It must be quite a few years since I needed to look at the galvanic table to show how metals which are ‘anodic’ or ‘less noble’ at the negative end of the series are more likely to be attacked
by corrosion.

For sailors the critical point is the difference in potential of the two materials being considered as a joined pair. A very small difference is likely to result in galvanic corrosion.

I am no physicist, and am open to correction by the sailor scientists, but I have been brought up to believe that stainless steel and aluminium and galvanised steel are too close
for comfort.  

The picture shows an aluminium anchor with a stainless swivel, and a stainless shackle (perhaps a bit undersize) made onto the galvanized chain. This was on a boat, raced quite regularly, and which was moored in a marina. The anchor was probably only used for kedging on a windless day during a race; but for a cruising yacht, one would need to think about arranging things so that the combination of metals did not encourage corrosion.  

When I checked this anchor over on joining the boat, I found the pin on the swivel had come completely adrift, and was lying on top of the chain and warp in the anchor locker. Charterers should always check over all safety equipment; the boat may have had a rapid turn-around and the gear may not have been properly checked.

There has been degradation of the swivels, and problems with the bolts on some anchor fittings. One owner claimed that the surface rust on his shackle helped to keep the pin in position; this may well be true, but is not a method to be relied on! I read of a sailor who pulled up his anchor one day, and discovered the socket head bolt through the anchor end of the swivel was out and only held by the last thread. Some get round this problem by superglueing the bolts in position, and some manufacturers do actually recommend this practice.

Top Tips

Another problem with these swivels is that the Allen key size is so small it usually twists before tightening the bolt sufficiently. I have always preferred a good sized shackle, set up so that it cannot work loose; remember that if you are not mousing a shackle – and I do recommend you should do so – that the pin can work loose if the jerking on your chain is in the wrong direction.     

To ensure you get this right, when you fasten the shackle pin in your ground tackle, hold the open shackle in your right hand with the open end away from you, and put the pin through from the left using your left hand. You should be able to see that any upward jerking of a pitching boat will tighten the shackle pin rather than loosen it. It goes without saying that the pin must be moused, and purists will mouse a galvanized shackle with galvanized wire and a stainless steel shackle with stainless wire.

For those of us who have been sailing for some time, the good old basic designs of CQR, Danforth, Fisherman’s, Bruce et al have now been supplemented with a number of new and well tested designs, some of which are a great improvement on older designs. If you are thinking of buying a new anchor, just be aware that some far eastern products may not deliver the service they are supposed to and anchors are not only sometimes badly bent but also lost when put to use.

As featured in the February 2012 edition of All At Sea