When you are in the market for a new luxury motor yacht, or a tender, or perhaps new engines, a stat that you always compare is “horsepower” or HP. But, do you know what that HP rating really means?
When trying to compare the performance of marine engines, you need to understand a bit more about HP ratings.
So why horses?
It may seem silly to still compare today’s modern engines to horses, but historically the term was a lot more relevant. We can trace the origins of “horsepower” to a Scotsman, named James Watt, who had built a steam engine that he wanted to market to local miners in the 18th Century.
The miners used horses to power the pumps that drained the mines. Watt needed a way to illustrate how many horses could be replaced by one of his engines, to show the owners of the mining operations how they could be economical. He needed a unit of measure, and Watt coined the term “horsepower.” After much experimentation, he determined that a Cornish horse could continually lift 330 pounds of water an average of 100 feet each minute. Multiplying 330 times 100, Watt set his “horsepower” at 33,000 foot-pounds/minute, or 550 foot pounds per second (FPS).
This number still stands today, officially sanctioned by the Society of Automotive Engineers as the standard value of one SAE (or English) horsepower. By the way if you are wondering if Watt gave his name to that other unit of power, indeed you are correct!
In honor of his contributions to the development of the steam engine, the now well-known unit of power the “watt,” was named for him in 1882 by the British Association for the Advancement of Science.
Horsepower applies to diesel engines, as well as gasoline, or hybrid engines. Horsepower is horsepower. There is no truth to the common misconception that “diesel horse power” is somehow “stronger” than gasoline horsepower. In terms of actual “horsepower” a 1000 HP diesel engine, is the same as a 1000 HP Gasoline engine. However, operating over the course of 10 hours, the diesel may produce more useable power, because of differences in fuel efficiency, RPMs and torque. That is just one of the reasons why when comparing engines, you have to look at more than just the HP ratings.
It is also very important to understand how a given engine’s HP was determined. You must read the fine print on the spec sheet of any engine. It will tell you if the HP rating was given for the engine operating alone, or powering various accessories that would be in use while you are underway.
A more accurate and valuable statistic, used by some but not all marine engine manufacturers, is shaft horsepower, or SHP. SHP is the power measured at the propeller shaft coupling flange, and takes into account the losses of the engine power drawn by accessories.
You also have to make sure that you compare apples to apples. There is a metric HP that differs from English, or “SAE,” horsepower.
Keeping Your Engines Trouble Free
As you can see, there is a lot more to your engine’s horsepower than you may have realized. Our engineers and maintenance technicians know all about HP ratings, and everything else there is to know about keeping your yacht’s engines running long and trouble free!
It’s all part of our On Demand Yachting solution. With On Demand, you can be sure that your yacht is well-maintained, and kept in top operational condition. And, since the system is completely transparent, when it comes to getting information about any repairs or maintenance issue, you can be sure you are getting it straight from the horse’s mouth!
Operating a motor yacht can be costly. You can reduce your expenses, and avoid costly repairs by keeping her well maintained. On Demand yachting from FYM can help. If you would like to learn more, or if you have any questions or comments about this blog post, do not hesitate to contact our Yacht Management specialists, or call us at (855) 318-6328.