We all are well known to Newton’s 3rd law of motion. it’s the essence of anything that moves us through the world. Similarly ships and planes are moved by propellers. They too use Newton’s third law, because a propeller pulls or pushes you forward by hurling a mass of air or water behind you. BUT we see airplanes mostly have their propellers in front (of the fuselage or wings) while ships and boats mostly have them at the back.
These are the main reasons, Why Boats Have Propellers at its Back?
- It helps Boat Moving Efficiently:- A boat needs to plane on the water to move efficiently. The angle of the propeller in the rear helps to raise the front of the boat up out of the water so it actually skims across the water. Placing it in the front of the boat would push the front of the boat into the water, creating more drag.If a boat’s propeller were kept out of the water, it could easily be in the front. But then the propeller would need to be much larger because not as much force can be generated against air as it can against water. This is obvious when you look at the size of a boat’s propeller compared to an airplanes propeller.
- Risk of damage to prop:- The a propeller at the stern is more protected and less likely to be damaged. If the prop was at the front there is more risk of harm in a grounding or if the ship hit a large object such as a log. A broken propeller blade can strand a ship.
- Mostly because of waves. Water is seldom flat and if the prop was in the front it would constantly be leaving the water and you would lose thrust. Think of it like if you were driving down the street and constantly tapping on your breaks. With the prop in the back the front is free to lift and fall and break the surface while maintaining thrust.
- Decrease Pressure on Seals:- Pressure is higher at the front because of the kinetic pressure of the fluid, and lower at the back for the reverse reason. By putting the prop of a boat in the back you reduce the pressure difference that the seals have to deal with.
With the boat, all that is required is to propel the boat forward, and that is best achieved by accelerating a mass of water in a direction opposite to the direction of boat travel.
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