Difference Between Shaft Horsepower and Horsepower

The term shaft horsepower refers to the power output that comes from an engine after it has been put through the gear train and to certain additional components where the outcome is a loss of power. It is often utilized when dealing with aeroplanes and ships, but it can also be useful in respect of the power output derived from a car’s gearbox.

The term brake horsepower, on the other hand, refers to the power an engine is able to put out at the crank and it is not a subject to loss. When compared to true horsepower, it is always higher, regardless of the circumstances. True horsepower, also known as rear wheel horsepower is a term that refers to the power accountable for the forward movement of vehicle during a drive, therefore it is extremely significant, especially when thorough comparison between motor vehicles is conducted.


The unit we use for designating the level of horsepower is horsepower itself and it can be also mirrored through the Watt metric systems: 1 hp = 0.75kW

  • Indicating horsepower is actually the power that is produced on the cylinder due to the expansion of gas and it annihilates the heat loss, friction and entropy that might occur within the system. The indicated power is calculated from the pressure enforced inside the cylinder and the instrument that measures it is called engine indicator.
  • Shaft horsepower is in fact the power that is accessible at the propeller shaft. Some refer to it as break horse power due to the fact that it is measured through a break. As a result of the diverse friction losses that occur, only a fraction of indicated power is accessible at the shaft. Top bearing, cross head and piston ring are kinds of frictional losses that might take place in the shaft.
  • Break horsepower can be measured when a resistance torque is applied on the shaft as a break and the heat that is generated by the friction is discharged by circulating water.

The formula for break horsepower is Bp=2пNRF

N – revolution of the engine per second

F- break or resisting force

R-the radius of force appliance

The torque of the engine shaft is measured by an instrument called torsion meter. The formula for measuring shaft horsepower is: Sp = 2пNT

T – torque measured by means of torsion meter

N – revolution of the engine per second

During these operations, a shaft power calculator can be utilized as a control unit that will account for higher percentage of reliability and efficiency. A shaft power calculator can be especially useful regarding the submersible pumps and the conduction of automatic control without utilization of level sensors.

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Anthony Hendriks

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