A propeller is a rotating fan-like structure that drives the ship by utilizing the power generated and transferred by the ship’s primary engine. The transmitted power is converted from rotational motion to thrust, which imparts momentum to the water, resulting in a force acting on the ship and propelling it forward. Bernoulli’s principle and Newton’s third law are used to driving a ship. Water is accelerated behind the blades due to the pressure difference formed on the forward and aft sides of the blade.
The propeller’s thrust is conveyed to move the ship via a transmission system composed of a rotational motion generated by the main engine crankshaft, intermediate shaft and bearings, stern tube shaft and bearings, and ultimately the propeller itself. Depending on the vessel’s speed and maneuverability, a ship can be equipped with one, two, or even three propellers.
Because they are used in seawater, which is a corrosion accelerator, marine propellers are made of corrosion-resistant materials. Maritime propellers are made from an alloy of aluminum and stainless steel. Nickel, aluminum, and bronze alloys are conventional common materials that are 1015 percent lighter and stronger than other materials.
The propeller is made by welding or forging several blades to the hub or boss in one piece. Although more expensive, forged blades are more reliable and stronger than welded ones. A nautical propeller is made up of helicoidal surface portions that work together to create a screw effect as they rotate through the water.
The ship is displaced in the water, and the propeller is utilized to propel the ship forward or backward, depending on the propeller’s rotational direction or pitch. The ship’s engine is linked to the vessel’s propeller via a shaft system. As the engine turns the propeller, the radiating blades of a specific pitch form a helical spiral, akin to a screw. This is accomplished by converting the power of rotation into linear thrust.
The engine’s crankshaft is first connected to the thrust shaft, which travels through the thrust bearing, the primary role of which is to impart thrust to the ship’s structure. The thrust bearing’s casing is comparable to that of the main engine bedplate, and the bearing is lubricated by the main engine lubrication system oil. Thrust shafts are typically made of solid forged ingot steel.
Watch the Amazing Production Of The Propeller & Crankshaft Of A Giant Ship in the video below.
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Video resource: FUTEK HD