Anchor Chain Grades U2 and U3 and How They Change Your Windlass

Grade is a strength statement, not a finish

Stud link anchor chain is ordered by the diameter of the round steel the link is made from and by its grade. AM/U2 and AM/U3 chain of the same diameter are physically interchangeable and are not mechanically equivalent: U3 carries a higher breaking load. That is the whole reason the grades exist. If class accepts U3 for your vessel, you can meet the same required breaking load at a smaller chain diameter, and every downstream item gets smaller with it.

What changes when the diameter drops

Chain weight per metre falls, so the load on the windlass falls and so does the weight carried in the hawsepipe, which is the worst place on a ship to carry weight. The gypsy, the chain stopper and the connecting fittings all step down with the cable. On our range, chain runs from 14mm to 80mm diameter and windlasses cover AM-2 chain from 12.5mm to 60mm, so the two ranges overlap across most workboat and merchant sizes.

The fittings have to follow the chain

A cable is not one continuous chain. It is shackles of chain joined by connecting links, with a swivel at the anchor end to take the turns out. Common links, enlarged links, open end links, swivels, D type end shackles and kenter connecting links are all sized by the same link steel diameter as the chain they join. Order them with the chain, not after it.

High holding power anchors work the same way

The AC-14 is classed as a high holding power anchor, so class accepts it at a lower weight than a standard hall stockless anchor for the same holding. It gets there through geometry: a much wider crown, thicker and longer claws, and longitudinal edges that bite rather than skate. Less anchor weight means less windlass, which is the same saving from the other end of the package.

What to send when you ask for a quotation

Vessel displacement, required chain diameter and grade, anchor type and weight, the height from the waterline to the hawsepipe, the recovery speed you want in metres per minute, and the classification society. That is enough to size the anchor, the cable, the fittings, the windlass and the chain stopper as one set.