RedactedNarrative: V1 was traveling over 20 mph when it hit a submerged object or rocks which ripped the lower unit off of the I/O.  The boat immediately filled with water yet operator was able to make it to shore. His attempts to secure the boat to  shore failed & the fast Missouri river current took the boat downstream where it sunk stern down & bow up.  The opinion of the investigating Officer is that operator hit a modified rock structure (used to aid in the reproduction of Sturgeon) since the water level was high and the time of day (at dusk) would have made it difficult to see the ripples, created by the structure.  The Operator failed to contact the Investigating Officer until 27.5 hours after the incident even though he admitted to discussing what he needed to do with his brother.