Speaking of gearboxes, I believe everyone is most familiar with the gearboxes of automobiles. The gearbox of a car can range from five or six gears to seven or eight gears. Large trucks can even reach more than a dozen gears. The purpose of setting gears in a car is to cope with various working conditions and improve the working efficiency of the engine, so the gearbox is a very important part of the car. The gearbox of the ship is the same as that of the car, and it is also a very important part of the ship, but the gearbox of the ship does not have multiple gears like the car (universal), but only one reverse.Since there are no multiple gears, what is the use of a marine gearbox? Next, let's talk about the functions of marine gearboxes.
The first function is to slow down. Deceleration is arguably the most important function of a marine gearbox. Why slow down? Generally speaking, the lower the rotational speed and the larger the diameter of the ship's propeller, the higher the propulsion efficiency. On the other hand, small ships generally use medium and high-speed engines, the engine speed is relatively high, and the gear box is matched to reduce the speed, which can reduce the speed, amplify the torque, and use a larger diameter propeller to improve the propulsion efficiency. It should be noted that most marine gearboxes do not have multiple gears like automobile gearboxes, but only have a fixed reduction ratio. Only a few ships with many working conditions will use gears with high and low gearsbox.
Medium speed machine + reduction gearbox + CPP propeller
The second function is to transmit the thrust of the propeller.The propeller of the ship is driven by the main engine to rotate the propeller to generate thrust, which is then transmitted to the thrust bearing through the drive shaft, and then the thrust is transmitted to the ship through the thrust bearing to propel the ship forward. For ships equipped with gearboxes, thrust bearings are often integrated into the gearbox, so that the gearbox has a very important function, which is to transmit the thrust of the propeller to the ship.
The third function is disengagement and reversing. Disengagement is what we often call the clutch function. Ships organically combine clutches and gearboxes. Reversing is the ability to move forward and reverse. Large ships use low-speed direct-drive engines, and its reversing is achieved by the reversal of the main engine; while the medium and high-speed engines used by small ships, most of these main engines do not have the ability to reverse, and can only have the ability to reverse through the gearbox.
The fourth function is to reduce the height of the output end of the ship's main engine and reduce the angle of the drive shaft. A larger diameter propeller will have higher propulsion efficiency, and a small ship has a shallower draft. In order to obtain a larger diameter propeller and ensure the draft, the drive shaft of the ship should be designed to be lower accordingly. However, the bottom of the main engine of the ship needs space for the crankshaft to rotate, so the output end of the flywheel has a certain height. Some main engines have oil pans, and there are certain requirements for the installation height, so in order to ensure the draft of the propeller, only the drive shaft can have a certain inclination angle. If the drive shaft has an inclined angle, the thrust of the propeller cannot all act on the propulsion of the ship, and as the angle of the drive shaft is larger, the propulsion force is smaller. In order to improve the propulsion efficiency, if the vertical non-center gearbox is used, the height of the output end of the main engine of the ship can actually be reduced, and the angle of the drive shaft can be reduced.
The fifth function is the power branch transmission. The marine gearbox with power branch transmission function can use this function to let the abundant power of the main engine drive some equipment such as shaft generators to improve the economy.
That's all for today, I hope it will help you！
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