RedactedNarrative: V1 had been traveling North under power inside of Shadow's Marina docks. V1 then made a turn to starboard to head toward the slip. Operator of V1 states when he went to shift into reverse, he had no control of the vessel. It was determined that an unsecured line from the deck of V1 entered the water and became tangled in the propeller, causing the operator to lose control. V1 began to drift North with its Port side heading North and the bow facing East. The port side of V1 collided with V2 which was docked and unoccupied.