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| Inboard/Outboard (Outdrive) A permanently mounted inboard engine connected through the transom of a vessel to an outboard propeller drive assembly that both propels the vessel and is turned from side to side to steer the vessel. This form of engine eliminates the need for a rudder, rudder post, shaft log, stuffing box, stern bearing, coupling, and conventional propeller shaft. The drive unit is known as "sterndrive†or “outdriveâ€. There are several companies manufacturing sterndrive units, but only two brands are commonly found on recent model boats, MerCruiser and Volvo Penta. Both brands have single propeller and dual propeller models, and gas, diesel and high performance models.
Sterndrive unit components differ slightly by model and brand. Part identification terminology also slightly differs. Large component unit drawings of MerCruiser Alpha and Bravo and Volvo Penta drives for quick reference: Volvo Penta Transom Shield Assembly MerCruiser Alpha Transom Plate MerCruiser Alpha Gimbal Housing MerCruiser Alpha Driveshaft Housing (upper) - U-joint assembly MerCruiser Alpha Driveshaft Housing (upper) - Upper drive shaft MerCruiser Alpha Gear Housing (lower) - Vertical drive shaft MerCruiser Alpha Gear Housing (lower) - Propeller shaft assembly MerCruiser Bravo Transom Plate MerCruiser Bravo Gimbal Housing MerCruiser Bravo Universal Joint Assembly MerCruiser Bravo Driveshaft Housing (upper) MerCruiser Bravo I Gear Housing (lower) |
MerCruiser Alpha drive unit
MerCruiser Bravo-I drive unit
MerCruiser Bravo-II drive unit
MerCruiser Bravo-III drive unit (dual propellers)
Volvo Penta SX drive unit
Volvo Penta DP drive unit (dual propellers)