Electric Sailboat

Discussion in 'Boat Design' started by jaxenro, Dec 7, 2009.

  1. jaxenro
    Joined: Dec 2009
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    jaxenro Junior Member

    I know this must have been discussed before but hypothetically if I used a electric motor to power a small (35-40 foot) sailboat could I then use the action of the propeller when under sail to turn a generator to charge the batteries? This way when using sail I could recharge the batteries and have the motor backup for docking and emergencies.
     
  2. marshmat
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    marshmat Senior Member

    Hi Jaxenro,

    The short answer is that yes, you can use the propeller to spin the electric motor while under sail, and an appropriate motor controller can use this energy to recharge the batteries.

    The downside is that a loaded, spinning propeller creates an enormous amount of drag. (This is why most sailboats either use a folding/feathering prop, or else lock the shaft.) Unless it's extremely overpowered and stable enough to make use of all that sail, the boat will act like it has an old car tire tied to the back of the keel: slower and more cumbersome than it ought to be.
     
  3. jaxenro
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    jaxenro Junior Member

    So the best results would probably be obtained by a combination? Let it create the drag to charge the batteries then feather the prop for smooth sailing?
     
  4. messabout
    Joined: Jan 2006
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    messabout Senior Member

    A wind charger is a more practical method. The windcharger will generate some drag but not as much as the submerged prop. The wind charger has the advantage of working while at anchor and has the plus feature of discouraging seagulls.
     
  5. alan white
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    alan white Senior Member

    I think there's a case for a small drop-down prop (cheap and light) that generates (maybe through a reverse-wired trolling motor ) enough to charge a battery while not slowing the boat much.
    I'm not talking about running heavy duty things but maybe those same things wind generators are used for.
    Particularly for long distance cruisers who don't need all kinds of electrical capacity, the kind of people who tread lightly.
    I can also imagine there are people who moor in rivers, like the Penobscot here in Maine, where a strong current reverses twice a day with almost no slack tide.
    Such a simple unit could fully charge a large bank of batteries for free while the owner worked ashore during the week. The cost would be a trolling motor, say 8 batteries, and possibly a controller (though the unit should already have one).
    Then, the trolling motor (if good sized) could also (ever so slowly) drive the boat without starting the engine. Mostly, it would be great for refrigeration and cabin lights, radio, etc., without running the engine, thereby saving fuel and wear.
     
  6. jaxenro
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    jaxenro Junior Member

    My thinking was if it was enough to charge the batteries to do the refrigeration, cabin lights, maybe a radio or other emergency gear, and a small motor to get out of trouble if need be you could dispense with an engine and be mostly self contained without the need for petrol. A low impact type of thing
     
  7. apex1

    apex1 Guest

    You would´nt be able to cruise free from a leeshore with such a tiny motor!

    We had this discussion here for several times, with always the same result: you cannot get rid of a proper IC engine at present.

    Regards
    Richard
     
  8. Timothy
    Joined: Oct 2004
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    Timothy Senior Member

    I once lost my transmition but continued on a four month cruise under sail while still using my engine to charge my batteries maintaing auto piolt refrigeration and all systems. As I have 2 dingies ,a 10 ' sailing dingy on davits and a 20 hp whaler I tow on a painter and bridle, I anchored out whenever I could. To save gas I used the sailing dingy as often as possible for transportation and provisioning. The whaler I used for diving, and as a tug for the times I needed to get my boat to a dock . I secured it to the transom and it was a simple matter to maneuver my boat. . This was many years ago and I have often wondered since , that with the advent of increasingly efficient alternative charging systems (solar ,wind, water), if a system could be developed that dispensed with the inboard diesel and utilized the dingy engine for auxiliary charging and or propulsion if no electric engine installed to replace diesel.?
     
  9. hoytedow
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    hoytedow Carbon Based Life Form

    Of course, the submerged prop would work at anchor if the boat were anchored in any kind of current.
     
  10. narwhal
    Joined: Aug 2009
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    narwhal Junior Member

    At present the power density of even the most efficient storage batteries can't compete with diesel (or even gasoline) in terms of either weight or space. Just as electrics make some sense for around town driving, where long range is less important than fuel cost, an electric auxiliary may be useful for short range use, for manuevering around a dock or mooring, rather than primary motive power at sea when the wind dies. When you run low of diesel or gas, you go buy some more from the fuel dock. When your battery bank is low, unless you are at a dock with a shore power connection, that solar panel or wind generator may take a while to charge your system.

    A significant advantage of the electric auxiliary is its relative silence compared to an IC engine, and for some folks, that's worth a lot.
     
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  11. electricheaters
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    electricheaters New Member

    I'm looking for some help with my latest project. I'm building a 32 foot trimaran and want to power it with a electric motor. I looking at either a Etek or Perm motor run at 48 volt. I would probably use a Sevcon controller with regen capabilities. My concerns is in two categories. First is in regen mode, what stops the batteries from being over charged. I assume that the controller cuts the connection to the batteries but what protects the motor from producing current if it is still free-wheeling. Second is the use of a generator for extended cruising under power. Being a 48 volt system what would be the best way to charge the batteries. The biggest marine generator is 24 volt at 200 amp. Would this still charge the batteries. I have a line on a 7 hp Kubota diesel which I plan to use to power the generator. Could I use a second Etek/Perm motor as a generator (how to protect the batteries)? What about using a switching relay to connect the generator directly to the drive motor.
     
  12. alan white
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    alan white Senior Member

    I think you need to get some info on the controllers that have the amp rating and regen capability you want. They ought to have built-in voltage control to prevent over-charging.
    An Etek or Perm is plenty big enough to run your boat (you could rely on at least 5 hp continuous in any case and maybe up to 19 hp for short bursts).
    The great thing about Eteks and Perms is the weight is very low. I don't think you need two, just belt the engine and the motor/generator together with a centrifugal clutch on the engine. Run this into a forward/reverse tranny so you can disconnect the prop when charging off the diesel.
    That way you can charge off the prop spinning, charge off the engine, steam with the engine while charging, and steam off the motor while the diesel's not running.
    You may need an additional programmable controller to do this so that when the engine is driving the boat it's only charging the generator to a lesser degree, allowing most of the seven hp to turn the prop. In other words, two charge rates. This would be ideal if it could be done automatically.
     
  13. capt vimes
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    capt vimes Senior Member

    electricheaters:
    diesel electric propulsion systems are already on the market...
    http://www.fischerpanda.de/products/eng/154

    and this is only one example out of a couple of sellers...
    the whole system includes e-motor, generator and all the electronic gadgets needed for charging the batteries and running the e-motor either from the batteries and/or from the generator...

    the solutions vary... fischer panda i.e. uses 400 V AC motors and an according alternator of course... so you would not be able to run the motor from batteries only...
    other systems with DC motors could be sometimes run from batteries of course...
    all together these systems are slightly more expensive than a solitary diesel engine of according size for a given boat...

    and no matter the e-motor be it AC or DC - both could be used as an alternator if you are sailing... but it will slow you down considerably...
     
  14. FAST FRED
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    FAST FRED Senior Member

    "My thinking was if it was enough to charge the batteries to do the refrigeration, cabin lights, maybe a radio or other emergency gear, and a small motor to get out of trouble if need be"


    This would require about 200ah per day at 12v.

    The only way you could create this much juice is to sail 35 hours every day in a hell of a wind..

    For efficiency a small very heavily loaded diesel might be best.

    Figure about 2 hp per ton (2240lbs) of displacement so most 40 ft boats would need perhaps a 15-20 hp engine at its 24/7 rating..

    Plan on using the engine for propulsion OR generation , but seldom both together.
    Really expensive batterys, Oddesy or similar and a huge alternator would allow minimum engine operation times.

    No "green" bragging rights , but cruising is more fun than entertaining the Yacht Club Patio.

    FF
     

  15. Timothy
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    Timothy Senior Member

    Fred .I use a similar system , two 12v alternators on 48 hp deisl, one 200 amp with field disconect for the house bank and one 60 amp for the starter. The problem is that the engine is under loaded when used only for charging and even with expensive agm batteries I have to run an hour twice a day for my amp hour needs. I think that with the addition of solar panels the run time could be reduced considerably, but that still leaves me with the problem of the underloaded diesel. The answer to that is possibly a bigger alternator for the house bank. The biggest Balmar makes is 350 amps , still a bit to small. I think you are right though. The way to go,at least with the technologies available today is with a system that uses a diesel engine alternator combination as its main component.
     
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