. Illustrating that different alloys have different characteristics. I have seen a bent and cracked Mantus toe - a poor weld. Cracking is not limited to alloy.
Jonathan
thinwater
Well-Known Member
Curiously, climbing carabiners have been 7000 series for decades. Lots of impact loading.
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Are anchors bent in use or during ham-handed recovery from under rocks? Do we know for certain (just because it came up bent does not tel us which of these was the cause). I'm not being sarcastic. It is a rare occurrence in my home waters, so I am curious. From an engineering perspective, bending during recovery seems far more likely.
In truth, bent vs. broken makes little difference for the next use; neither will dig and you will be using your spare.
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It's an interesting question, but in most cases, bent is just as bad as broken.
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It seems like we are off the point. Corrosion and mechanical failures are theoretical but are not actually happening. Real world, not lab. The setting question is more interesting.
rszemeti
Well-Known Member
I wasn't so much thinking of ham-fisted recovery, but when it gets caught up in a rock in a bit of a blow, and you end up side-loading the shaft ... the steel anchor will just bend and hold ... the alloy one, well, I suspect it may bend and fracture ... not hat you want at 3am in a big sea ...
thinwater
Well-Known Member
Well, this has happened to Fortress anchors. Just Google "bent Fortress anchor." They bend. I think I've seen a photo of every major anchor bent. There is no evidence that it is more or less likely. I've never heard of a fracture.
In my experience, nearly all--probably greater than 98% of anchor dragging events--are from failure to engage and hold, not mechanical failure. We're looking at the wrong problem.
Can an aluminum anchor dig as well, in all bottoms? That is the question. We know some do very, very well in certain bottoms. We know Fortress is not good in some bottoms, but not because it is aluminum. I'd love to hear about aluminum Spade and other anchors. I think there are also more interesting things to be done with high strength steel that we have not seen yet.
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Neeves
Well-Known Member
The only people who can answer this question are those who have actually compared similar models in both steel and (aluminium) alloy. This limits the information base to those who own, or have owned, an alloy Spade and steel Spade or an alloy Excel and a steel Excel. Whereas Danforth and Fortress look similar there are differences (especially as genuine Danforth come in a variety of versions) and only NormanS admits to have owned a genuine Danforth and Fortress and when last heard was trying to offload the Danforth.
Frankly I cannot tell the difference between our 2 Spades and our 2 Excels and our steel versions, of both Spade and Excel, are collecting dust in my workshop. In a hard seabed the Excel, well - excels - its has a sharper toe.
Jonathan
NealB
Well-Known Member
Over the years, I've (so far) owned 16 cruising boats, of a fairly wide variety (eg long keel, twin keel, fin keel, monomaran, catamaran, racy, sedate, gaff rigged, bermudan rigged).
All were bought secondhand, and came with an array of different types of anchor.
I always like to have at least 3 different types of anchor onboard.
I've had several genuine Danforths, and I've also chosen to carry a Fortress on all my latest boats.
So I qualify to join NormanS's elite club.
As noted by others, both types are not the best at resetting when the tide turns, or in weedy areas, but they do have the great benefits, for me, of fantastic holding in mud and light weight.
We anchor a great deal (we generally avoid marinas), but I've never managed to bend a Fortress.
We did bend the stock of a genuine Danforth, during a tremendous 3 day storm in the tiny Italian habour of Ventotene, in around 1990.
The stock of a genuine CQR was also bent during the same storm. I've no idea whether they bent whilst subjected to horrible shock loadings, or when, after a huge struggle, we eventually managed to lift them.
doug748
Well-Known Member
Great stuff, real experience.
Did you notice any difference in the performance of these similar anchors? Thanks.
Neeves
Well-Known Member
I'm no Danforth expert, at all. Danforth comes in more than one version - I think you need to know which version. I think originally it came with a drop forged shank, an 'H' section like CQR. They made a HT version, I recall, presumably High Tensile steel.
If Thinwater comes along he might clarify.
And NormanS has a genuine Danforth looking for a home, or did have a few week ago.
Jonathan
If Thinwater comes along he might clarify.
And NormanS has a genuine Danforth looking for a home, or did have a few week ago.
Jonathan
NealB
Well-Known Member
Hmmm .... a very good question, to which the brief, honest answer is, "no, not really".
Both types have held us safely in sometimes demanding conditions, but, then again, so have genuine and fake CQRs, Bruce, Mansons and others.
Without like for like testing (a bit like YM do every few years), in identical conditions, with measuring equipment, it's not really possible to give any really valid conclusion..... and, in real life, usually with just two of us onboard, we've never felt the inclination to start playing with different anchors.
We always make sure the anchor (or occasionally anchors) is really well set, and then, in demanding conditions, keep watch and hope they continue to hold, or clear out if necessary.
With very few trivial exceptions, our anchors, regardless of type, have always given us wonderful service and kept us safe.
(Yes, of course ,I'm crossing my fingers whilst writing this, not wanting to tempt fate).
Bouba
Well-Known Member
One thing about the market is that only half of it is sailing boats. The other half, motor boats, can sometimes benefit from extra weight on the nose. But the main reason I’ve never considered an alloy anchor is that I’ve never seen one! But the real question I want to ask is what type of rode goes with an aluminium anchor?
NormanS
Well-Known Member
The second anchor which came with my present boat was a 20kg (genuine) Danforth. It was only used occasionally, although several of these occasions involved leaving our 36ft ketch for four weeks at a time, in a sealoch in the Outer Hebrides. When doing this, I rig a Bahamian Moor, with my 20kg (genuine) Bruce, and originally the Danforth. Moored thus, the angle of pull on the anchor is restricted, so that even in a major wind shift, the anchors are not disturbed or required to reset.
As Danforth anchors and Danforth type anchors are difficult to cope with on a bow roller, the Danforth was never used as the primary anchor. It would be used in a heavy blow in a Vee with the Bruce, usually laid out by dinghy, but sometimes direct from the boat, if I had left it too late to lay it out by dinghy. 20kg is not that heavy to handle (our previous boat's anchors were 140lbs) but we decided, at our age, to treat ourselves to a Fortress FX23 which although having roughly the same dimensions as the Danforth, is less than half the weight.
It is difficult to be precise, but I have been unable to detect any appreciable difference in the behaviour of the Fortress and the Danforth. Put it this way, I have enough confidence to leave my boat anchored unattended, in the Outer Hebrides, now using the Bruce and the Fortress, and subject to any winds.
GHA
Well-Known Member
:encouragement:
Perfectly acceptable on forums of course, imagine a tiny pattern and inflate it up to an obvious cause and effect
JumbleDuck
Well-Known Member
I'm puzzled by this "weight in the nose" business. A Bavaria Cruiser 34 weighs 5.3 tonnes empty, so about 6 tonnes in cruising trim. Spade#s "Anchor Selector Wizard" recommends either a 15kg S80- or a 7.5kg A80 (note to sceptics, yes, they recommend aluminium for the main anchor) for that size. Going for steel instead of aluminium will shift the centre of gravity forward by (7kg x 5m) / (6,000kg) = just under 6mm. How terrible is that?
dgadee
Well-Known Member
I've just brought an Fx-16 back in my luggage from US ($220). Wouldn't have bought it here at local price. Not sure how I'll use it - happy with the Ng one I have - but I'm getting to the stage in life where you can't have too many of them.
vyv_cox
Well-Known Member
I believe that Fortress recommend all rope. Most people place a short length of chain next to it for abrasion resistance, ours is 5 metres. I have certainly seen all chain used.
Galvanic corrosion is just not an issue with anchoring gear, the electrical connection is never very good and the equipment spends relatively short time immersed, even for liveaboards. An aluminium anchor might be anodic to steel but not to zinc galvanising. The zinc on my chain suffers slightly adjacent to a stainless steel swivel and shackle but still the last four links last five years before rusting.
noelex
Well-Known Member
Weight in the ends can have a theoretical effect on a sailing boat. So 7.5 kg in the bow balanced with similar weight in stern would not change the COG, but in theory it could effect the performance, but only to a tiny degree in some conditions.
However, I agree in reality 7.5 kg (or even significantly more) of extra on the bow of a 34 foot cruising boat will make no practical difference. The chain weight will have more impact. A 34 cruising monohull may have 50m of 8mm chain, as an example. The chain will weigh about 70 kg.
The other way of looking at the problem is that 7.5 kg is equivalent to around 5m of anchor chain. The anchor chain is not quite as far forward and lower down than the anchor itself, so lets round it up to 6-7m. So reduce the chain length by 6-7m and the sailing performance will once again be identical even in the theoretical world. A better strategy is to keep the chain and the steel anchor and do a tidy out of the V berth. If your boat is anything like mine, a tidy out will save more than 7.5 kg
.So switching to an aluminium anchor really does not generally make sense from a sailing performance perspective for a cruising monohull.
However, where the 7.5 kg saving is really appreciated is if you carry the anchor around or transfer it to the tender. So for a secondary anchor the weight savings of an aluminium anchor are very beneficial. This is especially true with an unballasted anchor such as the Fortress. The weight savings converting the unballasted Danforth design to aluminium are greater than a design like the Spade.
As well as the application of a secondary anchor, the weight savings of aluminium construction are especially beneficial if the vessel has no anchor windlass, or on some high performance racing yachts.
The final category is lightweight catamarans. With these vessels the chain is usually stored centrally, but often the anchor is still on the bow. The chain weight increases the total displacement, but has little impact on the moment of inertia. Only anchor weight contributes to the bow weight. Some catamaran designs are sensitive to bow weight. Hull entries are often fine. Pitching can induce unpleasant wave slap on the bridge deck in the wrong conditions. So once again with this type of vessel the reduced performance of an aluminium Spade (compared to the steel version) can be a justified compromise depending on the cruising ground. This is by far the biggest group I see using an aluminium Spade as a primary anchor.
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