Anchor Chain

The anchor chain is the basic component of the anchor rode which consists of a combination of the following parts:

• Anchor Chain: basic link between the anchor at the sea bottom and the vessel. Chain is desirable for it's durability, strength and weight. The weight of the chain aids the natural burying design of the anchor and helps to keep the departure angle of the chain at the anchor shaft low.

• Anchor Rope: a part of the anchor chain may be replaced by a strong nylon rope. This is easier to handle and due to it's elasticity, better suited to absorb shock loads while the the vessel is riding on the anchor or pitching and straightening out the chain. On the other hand an all-rope anchor rode is unsuited for rocky bottoms where it will be destroyed quickly due to chafe. Also an all-rope anchor rode requires more scope to prevent the anchor from braking out.

• Anchor Snubber Line: when using an all-chain anchor rode which - under strong gusty wind conditions - may be pulled straight tight, a nylon rope of 5 to 10 m shunting the upper part of the chain, should be used to absorb the tugging on the anchor chain. A chain hook is used to fix the snubber line to the anchor chain.

Anchor Chain vs. Anchor Rope

Anchors and anchor chain is always a compromise: on the anchorage anchor and chain should be as heavy as possible whereas under sails, they should be light as well as easy to store and handle. In this scope, also the discussion on how to optimize an anchor rod system must be seen. The result will always be a compromise between optimal functionality and optimal handling.

Advantages of anchor chain

Anchor chain is supple, abrasion resistant, strong, and relatively inexpensive, and therefore it is used in almost all anchoring and mooring systems. It has a number of properties that make it handy in boating applications:

• Chain is flexible, like line or wire, so it can be stored compactly and it conforms to contours. It rolls smoothly over the gypsy of a windlass and self-stows in the chain locker.

• It is relatively strong, so it can withstand lots of tension before breaking. It has a long life and can be rejuvenated with a trip to the galvanizing plant.

• Chain is highly abrasion resistant and much more resistant to chafe than nylon.

• Chain is heavy, which helps anchor holding power by pulling the anchors parallel to the bottom. Its weight aids the natural burying design of the anchor. Chain can be used with a shorter scope than required for nylon. Also the weight results in a favourable caternary curve of the chain between vessel and anchor and so acts as a natural shock absorber to smoothen out the pull on the anchor in heavy weather. This advantage becomes a disadvantage if the chain is pulled straight, so bigger chain is desirable not so much for its higher strength as for its additional weight to keep this curve from straightening out.

But anchor chain also some disadvantages which are mainly related to weight and handling:

• Chain is heavy. 100 meter of standard galvanized chain weighs about 250 kg. Add that weight to the 20 to 30 kg of anchor hanging on the bow, plus the required electric windlass, and the total becomes nearly 350 kg. Multihull sailors are acutely aware of this weight. But, as cruising monohull design evolves toward better performing sailing shapes, and as more sailors set off voyaging in fin-keelers with moderate to light displacements, the weight of all-chain in the bow begins to become an issue. The weight can, in fact, change the sailing characteristics and sea keeping abilities of a boat, promoting pitching in a seaway, nose-diving in heavy running conditions, and a mushy feeling on the helm.

• Chain is dirtier than nylon. After anchoring in a muddy bay or river, a chain rode will be clogged with ooze that needs to be hosed and brushed off to keep it from festering in the chain locker. Anchoring for a long period in one place in the tropics, will transform the chain in the water into an undersea marine garden, complete with its own blossoming ecosystem. It takes a wire brush to clean it.

• Using chain for long periods in coral or rocky anchorages, will damage the rust protection of the chain and the links will begin to rust, leaving the anchor locker and everything that comes into contact with the rode stained with the color of burnt ocre.

• In an all-steel rode system, it must be avoided to mix different kinds of steel (e.g. stainless shackle with galvanized chain). The galvanic differences between these different kinds of steel will result in electrolytic corrosion in salt water environments.

If chain is the conventional choice, then, it is so despite its drawbacks. After its resistance to chafe, the single most compelling reason to carry an all-chain rode on the primary anchor is the ability, with a robust electric windlass, for one person to get the anchor up easily and in a hurry. This is a safety issue as it should be feasible to easily re-anchor should the wind direction change, or should the yacht begin dragging.

Anchor Chain suited for Windlasses

Many chain types differing in link size, grade number and finishing are around that may be used in combination with the windlass systems used on leisure boats. Principally, all the windlass-suited chain types are declared as "short-link chain". But to complicate things, there are some different standards for the specification of their characteristics: ISO, AISI, DIN and ACCO that are all different! In Europe DIN 766 short-link chain standard is widely established and also complies with the corresponding windlass chain wheels.
One of the basic strength specifications of chain is the grade number. Grade refers to the tensile strength of the metal. The grade number used by manufacturers is an indicator towards the ultimate break strength of chain. The higher the grade the greater the break strength. However, different manufacturers use different systems by which to label chain grades. Distributors and resellers can confuse matters more. Grades equate at some point to a tensile strength figure, usually in metric units (Megapascals).

Types of Chain

The following are the most used types of steel available for anchor chains on pleasure boats.

• Low Carbon Grade 30 chain
  Marine chandlers offer two types of this grade 30 chain: "Proof Coil" and "BBB". This is the least expensive type of low-carbon steel chain on the market. Proof Coil is frequently used for fixed moorings such as tow chains and logging chains. While its rated breaking strengths are similar to BBB, Proof Coil has longer chain links and these do not fit into the gypsys of most modern windlasses. Moreover, under extreme loads, proof coils longer links have a higher tendency to collapse than either BBB or high test.
  
  BBB ("3B") is low-carbon, galvanized steel chain found as anchor chain on many leisure yachts. It is economical, it has very low stretch, and it fits most windlasses. BBB has been the standard for a generation of yachtsmen, but it has a low strength to weight ratio (see table below). Nevertheless BBB is popular for anhor cain because it is heavier (more links per length). This extra weight forms a deeper caternary curve from the vessel to anchor and so acts as a better shock absorber to smoothen out the pull on the anchor in heavy weather.

• Stainless steel 316L chain
  This type of chain has the principal advantage of very good corrosion resistance provided some precaution is taken in keeping the corrosion prevention active. This includes that the anchor and all other steel components of the anchor rode must also be made of stainless steel. Stainless steel requires oxygen to create a barrier coating on the surface so that it does not corrode. If it is immersed in water or mud for a long time this can not happen and corrosion will take place.
  Besides corrosion resistivity, a further advantage of stainless steel chains is that they run smoother on the windlass gypsy and "pile" less than galvanized chains in the chain locker. Stainless steel is susceptible to crevice corrosion, so the principle challenge with stainless chain is ensuring quality in order to guarantee that the welds on the links are properly made with little chance of porosity or voids. Problems with the weld can lead to inter-granular corrosion or "sensitization", which will lead to rapid failure of the weld itself. Poor steel or welding quality, or lack of finishing treatments will lead to surface rusting and drastically reduced strength. High quality stainless chain is expensive but it is likely to last 3 or 4 times longer than galvanized chain.

• Galvanized High-Test Grade 40 chain
  is fabricated from high-carbon steel with a higher breaking strength than BBB-type steel. This type is also known as "High-Test" chain or "G4". High-Test chain has a better strength to weight ratio than BBB (by up to 50%) and has grown in popularity among boatsmen. Most windlass manufacturers sell their products with a standard High-Test gypsy.

Size, Dimensions, Working Load and Weight

Chain is made of a series of connected chain links. Chain size refers to the diameter of the link material, but chain size is often also a trade or product name. A 10-mm chain from the European continent may be sold as 3/8"-chain on the American continent.
To make things even more complicated, there are some different standards on chain link dimensions in the world (e.g. DIN 766 and ISO 818 for short-link chain). Chain link dimensions are important e.g. when looking for an appropriate windlass chain wheel (gypsy).

The following table gives some approximate values on dimensions and working loads for DIN 766 short-link chains.

	Chain Size	Dimensions [mm]				Low Carbon Steel Grade 30 (BBB)		Stainless Steel 316L		Galvanized HT Steel Grade 40 (G4)
		A	B	C	D	Load	Weight	Load	Weight	Load	Weight
	8 mm	8	40	26	24	880	1.75	1100	1.70	1750	1.72
	10 mm	10	48	34	28	1250	2.50	1600	2.35	2450	2.20
	13 mm	13	62	44	36	2150	3.80	2900	3.80	4150	3.80

Notes:
1. Size and Dimensions apply to DIN 766 short-link chain and comply with standard windlass chain wheels. The link dimensions for DIN and ISO standards are identical for 8- and 13-mm chains. The 10-mm chains have a different link size: 30 mm for ISO and 28 mm for DIN standard.
2. Load given in DaN is the Working Load, which is typically 3 to 4 times lower than the maximum load.
3. Weight is Specific Weight given in kg/m. Notice, that under water bodies have lower weight than in air. Steel has a specific weight of about 7750 kg per cubical meter. Under water, a body of one cubical meter has an uplift of 1000 kg. So the weight of steel bodies will be reduced by about 13% (1000/7750) by submerging them into water.

Different steels used for chains are specified with a grade number. However there are a number of different nomenclatures to what the grade number specifies.
In one nomenclature, the grade number is equivalent to one tenth of the yield strength of the material expressed in Newton per square millimetre and thus is directly related to the tensile strength of the chain links. The total strength of a chain only depends on the chain size and the grade number:

Lyield = π * ( Chain_Size / 2 )2 * Grade_Number * 10

with L_yield in DaN and Chain Size in mm.

For a 10-mm grade-40 chain the approximate yield load is: π*25*40*10 = 3140 DaN. But it should be noted that this is yield load and NOT working load, which is normally used in practice (e.g. in catalog specifications) and is typically about 50% lower than the yield load.

Solving some of the Chain Problems

Chain comes with its own set of problems, as noted above. On many modern boats, the weight of the chain in the fore peak will alter the way the boat handles. There are few ways to combat this problem:

• use High-Test (HT) chain with better strength-to-weight ratio,
• move the anchor locker aft, right over the keel if possible,
• carry only the minimum length of chain in the fore peak with an extra length (and chain shackles) stored low in the middle of the boat to be used in unusually deep anchorages,
• when going to sea, move the anchor and chain to a cockpit locker.

While none of these suggestions is as simple as leaving the chain in the fore peak, making the ends of your boat lighter will enhance its sailing performance in all conditions.

Chain is going to create a certain amount of mess on deck and in the chain lockers as it brings mud, sand and marine life up with it from the bottom of the anchorage.
A high-pressure deck wash for cleaning the anchor chain may improve chain handling on deck. A deck-wash outlet near the bow should have a length of hose long enough to reach into the chain locker or over the bow and down to the waterline. This allows for cleaning the anchor locker and also chain cleaning when barnacles have to be scraped off the chain as it comes aboard.

When chain winds in over the windlass and then drops into the chain locker, it has a tendency to build mounds or chain castles that grow and then topple over on themselves in tangles. The simplest solution is to flake the chain by hand as it drops in. Not a popular job, particularly if the chain is rusty or still slimy with bottom ooze. If there is room in the chain locker, a simple chute, narrow at the top and wider at the bottom and lined with sheet metal, will help the chain to flake naturally as it falls from the chute into the locker.

Over time, a chain rode that is used all the time will develop a twist that will create tangles in the chain locker and impede the efficiency of the gypsy on the windlass. The twist comes from inevitable but slight misalignment between the gypsy and the bow roller. A chain swivel between the rode and the anchor will help. But the best solution is to use a notched roller in the bow roller that will align the chain with the gypsy as it comes over the bow.

Corrosion that ends up as rust will start to eat a chain rode that is used actively, especially in coral and eventually in rocks where the galvanizing is rubbed off. Wet chain lying in a damp anchor locker exacerbates the problem. There is no complete solution, but there are preventive measures that will lengthen the chain's useful life. Make sure that the anchor locker is clean and that it drains well; spray it out with fresh water from time to time and clean out limber holes that can be clogged with mud or rust flakes.
It is a good idea to end-for-end the chain once a year, so the whole length wears evenly. Make sure the gypsy on the windlass does not wobble under strain or have sharp edges that will chew the galvanizing off the links. Finally, chain that is used aboard a voyaging boat will need to be re-galvanized after three years of cruising, a process that can be found in just about any developed port city.
Depending on use and deterioration, a chain rode should last voyagers five or more years. For those cruising only part time, the chain will last a decade.

Galvanized Chain

Zinc coating or galvanizing, coats the surface of the steel with zinc. Hot dipped galvanisation gives best results: the chain is immersed in a bath of molten zinc and coated to a significant thickness. Hot dip galvanizing may change the temper of the steel but unlike to what is often written, it does not change the structural strength and it can be applied also on HT steels (e.g. galvanized HT grade 40 steel).
The zinc coating serves as an anode much like a zinc anode on the propeller shaft. It is a sacrificial coating and will dissolve after some time. When the zinc coating is dissolved, the underlying chain will start to rust. As soon as rust appears, anchor and anchor chain must be re-galvanized, else they start losing strength and weight. Before re-galvanization, rust must be thoroughly removed from the chain or anchor. Take into account, that after re-galvanisation the strength of the chain or anchor will be reduced by about 10 to 15%.

Other Considerations

More links per length will make the chains more supple (less likely to kink), and means the windlass can get a better grip on the chain (on more links).
If the anchor rode is chain, there must be a means of quick release in an emergency situation. For this purpose, a nylon line should be attached to the bitter end of the chain with a floating device so the anchor rode can be recovered later.