With modern technology we are familiar with instrumentation providing lots of information about the performance of machines and equipment. Our Volvo car provides information to the driver on average and instantaneous fuel consumption, how many miles to the next refuelling, and average speed.
Albert, of course, is very low-tech with just oil pressure and water temperature gauges in sight of the steerer. However, below decks there is the control panel that was supplied with the engine. It contains water temperature and oil pressure gauges, an electrical hour meter and a mechanical revolution (RPM) meter. It was the the last two that got me thinking.
I scarcely note the RPM meter except when moored-up or when someone else is steering. However, when asked "What engine speed do you use when cruising?" I usually answer "Between 500 and 600 RPM on canals and maybe 750 RPM maximum on rivers". It has recently occurred to me that because the original mechanically-driven RPM meter incorporates an equivalent hour meter I actually have information available for a more accurate answer, at least on the overall average speed.
The mechanical hour meter effectively counts engine revolutions but it displays them as hours assuming a speed of 1500 RPM. If you are operating an engine at constant maximum speed, for example in a generator set, then this would be very useful information - particularly for servicing. On Albert I had yet to find it useful but recently I decided that it might have a use in calculating the average speed of the engine.
I believe the electrical hour meter was installed new with the engine and that the mechanical hour meter was set to zero on delivery; certainly I have not reset them and a majority of the hours on the engine have now been done in our ownership. So, taking the mechanical meter reading (at the moment 838.4 hrs) dividing this by the hours done measured by the electrical meter (at the moment 2381 hrs )and multiplying this by 1500 (the nominal RPM), should give the average RPM achieved by the engine. The answer is 528 RPM.
This sounds about right given the occasional higher speed periods spent travelling along rivers and the periods spent idling in locks.
Surprising what information simple technology can give. Of course it isn't directly accessible and it doesn't come up on a fancy display at the touch of a button!
