Why do engines use the unit horsepower instead of the more widely used Watt? Ironically, this unit of engine power measurement was actually invented by the Scottish engineer James Watt himself and has quite an interesting backstory!
In the early 1780s, Watt came up with a massively superior steam engine when compared to the classic Newcomen steam engine which used about 75% less fuel and eventually became the backbone of the industrial revolution. Unfortunately, Watt didn’t have Wonderful Engineering’s platform for the publicity of his invention, so had to rely on his creativity and shrewdness to market the discovery.
At first, he tried to raise awareness by putting the sale of his engine on a royalty scheme, where his customers owed him one-third of the money if they chose his engine over the Newcomen one. The idea was right, but the problem was that people simply didn’t use any kind of engines back then, and the most widely used mode of transport of people and goods was through horsecarts. This meant that the “all impressive” Watt’s engine was simply of no concern to the common people, neither was the 75% efficiency figure.
Ever the inventor, Watt decided to scrap the royalty scheme and came up with an ingenious solution to invent a new unit for engine power, horse power. The naming was strategically chosen whichreferred to the strength of draft horses, so that the common people who haven’t used an engine in their life could easily understand and relate.
To determine a ball park value of the power of a typical draft horse, he came up with some experiments for which we have conflicting accounts. In the end, he declared that a typical draft horse could perform about 32,400 foot-pounds of work in 60 seconds while maintaining the power rate throughout the workday. He rounded up the figure to 33,000 foot-pounds per minute for one horsepower.
So, by his estimation
“a good draft horse could lift 33,000 pounds of material 1 foot in 1 minute or 3,300 pounds of material 10 feet in one minute, and so on.”
While the estimate was a very generous compliment to the horse’s abilities, the accuracy of the number was of no concern, but rather the unit’s name. Also, by overestimating a horse’s workload, he made sure that when people do use his engines, they would get the impression of a marked difference and over delivery, a great tactic for generating word-of-mouth marketing.
In the end, Watt’s idea did manage to make his steam engine famous and played a crucial role in speeding up the process of building the technology we enjoy today. And while as an engineering student it is always a pain to keep converting units, you can always use the conversion charts and resources like these to help you convert quickly!