A form of transmission between engine and propeller in which a horizontal shaft from the engine passes through the transom to bevel gears which turn a vertical shaft running down outside the hull to a point below the waterline. Here a further set of bevel gears achieves a second right-angle turn to rotate a more or less horizontal propeller shaft. This form of drive allows the engine to be sited well aft in the hull and (usually) allows the ‘drive leg’ with the lower gear housing and the propeller to swing clear out of the water for inspection or repair. Transom drive, and inboard-outboard are other names given to this arrangement but the term ‘Z-Drive’ is the property of a single manufacturer.