Al-anchors

[wagenaar]

Anchors appear often in this forum. A frequent reason to ask about anchors is the desire to go long-term cruising and from the answers it seems that the CQR is probably the most used anchor in this situation, although often it is suggested that it makes sense to have a complete different type of anchor for the situations when a CQR does not hold. A frequent writer about anchors, HYLAS, the designer of the SPADE-anchor recently gave an extensive explanation of the factors determining the functioning of an anchor. For one thing he concluded that all hinged anchors were inherently unstable. I concluded from his explanation, that weight of an anchor only plays a role in the beginning of the penetration into the bottom. As soon as a small part of the anchor gets "hooked", the forces exerted upon it will cause it to penetrate deeper.
The foregoing is kind of an introduction to my question. If weight has little importance in an anchor, why do so few people use an aluminium-anchor. As far as I know there are currently two types of aluminium-anchor available: Fortress and Spade(although it seems that most Spade-anchors are made of steel) . I used a Fortress myself as a kedge and was rather satisfied with it. It may be necessary to adjust the manner of dropping the anchor as compared to a steel-anchor, but I found it easy to use and the decrease weight was a definite advantage. In this forum this anchor is every now and then suggested as a kedge. Evidenly people have some trust in this anchor.
Up to now I have not found an Al-anchor mentioned as the main-anchor. Has anyone done so and what are the experiences. In particular for multihulls, which are more sensitive to weight than monos, the use of an Al-anchor seems to make sense. Another advantage is the reduction of weight, which makes the anchor easier to handle for older people.
I put this question also in a multihull-forum, but did not get any answers.


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[Shakey]

I've worked in boats that had Al kedge anchors, they were Danforths.

They were so light you'd think they'd float.

Experience was however, that they didn't hold very well, or rather it was harder to get them to set. Perhaps they lacked the initial weight to get them dug in.

<hr width=100% size=1>It could have been worse - it could have been me.

 

[scarlett]

If my 3 kg Fortress set it would hold my 2 tonne yacht in a 7 in sand but it did not always set. For example in weed, never.

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[Trevor_swfyc]

I had the pleasure of chartering a Bavaria 44 in the Ionian this year, it had an aluminium kedge with chain and warp for anchoring bows to and a CQR main anchor with chain only.

I decided before trusting the kedge I would test it, I tried several times and all it did was drag along the bottom, several times it appeared to hold but then suddenly pulled free under load. Clearly this was an accident waiting to happen so it remained in the locker. When in Gaos on Paxos we were hit by a storm with strong winds hitting the yachts on the port side, the wind was strong enough to blow chairs and tables over but the good old heavy CQR held firm.

Trevor


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[wagenaar]

I used my Fortress quite a number of times in the Med. It held very well in Trappini, W-coast of Sicily, even had difficulties to get it out. In Ustica, island N. of Sicily, the anchor held very well, even with a strong wind from starboard. Also in Gaos the Fortress held well, but we did not have strong winds. According to Hylas the good holding power of the Fortress is due to its big flukes. The Fortress did not hold well in Lipari (island N. of Sicily). As soon as the eastern wind began, it dragged and we had to leave. Also on one of the croatian island it started to drag and we left.
On the other hand when anchored in Denmark in a bay on the S-side of the island of Fünen, the main anchor, a CQR, dragged. On other occasions it held very well.
All this points to the fact, that NO anchor is good in all circumstances.
Henk.

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[gjeffery]

I am in the market for a light alloy anchor, and it would be interesting to know how much chain was in use, and what size.

I think the anchor/chain combination is crucial, and that to set, a light anchor needs a heavy length of chain to ensure a horizontal pull on at the sea bed. If Fortress anchors are pulling out after being set with a heavy length (eg 10m x 8mm), then I would look at somethng else!

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[snowleopard]

one reason for lack of take-up of aluminium anchors is cost. for example the spade website quotes £274 for a 15kg steel anchor, £307 for aluminium of the same dimensions and £659 for one of the same weight.

The spade people claim that you get the same holding power from a given size of anchor regardless of weight but i suspect few people intuitively believe that and would prefer a nice heavy anchor whatever the test results show.

if you want a second anchor to hold when the main one drags you would be well advised to carry a selection of widely different types so if your main anchor is a plough type, a danforth and a fisherman would give the best range for a wide variety of bottoms.

i have a delta for main anchor and on the rare occasions it has dragged (usually in soft ooze) the fortress i carry as a kedge has held extremely well. on the other hand i have tried to use the fortress on sand and it has skimmed across the bottom without biting at all. for that reason i wouldn't consider a fortress for a main anchor.

i have looked at the question of using an aluminium anchor, perhaps a spade, as my main anchor but using the same weight as my current steel one. the idea was that it would be no harder to handle but would give vastly greater holding power (though at considerable cost). i posted the suggestion here but the response varied from disbelief to contempt! the subject of anchors seems to be second only to choice of boats in the "i'm right and how dare you disagree with me" stakes.

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[ianabc]

There are many "Delta" Look-alikes here on the west coast of Canada....

Welding up a steel Delta type is quite straightforward.....
I have seen 6 identical Delta types (ungalvanised steel waiting to be dropped off at the galvanizers? ) in a used marine store.

SO.....cutting (using a metal cutting blade in a portable circular saw with LOTS of candle wax on the blade works well) say 1/2 inch thick 5000 series (marine grade) aluminium plate and having it welded up by a professional and qualified aluminium welder into a weight say equivalent to 30 or 45 pounds of the steel Delta would give one mighty hefty aluminium anchor.

So who's going to try it first......

(My wife says I have to lauch the boat in August so the nesting (11 foot) aluminium dingy and anchor will have to wait....)

Ian / Home of Worldwide Sailing Directions on CD

<hr width=100% size=1>Building a steel sailboat in Comox, B.C. Canada.

 

[wagenaar]

I used my Fortress anchor with some length of chain, which I had, some 8 mm and some 6 mm, in total about 6 or 7 meters of chain and then something like 20 meters of rope. The first time I used the fortress anchor was in very clear water and I saw it go down like a leaf of a tree. To make it go down faster I then started to drop first some 4 or 5 meters of chain before dropping the anchor. The idea being that the chain pulled the anchor down. This normally worked OK.

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[hylas]

The field of anchoring is indeed one where old beliefs are well deeply rooted.. Sailors believe in HEAVY anchors and HEAVY chains..

Since more than ten years now, I've tried to promote the idea of holding related to the surface area of the anchor and the use of nylon wrap to attach it to the boat.. (I'm not selling neither chain nor rope....)

Each time I explain my theories, giving the mathematical proofs, I'm sure to create a lot of contestation and critics... (mostly from people who spend most of their time seatted behind a desk in a confortable office!) But fortunately, more and more open minded poeple are thinking the same way.. (See the very interesting Web site of my good friend Alain Fraysse : http://alain.fraysse.free.fr)

Since 13 years now, I've been living full time in my boat, mostly anchored (when not sailing..) .. Since the 15 of August this year, I didn't spend one single night attached to a quay in a marina, and for me, anchoring is a vital question..

One very interesting test is to compare a Steel Spade anchor, with an Aluminum Spade.. not because they are "Spade".. but because (with the exception of the constitutive material and weight) they are absolutely identical..

During INDEPENDANT tests done by the French nautical magazine "Voile Magazine", they have compared a 15 kg - S 80 - Spade anchor (steel) with a 7 kg - A 80 - Spade (Aluminum - same model, same size) . The conclusions are:
"Les résultats que nous avons obtenus sont identiques a ceux de l'ancre acier: excellente tenue sur les deux types de sols, enfouissement rapide et résistance de chasse constante et lente. Ces résultas prouvent que la tenue de l'ancre est directement liée à sa surface et à sa géométrie, le poids ayant une influence minime.."
(the results we have obtained are identical to the results of the steel anchor: excellent holding with the two types of ground, rapid digging in and constant and low dragging . These results prove that the holding is directely related to its surface area and its geometry, the weight has a minimal influence..)

BUT... if holding has nearly no relation with the weight.. weight is important for the first part of the process.. the penetration of the anchor. A steel Spade anchor will give better results than an aluminum Spade (of the same size) in difficult grounds such as weed, hard sand or coral.. But also on the same time, the weight repartition on the tip of an 7 kg aluminum Spade anchor (50%) (equivalent to a 15 Kg steel Spade anchor) will be about 3,5 Kg; this has to be compared with the weight of the tip of, for example, a 15 kg CQR anchor, only 2,7 kg...
Then obviously, an Aluminum Spade anchor will have more chance to penetrate than any competitive steel anchor of the same size..
The weight repartition on the tips of a 7 kg Fortress anchor is about 1,26 kg.. and this is the reason why the Fortress anchor has a poor penetration on weed and hard sand...

If you are anxious by nature!.. take an aluminium anchor of the same weight than your old steel anchor. You will have the same weight on your bow, but a "monster" of anchor and enough holding power to hold four boats like yours...
Now, if you also consider the higher price of the aluminum model?? compare the price of all constitutive components: a steel anchor, 60 meters of (heavy) chain, and a good electric windlass to be compared with an (expensive) aluminum anchor, 60 meters of rope spliced on 10 meters of chain .. and NO windlass (you don't need it anymore); Aluminium anchor is still the winner...

Aluminum Spade anchors are sucessfully equiping quite a lot of multihulls where weight on the extremities is a big concern..

Now, if you are trying to save weight.. why using an heavy chain to attach a light weight anchor to the boat?? The chain will absolutely not help for the anchor penetration, and will only MARGINALLY improve the holding of the anchor*.. I will suggest only one lenght (or max. two) of the boat in chain (to avoid chaffing of the mooring line on the sea bottom), and then a Nylon wrap, directly spliced on the chain.. (http://www.bluemoment.com/warpchainsplice.html)

But, I perfectly know that some sailors will still consider my theory as absolutely wrong.. It doesn't matter.. it is just a question of ten (or twenty..) more years before they will accept it.. :0)...

Peacefull anchorages to all..

(*) the holding of the chain itself, is approximatively twice its weigth, i.e. for 30 meters of 10 mm chain the holding related to the chain is about 67 daN.. just ridiculous.. When you will the most need it, for example with winds greather than 40 knots, the chain has (nearly) no more catenary and no shock absorbing effect, its pulling angle on the anchor is comparable to the one of the wrap line of the same lenght.. In the same conditons, a nylon wrap has still a good shock absorb


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[wagenaar]

Hylas, you make a mistake when you quote the forces the points of the anchors exert on the bottom. The weights you quote are the weights in air, but an anchor is in water and one should correct for that. The weight of an AL-spade of 7 kilos in air is only 4.4 kg in water and the force on the tip 2.2 kg. A 15 kilo CQR weights 13.1 kilos in water and the weight on the tip 2.36 kilo, just a bit bigger than the Al-Spade.
I have a similar problem when you say that the the 7 kg Al-spade is equal to the 15 kilo steel-spade. Considering the specific gravities of steel and Al, 7.87 and 2.7 gr/ cm3 respectively, an Al-spade of the same dimensions should weigh 5.2 kilos. Evidently the two anchors do not have the same dimensions. I guess that equal means that the surface-area of the two anchors are the same and therefore the holding-power.
Aside from these mathematical mistakes I agree with you, that a nylon rope spliced to appr. 10 mm of chain is a better solution than an all chain anchor-rode. I feel that an anchor fails due to what I would describe as "fatigue", due to the impact of the waves on the ship, which lead to impacts upon the anchor. The nylon rope will accomodate these impacts better than a chain stretched till it is straight and therefore exert smaller impacts upon the anchor.

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[Birdseye]

I agree with you that in an extreme situation where a chain rode would be almost straight, simple physics suggests that a nylon rode would tranmit lower forces to the anchor. It stretches more, therefore the deceleration of the boat is less, therefore the forces are less. But most of the time we are not in that extreme situation, and I certainly found on my catamaran that a chain rode gave a more peaceful night with much less boat movement. It was less antisocial in an anchorage.

All other things equal, the anchor with the heaviest point load and sharpest point will dig in best. So get out the angle grinder and sharpen your anchor. But once its dug in the bottom, then I guess that profile and area will matter more. But surely some anchors like the CQR are designed to slowly drag through the bottom, whereas the Danforth types are intended to present the max area and max holding whilst stationary. I would have thought that when they gave, they would give suddenly and unpredictably. Do they?

Personally, I have long used an aluminium anchor as a lunch hook because it is easy to raise. But overnight it is always a CQR, and I have never yet dragged.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[TonyMS]

We have a 7Kg Fortress (actually a cheaper Italian copy) and a 12Kg CQR on our 9.2m cat. We use 15m chain, then rope.

We've found the trickiest anchoring is in very hard sand, in particluar Green Bay in Scilly, and the inner harbour of Isle de Sein. In both cases, it has proved hard to get them to dig in initially. In Green Bay this summer, we had to bury them by hand at low water - done by me standing on it while the mate winched in.

On the other boats in the bay, it seemed to me that Spades worked best, with Deltas second. One regular had brought spikes, like the ones used on narrow boats, and banged them in with a sledgehammer.

Once the Fortess has set, it will hold anything. But if the wind or tide change, and it has to reset...

Tony

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