Anchor Cable Guide
The holding power when at anchor is due to the horizontal pull of the anchor cable along the sea bed, NOT just the Anchor itself. The holding power is greatly increased if the cable is all chain or a length of chain is positioned between the anchor and the nylon warp.
The following table is a Guide to chain and Warp cable sizes.
|ANCHOR CABLE GUIDE|
|Boat Length||Chain Size||Rope Size||Chain Size||Rope Size|
The figures quoted above are for rope supplied by South Wales Marine. Always check with the Manufacturers Technical Information, as there may be discrepencies due to the various rope construction and material used.
Scope of cable veered when at anchor depends on the depth of water. A rough guide is; A minimum of 3 x Depth of water at high water if anchoring with chain IN CALM WEATHER.
A minimum of 5 x Depth of water at high water when anchoring with rope IN CALM WEATHER.
If using a rope anchor warp, we recommend a short length of chain (at least 5 metres) between the anchor and rope to stop the rope chaffing on the seabed, and to give a little bit of horizonal pull along the bottom.
The rope should be nylon because it sinks and has a shock absorbing quality.
If using all chain, you should also have onboard a 10 metre length of nylon rope of appropriate diameter and strength, with a chain hook or chain shackle spliced into one end around a thimble eye. After anchoring this should be attached to the chain via the chain hook or chain shackle just outboard of the bow roller. The inboard end of the nylon rope should be attached to a strong point on the deck. Once the rope is secured on deck veer a couple more metres of chain so the weight comes onto the nylon rope. The purpose of all this is because if the weather picks up you don't want the boat yawing and snapping back on the anchor chain alone. This would cause dynamic loading on the fittings holding the chain e.g. windlass or cleats, which in turn could be ripped out of the deck. By introducing the short length of nylon into the system prevents shock loading due to the properties of the rope. Always remember to wrap rags around the rope where it passes over the bow roller or where it touches any edging. This is to prevent chaffing of the rope
If you have no other choice be to anchor in bad weather, or you are at anchor in rapidly deteriorating weather, you may have to veer up to 10 x the maximum depth of water, preferably of all chain, and lower a 'clump weight' down the chain (to get a more horizonal pull along the seabed). It has been found that you do not obtain any greater holding power if you veer more chain than 10 x the maximum depth of water. Therefore, as far as our knowledge and research goes, the two places in the World with the highest rise and fall of tides are the Bay of Fundy, and our good old Bristol Channel. So if your boat / Yacht can handle the weight of 140m of chain in it's bow, then this is what we recommend. If your Boat / Yacht can't handle this much weight in the bow then you will have to find a happy medium. But the more chain you can use the better.