The positioning systems for long term sea going operations should be based on accurate (0-5 m) and reliable (24x7) instrumentations. The modern differential GPS by satellite links used by the offshore industry are well within there recommendations. The navigation and ancillary data should be acquired and recorded in digital form, suitable to be easily reprocessed and standardized within well known time and geographic datum frameworks. This is of paramount importance when dealing with extra accurate bathymetric surveying, such as in nearshore areas with strong tidal excursions (in these cases the use of RTK DGPS techniques is recommended).