Abstract: A riser angle positioning system and process provides information for dynamically positioning a floating vessel having a riser extending to a wellhead on the ocean floor. The system comprises an acoustic system for generating acoustic data signals representing the position of the vessel with respect to the wellhead, top and bottom riser inclinometers for generating respective sensor signals indicating angles of deflection of the riser at the top and bottom, respectively, thereof, and a processor responsive to the acoustic data signals and the sensor signals for generating positioning information. The riser angle positioning system and process serve as a backup system and method for checking the acoustic data for large errors, and additionally provide the sole position determining system and method in case of acoustic blackout.