It’s important to note that there are a variety of different anchor types with each anchor having a different set of characteristics best suited to different seabeds. Each anchor design has certain dimensions specified. Each anchor and the chain and/or line attached to it is then specified dependent on the LOA of the vessel (Length Overall) and / or the vessel’s Thames Tonnage.
It’s important that the correct warp, chain and anchor type and size are selected and, if cruising, it’s quite possible that selecting a slightly over-engineered solution might just save your boat in challenging conditions.
The best publication we’ve come across for determining what sort of anchor, chain, warp and other control lines should be used on any specific yacht are set out in the extremely comprehensive, The Boat Data Book by Ian & Richard Nicolson.
In brief, it is sensible if the anchor warp (if you employ one) is made of nylon (polyamide) or polyester (Dacron or Terylene). These materials will stretch under load (which you want when moored or at anchor). Floating line such as polypropylene, should be avoided for anchor warp.
In simple terms, the following specifications are set in the Boat Data Book mentioned above.
|Yacht's LOA||Thames Tonnage||Anchor Rope with short chain||Anchor Weight (add 20% for Fisherman's style anchor)|
|7.3 - 9 Metres||4 - 8 tons||55 metres of 13mm 3-strand plus 5 metres of 8mm chain||
1 x 23KG plus
1 x 10 KG
|9 - 11 Metres||8 - 12 tons||70 metres of 16 mm 3 - strand plus 7 metres of 11 mm chain||
1 x 27 KG plus
1 x 16 KG
|11 - 13.5 Metres||12 - 18 tons||90 metres of 16 mm 3 - strand plus 7 metres of 11 mm chain||
1 x 34 KG plus
1 x 20 KG
|13.5 - 16.5 Metres||18 - 30 tons||120 metres of 19mm 3 - strand plus 7 metres of 13 mm chain||
1 x 50 KG plus
1 x 25 KG
Chain sizes can be calculated. However, as a rule of thumb;
|Chain Size (mm)||Weight (per 30.5 metres)||Working Load Limit (KG)||Approx Storage Space for 20 metres|
|8 mm||48 KG||862 KG||0.01 Cubic metres|
|11 mm||98 KG||1,590 KG||0.021 Cubic metres|
|13 mm||122 KG||2,040 KG||0.03 Cubic metres|
A more robust engineering solution might be recommended for long term cruising. A lighter solution for inshore race boats. In all circumstances the Thames Tonnage should be calculated, not assumed, and consideration should be given to weight and safe stowage.