How to Choose the Right Anchor Chain: DIN vs ISO, G30–G70 Grades and Galvanised vs Stainless

Selecting the right anchor chain for a sailing yacht is more involved than simply picking a diameter. Behind the scenes are several important specifications: the chain standard (DIN 766 or ISO 4565), the chain grade (G30, G40, G70 and more), and the material (galvanised, stainless steel, duplex or high-tensile alloy). Each element affects strength, durability, corrosion resistance and, most critically, how well the chain works with your windlass.

This expanded guide walks you through everything you need to know so you can confidently choose the correct anchor chain for your yacht.

DIN vs ISO: What these standards mean and why they matter

Anchor chain used on yachts is almost always calibrated short-link chain, built to very specific dimensions so it runs smoothly through a windlass gypsy. Two main standards define these dimensions.

DIN 766 is the long-established German specification, widely used throughout Europe. By contrast, ISO 4565 is an international standard used by many global windlass manufacturers. While both define short-link calibrated chain for marine use, the tolerances and, most importantly, the link pitch differ slightly. These small dimensional differences are the reason why one chain may feed perfectly through a gypsy while another keeps jumping, jamming or wearing prematurely.

On paper the differences seem minor, but on a yacht they are critical. Windlasses rely on each link seating precisely into the gypsy pockets; if the pitch is too short or too long, the chain simply will not run smoothly. For this reason, the first rule of anchor chain selection is simple: always match the chain to the windlass specification.

Comparing DIN and ISO across the common yacht sizes: 6 mm, 8 mm, 10 mm

Most sailing yachts use 6, 8 or 10 mm anchor chain, and the differences between standards become more noticeable as the chain gets heavier.

For 6 mm chain, DIN and ISO dimensions are nearly identical. The pitch is around 18–18.5 mm, and in practice most 6 mm gypsies will happily accept either standard. This size is mainly used on smaller yachts or larger performance dinghies.

At 8 mm, the two standards again align closely, both using a pitch of around 24 mm. This is one reason why many 8 mm windlasses are designed to accept both. For yachts between 30 and 38 ft, 8 mm is the most common diameter and the least problematic in terms of compatibility.

The situation changes noticeably at 10 mm. DIN typically uses a pitch of about 28 mm, while ISO chains follow a 30 mm pitch. Those 2 mm are enough to dramatically change how the chain engages the gypsy. A windlass built for 10 mm DIN chain may struggle to pull 10 mm ISO chain reliably, and vice versa. For yachts in the 40–50 ft range where 10 mm is standard, identifying the correct specification is essential.

Chain Size	Standard	Wire Ø (mm)	Internal Length (mm)	Pitch (mm)	Notes
6 mm	DIN 766	6.0	~18.5	~18.5	Almost identical between DIN/ISO — interchangeable for most gypsies
6 mm	ISO 4565	6.0	~18.5	~18.5
8 mm	DIN 766	8.0	~24.0	~24.0	Most 8 mm gypsies accept either standard
8 mm	ISO 4565	8.0	~24.0	~24.0
10 mm	DIN 766	10.0	~28.0	~28.0	Critical difference — must match gypsy
10 mm	ISO 4565	10.0	~30.0	~30.0	2 mm difference causes gypsy mismatch

Materials: galvanised, stainless and high-tensile alloys

Once you know the correct anchor chain standard, the next decision concerns the material. Most cruising sailors choose hot-dip galvanised steel, which offers an excellent balance of cost, strength and corrosion resistance. The quality of galvanising varies between manufacturers, and better anchor chains use thicker zinc coatings and superior surface preparation for longer service life.

Stainless steel anchor chains are also common, though they behave differently. AISI 316 stainless offers excellent corrosion resistance and remains bright and clean on deck, but it is not as strong as high-tensile galvanised chain and is vulnerable to crevice corrosion, particularly inside links. At the higher end, duplex stainless steels such as 2205 provide greater strength and outstanding corrosion resistance, making them popular on performance yachts and superyachts.

High-tensile alloy chains sit somewhere in between. These are typically galvanised chains in higher grades (G60, G70 and above), offering exceptional strength for their weight. They are especially attractive for weight-sensitive bow configurations, but the higher hardness can shorten galvanising life, and not all high-tensile chains are suitable for windlasses unless they are specifically calibrated for marine use.

Understanding anchor chain grades: G30, G40, G70 and beyond

Where the standard defines dimensions, the grade defines strength. Anchor chain grades correspond to the tensile strength of the steel.

Grade 30 (G30) is the traditional mild-steel chain used on many smaller yachts. It is affordable and reliable but the least strong, meaning heavier chain is required for equivalent performance.

Most mid-sized sailing yachts now use Grade 40 (G40), which represents a good balance of price, strength and durability. It offers a significant jump in performance compared with G30, often without changing anchor chain diameter.

For sailors wanting higher strength without increasing anchor chain size, or looking to reduce bow weight, Grade 70 (G70) is the next step. This high-tensile heat-treated alloy steel offers a substantial increase in breaking load. Performance cruisers, race yachts and bluewater sailors often select G70 for the combination of lower weight and high strength.

Higher industrial grades like G80 and G100 exist, though they are generally unsuitable for leisure use. Their extreme hardness makes galvanising more difficult and can reduce compatibility with marine windlasses, making them the preserve of specialist or commercial applications.

Diameter	Grade	Min. Breaking Load (kN)	Approx. SWL (kg)*	Notes
6 mm	G30	~25 kN	~650 kg	Traditional mild steel
6 mm	G40	~35 kN	~850 kg	Common mid-market choice
6 mm	G70	~55 kN	~1400 kg	High-tensile, weight saving
8 mm	G30	~40 kN	~1000 kg
8 mm	G40	~55 kN	~1400 kg	Common cruising spec
8 mm	G70	~85 kN	~2100 kg	Premium/high-performance

Breaking load, working load and what yacht owners should care about

Two strength values matter when choosing anchor chain: the breaking load and the working load. The breaking load is the maximum force the anchor chain can withstand before failure, while the working load limit (or SWL) is the safe, everyday operating limit. Higher-grade chains offer significantly higher values for both, often enabling sailors to use the same diameter with greater confidence or reduce diameter while maintaining strength, provided the windlass gypsy is compatible.

How to choose the right anchor chain for your sailing yacht

The best way to specify anchor chain is to follow a simple sequence. Start with the windlass, because the gypsy dictates the chain standard and diameter. If the gypsy is marked “8 mm DIN”, that is the specification you must use. If it is not marked, measure your existing chain or refer to the windlass manual.

Once the standard is confirmed, consider the anchor chain grade that suits your sailing style. For example, 6 mm or 8 mm G40 suits most cruising needs. Larger yachts or those venturing offshore may benefit from higher-grade options like G70, especially if weight reduction forward helps balance or performance.

Finally, choose your material based on your sailing environment. Galvanised chain is ideal for most cruising yachts, stainless steel suits those who prioritise low maintenance and aesthetics, and duplex stainless or high-tensile galvanised chains suit more demanding applications.

Across all materials and grades, ensure the anchor chain is calibrated. Only calibrated chain guarantees consistent dimensions that match your gypsy and ensure smooth, safe operation.

Summary on Anchor Chains

Choosing anchor chain is about much more than size. DIN and ISO standards govern link dimensions, and these must match your windlass. Anchor chain grade determines strength and performance, while the material affects corrosion resistance and longevity. By understanding each element—standard, grade and material—you can confidently select an anchor chain that delivers reliability, safety and smooth operation for years to come.

Need help choosing the right anchor chain for your yacht?

If you are unsure which anchor chain standard, grade or material is right for your yacht, we are happy to help. Contact our technical team for personalised advice or to request a quotation.

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