Rusting Anchor Shackles

Malcb

Malcb

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I've been walking up and down a few pontoons of late and I have been noticing the number of rusting shackles that attach the chain to the anchor (I know, I need to get out more).

I've noticed that invariably the anchor and shackle and chain appear to be galvanised, but the shackle pin has been wire locked with what looks like stainless steel wire.

Is this the contributing factor,; if so, would it be better to lock the shackle with a cable tie (or a big hammer smacked on the other end) ?
 
There is a thread running on cable ties being not much good. I use mousing wire, but also peen over the threads on the shackle pin. Belt and braces.
 
I used mousing wire, I assumed stainless but maybe monel, on a shackle last March and this November the shackle had to be cut off with a hacksaw. This was on a sailing association boat which has been out and about more than in the marina. I've also, as I said, noticed a number of corroding shackles that have been locked off with 'bright looking' wire.
 
Two reasons: 1: Monel metal mousing wire contains copper, and forms and in contact with zinc forms an electrolytic cell: in saltwater the zinc dissolves quite fast and the shackle is rusting in no time. 2: Cheap shackles are often zinc-plated: the coating is much thinner than on hot-dipped galvanised chain (and anchors) so it is the weakest component in terms of rust-resistance, and probably in strength too! The solution is to use only tested hot-dipped shackles. Far more expensive, but only fools penny-pinch on their ground-tackle.
 
I confirm that many 'galvanized' shackles are plated. I think some may even use Cadmium rather than Zinc. In any case the plating vanishes PDQ.

You can tell a plated one because it is smooth & shiny whereas a proper galvanized one is rough and lumpy.
 
Beware using any shackle to secure the anchor to the chain. Even the best quality shackles have a working load of far less than the working load of the chain or the anchor. You can buy proper anchor connectors (not necessarily swivels) which are torpedo shaped and have a rated load similar to the chain that they are designed to be used with. Last time I checked the figures for my 10mm chain, the shackle would have been rated for 800kg and the chain for 1500kg (or thereabouts, figures are from memory). Based on my research I bought a galvanised Plastimo connector for my galvanised anchor and chain. I have spent over 70 nights at anchor since and the connector shows no signs or rust or damage.

Edit:- Corrected spelling mistake
 
IMHO most unwise to use a stainless shackle in ground tackle. Lack of oxegon will cause rapid loss, and besides the SS shackles have a lower BS for given size compared to test galv items.
 
Each component - chain, anchor connector and anchor should be rated for a similar working and maximum load. There is no point in having a chain rated for, say, 3000kg and then fix the anchor with a connector with a breaking load of, say, 800kg! With a shackle, you need to be careful to mouse the pin to prevent it coming out in use but also inspect the pin carefully for wear - shackles tend to be quite sloppy where they connect to the anchor whereas an anchor connector makes a snug fit.

The reason why you shouldn't mix different metal types is that dissimilar metals corrode when placed together in sea water. However, if only used occasionally stainless isn't a major problem with galvanised. Nevertheless, why use a stainless (or any other kind of shackle) when you can fit a purpose-designed anchor connector? They are widely available in all chandleries and they are not terribly expensive - £10 to £15, ISTR. Anchor connectors are available in stainless and galvanised from Plastimo (i.e. available from every chandlery and online sources throughout Europe).
 
Was there not a warning on a previous thread about using anchor connectors - or was that in relation to chain connectors?
 
Be aware of course that anchor chain size is usually chosen for weight rather than strength. The shackle is usually chosen as the biggest that will suit the chain and anchor. I seriously doubt a lower max load shackle would ever give way compared to the holding power of the anchor it self.
With anchors we are more concerned about cosmetics as it sits on the bow rather than with moorings where no one cares what it looks like but just it's longevity. I suggest that a stainless steel chain, shackle and anchor, if you can afford it would be good for the occasional use it is actually in the water.
ie failure of SS is only likely with long term emersion. or so it seems to me. olewill
 
[ QUOTE ]
Be aware of course that anchor chain size is usually chosen for weight rather than strength. The shackle is usually chosen as the biggest that will suit the chain and anchor. I seriously doubt a lower max load shackle would ever give way compared to the holding power of the anchor it self.

[/ QUOTE ]From the Plastimo website, typical shackles of a size that would suit a 10mm chain had a rated working load of 340kg. An anchor connector for 10mm chain has a safe working load of 3000kg. To try to put this into perspective, 10mm three-strand nylon has a breaking strain of 2200kg. 8mm galvanised chain has a bs of 3200kg and 10mm chain has a bs of 5000 kg. While we are on the subject (and on the Plastimo website) a 10mm anchor chain joining device has a swl of only 200kg!

As for the actual forces to be expected, Nigel Calder says that for a 40 foot yacht the design load should be 1090kg at 42kt wind, and 2180kg at 60kt. Clearly, ordinary shackles are nowhere near strong enough for safety.

Will, I cannot see why there is such resistance against using the part for the job. The anchor connector (preferably without swivel, IMO) is designed for the job and is far stronger than any shackle. It isn't particularly expensive, either. If the anchor fails it can easily lead to the total loss of the vessel and loss of life. Why penny-pinch on such a vital component?
 
I think you will find most 'galv' shackles sold are made in China. There is more than one 'brand name' buying them from the same factory I do. Most Chinese 'hot dip galv' is actually washed zinc plating hence the rust issue. These shackles are weaker than most chains size for size. A 10mm chinese common shackle breaks just below a Grade 30 8mm chain (not chinese made chain). Always put the biggest shackle that will fit on.

Stainless Steel shackles are fine on a anchor system where it goes in and out of the water NOT on a mooring system where it is permently immersed. Contrary to general comments it is easy to get stainless shackles that are stronger than lower grade steels i.e a Grade 30 (the common stuff) chain for example.

Tested Hi-load shackles (green pin, blue pin and most of the rainbow coloured pins) are a lot stronger than the common ones. Higher tensile steels tend to be a bit more brittle than lower grades and don't like shock loads so don't be smart and cut the size down. They are good to use but still fit the biggest possible.

Anchor connecters rock and also look cute.

Swivels are fine and a good safety measure in a few cases as long as it is a well made fitting. 1/2 the boats I see with swivels on don't need them.

Mind you.
What if the weather is so bad all hell is breaking lose to the point something has to break. In extreme stuff I'm talking when are about to bust.

The choices:
1, Lump of deck pulls out under the Winch/bollard. Possible big hole in deck, anchor system gone.
2, Winch/bollard tears out of the deck. Smaller hole in deck, anchor system gone.
3, Anchor tears to bit (as it was stuck in a rock). Bye bye anchor. Could dive to pick up bits later. Chain drags along sea bed.
4, Chain/anchor connection breaks. Bye bye anchor. could dive and pick up later. Chain drags along seabed.
5, Chain breaks. Bye bye anchor. could dive and pick up later.

Which would you choose?
 
Not Cadmium. Poisonous and rarely used these days. PZP Passivated Zinc Plate.
About as much use as chocolate coating. Always buy hot dip galvanised and replace if rust sets in.
 
Totally agree. A load tested shackle is preferable cos you know what it will do. With all the Chinkie crap on he market beware of swivels of unknown origin. When I was working in shipbuilding I tested some. The ones that didn't break are now on my boat! The big problem with shackles though is they won't pass through the stemhead fitting and having a cat that sails around its anchor all the time I like a swively one...... Cutting the tab off and belting shite out of the thread end just ensures you can never get it undone again and it will rust immediately it hits water...
 
[ QUOTE ]
Which would you choose?

[/ QUOTE ]There is NO acceptable point of failure - failure is life-threatening. All parts of the anchoring system should be spec'd for an expected max and working load, and that includes the rating on the samson post, or whatever strong point designated. Incidentally, windlasses are not generally spec'd for load-bearing and in severe conditions it is usual to spread the load across several cleats or strong points to prevent failure of the deck structure.
 
Given the circumstances that GMac describes (forces of nature way in excess of intended design capability of equipment), designing in a mode of failure that will itself cause least damage is a sound engineering principle.

You may not want any part of your ground tackle to fail, but if things get so bad that something has to give, surely it's better if the failure is predictable - ie the anchor is left intact on the sea bed and the vessel drifts off dragging the chain. If on board at least you have a chance to get her under command and navigate to safety. If no-one is on board, it is lap of Gods but she might just be salvaged undamaged from somewhere. On the other hand, if the failure tears out a great chunk of samson post & foredeck for example, she will probably take on water and go down.

The same principle applies in many other areas of life - specially designed crumple zones on cars, fuses on electrical kit, safety valves on pressure vessels etc, etc. All these things are designed to "fail" at below the ultimate capability of the rest of the kit to protect the more important bits. So I'm with GMac - it's a very good idea to have an anchor connector which is (slightly) weaker than the rest of the tackle.
 
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