It´s spring and that means high season for boat dealers: All the new yachts have to be commissioned and handed over to our clients. This means a lot of travel, at least some sailing and a load of talking, lecture and chat. I recently noticed a detail that I found interesting and decided to make a little article about. During handovers, when it comes to the Diesel engine of the yachts, I very often get the question: “What is an engine hour?” Well. It seems kind of ridiculous, but there´s a true … let´s say … misconception behind it.

Ignition activated: Time is running?

Whan switching on the main power supply for the starter engine battery on the panel, the operating hours of the Diesel engine will be on display. Since all of Beneteau´s yachts will be thoroughly tested in a pool back in the shipyard, they will also run the engine for a while and that is the reason why all of our new yachts will show a total of one to three engine hours upon handover day. But somehow, there is a persistent myth regarding the method of counting around that number.

A myth surrounding the operating hours of a boat Diesel

It goes like this: Back in the day when everything was just mechanical and there wasn´t any plastic box containing some digital stuff mounted to the engines, the only way of counting an hour – meaning time – was to use the revelations of the engine. The “counting box”, as they say, used the RPM to somehow extrapolate from the revelations of the engine a running time. Maybe that is something they really did some 30, 40 or more years ago, with it comes an interesting detail.

Modern vs. old boat Diesel engines

Since this “RPM-to-hours”-box was just an approximation this meant that there would have been a difference in the operating hours on display. Imagine an engine running with low RPM and one running with high RPM. The “counting boxes”, since just approximations, would show less operating hours for the slow Diesel and subsequently more hours for the sprinting Diesel. Which, usually those people conclude, would be much better for assessing the general condition of a Diesel engine. The one running low would have “suffered” much less, hence less hours and much more attractive to buy compared to the Diesel that was running with high power all the time, displaying much, much more hours as it was “suffering” much more. Sounds believable?

Pretty accurate counting

Well, I´ve talked to many Diesel-specialists for this little article. All of them gave me a smile and the same answer. Be it the Nanni Diesel guys back in La Grande Motte boat show, my German Volvo-Penta importer or our own Diesel specialists in the shipyard: This is just nonsense. At least for modern or recently built boat engines. An hour … is an hour. That said, if you see 30 engine hours on your display, does it mean that it was running for 30 hours in total? Well, not quite …

Not an hour of turning props though

A timer will start once “ignition” or current supply by the starter battery is activated. Time is running now. And counting. But since we usually start the engine mere seconds after this event (more so because we want to mute the enervating beep coming out of the panel), the time delay between the start of the counting and the actual start of the engine is minimal. Nevertheless, on a charter yacht with 3.000 operating hours, the “empty seconds” could add up over the lifetime of the engine. To maybe 3 hours? Okay. Now that this is cleared, let´s have a look at stories that maybe really matter.


Related articles of interest:

A common misconception regarding bow thrusters

Volvo-Penta or Yanmar? Which boat Diesel to choose?

Seafarer´s superstitions