What is the issue?Investing in the correct rode and ground tackle is not straightforward. There are a large range of different anchors, rode and chain sizings.
Why address this?Implementing correct ground tackle is essential for the welfare of the vessel and crew. Sleeping serenely whilst at anchor is largely a measure of confidence in the ground tackle and the manner in which it has been deployed. I have spent many a dark night riding out a gale, and one full-blown hurricane, praying for the survival of the ground tackle that the vessel is dependant upon. Having some science to apply to the selection helps find the correct ground tackle and provides a measure of peace of mind when it is called upon.
How to address this?The below guide provides a guide for anchor and rode selection for a moderate displacement sailboat in an anchorage with good holding, to 40 knots of wind, gusting higher:
MCA (Maritime and Coastguard Agency) Code of Practice shown in italics.
* Short link galvanized chain made to EN 24565 (ISO 4565, BS 7160) and calibrated to DIN 766. This fits most new windlasses, but check with the supplier of the windlass.
** As above
*** This is three-strand nylon, three-strand polyester or Anchorplait
Some additional notes:
- • For a light displacement boat, go one boat size smaller, for a heavy displacement boat, go one larger.
- • It is advisable that the primary rode is all chain.
- • Rope rodes should have at least one boat length of chain.
- • Beware of cheap imitation CQR anchors.
- • A Danforth is a useful second anchor but not a primary anchor. Danforth’s own selection charts give recommended sizes for winds up to only 20 knots. Some manufacturer’s recommendations give a lower weight anchor than the Code of Practice.
- • American chain sizes do not directly convert into European chain sizes. Not only is the pitch different but in the USA the wire size of a chain link is actually 1/32” larger.
- • In severe weather conditions it is always advisable to deploy two anchors laid from the bow, 45° apart. Protect rope rodes with canvas, polyurethane or leather sleeves at wear points.
Tension on an anchor rode.
Another useful table is an anchor rode tension guide. Below is the estimated tension imposed on an anchor rode by various wind velocities acting on a 36’ (11 metre) cruising sloop with its sails furled:
- • 20 knots = 150 lbs or 70 kg of rode tension
- • 25 knots = 225 lbs or 100 kg of rode tension
- • 30 knots = 300 lbs or 140 kg of rode tension
- • 35 knots = 400 lbs or 180 kg of rode tension
- • 40 knots = 550 lbs or 250 kg of rode tension
- • 45 knots = 700 lbs or 310 kg of rode tension
- • 50 knots = 900 lbs or 400 kg of rode tension
- • 60 knots = 1200 lbs or 550kg of rode tension
The load on the anchor rode is substantially less than the safe working load of the chain or rope used to secure a boat of this size. For example, the safe working load of the 8mm chain recommended for a 36’ boat of this type is 800kg, with an ultimate breaking strain of around 3200kgs.
So, unless there is a “weak link” in the system such as a bad splice or deficient shackle, the factor which most effects security is the strength of the connection between anchor and seabed. In most cases, the ultimate strength of the anchoring system vastly exceeds the load at which the anchor will break out. Numerous anchor pull tests compare the break-out load for most of the popular anchor types. There is little consistency in these tests, sometimes one type of anchor wins, in another test that anchor might come out as the worst! The interesting thing is that the majority of the test results, and all the manufacturers’ data, credit the popular anchors with a greater break-out load than would be necessary to hold the boat in the circumstances of the selection chart. So, as long as the anchor is properly set, in the bottom for which it is suited, you can feel confident in ground tackle selected from the chart.
For more information Cox Engineering, a technical information resource for yacht owners, has tested the breaking points of a wide range of chains.
With thanks to:Salty John, specialising in a select collection of tried and tested sailing equipment. Web site: http://www.saltyjohn.co.uk/ phone +44 (0) 1995 672556 e-mail: email@example.com
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