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Old 18-06-2017, 15:53   #16
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Re: Small generator + electric propulsion for dingy

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Actually they do my tohatsu has a 6amp alternator built in .
A 2 horsepower?
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Old 18-06-2017, 15:56   #17
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Re: Small generator + electric propulsion for dingy

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A 2 horsepower?
No not a 2 horse it was a 6 horse. Now I have an 8 with a 10 amp alternator. It is both my primary engine and my tender engine for longer distance than I want to row.
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Old 18-06-2017, 16:06   #18
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Re: Small generator + electric propulsion for dingy

Honda makes a charging kit for their little 5 horse engine only 3.75 amps but it is charging.
https://marine.honda.com/parts/acces.../charging-kits
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Old 18-06-2017, 16:33   #19
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Re: Small generator + electric propulsion for dingy

I figure my first attempt at this would be using my small 12v generator from a weed eater and an extremely small alternator from a tiny car engine. This was not built with this or marine application in mind so I forgot I already have that, just haven't tried it with the trolling motor in the dinghy yet. Eventually I'd like a propane carburetor since the only gasoline I want on my boat is for cleaning paint brushes and such. My big 4kw generator and main power is diesel. Cooking is propane and microwave/electric convection oven with a bread maker attachment I built. I have no problem with going against the flow, I have a milling machine/lathe in the engine room, I have a composting toilet, RV washer dryer, and will have a walk in tub head. I also have a bicycle with full size fold up wheels that will eventually fit carry on luggage and it will also eventually have a propane motor for it. I've already traveled from Kansas to south Florida on a weed eater powered bicycle. I enjoy creative solutions to problems.
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Old 18-06-2017, 16:56   #20
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Re: Small generator + electric propulsion for dingy

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No not a 2 horse it was a 6 horse. Now I have an 8 with a 10 amp alternator. It is both my primary engine and my tender engine for longer distance than I want to row.
Handy. But the OP is talking about much smaller engines.
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Old 18-06-2017, 17:06   #21
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Re: Small generator + electric propulsion for dingy

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Handy. But the OP is talking about much smaller engines.
True however there are also the torquedo electric outboard motors that rate up to several horsepower. As well.
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Old 18-06-2017, 20:11   #22
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Re: Small generator + electric propulsion for dingy

My idea was to justify the generator as a dual purpose device. My calculation includes 20 lb for the generator, 5 lb for the transformer, 10 lb for the motor - still half the weight of a 2 hp outboard.

The battery I have not decided on. The problem is that you want to draw at least 50A to power the motor and for that you either need a heavy wet cell or an expensive Lifope4. The reason why they do bit put alternators on small engines turns out to be weight and inefficiency. Apparently, a 12V DC alternator is less than 40% efficient. To get the high efficiency of inverter generators (>70%) they generate high voltage AC, then high voltage DC then invert it. It turns out the whole trip is more efficient. Hence you can get 800W from a small 1.4HP engine. I agree that it is a low utility project. It looks inexpensive at first but the usability is low. May be if I could put the exhaust in the water it could help but it is complicated.

I have pretty much decided that the best way to spend money on a sailboat is to invest in new sails.
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Old 18-06-2017, 20:48   #23
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Re: Small generator + electric propulsion for dingy

My 3.3hp mercury weights 28 pounds and is all in one package. I think the Honda is even less.
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Old 18-06-2017, 21:18   #24
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Re: Small generator + electric propulsion for dingy

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My idea was to justify the generator as a dual purpose device. My calculation includes 20 lb for the generator, 5 lb for the transformer, 10 lb for the motor - still half the weight of a 2 hp outboard.


I have pretty much decided that the best way to spend money on a sailboat is to invest in new sails.
Ok the honda 2.3 horse air cooled 4 stroke outboard with integrated fuel tank weighs #31 for the long shaft model which is lighter than your listed parts not including the battery.
The last part of your post is the best part of this post.
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Old 18-06-2017, 21:40   #25
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Re: Small generator + electric propulsion for dingy

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My idea was to justify the generator as a dual purpose device. My calculation includes 20 lb for the generator, 5 lb for the transformer, 10 lb for the motor - still half the weight of a 2 hp outboard.

The battery I have not decided on. The problem is that you want to draw at least 50A to power the motor and for that you either need a heavy wet cell or an expensive Lifope4. The reason why they do bit put alternators on small engines turns out to be weight and inefficiency. Apparently, a 12V DC alternator is less than 40% efficient. To get the high efficiency of inverter generators (>70%) they generate high voltage AC, then high voltage DC then invert it. It turns out the whole trip is more efficient. Hence you can get 800W from a small 1.4HP engine. .

Just stick a propeller on it and you get 2 HP from a 2 hp motor.

Looking at the specs, the dry weight of a Honda 2 is 27 lbs.

So an outboard will be lighter, cheaper, more reliable, safer and more effective. It'll also take up less space in the dinghy.
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Old 18-06-2017, 23:44   #26
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Re: Small generator + electric propulsion for dingy

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My idea was to justify the generator as a dual purpose device. My calculation includes 20 lb for the generator, 5 lb for the transformer, 10 lb for the motor - still half the weight of a 2 hp outboard.
Incorrect. The Suzuki 2.5 four stroke weighs 30 pounds.
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Old 19-06-2017, 04:15   #27
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Re: Small generator + electric propulsion for dingy

I'm surprised that no one has mentioned the Torqeedo in this discussion. It is an electric outboard motor with equivalent thrust of about 3 HP. It is powered by its own self contained low voltage battery. The entire thing is lightweight and easily carried in one hand. The battery can be charged from any 12V source, like ship's power, for example. I've been using one to power my dinghy for 4+ years and I think it's just great.
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Old 19-06-2017, 04:25   #28
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Re: Small generator + electric propulsion for dingy

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I'm surprised that no one has mentioned the Torqeedo in this discussion. It is an electric outboard motor with equivalent thrust of about 3 HP. It is powered by its own self contained low voltage battery. The entire thing is lightweight and easily carried in one hand. The battery can be charged from any 12V source, like ship's power, for example. I've been using one to power my dinghy for 4+ years and I think it's just great.
Certainly a much cleaner, lighter, more practical solution.
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Old 19-06-2017, 04:59   #29
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Re: Small generator + electric propulsion for dingy

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Originally Posted by fguptill View Post
I'm surprised that no one has mentioned the Torqeedo in this discussion. It is an electric outboard motor with equivalent thrust of about 3 HP. It is powered by its own self contained low voltage battery. The entire thing is lightweight and easily carried in one hand. The battery can be charged from any 12V source, like ship's power, for example. I've been using one to power my dinghy for 4+ years and I think it's just great.
Good old magic EP again. Somehow, according to Torquedo, 480W output power (0.64HP) = 3HP.

You cannot directly equate thrust to HP!!

At least Minnkota are honest:
https://www.minnkotamotors.com/faqDetail.aspx?id=1397

"Although there is no direct correlation of thrust to horsepower you can approximately calculate the horsepower rating of any electric motor. Just multiply motor amp draw times voltage to find the wattage of the motor. Wattage divided by 746 will give you the horsepower rating of the motor (746 watts equals 1 HP)."
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Old 19-06-2017, 05:38   #30
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Re: Small generator + electric propulsion for dingy

Another issue with the generator in the dingy. Do you have to install some sort of custom exhaust system?

With an outboard, the exhaust either goes out the prop or at least points to the stern away from the boat as you are moving forward.

A generator inside the hull will pump that heat into the boat. Make sure it isn't close to the sides of an inflatable or it could melt a nice hole very quickly.

There are just so many failure points in this idea it's crazy.

+1 on the magic electric HP response. I could pull the queen mary across country with a 5hp lawnmower motor if I hooked up the right gearing and mechanical advantage. Doesn't make it "equivalent" to her 50,000hp main engines.
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