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We received several letters regarding the article Hybrids Are Not The Answer, in the March 2011 issue. Here are these interesting exchanges on the subject, which will shed even more light on the question of hybrid propulsion for boats.

Norman Nudelman, Editor

M. Gerr,

I read with interest your article about the inefficiencies of hybrid systems. I must agree that when vessels are driven at their most efficient design speed, with the right propeller and the right gear, it is difficult but not impossible to be bet-ter than a new technology diesel.

However, boats are often sailed at the wrong speed, such as in and out of port, waiting for bridges or dock space, to meet certain demands (fast or slow) or in bad weather where the best drag curve has no meaning. The world is not perfect and the best use of hybrid’s automation is to optimize the operation of all available resources of electric, batteries and generator to match variable demands. Furthermore, most modern boats have fairly hearty electrical house loads, even if they aren’t cruise ships. The best way to create all that energy, apart from a shore connection, is with a good vari-able speed, light and highly efficient permanent magnet DC generator. New-technology HVDC generators are 70% more efficient over their lifetime than a fixed-speed AC generator. We are working on optimizing hybrid propulsion for large boats, and our experience is that there are substantial en-ergy savings with a properly designed system. Not to men-tion the many other benefits of hybrid power, such as re-duced noise, no fumes in electric mode when docking, and comfort at anchor where the battery bank provides quiet power.

We would be happy to converse with you on this subject, should you wish.

Best regards, Pierre

Pierre Caouette President

ReGen Nautic USA Inc.

Dave Gerr replies:


Thanks for your comments on Hybrids are not the Answer. You present an interesting and valid case for using hybrid propulsion on boats. You are essentially recommending hy-brid propulsion for the same off-speed applications where it can make sense on ground vehicles.

Yes, this is a situation in which hybrid propulsion could show some gains. You would have to assume; however, that the boat equipped with such propulsion

operated a significant portion of the time at such off spe to make this worthwhile. That is not very common, thoug certainly can be the case on specific vessels. Of course, there are still the loses incurred with changing forms of e ergy--mechanical to electrical and back; or mechanical to battery/chemical to electrical and back to mechanical.

This also does not take into account the excellent option for conventional non-hybrid propulsion to meet these off-speed operational needs. Controllable-pitch propellers ar usually the best way to address regular operation at varia speed and variable loads. Controllable-pitch propellers ar very reliable, and--compared to a hybrid propulsion syste inexpensive and simple.

The next option--for situations involving protracted operat at low speed--would be a controllable-pitch propeller with small "loiter" engine that is clutched in to the main shaft, with the high-power main engine decoupled for low spee This too is established technology, and leads to very effici operation at low speed. Again, there are none of the lose involved in changing forms of energy, and it is still less ex pensive than most hybrid packages would be.

It's hard for me to come up with a scenario in which the above two conventional options wouldn't out perform a h brid propulsion package in both efficiency and in cost (sh term and long term).

In order to really justify the additional cost and complexit a hybrid system on a boat (even one that operates for lon periods at off speed) you would also have to factor in larg and variable domestic electric demand. You mention this your comments. A careful analysis of such a vessel (long periods at off speed and high but variable domestic load could well show an overall net gain in efficiency. In my op ion, this would not be common on most boats, however.

Finally, there is the efficiency of cost. This is too often ov looked. Westlawn Institute has a question in one of its ad vanced systems lessons that asks students to calculate t number of hours a boat with a higher-cost diesel engine would have to operate to make up for/break even with th lower initial cost of a gasoline engine of the same power. The answer surprises most students as it is a very large number of hours. The still greater costs involved in a prop hybrid-propulsion package for a boat make the differenc cost between conventional diesel or gasoline look paltry.

What does this high cost of hybrid propulsion mean? It means that--even in those instances where you could de onstrate improved operational efficiency with the hybrid package--you would still have to operate thousands of ho

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