I am really very grateful for all your suggestions and help. However, I am going with HARBOUR ASISTANT (mainly because the managers at PORTS IB itself reject the term ‘harbour master’ in this context!)
Nonetheless your efforts spurred me on again and at
http://www.harbourmaster.co.uk/I found ‘Responsibilities of a Harbour master’ at
http://www.harbourmaster.co.uk/page.cfm/id/13604 and then information about ‘Career As A Harbour Master’ including a job description of a HARBOUR ASISTANT, which fits the bill admirably. Thank you all again.