Thanks for your answer. The reason for my needs for a accurate vesselposition is due to structurescanning and beeing able to verify pipes, cables and other thing laying at seabed. I think if i can have a GPS pos. Within 0.5m that should be good enough.
Is there a rover that carries a slot for simcard to be able to get RTK from 3G or 4G?
That is a option that will be ore userfriendly on a vessel than a base.