(a) any port or place, dock, wharf, quay or similar premises, if that Government is satisfied that dock work is only occasionally carried on or the traffic is small and confined to small ships and fishing vessels at such port, dock, wharf, quay or similar premises; or
(b) any specified ship or class of ships, if that Government is satisfied, having regard to the features of such ship or ships, the nature, quantum and periodicity of dock work carried thereon and all other relevant factors, that it is necessary so to do: