Q&A: Breaking Load Of Anchor Chain

Our latest thinking on chain starts with this chapter.

Question: Do you have views on breaking load of main anchor chain compared to weight of boat? Our new boat is 40’ long and weighs something like 12 metric tons (26,000lbs) and a ‘standard’ 10mm (about 3/8”) galvanized chain has a breaking load of approximately 6 tons.

Answer: Some thoughts that may help you choose chain:

  1. There is a lot of very poor chain around, made in the Far East, that should be avoided. In the USA and Canada we always recommend that people buy chain from Acco only. I’m not sure if this chain is available in Europe but I’m sure that there must be a good chain made in Europe. The key thing is that the manufacturer should have proofed (tested) every link and be willing to put that in writing.
  2. For a boat your size we would normally suggest 3/8″ (just a tad smaller than 10mm) chain if BBB type with a safe working load of 2650lbs (1202kg).
  3. We prefer to talk about safe working load (SWL), not breaking load, since chain repeatedly subjected to loads above its SWL will, in time, weaken and become unsafe. Generally, SWL is about 1/4 of breaking strength.
  4. Although BBB chain used to be the standard for anchoring, on Morgan’s Cloud we use, and are increasingly recommending, Acco G40 high tensile chain that is over twice as strong as BBB. For example, G40 3/8″ has a SWL of 5400lbs (2449kg).
  5. The challenge with using high tensile chain is that you must find high tensile shackles to get a strong enough shackle to match the chain. We use G209A from Crosby.
  6. There is an even stronger chain called G70, but here, to get the same strength in the shackles, you must order it with special oversized links at each end.
  7. On your boat, by using the right high tensile chain, I think you could go down one size to 5/16″ (8mm) and save a lot of weight that could then be put into a bigger anchor.
  8. Many people will tell you that you need much heavier chain than the sizes we are talking about here, but we feel that is not correct and that weight is better put into a larger anchor or more chain length. For example, Steve Dashew tells me that one of his Sundeer 64 boats went through the big hurricane in Grenada anchored on 3/8″ Acco G70 chain with winds of well over 100 knots and big seas.
  9. Also, although it is purely anecdotal information, I have never heard of a yacht’s chain rode breaking though we have all heard of boats being lost due to a dragging anchor. Keeping that in mind, I know where I want to put the weight.
  10. I do think it is important that a nylon snubber is used in extreme anchoring situations to relieve the chain and gear of shock loads.
  11. I think that the idea that the catenary caused by heavy chain has benefit is wrong since on Morgan’s Cloud in winds of gale force, even with all 100 meters of our 7/16″ (about 11mm) chain out, it pulls out straight. So at the very time you need it most, there is no catenary.
  12. When we next buy chain we might go down to 3/8″ G70 chain to save weight and carry an extra 30 meters. Our thinking is that once you have a good type of heavy anchor (we like SPADE), having plenty of rode length is the next biggest contributor to anchoring security. It also lets you get away from the bumper-cars games in some crowded anchorages, by allowing you to anchor in deeper water than most other boats can.
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John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

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