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Thread: Electric Drive Question

  1. #1
    Join Date
    Jul 2017
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    Philippines
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    Default Electric Drive Question

    My plan pack for a 20 ft stitch and glue catamaran suggests a 6hp outboard for aux' power.

    I will have 2 x 12v batteries on board with solar panel charging arrangements with a Honda silent running, inverter generator (1600 watts output) available.

    I intend very limited use of the motor, 3 miles distance per day. Max speed desired would be 3 knots.

    The cost of an outboard is considerable considering my intended use.

    I was wondering if any member has a set up incorporating an electric motor and would advise of any problems encountered.

    Any comments would be much appreciated.

  2. #2
    Join Date
    Mar 2015
    Location
    Victoria BC Canada
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    178

    Default Re: Electric Drive Question

    A generator, batteries, solar panels, electric motor, a controller...
    Why not just a little gas engine to a prop?
    The only problem I can see is too much weight and too much money.
    Other than that a 3 hp will move you along at half power at 3 knots.

  3. #3
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    Jul 2017
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    Default Re: Electric Drive Question

    Thanks for your thoughts Tom.
    I'm sorry I did not state the proposed set up more. I will have the batteries and solar panels regardless of the aux power option.
    The generator I have already. An outboard is an easy option but I wondered on the benefits of the electrical drive option.

  4. #4
    Join Date
    Apr 2010
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    Default Re: Electric Drive Question

    Electric drive is quiet. Most trolling motors are designed for trolling, ie very slow. Ive read that model aircraft props can be substituted for the standard prop, which is supposed to fix that.Never tried it though. Also seen setups where the electric motor and prop are nicely encased in a flip up rudder, rather than just hanging a usually over length electric outboard off the back. Newer control systems are more efficient than the earlier versions. But I dont know any of the detail.

  5. #5
    Join Date
    Jul 2000
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    N.E. Connecticut.
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    5,300

    Default Re: Electric Drive Question

    What are your plans for the Honda generator? That's not something that particularly belongs on a boat,... especially not 'below decks'.

  6. #6
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    Jul 2017
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    Philippines
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    Default Re: Electric Drive Question

    Hi nedL
    My description is really bad, sorry. I listed the generator as an asset only, as a part that could be utilised if required for a proposed set-up.
    I do intend to take the generator on board for protracted stays on the boat, primarily whilst at at anchor to charge the house batteries if required.
    On a previous boat, a new Jeaneau 34 footer, I ran a 36inch screen TV, video player, electric kettle, micro wave etc. with a similar electrical set-up. My wife even took her hair dryer? I did not have a propane system on board.
    The generator will be situated above decks to vent the exhaust whilst in use.
    Whilst still in the pre-build stage I am considering an electrical drive system though the commercially available systems are extremely expensive when viewed against my intended hours of use.

  7. #7
    Join Date
    Apr 2009
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    Mountain lakes of Vermont
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    9,716

    Default Re: Electric Drive Question

    I just finished building an 18' fantail launch and powered it with a 24 volt 80 lb. thrust trolling motor. With a three bladed trolling motor prop, it has a top speed of 5.5 mph. I've only been out a few times, but at top speed I can go a few miles and use up 20% of my battery. I've tried the model airplane props (post #4) and can get another .5 mph out of it, but with vibration. Plus, they are fragile.
    I believe MiniKota has a 101 lb. thrust and also a 160 lb. thrust that attaches to an outboard.
    Your cat should be an easy hull form to push through the water.

    I was born on a wooden boat that I built myself.

  8. #8
    Join Date
    Dec 2003
    Location
    Sound Beach, NY
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    3,205

    Default Re: Electric Drive Question

    I have used an off the shelf electric trolling motor and dual purpose RV batteries to power a 20' keel sloop (one ton) a 24' light double end ketch (weight unknown, but probably similar) and a couple of dinghies. I probably never powered more than a mile, but one trip never killed even a single battery. I think the motor is 55lb thrust. It would not drive the keelboats into any significant breeze, but I only used it in a calm.
    I suggest you look for a used trolling motor and try it out. A 20' cat should drive easily. Bring a long oar too.

  9. #9
    Join Date
    Nov 2016
    Location
    Everett, WA, USA
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    430

    Default Re: Electric Drive Question

    I've been experimenting with a 55lb thrust trolling motor lately on a dinghy. A group 24 deep cycle lead acid battery (12V 85Ahr) seems to last about 45 minutes at full power. It will keep going but at a noticeable drop in power after that. That motor pushes my dinghy at just over 4 mph. The motor pulls 600 watts of power at full throttle, (12 volts @ 50 amps). That's 0.8 hp.
    Pushing a 20 ft stitch and glue cat at 3 knots seems reasonable with this setup. With (2) batteries, you could expect about 1.5 hrs run-time using full throttle. That should be able to give you a 4-5 mile range (flat water, no current, no wind).
    Travis.

  10. #10
    Join Date
    Jul 2008
    Location
    Lodi, CA
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    137

    Default Re: Electric Drive Question

    I will second nedL's cautions on the generator. They can cause serious injury, illness, or death if not specifically set up for marine use. Check with Honda, but my understanding is they do NOT recommend their generators for boats. If you want to take along the generator, and use it ashore at your destination that is one thing. Using it aboard is a bad idea.

  11. #11
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    Default Re: Electric Drive Question

    Out there in the real world many, many cruisers use small portable gas powered generators such as the Honda. Some store them below and bring up on deck for use. Some stow them on deck with a canvas cover. They are cheap, reliable, quiet, very little vibration, no installation cost, no through hulls. For most cruisers a heavy, expensive, hard to service, noisy complicated dedicated marine diesel genset makes no sense at all. Just sayin.

  12. #12
    Join Date
    Jul 2017
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    Philippines
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    Default Re: Electric Drive Question

    Thanks for all the comments and the heads up regarding safety and generators. There are risks attached to every item and activity, knowing the risks and using safe working practices can minimise most risks. I have used a Honda generator on board for over five years.
    The petrol fuelled outboard has been ruled out, it will be the electric drive option for various reasons.
    A motor in each hull with fixed props has been suggested which brings the option of a limited recharge of the batteries whilst sailing. The proposed motor supplier is to provide costs, weights and performance figures re thrust and recharge.

  13. #13
    Join Date
    Feb 2004
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    Texas
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    9,371

    Default

    Quote Originally Posted by ThomRose View Post
    I will second nedL's cautions on the generator. They can cause serious injury, illness, or death if not specifically set up for marine use. Check with Honda, but my understanding is they do NOT recommend their generators for boats. If you want to take along the generator, and use it ashore at your destination that is one thing. Using it aboard is a bad idea.
    What are the isdues with them that causes these problems?

    Sent from my BLN-L24 using Tapatalk

  14. #14
    Join Date
    Mar 2015
    Location
    Victoria BC Canada
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    178

    Default Re: Electric Drive Question

    Quote Originally Posted by peb View Post
    What are the isdues with them that causes these problems?

    Sent from my BLN-L24 using Tapatalk
    Primarily carbon monoxide poisoning.
    CO is hugely toxic, odorless and neutrally buoyant in air.
    Our haemoglobin has a 250 times greater affinity for the CO molecule versus O2.
    And with a half life of 5 - 6 hours, it's no wonder so many die from it.
    Ventilate well and be sure the exhaust fumes are travelling away from your boat.
    Know the signs and symptoms and beware.

  15. #15
    Join Date
    Jul 2008
    Location
    Lodi, CA
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    Default Re: Electric Drive Question

    Besides the CO2 issues Tom talks about, there are problems with the grounding of non-marine generators in a marine environment. This can cause electrocution, either on the boat or for people in the water in the vicinity of the boat. Like GrahamH mentions, there are risks with any activity, and boating has many inherent risks. I won't tell you not to use the Honda generator in this situation, but you should know the risks to yourself and others around you.

  16. #16
    Join Date
    May 2007
    Location
    north vancouver isl. Canada
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    973

    Default Re: Electric Drive Question

    Have used a portable Honda generator on a 30 foot ex troller many times but yes some common sense is needed. Run the thing on deck not near any venting you may have. It takes for ever to burn a pint of gas so we're not talking about a lot of emission here just make sure it drifts away. The Honda's have thick rubber feet, on a wood boat not a concern for stray current IMO. Whether you're running 110 to the engine room or 12 volt or whatever for battery charging have good waterproof portable wiring (extension cord). We never used the thing steady for hours just a few hours here and there which sounds like all you need as well. For continuous use a little marine diesel unit would be the ticket.
    Last edited by SaltyD from BC; 08-17-2017 at 11:42 PM.

  17. #17
    Join Date
    Apr 2012
    Posts
    201

    Default Re: Electric Drive Question

    My semi-portable generator is supposed to have the frame grounded when using. How do you do that on a boat?

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