Anchor Chain Selection, Regalvanising

and a case of Caveat Emptor 

 A suggested article for the Blue Water Bulletin writen by Jim Putt of Morning Tide

FINAL DRAFT

 In 1983 we decided to change to an all chain anchor rode;  the then Marine and Harbours issued a leaflet recommending 9.5mm chain diameter for a 10.5metre vessel. Though not stated I believe this referred to the standard low tensile strength chain, type “L.”

There are a number of factors influencing the choice of link size and length of anchor chain. Vessel displacement, freeboard, under water profile and above deck clutter being the most important. Other considerations are, depth of water likely to be encountered when anchoring and the nature of the bottom, sand, coral, bombies.  On the assumption that peace of mind is important the following factors should be kept in mind. A scope of 5:1 is preferable in an open anchorage.  In tidal waters, the range can reach as much as 10metres. Under these conditions a minimum of 60 metres of chain is desirable. Two anchors are of limited help if the first one barely reaches the bottom.

In the case of our yacht, the S&S 34 is fine in the bows and stern and weight distribution is all important. For a maximum chain weight of 100kg we had the choice of 70metres of 8mm high tensile hot-dip (HD) galvanised chain or 44metres of 10mm low tensile “L” HD galvanised chain.  Weight per metre is the same for high tensile and “L” chain, for any given chain diameter. We settled for 60 metres of high tensile chain on our primary CQR anchor and the balance of 10 metres on our secondary Bruce or Swarbrick anchors, augmented by 100metres of 16mm Marlow nylon multiplait. The multiplait also served for the drogue. This arrangement served us well. Continual use of the chain has meant regalvanising the 60m of primary chain. This has been done twice before, roughly every seven years.

Our primary chain is now in need of regalvanising. Before embarking on this process it seemed reasonable to ask the question, “how often can you regalvanise chain?” Since the galvanising process involves heat treatment, the thought occurred that this process could further anneal the chain. A quick telephone call to a local chain agency informed me that each heat treatment process could reduce the chain strength by 25%. This was alarming to say the least. So I continued to ask around and received a variety of differing answers.  I then started to correspond with chain and wire rope manufacturers. I also found 12metres of original chain left over from the initial purchase.  It turned out to be quite difficult to find the answer to what seemed a straightforward question. Finally I received an offer from Bullivants to carry out a destructive test on the chain. So, armed with two samples of HT galvanised chain, both samples from the initial purchase, one sample having seen active service, I set off to find the answer.  

The first 2metre sample tested was the “in service” chain from our anchor locker, it failed at 5.8 Tonnes.

The second 2metre sample was the “unused” chain found in our garage, it failed at ……   …5.3 Tonnes.

This gives a safety factor of four when compared with the recommended working load limit of 1.2Tonnes

Both samples failed at the point of attachment to the test gear, this may explain why the unused chain failed at a lower figure.

What conclusion can be drawn from these tests?

I now feel confident in taking our anchor chain for regalvanising. For the purest, I should mention that it is a requirement of AS 2321 that any regalvanising should only be carried out by the original chain manufacturer.

By using high tensile chain the factor of safety is twice that of Grade “L”(see table below) Alternatively, it is possible to carry a more useful length of chain without the penalty of additional weight.

Note: A scope of 5:1 is our preferred option. The catenary adopted by the smaller (lighter) diameter chain will be less (flatter) than that by the larger (heavier) diameter chain. 

 Before purchasing chain, ensure the chain has been manufactured to AS 2321-2001.  Some imported chain may not comply.

Chain is often sold as “proof tested.” Ensure that the proof test complies with AS 2321.

Australian chain manufactured to AS 2321 is required to be stamped every metre or 20 links   indicating the manufacturer and grade of chain. Typically, PWB-L for standard low tensile chain and PWB-P for high tensile chain. If the chain is not stamped it is reasonable to assume the chain may not comply with AS 2321.

Swivels and shackles should similarly comply. AS 2318 and AS 2741 respectively

On a previous occasion when I have seen anchor chain taken to its limit, it was the anchor winch that failed before the chain yielded.

Check what you have ordered is what you have received.

As a final twist to this saga we were able to identify the grade of chain we had purchased. Yes, it was high tensile chain but of the type supplied to “truckies” for tying down loads and not specifically recommended for anchoring! 

Comparison of chain strength: as supplied by PWB.

Grade L chain (low tensile strength)

8mm    WLL 0.64 Tonnes

10mm  WLL 1.00 Tonnes.

                Grade P chain (high tensile strength)

                8mm    WLL  1.28 Tonnes

                10mm  WLL  2.00 Tonnes.

The Working Load Limit (WLL) for grade L and grade P is the maximum mass which the chain hanging vertically shall support in general service. (heaven forbid)

I would like to acknowledge the help given to me by Bullivants, they carried out the tensile tests without charge and to PWB Anchor.

Jim Putt.  S/V “Morning Tide”  10^th June ‘04