chocks on the wheels is one way of preventing the vehicle from moving on a slope. Motorcycle drive shafts Drive shafts have been used on motorcycles since before WW1, such as the Belgian FN motorcycle from 1903 and the Stuart Turner Stellar motorcycle of 1912. As an alternative to chain and belt drives, drive shafts offer long-lived, clean, and relatively maintenance-free operation. A disadvantage of shaft drive on a motorcycle is that helical gearing, spiral bevel gearing or similar is needed to turn the power 90° from the shaft to the rear wheel, losing some power in the process. BMW has produced shaft drive motorcycles since 1923; and Moto Guzzi have built shaft-drive V-twins since the 1960s. The British company, Triumph and the major Japanese brands, Honda, Suzuki, Kawasaki and Yamaha, have produced shaft drive motorcycles. Lambretta motorscooters type A up to type LD are shaft-driven the NSU Prima scooter is also shaft-driven Motorcycle engines positioned such that the crankshaft is longitudinal and parallel to the frame are often used for shaft-driven motorcycles. This requires only one 90° turn in power transmission, rather than two. Bikes from Moto Guzzi and BMW, plus the Triumph Rocket III and Honda ST series all use this engine layout. Motorcycles with shaft drive are subject to shaft effect, where the chassis climbs when power is applied. This effect, which is the opposite of that exhibited by chain-drive motorcycles, is counteracted with systems such as BMW's Paralever, Moto Guzzi's CARC and Kawasaki's Tetra Lever. Marine drive shafts On a power-driven ship, the drive shaft, or propeller shaft, usually connects the propeller outside the vessel to the driving machinery inside, passing through at least one shaft seal or stuffing box where it intersects the hull. The thrust, the axial force generated by the propeller, is transmitted to the vessel by the thrust block or thrust bearing, which, in all but the smallest of boats, is incorporated in the main engine or gearbox. Shafts can be made of stainless steel or composite materials depending on what type of ship will install them. The portion of the drive train which connects directly to the propeller is known as the tail shaft. Locomotive drive shafts The Shay, Climax and Heisler locomotives, all introduced in the late 19th century, used quill drives to couple power from a centrally mounted multi-cylinder engine to each of the trucks supporting the engine. On