Anyone ever consider

[sailaway78]

There seems to be constant and mixed opinions about solar panels vs wind generators and both do have their advantages/disadvantages. Solar of course needs sunlight, which limits you at best to 10 or 12 hours a day in the summer, less in the winter. Wind generators need a good breeze to make decent amounts of power, and in this area there are lots of pretty calm days during the summer. Has anyone ever thought about modifying a troll motor to make power. It seems to me that this would be the ideal solution when making a fairly long or offshore passage. No good of course when anchored. Usually when going coastal I motor a fair amount, and stay in marinas every few days, so not much problem keeping batteries charged. If you could make a simple fold down mount, for a troll motor, and get 5 amps or so from it, that would produce 100 ah's a day. Plenty for most boats. Any thoughts or ideas on doing this. Drawbacks.

 

[Tom Spohn]

Lure

How would you keep the fish from thinking this was a lure?

 

[Calif. Ted]

I do remember hearing of an

explorer scout ship that used a car generator on deck attached to a long stout line with a propellor trailing behind the boat. Reason I heard about it was 'cause they caught a great white shark with it.

 

[kloudie1]

Water Power

Interesting .. I have seen a small automobile alternator mounted on the stern rails, with a fairly long rope leading to a propeller that was weighted.. The prop was deployed at sea and spun the alternator, making power..(go to hamiltonferris.com, look at waterpower) I’d guess that on Ponchartrain, we could collect crab traps instead of ampere hours with such a device.. I have also seen alternators driven off the prop shaft ..

 

[Napa Ed]

duogen.com

pricey

 

[Rich Stidger]

If you are motoring a fair amount, I think your best.....

bang for the buck would be to install a high-output alternator on the engine itself. A decent hi-ouput unit with a 3 or 4 stage external regulator will put out well in excess of 50A for several hours.

BUT, if you do, be SURE to install a temp sensor on the alternator and provide some way to add external cooling air to the alternator.

 

[sailaway78]

HHHHHHHHMMMMMMMMMMM

I know this is somewhat of a stretch. But, consider the alternatives. The bigger alternator kind of just makes the necessity of running the $%^ diesel just a little less, but still requires running it. To make the most of it, also requires a high tech regulator, which from my reading do not seem to be the most reliable things ever made. And still have to run the stinking diesel to make things work. I have seen and thought of the alternator mounted on the rail, with a trailing prop, but it seems like more of a Rube Goldberg arrangement than I want. I don't see how a rope would do anything more than just twist up, so some kind of cable would be needed, plus the mounting, and making some kind of hookup to get the prop on the cable. The Duo Gen is a really neat deal, but very pricey for no more offshore than I do. They are also fairly large, and from what I see, not an quick and easy task to switch from wind to water. What interests me about a small trolling motor is the shaft and prop come with it. Seems to me that it would be fairly easy to make a folding/sliding mount that would be out of the way when not in use, easy to deploy when wanted, and make enough power to keep the batteries up for a week or so. If the output isn't a lot of amps, no regulator would be needed. Would be very simple to just put an of/off toggle switch in the circuit. Of course, a big fish could put you out of business in a hurry. But that would be the same with any water powered generator.

 

[Stu Jackson]

Am I missing something?

You wrote: "Usually when going coastal I motor a fair amount, and stay in marinas every few days, so not much problem keeping batteries charged"

The challenge has always been to put back in what you take out. Given you "habits" (all good, we presume ), then why complicate matters with something else for which you appear to have no use or need?

 

[Ross]

Evidently the asnwer is a resounding YES!

I googled "towed electrical generators for sailboats and this is the first of several thousand hits.

 

[Dennis W.]

Taffrail Generators

A taffrail generator was patent 4102291 in 1978, a Mr. Ralf Sebald of Munich was the inventor

 

[John]

saw one at boat show

There was a booth displaying exactly what you suggest at the Northern California "Strictly Sail" boat show a few months back. It looked like a neat contraption, but I got to thinking: If it's worthwhile getting a folding prop because of the drag of a regular one, then how much drag is there as a result of this generator? And if you use it while motoring, then how much extra fuel would you have to use to compensate for this drag, compared to the amount of electrical energy it produces? It seems to me that the one time it would definitely be worthwhile is if you are anchored or moored at the mouth of a river or where there are very strong tidal currents.

 

[sailaway78]

My usual

habits the majority of the time are coastal. And then I do run the motor some, or quite a bit, and stay in marinas fairly often. But sometimes I do some offshore work. From where I live, here in the New Orleans area, it is a six or seven day run to Key West, Isla Mujeras etc. This is what the request was about. Not for when I am going coastal. I can't make six days on batteries, and run a fridge. For these times I would like something that is easily removable, easily deployed, and not in the way. The idea of the trolling motor is something I have been running around in my feeble little brain for some time, and if I can figure out a really simple and workable mount, it seems to me to be the best way to go.

 

[George B]

Duo Gen

I recently sailed (08 Pac Cup) to Hawaii using a Duo Gen for power generation. The towed mode is much more efficient as it produces 20 Amps @ 9kts boat speed than the wind mode where you would need 30kts AWS to achieve the same output. The main downside to the Duo is there is no clutch/brake in the system so it is “always on” which the regulator compensates by dumping excess power to a resistor bank similar to a diesel-electric locomotive. We monitored power generation and hoisted the unit into it's stowed position once our charging needs were met for each day. The Duo people quote very little drag as the unit’s impeller head rides directly behind the transom in the disturbed water from the boat’s wake. Certainly no more drag than what is produced by a free wheeling propeller when using the engine for recharging. At sea, it would be very impractical to switch out the water impeller head for the windmill head. Once in Hawaii, we used it in the wind mode but the problem being not much wind in the harbor and windmill having to spin a pretty substantial generator. It probably is much more effective in an anchorage than being tied up against a quayside. Duo Gen does have a procedure for feathering the unit in wind mode. All in all, the unit worked well for us. Our biggest problem was coming up with a successful installation as the boat had a vintage IOR style stern and valuable real estate was already taken up by a monitor wind vane.

 

[Ross]

One hp is about 760 watts or about 63 amps at

12 volts. 10 amps then would be about 1/6 hp. That ain't much drag.

 

[Don12364]

Motors Used as Generators

I have often thought about using a motor as a generator but there are problems with achieving a high enough RPM to give sufficient output voltage.
The troll motor is designed to run from 12V DC. This means it's own series resistance will render it's output voltage somewhat lower when generating and even less when charging or running an electrical load.
Also consider the motor speed:- When motoring the motor (not the propeller) will need to run at an efficient speed e.g. 3000 rpm and the 'slip' of the prop in the water will mean the prop will be rotating as if the boat were doing 15 knots or more.
Again, when generating the 'slip' works against you so you would need to be doing 30 knots to get the same current out as you would be putting in during motoring.
These two effects will defeat the object of the exercise.

A partial solution would be to fit a much larger and much finer pitch prop, and/or alter the ratio of the gearbox - but with no real guarantee of success.

For info some folks have run a generator which was belt driven off the boat's main prop shaft, left out of gear and thus free to rotate whilst sailing. This way they use the belt/pulley ratio to compensate for the low rpm of the prop.

 

[Ross]

Donalex, DC motors can be series wound , parallel

wound and permanent magnet field, and electronically commutated. Some DC motors may be used as motor/generators but the power out never equals the power in with either configuration. Efficiency is always a factor. A very low pitch would result in excessive drag and a high pitch would result in lost power. Considerable research will be needed to determine the optimum motor/propellor combination.

 

[Don12364]

Ross

Ross,
It may surprise you but, having run the design team for one of the Alfa Romeo's automotive alternators, I do know about motors and generators.
All the things you say are true but all are irrelevant to this enquiry.
Of course a low pitch prop will cause more drag and this is so BECAUSE we need more RPM and thus more power from it.