HUGIN is an untethered underwater vehicle (UUV) intended for bathymetric data collection for detailed seabed surveying. The HUGIN sensor suite, consisting of standard commercially available navigation sensors and a multibeam echosounder, is briefly presented. A Kalman filter based post processing integration of UUV sensors and survey vessel sensors is discussed. Resulting UUV position and heading accuracy and important characteristics of the post processing filter is shown with simulation results and results from a commercial survey operation. Finally, we briefly show how the claimed position and heading accuracy has been verified.