Restricted in ability to maneuver

RAM

A vessel restricted in its ability to maneuver is one whose ability to maneuver as required by the Rules is restricted by the nature of its work.

Examples specified in the Rules include certain vessels:

laying or servicing navigation marks or cables

dredging

surveying or underwater operations

replenishing or transferring persons, provisions or cargo while underway

launching or recovering aircraft

engaged in mine clearance

engaged in certain towing operations that severely restrict deviation

It does not simply mean "large," "slow," or "hard to steer."