Managed to get in touch with a pal from Hoverspeed and he gave me some info on the SR.N4 crews.
From memory he says that the First Officer was normally a Master Mariner and the Captain would have a Masters Certificate. The Flight Engineer, however, did not need any qualifications - surprising as that sounds! The role of the Navigator was a hard one apparently. The English Channel being the busiest sea lane on the globe, he had a hard job in the fog!!
Pay wasn't bad - about £25-34k per annum.
The pilots were understandably gutted when Hoverspeed stopped using the hovercraft and most went on to sail the Seacat or fly aircraft.
Hope that is of some interest, apologies for the delay in posting the info.
VFE.