If you have two gas engines the engines both rotate the same way. The transmission is the means to left or right hand rotation.
Also. If it has one engine then it's a normal right hand rotation. If it's two then one propeller is right hand the other left. The starboard (right) is right hand, the port (left) is left hand.
Right hand turns clockwise, left hand turns counter clock wise. In other words when a blade is at the top it is moving to the right on a right hand prop. When it is a left hand prop the blade is moving to the left.
However this depends. Most boats are set up this way, but some manufacturers use just the opposite with the props turning inward iinstead of outward.
The reason for this is if both props turn same way the boat tends to crab sideways in the direction of prop rotation. If each turns a different direction the boat goes in a straight line. Also you can use prop rotation to your advantage when turning and docking. If you keep the right in forward and the left in reverse the boat spins on its axis to the left and vice versa. Or even if you are just docking and want to bring the stern into the dock you can walk the stern sideways by stopping the left prop and going ahead slow on the right prop. Again you can reverse the procedure on the left side.
Hope this helps.
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