Pz8 is a series of two-page wargames rules. Among them are is a set of free wargames rules for coastal actions.
PT Boats
Hunters On The Shoreline 1/600 Coastal Miniatures Rules
Hunters on the Shoreline is a set of free wargames rules for playing WWII coastal naval actions using 1/600 miniatures. It’s available from PT Dockyards.