By Tom Burden
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 rode for a lunch hook or spare anchor, however, an all-nylon rode functions quite well.
Combination Rodes: A good compromise between all nylon or all-chain rode is to use 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, and the weight of the chain is pretty ineffective in keeping the pull on the anchor horizontal; 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. Long scope (7:1) must be used to compensate for the lack of weight to keep the pull horizontal. Nylon is preferred for its elasticity. Its stretch reduces peak loads on the anchor and on your boat.
Rope-to-chain spliced rodes: One drawback of the normal combination rode with nylon and galvanized chain is the interface between them consisting of a shackle and a galvanized thimble. While long-lasting, this connection is bulky and adds a shackle to the system which could possibly fail or lose its pin. Therefore, many boaters splice their nylon line directly to the last link of chain, a technique originally developed for self-tailing windlasses (see The West Advisor on Windlasses for more information). This produces a very sleek rode which stows easily, passes through a chain pipe more easily than a splice/thimble, and which retains about 90% of the breaking strength of the line compared to new line.
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 to 600lb. in the bow and can adversely affect the performance of your boat. Owners of modern, lightweight cruising boats are probably unwilling to suffer the reduced speed and increased pitching caused by this extra weight.
A logical compromise: Because we feel strongly that a decent length of chain is critical for effective anchoring, and because we also like boats that perform well, we offer the following suggestion: Use 60'-100' of high-test chain spliced to 250' of 3-strand nylon line.This combination provides sufficient chain to ward off bottom abrasion, and in shallow anchorages, you may not even need to pay out nylon. It is reasonably light (as little as 65 lb.) and tremendously strong.
High Test: Grade 43, called G4 or HT; made from high-carbon steel. G4 is the preferred chain for anchoring or windlass applications, and has twice the working load of BBB chain, so you can use a smaller size with the same strength.
Proof Coil and BBB: Grade 30; made from low-carbon steel. BBB or "Triple B" has a uniform pitch short link, and works well on windlass gypsies. BBB used to be the most popular type for windlass designs of the past, but has been replaced by G4. Proof Coil does not have a uniform pitch and does not work with anchor windlasses.
Grade 70: called G7 or Transport Chain; extremely high strength-to-weight ratio, is substantially stronger than G4 High Test, and resists wear because of its exceptional hardness properties. Compatible with very few windlasses, but recommended by some noted cruising authorities.
Every anchor windlass is equipped with a gypsy, the wheel or capstan on the winch that hauls the rope and/or chain up and down. Each gypsy fits one or more diameters of line (of three-strand, twelve-strand or eight-strand construction) and specific types and diameters of chain (like 1/2 Grade 43, 5/16" BBB or 3/8" Grade 70, for example). The gypsy and rode must be an exact match, and most windlasses are available with a choice of gypsies to fit some different line and chain types. Check for compatibility before buying your windlass or rode. Note: Maxwell RC and HRC Series windlasses include a Wave Design chainwheel compatible with all types of marine chain.
The classic rule is to use seven times the sum of the water depth plus the boat's freeboard. Many boaters will use a scope of more like five times, and will compensate with more chain or more vigilance.
The simplest anchor rode involves connecting the anchor directly to a spliced nylon anchor line. An example uses a West Marine 8lb. Traditional Anchor, a 1/4" shackle, and a 3/8" x 150' New England Ropes anchor line. This is great for day use with a small boat. It's lightweight, inexpensive, and will hold well as long as the scope is sufficient.
To make this anchor package even more effective, you can add a short length of chain between the anchor and the line. The classic rule is to add a boat length of chain, which does two things: it protects the nylon line from chafe caused by seabed rocks and debris, and the chain's weight keeps the angle of pull on the anchor parallel to the bottom. But even a short length, like coated ACCO chain, will make a big improvement in anchor performance and the longevity of the system.
Small galvanized shackles connect the anchor to the length of chain, and attach the chain to the thimble on the anchor line. Remember to use the "next size up" in shackles; a length of 1/4" chain would be matched to a 5/16" shackle. This system, with a long length of three-strand nylon line, a moderate length of chain and a properly sized anchor will satisfy the needs of the majority of boaters, with boats up to the 30' size range.
If you own a boat over 40' of length and cruise to lots of different anchorages with a variety of seabed types, you should consider an all-chain anchor rode. There's nothing like the feeling of security provided by the strength and abrasion resistance of chain for open-water and heavy-weather anchorages.
The negative side of chain is its weight. Since boats require 200' or more of chain for an all-chain rode, and since chain is very heavy, all that chain adds up to a bunch of weight in the bow of a boat. That's why many boaters (and especially sailboat owners with big and lightweight boats) choose higher-strength Grade 43 or Grade 70 chain. These save about 30% of the weight since you can "go down a size" in chain, yet achieve the same working load and ultimate strength.
Matching anchor chain to a specific vessel can be challenging, since the windage of the vessel is probably the key selection factor, and windage is hard to determine. You might want to consult a naval architect or marine surveyor for advice on how to size ground tackle on boats over 60' or so. The West Marine Master Catalog and West Advisor articles have suggestions on how to size this gear on boats up to about 60' or 70'.
Determining the length of anchor chain is based on the maximum water depth and the freeboard of the vessel, but since chain is so heavy, generally you can plan on using 4:1 scope. And, due to the weight of the chain, you actually need less scope as the water depth increases. Many boats will use 200-250' of chain. Others may use 200' of chain and then bend on another 300' of line for extremely deep anchorages. Regardless of whether you use nylon rode, it's extremely important that boats with chain rode have some nylon at the bitter end so that the anchor rode can be cut in an emergency.
When recommending anchor rodes for our customers, we generally use the following guidelines:
In general the load on an anchor line varies with the square of the LOA of the boat. A high windage, heavy displacement boat such as a trawler or fishing boat will require heavier anchor rode than an ultra-light racing sailboat of the same LOA. 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.
|Light Boat||Medium Boat||Heavy Boat||3-Strand Nylon Diameter||Chain Diameter|
|41'-45'||37'-40'||33'-36'||9/16"||5/16" PC/BBB or 1/4" HT|
|51'-60'||46'-54'||41'-48'||3/4"||3/8" PC/BBB or 5/16" HT|
|61'-70'||55'-63'||49'-56'||7/8"||1/2" PC or 3/8" HT|
|71'-80'||64'-72'||57'-64'||1"||5/8" PC or 1/2" HT|
In inland, coastal, and performance cruising applications, boaters should use a combination of nylon line and galvanized chain. For serious cruisers, all-chain rode may be a better solution. The trade-off is one of weight vs. abrasion resistance.