there's a floatplane operation on Loch Lomond in Scotland, not ocean based but might be able to give you an idea they use the following:
6 seat (5 passengers + Pilot) Cessna Turbo Stationair T206H
Wipline 3450 amphibious floats
Fuel injected 310 horsepower TIO-540 Textron Lycoming engine
Range - 713 nautical miles
Gross weight 3792 lbs
Take-off run (water) 1,700' at gross weight
Take-off run (land) 900' at gross weight
Landing distance typically less than 500' (water)
Cruise speed (75%) 128 KTAS
27,000' service ceiling
Interior: Leather seats, State of the art avionics including a GPS colour moving map display, Autopilot
The website address is
http://www.lochlomondseaplanes.com