Well, Flightgear over time changed to GearGear or GearSim or SimGear (wait a second...) anyways. Though it focuses on aviation, the border became eroded over time: Pushback, snowplow, carrier, cars, trucks, wheelchairs, AI ships...
As far as I can tell, the intersection between nautics and aviation are huge, just the emphasis are somewhat different. Seaplanes would profit from tidal simulation, waves and a simple hydro physics for sure, while nNautics need all the stuff a flightsim needs: Descent weather, graphics with large view distance including mist and fog, night and day change, support for realistic light buoys etc... Flightgear has it yet.
Thorsten is developing a very promissing local weather system with fog banks - who doesn't have an association with nautics?
So I am positive that descent support for ships will come sooner or later.
Crashpilot