Installing electric propulsion on a 14.6m motor cruiser: realistic and feasible?

Discussion in 'Hybrid' started by watervole1, Jul 27, 2008.

  1. watervole1
    Joined: Jul 2008
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    watervole1 New Member

    Hi guys. I hope I have put this thread in the right forum and apologies if it's not.

    I am thinking of purchasing a restoration project, a motor boat.
    The boat was built in 1925, was apparently blown up on a mine at some stage in its life and completely restored. It is now in a poor state, although can still restored.

    It is 14.63m long, 3.2 metre wide with a draft of 1.06metre, and weight about 17 tons. Both the diesel engines are pretty knackered I understand.

    So my first question really is: would it be realistic and feasible to replace those diesels with electric propulsion, or some sort of hybrid installation, with a generator charging the batteries?. The boat would be used on inland waterways, mostly. Possibly as a liveaboard, so moored every night, when cruising.

    I know very little about electric propulsion, as you probably will be able to tell from daft questions that may appear on my part! But I am keen to learn.

    My second question: What sort of installation is needed? Motors? batteries? There are two diesel engines on the boat, would it need to have two electric motors?

    Many thanks Joel

    Is it possible to get some idea of what the cost for such installation would be?
  2. juiceclark

    juiceclark Previous Member

    We've been discussing hybrid propulsion non-stop on this website but too little of it makes it onto this "hybrid" page! It seems a piece of cake...just buy plenty of genny and, with all the torque of electrics, have plenty of prop. I'd say a 30k Isuzu genny (1.8 g/p/h) will give you a nice, slow boat.

    Direct drive:

    Belt driven:
    sorry, can't find that link...around here somewhere

    Hybrid diesel doing both now on the market:

    I know what you're thinking...everybody should be utilizing electric or hybrid with all these no wake areas and the joy of slow, silent and efficient cruising. Why aren't boats for sale with this now? Blows my mind really kind of pathetic.
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    FAST FRED Senior Member

    Cheapest would be to be willing to go slow , and install used diesels of about 50 hp each.

    There is no "electric " way to go that wont run over $100K $200K US and be a bear to design , install and operate.
    Actual performance and resale value will be really iffy.

    There is little IF in an off the used shelf diesel.

    How about repairing the existing engines?

    What are they? Some old engines are a snap to rebuild .

  4. mkamakazi
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    mkamakazi New Member

    I have been doing quite a bit of research on this subject as I also want to converto to electric propulsion. It is expensive, but I think in the long run the value you will get out will be good. Eventually I would like to see the electricity come from fuel cell technology run off hydrogen plus additional power from solar panels.
  5. Guest625101138

    Guest625101138 Previous Member

    Not much point in using electric unless you have a substantial proportion of your energy coming from wind and/or solar.

    You can run a diesel electric system at about the same economy as diesel but why bother with the complexity and cost. You are still stuck with the diesel just a bit more flexibility in where it is located and you might be able to run it closer to top efficiency in varying conditions.

    Boats are not like automotive where there is real advantage in regenerating from the brakes particularly in city traffic. Not often you need to apply brakes in a boat.

    Rick W
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    FAST FRED Senior Member

    "there is real advantage in regenerating from the brakes particularly in city traffic."

    And the latest method of using the brake energy is to charge up a big capacitor , and use that energy all up accelerating when the light changes.

    Too slow and inefficent to attempt to recharge a battery.

  7. juiceclark

    juiceclark Previous Member

    Brakes? Screw the brakes! Running a big diesel without somehow utilizing the thousands of free watts produced from an attached, free-spooling electric motor seems inefficient. That very small hybrid diesel from Steyr makes 7KW while running. What a colossal waste to not use it. There's so much potential cogeneration not being utilized in boating that industrial machinery has long been tapping.
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    FAST FRED Senior Member

    There's so much potential cogeneration not being utilized in boating that industrial machinery has long been tapping.

    There is NO free power . If that Styer is producing electric it will be in the fuel consumption , and you WILL PAY for it.

    Free you can use the heat from the cooling system , usually for heating the outside hand rails on charter fish killers, or simply for domestic hot water and cabin heat in cool areas.

    The exhaust heat can be run to a turbo, with all the hassles at slower speeds that gives , or to a warming oven.
    As an exhaust leak might allow exhaust into the cabin its seldom used for cabin heat.

    Exhaust heat was also used long ago to help distill water for the vessel , but I haven't seen a small unit in decades.

    If you could build a nice air cond that worked on exhaust heat , or hot water , the world would beat the mythical path to your door! Co generation is all well and good , but creating electric aint free!

  9. Rvanvoris
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    Rvanvoris Van

    It seems to me that with the price of fuel the front end cost of a diesel/electric propulsion is worth it if one is comfortable with a relatively slow boat.
    I am currently building a 32-ft Jay Benford designed Friday Island Ferry for a live aboard. I am going to change the designed 20-hp diesel for a ST38 by Solomon Technology. This motor should drive the boat at about 6-knots cruising speed. Although the initial cost of installing this system along with Gen set and batteries is $10,000 more than a conventional engine I think the payback of much less running cost, plus the advantage of quiet cruising, less maintainance and higher resale value boat justify the expense.
  10. juiceclark

    juiceclark Previous Member

    Please share photos and describe your project as it happens?!

    A charter sportfishing boat has to troll all day long at 7k with clients sucking the diesel fumes of the big diesels. With a 20k genny already on board, a Solomon electric motor on the shaft would be great if it could give us 7k with the prop. appropriate not for it but for the primary engine.
  11. Guest625101138

    Guest625101138 Previous Member

    The reason you get a fuel saving is because you are happy to go slower. It has nothing to do with overall system efficiency.

    The system makes sense for a live-aboard where you have many auxiliary needs and just occasional short range motoring. For long range cruising it would be more economic to just go with a smaller diesel and save on all the control gear that will have its maintenance problems.

    Rick W.
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    FAST FRED Senior Member

    This motor should drive the boat at about 6-knots cruising speed.

    I would think 6K is not realistic for electric power ,.

    The boat is probably 25 ft LWL , so the sq rt of that (SL) is 5K , a more realistic speed .

    The cheap power requirement for most boats is SL times between .9 and 1.1

    1.34 is "hull speed" which will require about doubble the power of SL.

    There is NO efficiency gain using a gen set to power a drive.

    ONLY if you get "free" fuel from a wind generator or solar set or "free to you" from the dock source does any savings come.

    There will be NO "much less running cost" unless you have a huge battery bank that can be charged hard enough to have the gen set operate at its "optimum" efficiency.Oversize even slightly and you will have the same efficiency as a std diesel loafing.

    I suggest you go to Professional Boat Builder and READ the articles by Nigel Calder on this subject , and the genset tests.

  13. alan white
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    alan white Senior Member

    Rick W. has it right. The whole idea of hybrid power in automobiles is based on the assumption that most of the energy consumed in normal engines/cars is wasted. Not so for boats, which are far more efficient (yes, they are) than cars. In other words, boats DO more with less energy (though they do a lot more than cars). In essence, they are like cars that are always going uphill. If you imagine a car that always goes uphill---- never down, that's what a boat does. And would anyone ever consider building a hybrid car that only goes uphill? Where's the regenration? The downhill never arrives.
    If a boat were to be designed to take advantage of electric propulsion, it would probably be only marginally more efficient than running a straight diesel or gas power plant. Initial cost would be high, but maybe offset by gains in slightly higher efficiency due to elimination of gearing with its attendant heat generation. The diesel could also run at optimum fuel-sipping RPM constantly, also contributing to lower operating costs,
    Still, the system is far more complicated (hence more initial expense to offset).
    There are banks of batteries, a genset, expensive controller, and the electric motor itself.
    All this means weight. More weight than a single powerplant and more space too.
    Also, while the word "hybrid" could be applied to such a boat, in truth it would be better termed an electric drive diesel, since the word hybrid causes one to think of very high efficiency (like cars that get double the mileage of their non-hybrid cousins). If fule savings could be realized in the electric/diesel boat, they wouldn't come close to cutting the operating costs in half, especially if amortized costs to cover a much higher initial outlay are considered.

  14. masalai
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    masalai masalai

    My research, using a catamaran configuration for a 39 ft live-aboard 24 ft wide, with very skinny wl (2 ft) hulls, indicates significantly higher capital cost, when motors, batteries, gensets and CONTROLLER/other controls were all added in.

    I tried to justify it based on difficulty of getting fuel in future and a capacity to use CNO from a retirement farm I would live on/near.... even to adding 3.5 kw of solar panels at around A$40k and hitch-hiker sails - all to no avail - the numbers just do not stack up....

    If you feel confident you can get fuel OK, then there is no perceived advantage in going electric... - - - Where "NO diesel" is taken into account - a sail-boat with an auxiliary for emergencies, solar panels and wind turbines for house batteries etc....

    I may yet go for electric, if solar panels are a lot cheaper and more efficient, and I can put at least 4kw collectors on cabin top as most use will be in cooking and all other ships services.... - - The batteries to give me 20 minutes, to clear anchorage and set sails, or to motor into the anchorage.... supplemented with maybe a single 10kw genset....

    - - - - The probability is, that direct drive diesel motor/s will be cheaper and more fuel efficient? - - - - - - - Saving on 2 expensive controllers, 2 motors and between 6 to 16 agm batteries, 18 x 200w solar panels & their regulators, additional wireing, heavy duty cables etc......................

  15. Autodafe
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    Autodafe Senior Member

    Hi Joel,

    Certainly electric propulsion is feasible on a motor cruiser.
    Diesel electric systems have been in use for almost a hundred years, and have proven reliable and efficient.

    A carefully designed diesel electric system can be more fuel efficient than a mechanically driven diesel system. How much more efficient depends on how good your diesels are to start with (this varies a lot, and depends on matching propeller to engine and boat as well as the engine efficiency) and how you drive your boat. If you are always travel at a steady cruise any system can be pretty good, and gains between systems consequently small.

    Electric motors have more flexible torque curves than internal combustion engines (witness the fact that electric cars do not require gearboxes). This means that the diesel powered generator can be run at a fairly constant (and efficient) speed while the propeller speed and torque adapts to varying boat motion. This also proves advantageous for low speed maneuvering as the genny can be revved to give lots of power while the prop speed is kept down at high torque to avoid cavitation, increasing thrust.

    You should note however that the very efficient generators and motors required to do better than mechanical drive are fairly specialised and not cheap. I have never bought a system like this, but the prices I've seen suggest a hybrid electric system will cost up to 150% of a direct drive system to install.

    If cost is you're only objective you should get quotes for both types of system and compare the difference to expected fuel savings and possible maintenance savings.

    The basics of the system are an electric motor (or two), motor controller (for each motor), and a power source. The power source can be either batteries or a generator or both. For a motor cruiser I would think there is little gain in having a lot of battery. Batteries are useful if you have intermittent generation(eg. wind, solar) and only require a short range under power (eg sail boat auxiliary for maneuvering in harbor), but are not required.

    In my opinion electric vs diesel shouldn't affect the number of motors. In general if you are set up for two motors it will be easier to stick with the arrangement - the boat will have been designed for thrust in a certain place. It will also allow you to use existing engine mounts and prop shaft arrangements. And two engines is *very* nice when moving in tight spaces.

    As with most aspects of boating, almost any option can work well if well designed, and you might as well go with whatever system you like best.

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