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Improving fuel efficiency

Nov 2, 2015
One key finding from Nigel Calder’s HYMAR hybrid drive testing is the necessity for keeping a propeller clean for maximum efficiency.

One key finding from Nigel Calder’s HYMAR hybrid drive testing is the necessity for keeping a propeller clean for maximum efficiency.

Nigel Calder

Recently, the European Union funded a HYbrid MARine (HYMAR) project involving several researchers and myself that explored the possibilities of hybrid marine propulsion. The effort, using my Malo 46 Nada as a test bed, enabled me to collect a mass of performance data from a conventional displacement hull. This data was used as a baseline against which we compared the performance of hybrid propulsion systems. The data we collected provided some excellent insights into the relationship between propellers, hull resistance curves, engine fuel maps and efficiency.

We collected plenty of interesting data, but as far as improving fuel efficiency under power is concerned, we did get are two clear ‘take home’ messages from our testing: 1) Keep the propeller clean, and 2) Slow down a knot or two.

We found that additional improvements in fuel efficiency with conventional propulsion systems can be achieved by careful matching of propeller curves and engine fuel maps. We also know that in many applications we can achieve further improvements with optimized hybrids. However, both of these approaches require significant technical resources. 

Ironically, the single greatest conservation measure we could probably apply to boating at the present time is ridiculously simple and non-technical. It is to install a miles-per-gallon (or gallons-per-mile!) meter, or even a cost-per-mile meter, at the helm station. Most owners, especially of displacement vessels, would be truly shocked at the doubling and quadrupling of fuel consumption and cost that occurs when they try to squeeze out the last knot or two of boat speed. They would immediately ease up on the throttle.

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