Anchor Chain and Rope Size Guide
Selection Process for determining the right size for your Main Anchor Chain and Rope
- What Size Anchor Chain do I need ?
- What Size Anchor Rope is compatible with my chain ?
- How much Anchor Chain do I need ?
- How much Anchor Rope do I need ?
Select your Anchor Chain and compatible Anchor Rope size
- Find the column in the table below that best represents your Boat Length Overall.
- Compare your displacement with the tonnage listed.
- If the displacement is greater than displayed in your column in the table, or the yacht is a multihull, consider moving across to the next column to increase the diameter.
- Consider the worst-case scenario for your anticipated Anchoring - this will dictate whether you go for the minimum required or the 'belt and braces' approach
- Select your Anchor Chain size first. The guide indicates the compatible rope diameter.
|Yacht Length Overall||< 6 metres||6 - 8 metres||8 - 10 metres||10 - 12 metres||12 - 14 metres||14 - 16 metres||16 - 18 metres||18 - 20 metres|
|Aproximate length in feet||< 20 feet||20 - 26 feet||26 - 33 feet||33 - 40 feet||40 - 46 feet||46 - 53 feet||53 - 60 feet||60 - 66 feet|
|Displacement in Tonnes||1 tonnes||2.5 tonnes||5 tonnes||9 tonnes||13 tonnes||16 tonnes||20 tonnes||25 tonnes|
N.B. This table is a guide with columns based on:
- Top Quality LIROS Rope
- LIROS recommendation
- Jimmy Green experience and customer feedback
- Top Quality Grade 40 Anchor Chain
Anchor Chain Size Rule of Thumb
There is an old rule of thumb that dates back many years which states a requirement of 1/8" chain diameter for every 9 or 10 feet of boat length - with approximate metric conversions:
e.g. 1/4" now available as 6mm DIN766 chain would be up to 20 or 23 feet Yacht LOA, 7mm DIN766 chain would be up to 23 or 27 feet, 5/16" now available as 8mm DIN766 would be up to 27 or 31 feet Yacht LOA, 3/8" now available as 10mm DIN766 and 10mm ISO would be up to 34 or 39 feet Yacht LOA.
5/16" US Specification (8.7mm) chain is also available from Jimmy Green Marine and the rule of thumb would be up to 29 or 34 feet LOA
This rule of thumb isn't far removed from the Jimmy Green Anchor Chain Size Guide but it is probably based on Grade 30 chain because Grade 40 is a relatively recent advance for yachting anchor chain.
Although modern yachts are generally designed and built with lighter state of the art materials, they are quite often kitted out with a lot more equipment to add the weight back on and the current trend is towards bigger anchors with much higher holding power which will inevitably lead to higher loads on the anchor rode.
Grade 40 Calibrated Anchor Chain is 25%+ stronger than Grade 30 Anchor Chain providing extra assurance when conditions worsen and your yacht is caught on a lee shore.
An Anchor Rode comprises all parts of your anchoring system - anchor chain, anchor rope and all the connections.
Decision Making Factors for sizing your Anchor Chain and Anchor Warp:
- Displacement to Length ratio i.e. is your yacht relatively light or heavy for her length?
- Monohull or Multihull - catamarans may be subject to greater anchoring stresses and strains
- Anticipated anchoring conditions e.g. depth, seabed holding characteristics, the length of fetch and degree of exposure to prevailing winds.
- Your overall assessment of the risks involved (worst case scenario).
- Weight and design of your bower (main anchor) and also the specification of your secondary anchoring system.
An Anchoring System includes every part of the anchor rode from the anchor to the bitter end: anchor, chain, warp and all the individual means of joining it all together e.g. connectors; swivels; shackles; splicing.
All the individual parts need to be comparable in strength. The Anchor System is only as strong as the weakest link.
The increased holding power of modern anchors means that all the joining elements are subjected to higher loads than ever before.
Rope diameters compatible with Calibrated Anchor Chain:
Compatibility rests on two main factors:
- Break Load Comparison
- Physical limitations of the Rope to Chain Splice i.e. the largest rope that will splice into the chain links, sit comfortably and articulate satisfactorily
6mm Grade 40 Chain c 2300kg MBL Compatible = 10mm Anchorplait Nylon, LIROS MBL 2400kg
7mm Grade 40 Chain c 3100kg MBL ~ Downsize = 10mm Anchorplait Nylon, LIROS MBL 2400kg or Compatible = 12mm Anchorplait Nylon, LIROS MBL 3300kg
8mm Grade 40 Chain c 4000-4400kg MBL ~ Compatible = 14mm Anchorplait Nylon, LIROS MBL 4400kg or Largest Possible for satisfactory splicing = 16mm Anchorplait Nylon, LIROS MBL 5600kg
10mm Grade 40 Chain c 6400-7200kg MBL ~ Slight Downsize = 16mm Anchorplait Nylon LIROS MBL 5600kg or Compatible = 18mm Anchorplait Nylon, LIROS MBL 7000kg
12mm Grade 40 Chain c 9100-9700kg MBL ~ Slight Downsize = 20mm Anchorplait Nylon LIROS MBL 8400kg or Upsize = 24mm Anchorplait Nylon, LIROS MBL 11800kg
If you are upgrading to Grade 70 AQUA7 Anchor Chain then the optimum solution is all chain because the largest possible rope diameter that is physically splice-able to the chain won't have the same break load capability. Yacht owners frequently ask the Jimmy Green Rigging Team to splice 16mm Anchorplait Nylon into 8mm Grade 70 DIN766 Calibrated Anchor Chain. We are happy to do so on request but the finished splice in 16mm is on the limit of articulation and the splice will need regular close inspection.
N.B. LIROS 3 Strand Nylon has the exactly the same break load characteristics and splicing limits as Anchorplait so compatibility will be exactly as described above. Anchorplait is more expensive but has valuable additional benefits: Flexibility, balanced Octoplait construction, behaves and flakes like chain, by far the best anchor rope for self-stowing naturally in the chain locker and emerging free of tangles and kinks when re-deployed.
How much Anchor Chain and Rope do I need ?
The generally accepted guide for the length of your anchor rode – An Anchor Rode encompasses Chain, Rope and the all the shackles and connectors – is 8 metres of rode for every metre of depth you will be anchoring in. This is referred to as the scope, in this case 8:1.
This works for the middle range of anchorage depths but starts to look a little out of kilter as you approach either end of the scale e.g.
- 8:1 in 3 meters of water equates to 24 metres total rode length which is possibly not a satisfactory anchoring solution in anything but benign weather
- 8:1 in 5 metres of water equates to 40 metres total rode length which may be adequate for Inshore and Coastal hopping
- 8:1 in 20 metres of water would be 160 metres of total anchor rode which would seem a little bit over the top !
However, Scope 8:1 for 10 metres of depth = 80 metres total chain and warp and this makes a good benchmark starting point for your final decision.
For long distance Offshore and Ocean cruising you may want to consider increasing the scope to 10:1 on all chain or even 12:1 on a chain/rope combination. This particularly applies to anchorages around some Pacific islands.
Budget and weight carried forward in the bow (chain locker) are the natural restraints on your final decision regarding the total length of chain and warp.
Your anchor rode is your primary safeguard when anchoring overnight in a foreign anchorage so aim for the longest and best affordable option, bearing in mind the detrimental effect of your yacht’s performance if you overload the bow with too much weight.
- All Chain : CALIBRATED ANCHOR CHAIN
- Rope / Chain Combination : ANCHOR WARPS SPLICED TO CHAIN
- Rope with additional separate chain : ANCHOR WARPS CALIBRATED ANCHOR CHAIN
Do I need Anchor Chain, Anchor Rope or a combination of Both ?
For those blessed with an adequate windlass, all chain is the popular choice, limited only by your budget, the size of the chain locker and the disadvantage of too much weight in the bow when under way.
50 metres used to be the norm, but 80-120 metres is much more prevalent in this day and age.
Where weight is a limiting factor, a balanced chain/warp combination is a very good solution e.g. 50 metres of chain spliced to 50 metres of rope. The balance can be adjusted proportionally but shouldn’t feature less than 30 metres of chain. The rope component should be as strong as the chain and as stretchy as possible to absorb the shock loads endured in big seas. The maximum diameter of the rope is generally restricted by the rope to chain splice.
For anchor retrieval with no power or mechanical advantage, a disproportionate warp/chain combination may be advisable with regard to retrieving the anchor, chain and warp by hand - Consider a long length of stretchy warp with a relatively short piece of chain to ground the anchor and negate the abrasive effects of the seabed e.g. anything from 50 up to 100 metres spliced to 5 or 10 metres of chain. Consider increasing the chain length and reducing the rope length if you or your crew are physically able to mange the extra weight.
The overall length of your rode, whether all chain or a combination should reflect the depth and type of anchorages you will encounter, and the degree of risk associated with your anchoring intentions i.e. your reliance on ground tackle as a primary yacht safety factor.
An anchor rode comprising all chain with no additional rope will require a snubbing strop or bridle.
This will help prevent the anchor chain from coming up short with a jolt which may have worrying results:
- Jerking the anchor from the set position in the seabed.
- Delivering a damaging shock load to the chain and/or the deck strongpoint fitting to which the chain is attached if the anchor doesn’t budge.
A combination Chain/Rope Anchor Rode may prove to be the optimum arrangement
The scope of the chain should still be more than adequate for anticipated anchorage depths and weather conditions.
The extra length of the rope extension will not only increase the scope, but also provide valuable shock absorbing capability if conditions seriously worsen.
A second (kedge) anchoring system is generally recommended in addition to the full specification primary (bower) system.
The specification can vary widely according to cruising intentions - from a full specification second storm anchoring system to a traditional Kedge e.g. lunch hook or stern anchor.
Different anchors have varying degrees of holding power according to the seabed, so the option of a geometrically different anchor may be advantageous if the primary system is not holding.
Traditionally, a second anchor system has less chain, more rope and a lighter stowable anchor - making the whole system physically easier to store on board and deploy when required.
Jimmy Green Marine offer a comprehensive range of solutions from leading brands for all your anchor rode requirements.
The Jimmy Green Rigging Sales Team are on hand to help you with your selection process.