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Old 11-09-2009, 09:21   #1
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Get-Home Power

I have a 20K genset. Would that power an electric motor driven propellor rigged up like the rat tail diesels you see in Asia? My boat is powered by a 200hp 8/71.
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Old 11-09-2009, 10:32   #2
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Assuming you could output 20K of power at 100% efficiency using a perfect electrical motor there can never be more than 26.8 horsepower. You can convert by math 20K by multipling by 1.341 Hp/KW. You might get 70 to 80 percent efficency. For a 63 ft trawler you won't be moving very fast.
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Old 11-09-2009, 12:12   #3
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Buying an outboard and mounting it to your transom as a "kicker" would probably be a more practical solution. A twenty horse outboard could push you back to port at two or three knots.
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Old 11-09-2009, 12:30   #4
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I would consider that if it were a diesel. I would not want to carry any more gasoline than 20 gls for my tender 6 hp outboard.
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Old 11-09-2009, 12:46   #5
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something similar has been odne

these guys did just that, albeit far more complicated, and using an 8 kw generator. I worked on the boat, insofar as the generator install. It did work, but they seem to have fallen by the wayside.

search for fast electric yacht systems (Feys.org - Propulsion System Yachts Resources and Information.This website is for sale!)

Yanmar used to make a diesel outboard, you may be able to find one for sale in another country, but not here.
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Old 11-09-2009, 14:28   #6
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It won't be cheap or easy because you'll have to do a lot of 'one off' engineering, but it can be done.


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Assuming you could output 20K of power at 100% efficiency using a perfect electrical motor there can never be more than 26.8 horsepower. You can convert by math 20K by multipling by 1.341 Hp/KW. You might get 70 to 80 percent efficency. For a 63 ft trawler you won't be moving very fast.
Hp ratings for electric motors just don't fit well into those handy,dandy thumbrules. Horse power means lifting a #550 pound object one foot for one second. Works well for mechanical calculations. However motor wattage is based on current times voltage, little to do with lifting or pushing, and trying to make direct horsepower comparisons will always leave you off by a mile. You're converting Kw to Hp back to Kw. Keep it in kw and look at it this way, with a 20Kw generator you could run a 36V motor at 550 Amps(forgetting the normal losses for a minute), or a 120V motor at 150 Amps.

Engines are rated at their peak HP. Motors are rated at their continuous hp. Most motors are capable of 8-10 times their continuous hp rating. That's why most of the electric car conversions are done using 5-25 hp motors.
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Old 11-09-2009, 14:52   #7
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glacier bay

Glacier Bay is manufacturing synchronous permanent magnet electric motors for marine propulsion, but even their smallest motor--20 hp--runs off 240 volts DC.

Glacier Bay - Products
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Old 11-09-2009, 15:23   #8
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Nordhaven has also done something interesting with a "come home" engine in the 62'. Next to the main engine was a smaller (about 30 hp) diesel. I can't remember the exact clutch arangement, but this setup would drive the main shaft in the event that the main engine crapped out. I can see this being cheaper than the electric alternative.

after another read, it's not clutched to the same shaft, rather is independent. see below.


"Get Home" power is a major concern for those venturing to far off places, and Nordhavn again gives this area special attention. Each 62 is equipped with a separate 4-cylinder wing engine that drives a feathering prop. The boat can be driven in open ocean conditions and is perfectly capable of being brought home if the main engine is disabled. The wing engine is installed with its own electrical system and is used to power the hydraulic systems for the bow thruster, windlass and emergency bilge pump system.
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Old 12-09-2009, 10:30   #9
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I would consider that if it were a diesel. I would not want to carry any more gasoline than 20 gls for my tender 6 hp outboard.

Check with Laborde Products (maybe Laborde Products Web Site, Yanmar, Mitsubishi, Hatz, Mase and FPT engine distributor) in New Orleans. They may still have a few of the 27 or 36hp Yanmar diesels around or know where you can get one.

I believe they can only sell them for export and you would probably be fined and the motor confiscated if caught using it in US waters - but as a get home motor might be worth the risk.
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Old 14-09-2009, 11:48   #10
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Nope they don't have any, and they said that when they were still selling them there was an 18 mo waiting list
thanx anyway
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