ANCHORING SYSTEMS & PROCEDURES
It is fortunately rare to have to anchor a ship in an emergency. In most circumstances it is unlikely that the ship’s anchors would be capable of stopping a large vessel if the rate of drift at the time of deployment is in excess of about a half a knot. As anchor holding power is not proportional to vessel size, the larger the vessel, the less effective emergency anchoring is likely to be in arresting the vessel’s motion. Despite this, in an emergency every available means, including use of the anchors, should be considered for use.
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Over half a knot, you'll probably just break the chain, if the anchor catches at all.
In danger, with no room to turn,
Ease her, Stop her, Go Astern.