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Why waste money?

None of us likes wasting money. None of us likes polluting the air. This blog comes in three flavours. A few words here, a short video on YouTube and a lengthy engineering assessment of the different ways of propelling a narrowboat.

When a narrowboat powered by a standard diesel engine is gently cruising down the cut, its engine is running at about 10% of its potential power, and 40% of its potential economy. That is, for every £1 spent on diesel, 60p is wasted because the engine is running so gently.

We can give the engine some more work to do, and as a consequence improve its efficiency by adding a generator that it drives in parallel with the propeller. The electricity generated can be used to drive a motor later in the day. By doing this we can reduce the waste to 50p. Good, but not brilliant because we're still not really challenging this engine.

If we really want to get the engine efficiency up, we need to use a smaller engine and get it to work hard, just generating electricity. Then use a motor to drive the propeller. This is a "series hybrid" system, and will waste less than 40p.

Please take a few moments to check out my vlog - carried out observing all government Covid protocols.

For the more academic, here is the technical analysy.

Narrowboat Drive System Efficiency
Download PDF • 269KB

If anyone has comments on this paper, I would be most happy to receive them and possibly improve the text.

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3 Kommentare

As an engineer myself I agree with your analysis. However I have always accepted that when cruisng I would be throwing a ten pound note into the water every couple of miles or so. This is the cost of narrowboating. Yes, the sound of my BMC 1500 throbbing away under my feet does to some ectent modify the birdsong but I still have no difficulty in hearing the shrill "kreee" of the kingfisher and the "chiff chaff" from the tree tops. My boat is approaching 40 years old. Increasing the engine revs by changing the gearbox from 2.0:1 to 3.5:1 has been considered but noise and vibrations could then beciome more of a problem. I do not think that …

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Dave Jesse
Dave Jesse
16. Nov. 2020

You are right, of course, but I had to bound the discussion somewhere. The efficiency I calculated was from fuel input to propeller shaft power output. Any system that adds "free" energy will look good, but it's unfair to make a comparison with straight diesel engines as they cannot play that game.

If you take this argument to its logical conclusion you get to mothership marine and Shine's almost completely solar power. I just have an Englishman's aversion to relying upon sunshine!

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Mark Bloxham
Mark Bloxham
16. Nov. 2020

You could always put plenty of PV panels on the roof. That would increase efficiency no end. The latest available 2.2m X 1m panel chucks out up to 460W and early next year a slightly larger one by Jinko Solar is 600W.

I'm putting three X 460W on my roof. with these:

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