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Towed Generator that We Really Need

6K views 32 replies 13 participants last post by  bobmcgov 
#1 ·
Similar recent thread talks much about trying to hack a trolling motor into a hydrogenerator. Reviewing that thread, it's clear that there are a lot of creative and resourcful people with interesting ideas. It's also clear that most of them don't understand the fluid dynamics involved and few of the ideas would have a chance of working.

Trolling motors are cheap things designed for lightweight use, running fishing boats around at slow speed. On the other hand the Torqeedo Electric Outboard is a much more powerful device and better designed for exposure in the marine environment.

Having been a product design engineer for 30 years, doing both mechanical and electrical design, I am highly suspect about the success of a hacked system. On the other hand, it certainly seems to me that the smart guys who designed Torqeedo could develop a similar version that could clamp on the transom as a hydrogenerator, with it's power electronics doing a controlled system charge. The same device could then be unclamped from the transom, clamped onto your dinghy. A quick prop change (yes towing is different than motoring), add the battery pack, and your ready to zip around the harbor. This seems a realistic goal for a product. It might cost 50% more than a regular Torqeedo, perhaps even twice. Even if it cost as much as a Watt & Sea generator, the Watt & Sea is only a generator. An outboard/generator would serve dual purpose for a typical cruiser.

Marine Industry: Are you listening?

G.J.
 
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#2 ·
I am onboard with this idea, GJ. Really. My only immediate critique would be the Torqueedo runs at higher RPM than most trollers, IIRC. That's one way it gets its HP boost. You need an alternator optimized for low speed output for most hydrogenerators to work. Not sure where a Torqueedo is on its power curve at 400 RPM.

But otherwise, I think the basic electric outboard/hydro-gen idea is feasible, whether hacked or purpose-built. Would to see the output of a basic troller in gen mode -- might be as high as 4A, even with the standard prop. But purpose-built could be better. You'd need to sell a few thousand a year to pay for development, tho. On a related tangent, a bunch of us brainstormed the possibility of decentralizing power distribution on sailboats. Instead of the current design -- big 12VDC battery bank, single breaker panel, fat wires run everywhere -- a system using a single 'spinal cord' down the center of the boat, or several smaller batteries (probably LiIon) was discussed. Also, higher DC voltages. Your Torqueedo battery could plug into a socket in the forepeak, to run a windlass or bow-thruster. It recharges via smaller diameter wires. When you need the dink, you un-dock the battery, plug it into your outboard, and off you go.
 
#3 ·
The problem with this type of combined system is that it would entail pretty significant compromises as either an outboard or a towed generator, or both. And frankly both systems independently are only moderately successful. Towed generators create a lot of drag and reduce speed significantly on cruising boats already, ough they do provide a lot of power when working. And electric outboards... Well the best I have heard an owner say about one was "meh" they work but aren't stellar performers.

I am afraid you would wind up with a system that is the same price as the two combined, but didn't perform half as well as the other options.



Bob,

On the distributed power... There are, and have been systems that do that on the market for years. The problem is it really takes a full rewire to justify it as a refit, and builders are slow adopters.
 
#4 ·
The problem with this type of combined system is that it would entail pretty significant compromises as either an outboard or a towed generator, or both. And frankly both systems independently are only moderately successful. Towed generators create a lot of drag and reduce speed significantly on cruising boats already, ough they do provide a lot of power when working. And electric outboards... Well the best I have heard an owner say about one was "meh" they work but aren't stellar performers.

I am afraid you would wind up with a system that is the same price as the two combined, but didn't perform half as well as the other options.

Bob,

On the distributed power... There are, and have been systems that do that on the market for years. The problem is it really takes a full rewire to justify it as a refit, and builders are slow adopters.
Correct on both points, Greg. Tho people will continue looking for alternatives to the gasoline outboard as long as those keep letting people down so often.;)

Some European custom builders are using more sensible wiring architecture -- not least because copper has gotten so bloody expensive. You can't be running 60' of 2/0 hither and yon. And some bow thrusters are already working off their own dedicated battery. It is a good solution for high-amp loads used in short bursts, with plenty recharge time in between. Like a windlass, or a thruster. If you only need an outboard to run your dink to and from shore -- versus exploring up river, or visiting dive sites two coves away -- an electric outboard is an okay solution. (But then, so is a pair of oars....) In which case, having a spare battery pack is handy. In which case, why not double its utility as the windlass batt?

Right now, I'd faint with gratitude if the industry would finally admit 12V is a stupid idea and upgrade to 24 or 36V. I'm told 48V starts getting too close to lethal for boat use, but sheesh. Who is gonna move first -- manufacturers? Electronics makers? Alternator builders? Europe is again ahead of the US here, but wiring boats to 12V is as dumb as wiring tractors to 6V was. We WILL be completely rewiring our boat, but too many systems are still clinging to 12V for us to mess with converters. Unless something changes radically in the next 2 years, we are stuck rewiring to 12V.:(
 
#5 ·
Bob, you make a good point. There are a number of items available now in 24 volts, some electronics lighting and wind generators to name some but as to a complete switchover that will be a long time coming if ever. The whole auto industry, RV industry and almost any other commodity using DC power are all geared to 12 volt.
It is feasable to use a hyrid 12v/24v system wiring some things 12 and others 24 off the same battery bank.
 
#6 ·
If you really planned it out from the ground up, I would be willing to bet you could go all 24v, or very close to it right now. It may take some creative options when it comes to equipment, but a lot of things that used to be 12V only are starting to show up in 24.

Trying to go to 48v right now would probably be close to impossible unless you were willing to take major restrictions on parts options.
 
#8 ·
If you really planned it out from the ground up, I would be willing to bet you could go all 24v, or very close to it right now. It may take some creative options when it comes to equipment, but a lot of things that used to be 12V only are starting to show up in 24.

Trying to go to 48v right now would probably be close to impossible unless you were willing to take major restrictions on parts options.
Weren't a lot of power boats from the '60s wired for 24 volts?

Anyway, count me in with Greg. Adding point voltage regulators for things like your LED lights should cost next to nothing. 12v regulation can be had on a single chip!

Tom
 
#10 ·
All of these things (motors, generators) require a shaft seal to keep water from entering the assembly as the shaft rotates. And shaft seals are typically something like a heavy graphite or other polished ring, pressing against a felt or similar seal. I'd be concerned that the seal in whatever unit you are adapting is designed to seal against thrust, rather than drag, so it is designed to seal with pressure "this way" not "that way". And then it is going to break down and leak in much shorter order, if it is being pushed the opposite way to what it was designed for.

But as long as whatever you are using seems to have a seal that will still work properly, th eonly other question should be figuring out how to efficiently prop it.
 
#11 ·
I keep coming back to the "no such thing as a free lunch" thought pattern.

That Honda 2000 generator putting out 1600 watts is needing a 3.5 hp engine to do so.

Dropping a towed generator over the side, or attached to the transom - if it generates 1600 watts of power, guess what? It's the same as hooking a 3.5hp engine running in reverse.

That's not drag, that's propulsion the wrong way.

If the marine industry really wanted to do something smart they would put a take off on the propeller shaft in front of the stuffing box running a belt drive to a low rpm alternator.
Of course then the whole folding prop market would go out of business.
 
#15 ·
Why re-invent the wheel? These products are here already to buy and install and from the video and the website of the product... it seems a viable product?

DouGen and the video of the product in full use in the water and conversion to wind...

Nick
Nick: Because the DuoGen is a miserable piece of equipment with corrosion problems and weak output. Because the same piece of equipment cannot work effectively in air at 15kts and water (100 times denser) at 6kts. It's not a good solution; if it were, you would see them on boats rather than on YouTube.

Chuckles: All the above issues were covered in the "Hacking a trolling motor" thread. As Greg says, a propeller is not an effective generating rotor. You cannot belt the shaft because you will lose 2/3rd of your power to pulley or gearbox friction. The very best water generators (Watt&Sea) produce ~500W max, more like 250W at cruising speeds. That isn't 3.5 hp -- that's 1/3 to 2/3 hp. And that's a purpose-designed device, without the inherent compromises and losses of an engine shaft, hacked trolling motor, or air/water combination machine. Supposedly the Ferris units are better than the DuoGen, but they require a substantial rotor conversion.

Water generation is a good solution for frequent passagemakers. That's a fairly small market for a device that is not easy to engineer properly. The OP's idea of a purpose-built, dual-function troller/hydro-gen is perfectly feasible -- but creating one that worked adequately in both modes would take more R&D than the likely sales volume would justify. Pity, cuz I would lust after such a thing. :(
 
#13 ·
Chuckles,

It's been done. An there are numerous threads here and on other forums detailing it. The issue is they don't really work very well. They do produce power, and lots of it, but lets just look at some issues with doing this.

1) prop size was optimized for pushing the boat, not turning a shaft. Pitch, shape, are backwards from what you really need for a water turbine

2) prop size and pitch are really wrong. First every boat has a different size/pitch prop that was selected to push the boat thru the water at a given speed and absorb a given amount of power based upon the engine of that boat. But most boats are likely to need roughly the same size generating prop, because speeds will be close to the same, and the size of the alternator will be roughly the same.
 
#26 ·
Chuckles,

1) prop size was optimized for pushing the boat, not turning a shaft. Pitch, shape, are backwards from what you really need for a water turbine

How about using a the small outboard system of reverse, prop leading for generator turn 180* bypass charge controls, motor away

Should be better then dragging it the other way, you would still need to compimise on the prop some.
 
#14 ·
"If the marine industry really wanted to do something smart they would put a take off on the propeller shaft in front of the stuffing box running a belt drive to a low rpm alternator. "
People have done that. The "marine industry" is concerned with making profits, not crafting boats, which is why it is an industry. And there's just no profit to be made in niche markets for tiny numbers, compared to industrial ones.

Before there was an internet people read books. Composed by authors, not sniping at tiny slices of subjects. I'm sure I've read about water generators, towed and shaft alike, in cruising books written in the 70's.

Putting an extra pulley and belt on the propshaft is easy. IF there's room in the engine space. IF there's room on the shaft. And IF you add a bearing to take the extra side loading off your stuffing box and cutless bearing.

Towing a genset is easy. If nothing eats it or fouls it and the seals hold. The latest iteration seems to be transom-mounted to avoid that. If they're also using new motor technology, rare earth magnets and the like, and getting enough efficiency...they're still expensive. And still need seals on a rotary shaft operating in salt water.

I suspect there's a reason why 30, 40 , 50 years down the line, this "solution" still hasn't become mainstream.
 
#27 ·
That is a joke, right?

First paragraph:
Statement of problem and declaration that people trying to solve it have no clue and little chance of success.

Second paragraph:
Stating the obvious about trolling motors with a gentle, but unfounded feature presentation of Torqeedo.

Third paragraph:
Statement of own superior qualification, and semi-clear suggestion how not glorious self, but Torqeedo could and should solve stated problem.
Very clear estimates of prices, engineering solutions proposed, without ANY base.

Closing:
Appeal to "Marine Industry" to listen.

Are you TROLLING???? :laugher
 
#29 ·
I have two of these panels I plan on installing to a dodger I'm going to make and try to fit them as best I can... sew them onto the dodger...

Here are the specs:

Electrical Specifications

PVL-128 18ft x 15½ in.x 0.16 in. 17 lb.
Electrical Specification: PVL-128
Rated Power Pmax 128 Watts
Nominal Operating Voltage 24 Volts
Operating Voltage (Volts)Vmp 33.0 Volts
Operating Current (Amps) Imp 3.88 Amps
Open-Circuit Voltage (Volts) Voc 47.6 Volts
Short-Circuit Current (Amps) Isc 4.8 Amps
Series Fuse Rating (Amps) 8 Amps
Min. Blocking Diode 8 Amps

That's 256 watts total for both panels... not bad.... they are a little long and have to figure how to attach to the dodger but I'm sure I'll work it out... :rolleyes:

These can be bought on Fleabay and they cost about $1 a watt or slightly higher... what is good about them is the flexibility and long wear since it must meet the current building codes... they are really tough and I have walked on them and so has my science kids when I used them for demonstration... very sturdy! :)

Nick
 
#30 ·
I went to fleabay and searched for "solar", nothing came up. Got a link?

I have two of these panels I plan on installing to a dodger I'm going to make and try to fit them as best I can... sew them onto the dodger...

Here are the specs:

Electrical Specifications

PVL-128 18ft x 15½ in.x 0.16 in. 17 lb.
Electrical Specification: PVL-128
Rated Power Pmax 128 Watts
Nominal Operating Voltage 24 Volts
Operating Voltage (Volts)Vmp 33.0 Volts
Operating Current (Amps) Imp 3.88 Amps
Open-Circuit Voltage (Volts) Voc 47.6 Volts
Short-Circuit Current (Amps) Isc 4.8 Amps
Series Fuse Rating (Amps) 8 Amps
Min. Blocking Diode 8 Amps

That's 256 watts total for both panels... not bad.... they are a little long and have to figure how to attach to the dodger but I'm sure I'll work it out... :rolleyes:

These can be bought on Fleabay and they cost about $1 a watt or slightly higher... what is good about them is the flexibility and long wear since it must meet the current building codes... they are really tough and I have walked on them and so has my science kids when I used them for demonstration... very sturdy! :)

Nick
 
#32 ·
To Bobmcgov
During the Vendee Globe the Watt&&Sea generators proved to be very reliable
Failures came from the attachment fo the generator to the boat Some showed problems even without hitting anything All repairs jobs had to be on the fixture! But keep in mind that these boats hit speed of 20knots for long hours .
Still an expensive item but I believe that you will see more of them in an ear future and probably will come as an option when buying a new sailboat
 
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