Hacking a trolling motor into a towed type generator - Page 2 - SailNet Community
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post #11 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

Trolling motors are theoretically a decent match for a tow-driven prop. But there's the real problem people forget when they confuse propellers with rotors: props PUSH water or air, rotors are PUSHED BY water or air. The blade pitch & convexity on any propeller are exactly wrong for generating power. It's alongside the people who set a box fan outside as a "cheap wind turbine" and attach it to a car battery. Wrong power band, wrong blade geometry.

There have been attempts at dual-purpose drivelines -- engine or hybrid-electric driven propeller in one mode, then rotate the blades 180 degrees and drive a PM alternator using boatspeed. I guess they work okay, tho the complexity invites trouble. Intriguing idea, tho -- esp. as more boat owners opt for variable-pitch props.

Nothing this side of dead dinosaurs puts out amps like a good hydro-gen. The prop diameter can be quite small -- water is 100 times denser than air. Drag is an interesting topic: I'd say at the boat speeds at which a water rotor becomes useful (6+ kts), its drag becomes trivial compared to wave-making losses; on planing boats, its drag is trivial compared to available horsepower. At low boatspeeds, the drag would be substantial -- but you may as well pull it out of the water then, because it is only making 3A anyhow.

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post #12 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

If I were the designer/architect of these yachts I would simply put two inlets allowing water to enter a tube and run the fan/prop/blades that in turn runs the generator... so either way whether the boat is leeing to either side one of the generators is always turning, best when the sailboat is tracking straight you wind up double generating units... the water simply comes in and out the tube... no lines, no unsightly cables, or breaking water as in the video... and probably very little drag... best example would be a liquid flowmeter...


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post #13 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

I will be watching this thread...
Not because I need a generator but because this is "old school" problem solving just like my father taught me and I would love to see it work. I will say that if I trip over an old trolling motor I will rig it up for fun.
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post #14 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

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If I were the designer/architect of these yachts I would simply put two inlets allowing water to enter a tube and run the fan/prop/blades that in turn runs the generator... so either way whether the boat is leeing to either side one of the generators is always turning, best when the sailboat is tracking straight you wind up double generating units... the water simply comes in and out the tube... no lines, no unsightly cables, or breaking water as in the video... and probably very little drag... best example would be a liquid flowmeter...

It has been tried, & the idea of a ducted or nacelled turbine does have much to recommend it. But imagine the fun when you suck a grocery bag into your intake, and you have to clear a shrouded, plastic-tangled rotor which may well be below waterline.... Can't put an intake screen over it, because the needed degree of solidity will massacre your flow rate. Which, BTW, it always the problem with all ducted, low-pressure turbines. The plumbing adds a shocking amount of drag and turbulence. That creates back pressure, so the water flowing over the skin of your hull decides to go right on by the intake. Bzzzzt. You'd need a proper manta-mouth scoop to overcome that, & I wager the drag on the boat would be many times higher than a naked propeller trailing behind. Which, if it eats a Kroger bag, can be hinged up, cleared, and lowered back down.

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Re: Hacking a trolling motor into a towed type generator

Here is an interesting page with some good info on using an alternator.

Using an Alternator in Renewable Energy Projects

You know this would be fairly easy to rig up something like this, with a floating paddle wheel set up and the whole thing pivoted where it connects to the boat. You would just need to work out the size of the wheel and pulley in order to get the rpms correct at the alternator.

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post #16 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

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Here is an interesting page with some good info on using an alternator.

Using an Alternator in Renewable Energy Projects

You know this would be fairly easy to rig up something like this, with a floating paddle wheel set up and the whole thing pivoted where it connects to the boat. You would just need to work out the size of the wheel and pulley in order to get the rpms correct at the alternator.

A few more pullies and my father would have this setup powering everything AND charging the batteries
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post #17 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

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What is the drag these produce on speed? I have often looked at these and wanted more informatuion on them.

Jon could you expand on your experiences with the Ferris one, I have seen them.
Difficult to quantify the drag, but I would classify it as barely noticeable... Just a guess, at between 5 and 6 knots, perhaps a quarter of a knot, at most? Even that estimate is probably high...

I'm a big fan of Ferris products, and I have the conversion kit to turn my generator into a wind-powered generator when at anchor... Takes a bit of time to make the switch and hoist in the rig, but well worth the effort if I'm gonna be someplace for awhile, and I really like the ability to stow all the gear below when not in use...



IMHO, a towed generator is really only suitable for offshore, or off soundings where there's no possibility of snagging a fishing buoy, etc... If you're using one on a coastal trip, you'd best keep a sharp lookout, and take it in at night. Only time I've ever lost a spinner, was after passing on the up-current side of a deepwater fishing float on a passage between Nantucket and Nova Scotia - just a stupid move on my part, you have to remember when you have it deployed, and certainly pass on the leeward or down-current side of any obstruction...

There's a bit of a learning curve in learning how to deploy and retrieve the spinner, but no big deal... All in all, a great piece of gear... Here it is, making good amps one day (and all night long) somewhere in the Bahamas...


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post #18 of 44 Old 01-16-2013
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Re: Hacking a trolling motor into a towed type generator

Whup! Time out. Regards any sort of paddlewheel, etc....

As sailors, we understand the difference between a lifting surface (when your sails are behaving like wings, generating fluid-dynamical forces) and a drag body (when you are sailing DDW and your working sails are just big old bags, being pushed against by the wind.)

Drag bodies stink for electricity generation. As tschmidty notes above, alternators produce better at higher RPMs, & the fastest part of a drag-body paddlewheel (tips of the blades) can never move faster than the water moving past it. You'll be lucky to get 100 rpms out of it, & the hub will be moving maybe 6/10s of a knot.

However. An axial thrust rotor (looks like a propeller) can achieve tip speeds many, many times the speed of the incoming water. The blades do this just as your sails do on a beam reach, by splitting the flow and generating lift over both surfaces. I can't find data on the Watt&Sea hydro-gen, but I'd bet it is spinning several hundred RPM at cruising speeds.



W&S have basically saved us the trouble of brainstorming the perfect unit -- they've gone & built it. Although ... I'm not a fan generally of downstream turbines. Face the blade to the front for maximum output. I am guessing they face it aft for impact protection, which is a fair compromise.

A trolling motor with a correctly-pitched prop might just do, however. A clever person with access to a 3D printer could possibly mirror a thrust propeller & print one out in polycarbonate.

The other thing about hydro-gens, of course, its that they only work when you are sailing. Good for driving the autopilot. But they won't keep your beer cold at anchor.

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Re: Hacking a trolling motor into a towed type generator

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It has been tried, & the idea of a ducted or nacelled turbine does have much to recommend it. But imagine the fun when you suck a grocery bag into your intake, and you have to clear a shrouded, plastic-tangled rotor which may well be below waterline.... Can't put an intake screen over it, because the needed degree of solidity will massacre your flow rate. Which, BTW, it always the problem with all ducted, low-pressure turbines. The plumbing adds a shocking amount of drag and turbulence. That creates back pressure, so the water flowing over the skin of your hull decides to go right on by the intake. Bzzzzt. You'd need a proper manta-mouth scoop to overcome that, & I wager the drag on the boat would be many times higher than a naked propeller trailing behind. Which, if it eats a Kroger bag, can be hinged up, cleared, and lowered back down.
Agreed... it was just a design idea and the working would of course be that of the designer to get it working right... that being said the real way to get energy out of the ocean is to get the voltage potential directly from the seawater... per square meter of electricity the scientists are getting around .1 to 2 watts currently... the polymers being used are being slowly designed to obtain 5 watts per square meter... sure it's not feasible to have some 10 meter by 10 meter polymer mat floating behind the boat to generate 500 watts... I can see the drag this would make...

It would be interesting what advances come later but at the current technologies we have: solar and gas generator (Honda type generator, alternator on the engine, etc) is the best at generating the electricity we need for the boat... wind energy would be last on the list... pedal power with a generator would be a good temporary solution... anything I missed?
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Re: Hacking a trolling motor into a towed type generator

Curious why guitar guy is down on wind. It's come a long way.Much quieter. Been reading Nigel Calder and others. Figured out an energy budget. Decided to go with solar and two D400s with extra alternator output. Don't like diesel generators - noise,more holes in the boat, expensive watts and some thing else to maintain. ?Did I make a mistake? Figured the marriage of wind and solar made sense as usually get one or the other and if the lord smiles both. Ferris is close to where I live. Very nice people and informative.They sell a unit that can be used as wnd or water generator. Seemed it would work well as water generator but thought wind configuration was problematic for my application . Like the idea of rigid water generators- clean, relatively small and light- simple concept. On sugar scoop boats would be easy to mount. Trailing stuff- not so much. Hope they come down in price. Very interesting thread thanks all.

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