Vessel 1 was in operation when it broke down in 4-6 foot waves and needed to call for a tow.  Vessel 2 was tied to the stern of Vessel 1 at this time.  Vessel 3 (a tow vessel) arrived on scene and began towing Vessel 1 back to shore.  While in route back to shore, Vessel 2 came untied from the stern of Vessel 1, requiring Vessel 3 to temporarily stop the tow.  Vessel 3 then unhooked Vessel 1 from tow, retrieved Vessel 2, and pulled Vessel 2 onto Vessel 3 before resuming the tow.  As Vessel 3 resumed towing Vessel 1, Vessel 1 began taking on water.  A de-watering pump was put aboard Vessel 1, but the pump could not keep up with the incoming water.  The sole Occupant aboard Vessel 1 was then taken aboard Vessel 3 and Vessel 1 submerged.
 
Investigation following the incident revealed that the motor compartment of Vessel 1 was the source of the incoming water as a modification made to the motor cover was allowing water to enter Vessel 1 as a result of the larger waves on the date of the incident.
Oregon