"he talked only of the dock-yard, the harbour, Spithead and the Motherbank"

Like Spithead, the Motherbank is a roadstead (a place outside a harbour where a ship may lie at anchor) in the Solent between Cowes and Ryde. It was often the last resting place for Royal Navy warships before they were decommissioned.

 

Map of the Isle of Wight and the Solent
Public DomainMap of the Isle of Wight and the Solent - Credit: Geographicus Rare Antique Maps