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Anchor Sizing

Anchor Sizing

Anchor sizing should always be interpreted as a guide only. Many factors influence anchor size selection (e.g., the boat displacement and windage). Also the chain size, weight and length is critical to anchor performance. Finally the vessel usage should also be taken into account. A vessel used for extended coastal and offshore cruising will have different demands on the ground tackle than a vessel used only for fair weather day trips. If in any doubt about anchor, the bigger anchor should be chosen. In bad weather or motoring failure, it will be the only thing that can be relied on to save the vessel and the crew.
Seasoned sailors will choose a larger size of anchor, including shackles, swivels, chain, and anchor windlasses than is recommended for the size of the boat, particularly if the boat has high windage or 'sails' at anchor. But keep in mind that you may have to pull the anchor up by hand before going too far for your everyday anchor. Marine stores and manufacturers have reference tables to help choose a size, usually based on boat length, displacement, or free board. A Bruce (M anchor), a CQR, or a Delta that is oversized for your boat will also be effective as a storm anchor.

The anchor-rode sizes given below assume winds up to force 7 for working anchors and force 9 for storm anchors, some protection from sea, fail holding ground and operation at an adequate scope to assure full holding capacity of the anchor. The anchor rode should have sufficient energy absorption capacity to minimize snatch loading on the anchor and boat fittings. If a nylon rope is used, it is recommended that chain of the diameter and minimum length tabulated above be included between rope and anchor to resist chafing on the seabed.
In rough weather, minimum recommended scope is 5 for an all-chain rode, 7 for a combination of chain and rope and 10 for an all-rope rode. It is recommended that zinc coated Grade 30 or zinc coated Proof Coil chain be used with load rated high-quality zinc coated shackles. These shackles exceed the strength of the chain while having pin diameters small enough to pass through the extremity links of the chain.

Bruce Anchor

Yacht Dimensions Anchor Weight Rode Anchor Shackle
Length Beam Storm Working Nylon Dia. Chain Dia. Min. Lenth Pin Dia. Body Dia.
ft m m kg kg mm mm m mm mm
32 10 3.5 10 6 14 8 6 10 8
39 12 3.8 15 8 16 10 8 11 10
46 14 4.2 20 10 16 10 8 11 10
53 16 4.8 30 15 20 12 8 15 13

Bügel Anchor

Yacht Displacement Anchor Weight
7.0 t 16 kg
8.4 t 18 kg
10.0 t 20 kg
16.0 t 25 kg
23.0 t 30 kg

Anchor System for 40-ft Yacht

For burying anchors of the "high holding power" type (Bow, CQR, Bruce, Danforth, ...), the rule of the thumb for the recommended anchor weight is:

  Anchor_Weight [kg] = 2 * LOA [m] 
From this the following anchor system may be considered for a 40-ft yacht (40 ft = 12 m):
  • Working Anchor: 25 kg Galvanised Steel Bügel-Anchor (or alternatively 25 kg Rocna) on 75 m of 10-mm chain
  • Secondary Anchor: 12 kg Aluminium Spade Anchor (A100) on 12 m of 10-mm chain and 80 m of 18-mm nylon
  • Storm Anchor: 25 kg Galvanised Steel Spade Anchor (S120) on 30 m of 10-mm chain and 100 m of 25-mm nylon

To handle these heavy anchors a large and powerful windlass (1500W) is required. Carrying around the weight of the windlass and two heavy anchors a the bow increases the yacht's pitching motion in a choppy sea. Anchors on small vessels are always a compromise and the additional weight at the bow may be reduced by stowing the anchor and rode at a more central position while sailing off-shore. In any case the storage for anchor and chain must be "roll-over secure"!

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