IBA: Qualifying trade: Dock undertaking
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.