We have purchased a twin-screw Cruise-a-Home Crusader with one engine, transmission and v-drive missing on the starboard side. What direction of engine rotation should we use and which direction should the props rotate?
In a standard twin-screw installation the tops of the propellers should turn outboards. Thus, viewing forward from the stern, the port prop turns counterclockwise and the starboard prop turns clockwise. The port prop is a left-hand screw and the starboard prop is a right-hand screw.
The whole question of direction of engine rotation can get kind of confusing and in fact could be different between boats with gasoline engines and diesel engines. First let's set down some definitions:
Front of engine - the anti-drive end. The end with the drive belts and water pump. In a v-drive installation, this end faces aft.
Rear of engine - the flywheel end where the transmission connects. In a v-drive installation, this end faces forward.
Right-hand engine rotation - Flywheel turns clockwise when viewed from the rear of the engine. In a v-drive installation, this would be viewing aft from the rear of the engine.
Left-hand engine rotation - Flywheel turns counterclockwise when viewed from the rear of the engine. In a v-drive installation, this would be viewing aft from the rear of the engine.
Gasoline marine engines, until recently, could be obtained in either right-hand rotation or left-hand rotation. I say until recently, because some of the newer electronically controlled fuel injected engines are only available in a single direction of rotation. The same is true for diesel engines; they are normally only available in a single direction of rotation. Thus in a twin diesel installation or when both engines have the same direction of rotation, one of the transmissions or v-drives will need to reverse the rotation.
One Cruise-a-Home owner reports that his gasoline engine powered twin Corsair uses opposite rotating engines and that the transmission/v-drives are both non-reversing. Thus in this configuration, the starboard engine is left-hand rotation and the port engine is right-hand rotation.
Another owner who had a 1974 single screw 31-footer reported that the v-drive was reversing. In that case, to have a RH rotation prop, the engine was RH rotation (a marine reverse-rotation engine). Later when he re-engined with a standard rotation marine engine, he needed to switch to a LH prop. In addition to the prop change, the oil pump in the Velvet Drive transmission had to be reversed and the oil pump hoses on the v-drive gear box had to reverse the input and output lines. In this case, the v-drive was not part of the Velvet Drive assembly.
"Standard" marine engine rotation is LH rotation.
"Opposite" or "Reverse" marine engine rotation is RH rotation.
Definitions obtained from the Crusader marine engine parts manual:
Engine Rotation is identified as "RH" or "LH" with the engine model number. Rotation always is determined from the flywheel end looking toward the front of the engine. In some instances, propeller shaft rotation may be opposite to that of the engine. When ordering a replacement engine, production block or parts for the engine, be certain to check engine rotation. DO NOT rely on propeller rotation in order to determine engine rotation. LEFT-HAND ROTATION is STANDARD ROTATION. (Flywheel turns counterclockwise when viewed from flywheel end of the engine.) RIGHT-HAND ROTATION is OPPOSITE ROTATION. (Flywheel turns clockwise when viewed from flywheel end of the engine.)