The definition of dock undertaking is not intended to be
restrictive. All it is intended to exclude are structures like
Southend pier, which are used for entertainment. Under the
definition a structure is a dock if it is possible for vessels to
ship or unship merchandise or passengers at it. It does not need to
be used that way in practice.
Marinas normally qualify as dock undertakings because they
usually consist of harbours where vessels can ship or unship
merchandise or passengers.