The occupant of the reporting vessel (V1) noticed another vessel (V2) out in the channel that seemed to be either anchored or drifting. 

The occupant then realized that V2 was moving backwards towards V1. The occupant of V1 started yelling at the occupants of V2 so they would stop their vessel.

One of the occupants on the deck of V2 looked up after a minute and noticed what was happening before yelling at the owner/operator of V2 that was below-deck. The owner/operator of V2 was presumably in the engine room working on something while V2 was under power and moving backwards. 

Before anything could be done, V2 slammed into V1's "starboard side between the front and middle part of the boat". V1's dock neighbors came outside upon hearing the yelling and the crash. As V2 was pulling back and away from V1, V2 also skimmed the side of the neighbor's skiff that was attached to the back of their fishing vessel.
Sitka Channel
Sitka                         