Water Driven Generators

[Irish Rover]

I have been performing some research on towed generators, and alternators attached to the propeller shaft of boats to charge batteries while underway. Could I get some feedback on what system seems to work the best. Links to products for sale and home made jobs are also greatly appreciated. I perform quite a bit of distance cruising and would like to help charge batteries without the use of the engine. I have already looked into solar and wind. I am interested if water driven would be a good alternate.

 

[Bill Roosa]

Been looking at this for a while. One thing that I have found is in contradiction to what most will tell you, alternator speed has NOTHING to do with output. That is for electricity regulated alternators not permanent magnet types. By manually controlling the field (the rotor winding that spins with the pulley) current make the alternator produce almost full output at 50 PRM. The rub then becomes do you have something that can produce that much torque and a way to transmit it to the pulley. The factory alternators regulator will not produce much current at low speeds due to its inherent current limiting resistance. If you power the rotor directly with sufficiently low resistance in the supply wire it will create a very large magnetic field which accomplishes the same thing as a lesser field at higher speed. You cannot just attach the field wire to the battery however. One the field will be so strong the rotor will lock and you will never get it going and two the rotor windings were not designed to handle that amount of current for very long.
more info
http://web.media.mit.edu/~nathan/nepal/ghatta/alternator.html
and
http://www.duogen.co.uk/

 

[Irish Rover]

I was looking primarily at prmanent magnet generators. I know they rely on RPM to produce the voltage and amperage. They are compact and simple, which is why I like them. I have worked out the RPM range I am looking for. I was curious if someone has built one of these. of if they know where I can buy one, so I can look at their design.

 

[Bill Roosa]

permenant magnet genset

The only problem with PM is how do you regulate it. The wind generator guys just connect to the batts and let them control the voltage. Then they use an inverter to make AC. Depending on how big (amps) a generator you are considering you would want to consider that a wind generator is usually connected to a MUCH larger (AH) battery bank than the normal boat has.
The electrically regulated type alternator does not have this voltage-speed or rotation problem
FWIW

 

[Irish Rover]

I will have to incorporate a voltage regulator/diode between the battery and the generator. PM generators can produce quite a bit of juice one you get around 5kts or more. I don't mind the thought of the voltage regulator as additional piece of equipment. There are some on the market that allow you to hook up to multiple units (Wind, Solar, Water) with all three of these devices, (correctly configured) a boat could nearly go off the grid. While underway there would be no need to run the engine for battery charging, and you could run all systems without worry of power consumption.

 

[Mike B1026]

I'm not an expert but have a couple of thoughts.

1) Have you noticed that it's not a very popular idea? Maybe you can come up with a new solution but it's not a new idea. There must be a reason. I enjoy thinking "out of the box" and figure out how to make them work but...

2) It would only work while you are under way. Time at anchor would be a problem. Wind and solar is always available.

 

[Old Skool Neil]

While you're digesting the electrical aspects consider also that you'll be towing a spinner similar to the traditional taffrail log. One reason mariners carried spare spinners is from the big fisheys viewpoint they're very efficient spinning lures.

http://www.robertwhite.com/cgi-loca...aster-log&categ=rw_yestertech&nav_bar=weather

 

[rpwillia]

Developments

There is actually a lot going on with this, but it is still at an early stage. The Duogens are interesting units, but they are not designed for long term continuous use.

http://www.hydrovolts.com/
http://www.ampair.com/ampair/waterpower.asp

 

[Roger Long]

The fellow who makes the Cap Horn wind vanes sailed a boat without an engine around the world years ago and generated all his electricity with a generator or alternator mounted on the stern pulpit and a towed fish. He even built a new fish (metal) by hand when a shark ate his spare. His video is well worth watching.

Of course, he didn't have refrigeration, electronic navigation, big screen TV, and all the other modern necessities.

 

[kenn]

As already mentioned, in-water generators are showing up. I've seen one dual wind/water generator where you can change the prop, tip it down and dunk it.

I suspect that the friction in a traditional inboard driveline would probably make such arrangements too inefficient to be used for turning a generator. An electric driveline with a lower-friction stuffing box would probably be useable for generation.

Still some room for home-brewing in this field, too...

 

[Irish Rover]

I like all of the input. Thank you all. I'm not big fan of the spinner on a line configuration of the typical power generators. Looks like a lot of setup and potential loss of equipment if fouled or eaten. I'm thinking there may be a more elegant approach. Jut not sure what that would be yet. I would like to keep this thread going to get as many weighing in on this as possible. Nothing like a virtual spitballing.