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Anchor Rodes
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What to look for
Not surprisingly, no one rode does the job for all boats. Each anchor rode is a combination of characteristics that must be chosen for a given type of boating.
Rode Types
All-Nylon Rodes: Small boats often use anchor rodes made entirely of three-strand nylon because
they are lightweight, inexpensive and, for boats without a windlass or anchor well, easier to stow than rodes with chain.
Although all-nylon anchor rodes can be quite strong, they lack the chafe resistance of rodes with chain and are therefore
not appropriate for extended use or for use in rough weather. As the primary rode for a lunch hook or spare anchor, however,
an all-nylon rode functions quite well.
All-Chain Rodes: Larger boats with windlasses generally use all-chain rode. This reduces the need for
long scope (except in shallow water) because the chain is heavy and lies on the bottom until severe conditions are encountered, when
more scope may be required. Since chain has very little elasticity, care should be taken to prevent the chain from becoming "bar tight"
in high winds by using a snubber made of nylon line. The drawbacks to all-chain rode are weight, expense, and the need for a windlass.
A windlass and all-chain rode may add 300-600 lb. in the bow and can adversely affect the performance of your boat. Owners of modern,
lightweight cruising boats probably are probably unwilling to suffer reduced speed and increased pitching caused by this extra weight.
Mixed Rodes: A good compromise between all-nylon or all-chain rode is a
short length of chain (6'-30') connected to the anchor, with a long length of three-strand nylon line
connected to the chain. This combination satisfies nearly all requirements of a good anchor rode,
except that it is not abrasion resistant over its entire length. Long scope must be used to keep the
pull on the anchor shank horizontal. Nylon is preferred for its elasticity. Its stretch reduces peak
loads on the anchor and on your boat. One myth we'd like to dispel is that a boat length of chain will
keep the pull on an anchor shank parallel to the bottom. Even a 15-knot wind will lift short lengths
of chain off the bottom. The primary function of chain is to handle the chafe from rough bottoms that
would otherwise abrade the soft nylon line.
Rode Sizes and Lengths
Scope is defined as the ratio of water depth (plus freeboard) to anchor
line paid out. Most anchoring texts and anchor manufacturers agree that a scope of 7:1 achieves
the anchor's designed holding power, and more scope is better than less. In theory, 7:1 scope
is great, but at a crowded anchorage most cruisers scoff at the idea of paying out more than
3:1 or 4:1-there just isn't much space for boats to swing. Any reduction in scope, of course,
must be made up for by using larger anchors and/or larger chain.
As a general guide, for winds up to 30 knots, we recommend the following anchor line and
chain diameters, using three-strand, high quality line. This table assumes an 8:1 working load
ratio.
Boat LOA : |
3 Strand : |
Chain : |
|
Up to 25' |
3/8" |
3/16" PC |
27'-31' |
7/16" |
1/4" PC |
32'-36' |
1/2" |
1/4" PC |
37'-44' |
9/16" |
5/16" PC/BBB |
45'-50' |
5/8" |
5/16" PC/BBB |
51'-62' |
3/4" |
3/8" PC/BBB |
63'-76' |
7/8" |
3/8" HT |
77'-90' |
1" |
1/2" HT |
Conclusion
In inland, coastal, and performance cruising applications, boaters should use a combination of nylon line and galvanized chain.
For serious cruisers, all-chain rode is a better solution. The trade-off is one of weight vs. abrasion
resistance.
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