Marine Gearbox: Everything You Need to Know

Marine gearboxes coupling are usually mounted securely at the engine’s driving end, between the propeller shafts and the engine shaft. In the same way, that propeller shafts and engines are connected to their gearboxes via mounting plates, flanges, or bolts, engines are often related to them through gearboxes via various connections. These machineries include gears, hubs, clutches, pressure plates, input, output, and coupling.

What’s the purpose of the marine gearbox

These transmissions provide a clutching arrangement to boats: clutch in or out. To engage the load shaft (e.g., propeller shaft), to the gearbox, and so to the driving motor that is always fixed, connect to the transmission, and clutch in. You can clutch in either forward clutch (ahead) or reverse clutch (astern).

This function is essential for propulsion, particularly on small boats. Safety is paramount. The engines can’t be started or turned on unless the gearbox has been in the neutral clutch or simply clutched out.

Additionally, gearboxes can reduce or subtract the rpm from the driving end to the load end or consumer. When a shaft speed-to-torque requirement is met, the gearbox rpm reduction can be used.

What is the working principle of a marine gearbox?

The working principle of a gearbox is not as complicated as it sounds. The gearbox is composed of an internal pump and clutches. The pump is designed to exert pressure on the clutches to select the gears required to engage, thereby creating the desired movement.

The rotation can be either counterclockwise or clockwise, depending on which gear is engaged. A neutral clutch is also known as a gear engagement. The clutch movement usually is transmitted from the Remote-Control System Engine RCS to a solenoid Valve which directs the oil directly to the gearbox clutch. The internal arrangement of the oil pump allows it to be driven mechanically by the engine’s driving shaft.

It is important to note that most small and medium-sized boats have twin propulsion setups. They require opposing rotation of the propellers to operate and complement the boat thrust.

Why don’t boats use transmissions?

With all the functions the gearboxes have to offer discussed above, not all ships use gearboxes/transmissions. Ships with gearboxes do not have transmissions like cars. This is because it is too difficult to maintain a more extensive transmission for boats with limited speed efficiency. Water friction increases as the propeller turns faster, making it more difficult to turn. Cavitation can also cause the propeller to wear down faster when in water. Ships do not need speed-adjustable transmissions, which are expensive and inefficient.

To know more about marine gearboxes or products like polyurethane engine mounts, you can visit Polyflex. They offer a range of products in the automotive and marine industry.

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