Anchor Chain Grades — U1, U2 and U3 Explained

Anchor chain cable is made in three grades. They are the same size and take the same fittings — the difference is the steel, and it is a large difference. This page explains what the grades mean, what they are worth in load, and which one your specification is probably asking for.

The three grades

Grade Also written Called In practice
Grade 1 U1 Mild steel The oldest and weakest. Rarely specified on new work. Supplied on enquiry.
Grade 2 U2 Regular strength The standard duty grade, and the common choice where the design load does not demand U3.
Grade 3 U3 High strength The usual modern specification for commercial vessels, and what most classed newbuilds call for.

We stock Grade 2 and Grade 3 in 12.5 mm to 76 mm, certified to Lloyd's Register, ABS or DNV. Grade 1 is quoted on enquiry.

The relationship worth knowing

There is a pattern in the IACS tables that makes the grades much easier to reason about, and it holds at every diameter:

The proof load of each grade is the breaking load of the grade below it.

Take 32 mm. Grade 1 breaks at 417 kN. Grade 2's proof load — the load every length is tested to and must survive — is 417 kN. Grade 2 breaks at 583 kN, and Grade 3's proof load is 583 kN. Grade 3 breaks at 833 kN.

So a Grade 3 chain is routinely proof tested to the load that would break a Grade 2 chain of the same size. Put the other way: going up one grade buys you roughly 40% more breaking load in the same section, with the same shackles, the same navel pipe and the same gypsy.

Grade does not change the size you need — it changes what fits

Under IACS UR A1 a vessel's anchoring equipment is selected from its Equipment Number, which is worked out from displacement, freeboard and the profile area of the hull and superstructure. That gives a required chain, and a higher grade lets the same requirement be met in a smaller diameter — lighter cable, a smaller gypsy, less weight in the bow.

That is why grade is usually fixed by the vessel's original specification rather than chosen freely. If you are replacing chain, match what the ship is certified for. Our sizing guide works through Equipment Number if you are starting from scratch.

Loads at every size we supply

Diameter Grade 1 (U1) Grade 2 (U2) Grade 3 (U3) Weight
per shot
Proof Break Proof Break Proof Break
12.5 mm 46 65.7 65.7 92 92 132 94 kg
14 mm 57.9 82 82 116 116 165 118 kg
16 mm 75.5 107 107 150 150 216 154 kg
19 mm 105 150 150 211 211 301 217 kg
22 mm 140 200 200 280 280 401 291 kg
26 mm 194 278 278 389 389 556 407 kg
32 mm 291 417 417 583 583 833 617 kg
34 mm 328 468 468 655 655 937 696 kg
38 mm 406 581 581 812 812 1,160 870 kg
42 mm 492 703 703 981 981 1,400 1,062 kg
44 mm 538 769 769 1,080 1,080 1,540 1,166 kg
52 mm 739 1,060 1,060 1,480 1,480 2,110 1,628 kg
58 mm 909 1,290 1,290 1,810 1,810 2,600 2,026 kg
64 mm 1,100 1,560 1,560 2,190 2,190 3,130 2,467 kg
76 mm 1,500 2,150 2,150 3,010 3,010 4,300 3,479 kg

All loads in kN. Sources: IACS Recommendation No. 10 up to 19 mm, IACS UR A1 from 22 mm. Weight is per 90 ft (27.5 m) shot.

Fittings must match the grade

A Kenter joining shackle is made to a grade the same way the chain is. A Grade 2 Kenter is not a substitute on Grade 3 chain — it becomes the weakest point in the cable, and it will be the thing that fails. When you order chain and shackles together, say the grade once and it applies to both.

See Kenter joining shackles, and the FAQ for fitting them.

These are not mooring chain grades

Anchor chain cable is Grade 1, 2 or 3. Offshore mooring chain is a different family entirely — R3, R3S, R4, R4S and R5, to IACS UR W22, for floating production units and offshore loading systems. The two do not interchange, and neither do their accessories.

If your specification says R4, or ORQ, you are in the other family — see offshore mooring chain and ORQ and oversize.

Not sure which you need?

Send us the vessel's specification, the old certificate, or a photograph of the stamp on the existing chain, and we will tell you the grade before you order anything. Contact us — 514-694-9830 or sales@dibbleeindustries.com.