RedactedNarrative: Operator and friend were drift fishing when he observed his vessel taking on water from the stern by oversplash from the waves.  He attempted to start the outboard motor and the battery was already underwater and the engine would not start.  The vessel sank very quickly.  Both persons went into the water.  They threaded water for about 15 minutes before being picked up and transferred to another vessel.  Both persons were evaluated at the scene by ems services and refused further medical treatment or transport to the hospital.  The operator/owner said he made sure the plug was in before launching and believes that rain water may have collected under the floor of his vessel.