Water Generator Concept Thread

[Bluemansailor]

>>I towed one for awhile.Made plenty of juice but it was freaking dangerous.Gawd help anyone who fell overboard and grabbed the towline.It would be a scene from a horror movie.What a pita to tame and get back aboard.<<

I used the split funnel, totally stopped the prop from turning and then just pulled it in -- if anyone does go the towed gen route- get or make the split funnel!

[Cpt Pat]

I just installed a Hamilton Ferris WP-200. The split funnel works like a charm. Issues so far:
1) Less-than-advertised output. 4 amps at 5 knots into a battery bank that's 12.7 volts. It might do a little better with lower state-of-charge batteries (haven't tested that yet).
2) Series diode supplied with kit (1N1200A) is only rated at 12 amps. As is common with ordinary silicon diodes, it's forward voltage drop is 1.1 volts. At at 12 amps, it'll dissipate (waste) 13 watts (1.1V forward voltage drop X 12A), which is a little high for the provided heat sink and the plastic "project" box it came in. The series fuse is rated at 20 amps, so I guess the diode is supposed to fail in order to save the fuse...
3) The supplied 0-25 amp ammeter is a little too optimistic, and makes reading the actual 4 amp output difficult since it's way down scale. (It's kinda like putting a 0 to 200 MPH speedometer on a Honda Civic.)
4) The supplied Sea Dog connector is wimpy.

I substituted a MBRH20045 Schottky diode rated at 200 amps that has only 0.4 volts forward voltage drop (the whole advantage of Schottky diodes) and therefore only dissipates (wastes) 5 watts at 12 amps (sending 8 more precious watts to the batteries). I used a 15 amp circuit breaker instead of the 20 amp type 3AG automotive fuse supplied -- I don't like replacing fuses locked up in little plastic boxes while underway. And I used a 0-10 amp Old School analog ammeter from Simpson (it cost $88, but I can actually resolve the 4 amp output now). My hull speed is 6 knots, and I don't expect to ever see more than 10 amps output from the generator -- but the meter will tolerate 15 amps sustained and I'd love to see it pegged, if that ever happens. Finally, I substituted a mil-spec Amphenol IP68 rated connector with a screw-on cover cap: if it's good enough for the US Navy, it's good enough for me.

S/V Ad Astra
26 foot Pearson Ariel

[LeaseOnLife]

Originally Posted by Cpt Pat

I just installed a Hamilton Ferris WP-200. The split funnel works like a charm. Issues so far:
1) Less-than-advertised output. 4 amps at 5 knots into a battery bank that's 12.7 volts. It might do a little better with lower state-of-charge batteries (haven't tested that yet).
2) Series diode supplied with kit (1N1200A) is only rated at 12 amps. As is common with ordinary silicon diodes, it's forward voltage drop is 1.1 volts. At at 12 amps, it'll dissipate (waste) 13 watts (1.1V forward voltage drop X 12A), which is a little high for the provided heat sink and the plastic "project" box it came in. The series fuse is rated at 20 amps, so I guess the diode is supposed to fail in order to save the fuse...
3) The supplied 0-25 amp ammeter is a little too optimistic, and makes reading the actual 4 amp output difficult since it's way down scale. (It's kinda like putting a 0 to 200 MPH speedometer on a Honda Civic.)
4) The supplied Sea Dog connector is wimpy.

I substituted a MBRH20045 Schottky diode rated at 200 amps that has only 0.4 volts forward voltage drop (the whole advantage of Schottky diodes) and therefore only dissipates (wastes) 5 watts at 12 amps (sending 8 more precious watts to the batteries). I used a 15 amp circuit breaker instead of the 20 amp type 3AG automotive fuse supplied -- I don't like replacing fuses locked up in little plastic boxes while underway. And I used a 0-10 amp Old School analog ammeter from Simpson (it cost $88, but I can actually resolve the 4 amp output now). My hull speed is 6 knots, and I don't expect to ever see more than 10 amps output from the generator -- but the meter will tolerate 15 amps sustained and I'd love to see it pegged, if that ever happens. Finally, I substituted a mil-spec Amphenol IP68 rated connector with a screw-on cover cap: if it's good enough for the US Navy, it's good enough for me.

S/V Ad Astra
26 foot Pearson Ariel

We had one of those...

Agreed, output is less than expected, but works up to 6 knots. Our hull speed is 7.8 knts, we usually reef before we reach that. The combination of ~7knts, typical tradewinds on open ocean (>=20knts), with a good following sea, made the prop jump out of the water, no matter how much additional weight we added. When the towed prop jumps, the lines loses tension and coils up. Even with the prop back in the water, the knot will not uncoil, wip around violently, the funnel does not pass the knot, does not stop the prop. The only way to recover is to stop the boat, lots of fun when running poled out, prevented out. Then let the prop hang by weight down in the ocean and uncoil slowly, and restart. We changed to a prop with less pitch, the output reduced greatly, and it still jumped, not as often, but still.... We kept trying, off and on, the paint failed, motor casing rusted, bearings failed, we gave up with less than 5000 miles on this thing.


For next time, we are looking into somthing like the electric trolling motors, on a kicker-motor bracket to get it in and out of the water easily.


Dirk

[donradcliffe]

I used the Ferris WP-200 for 12 years and 80,000 miles with extra weights and the high speed prop. Typical output was about 3-4 amps at 5 knots, rising to 8-9 amps at 7.5 knots. On a typical tradewind passage, I got 200 amp-hrs/day, which was enough to run the boat. It got pretty hot at 8 amps, and I wouldn't have wanted to push it harder.

It was a high-maintenance item, as it had to be painted every 2 years due to the rust, the bearings and brushes had to be replaced and the line would chafe at the ends. I lost the propeller twice when the line chafed through, and once lost the entire unit at 0300 off the coast of Australia when something very big decided it was edible.

As the previous poster says, downwind in over 25 knots it would tend to jump out of the waves and kink the line--putting 20 feet of garden hose over the prop end of the line kept the kinking down, but sometimes I would have to pull it in. It also had a habit of being clogged with Sargasso weed in the Atlantic.

It also caused quite a bit of static on the SSB.

All that said, I haven't seen a water generator which I could recommend. There was a British unit which flipped down from the transom, but they put the generator part UNDER WATER! The Duo-gen also flips down, but is quite prone to breakage. The last Vendee Globe race used flip-down units, but experienced a lot of problems at the speeds they were going.

If I was to do it over again, I'd spend the money on solar panels.

[seandepagnier]

Originally Posted by Cpt Pat

I just installed a Hamilton Ferris WP-200. The split funnel
I substituted a MBRH20045 Schottky diode rated at 200 amps that has only 0.4 volts forward voltage drop (the whole advantage of Schottky diodes) and therefore only dissipates (wastes) 5 watts at 12 amps (sending 8 more precious watts to the

They make active switching mosfets drop in replacement for diode which would drop about .05 volts. Your losses would go down to under 100mW.

To get maximum power, you need to do peak power tracking.. Basically adjusting duty cycle using mosfets can do this. If you are clever you can use the same mosfets to do the sync rectification.

[Cpt Pat]

Originally Posted by donradcliffe

I used the Ferris WP-200 for 12 years ...

It also caused quite a bit of static on the SSB.

I haven't done extensive testing (nor am I sure I will - I'm still waiting for a reply from Ferris on the lower-than-advertised output) but I wound eight turns around this toroid near the generator, and I didn't detect any noise on my SSB with a few tests between 2 and 30 MHz: 28B2400-000 Laird-Signal Integrity Products | 240-2120-ND | DigiKey.

The toroids are cheap (less than $4) and I've used the same product to quiet the switching noise from my MPPT controller for my solar array. The MPPT noise was substantial before I installed the toroid. I was hearing what we hams call "birdies" every 50 kHz all across the LF/MF bands. RFI is a real problem with any switching-mode controller (including those in LEDs). I also had to use one of those toroids with my LED masthead light.

I'd expect the generator to just produce random hash (static) from commutator/brush arcing. Ye ol' Spark Gap transmitter effect.

If you try this, be sure to wrap BOTH positive and negative wires together without allowing the wires to cross over in the turns. If you wrap only positive or negative, the toroid will saturate and provide virtually no RFI suppression. With both wires together, the algebraic sum of the DC currents is zero. To common-mode RFI, it looks like a transformer with an open secondary (infinite impedance). Keep the "input" and "output" turns some distance apart to limit capacitive coupling.

[capt-couillon]

Background

Am setting up to build my own "taffrail generator" as like most things marine, the cost of a commercial unit is (in my opinion) way out of line with the cost of a diy version, not to mention way out of line with my budget. The Solitaire is being refit with the goal of absolute minimum power usage. Your mileage may vary. With only a small kicker for aux power, some sort of electrical generation is required. While solar prices have come down to a level that makes their use as a power source while on the hook extremely practical, space requirements and susceptibility to damage make them impractical for use off-shore. I used a wind powered generator for 15 years on board my previous vessel, but suffered usual complaints (noisy, poor performance at anchor / downwind, etc) but was better than running the diesel . Having gone from a 14M vessel to an 8M vessel, no longer have the space for a wind generator, and as max power use underway on the Solitaire is designed at less than 3 Ahr a taffrail generator seemed an obvious solution.

This is a work in progress. Proof of concept prototype expected to be complete within 2 weeks for testing behind a friends power boat. Will finalize design after that. I thought I would share the design here along with some additional information I have found during my research that could answer some questions posted in this thread and elsewhere. Thanks to Eric onboard the s/v Sarana for his suggestions and pointers, as well as the folks at windynation.com for their DC motor / generator calculations.

The design is a "standard" towed prop configuration using 1/2" line to drive a permanent magnet DC motor as a generator. The components may change after proof of concept tests.

Prop End Details and Calculations

The prop end is based on the design used by Everfair Enterprises as a modification to their wind generators. The last reference to this I was able to find was in 2002 so seems to be no longer in production. I was able to find a great photo which is located as an attachment at the very end of this post.

One of the most interesting aspects of this design is the "downrigger foil" which is mounted to a free turning bushing on the prop shaft. Eric says he can reduce his line length to 25' using this gadget rather than the 75-100' usually required to keep the prop from "skipping"

The prop used in this design is a 8 1/4 x 5 plastic prop. I am using an aluminum prop, same diameter and pitch. Prop is mounted backwards as you are towing it, not driving it. I picked mine up at a local outboard shop, used, for $20.00

A short primer on pitch/rpm. The following calculations will allow you to determine the rotational speed (in rpm) of a towed prop of a given pitch (in inches) Diameter doesn't figure into rotational speed, but anything over 10 inches is going to be hard to handle and stow, and anything under 8 inches will probably lack enough power to spin the generator under load. Prop pitch = the distance through the water the prop will move in one revolution

rpm/knot of towed propeller = 1215.36 divided by pitch of prop in inches
Example: 5" pitch prop 1215.36 / 5 = 243 rpm/knot

So our proposed prop being towed behind a vessel travelling 4 knots will (in a perfect world) spin at 942 rpm (243rpm/knot times 4 knot). Real world factors such as slip and drag will reduce this theoretical output. How much? my WAG is about 20% leaving us with ~800 rpm.

Motor / Generator End Details and Calculations

A permanent magnet DC motor makes a great little generator when you spin it. Unfortunately while e-bay used to be a great place to find these motors cheap, now days every PMDC motor even close to suitable is marked as "perfect for a wind generator" and priced accordingly. They are still not terribly priced and with some searching you should be able to find a suitable candidate in the $40-$90 dollar range. BUT! the key word here is "suitable" . Its really pretty easy to determine if a given motor will give you what you need, but if the seller does not provide enough info to plug into the following calculations, search on .... Especially problematic with "treadmill motors" Widely available in the $30-$40 dollar range they rarely have the rated rpm at rated voltage as they are designed as a variable speed motor. While some are very well suited for our needs, some are absolutely useless. No rpm = no buy.

That being said, here is how to figure out whether a given motor will work as a suitable generator. (Thanks again to Windy Nation )

First assumption is our generator will need to put out at least 15 Vdc at 700 rpm (speed our towed prop is turning at a little less than 4 knots) So how to we translate the motor specs DC voltage DC rpm into that information?

Divide DC voltage by rpm.
As an example if we have a motor that says on the nameplate, 100Vdc 3000rpm. its volts to rpm ratio is 0.033 (100 divided by 3000)

To determine its output at 700 rpm (our above prop towed at a little less than 4 knots), (700 rpm) x (0.033 Volts/rpm) = 23 Volts
In the real world the motor when being used as a generator is only 80-85% efficient so we correct the above by multiplying 23 x .8 to arrive at a real calculated output of 18 Vdc at 700 rpm.
This motor would be suitable for our setup.

Generally what you are looking for is a high voltage, low rpm motor. Anything with a voltage/rpm ratio above 3 should be good. Below that, your mileage may vary

Amperage Rating This is a quote from Windy Nation's article. It pertains to wind generators but also applies here. The higher the amp rating the larger (physically) the unit will be.

The next item is the amperage rating of the motor. This provides information regarding how much current the motor will put out as a generator. From our experience, it is very difficult to predict what type of current your motor will put out as a generator. We’ve seen motors that expel more amps than that for which they are rated. However, one thing remains true: The higher the amperage rating, the better. You should be looking for a motor with a minimum amperage rating of at least 5 Amps. Anything above 5 Amps and you are good to go.
The power that a wind generator produces is directly proportional to the amps and voltage:

Hope this helps someone else out there, open to comments as to somewhere I might have gone seriously astray... Picture of old Everfair Enterprises/FairWinds system is below.
Regards,
Cap' Couillon
Onboard s/v Solitaire

[donradcliffe]

Originally Posted by capt-couillon

Background

So our proposed prop being towed behind a vessel travelling 4 knots will (in a perfect world) spin at 942 rpm (243rpm/knot times 4 knot). Real world factors such as slip and drag will reduce this theoretical output. How much? my WAG is about 20% leaving us with ~800 rpm.

My guess is that real world drag/slip will reduce the theoretical rpm by 50% or more. This is based on listening to the rpm drop when the generator is connected to the batteries--loaded vs unloaded.

[capt-couillon]

Thanks for the input Don....

What kind of load are you running on the gen-set? I am shooting for a 10A output at around 14V (140W) or <0.20 hp. A 100A alternator will suck > 2hp . The drag/slip number I was guessing at is for the prop in a no-load condition. The bottom line will show up in the proof of concept tests but I don't expect an 8 1/2 inch prop to stall with a 0.20hp load. But it would not be the first time I have been wrong. it will be interesting to see what the rpm is with the outputs shorted.
Tks again for the input.
Cap' Couillon

[Cpt Pat]

Originally Posted by donradcliffe

My guess is that real world drag/slip will reduce the theoretical rpm by 50% or more. This is based on listening to the rpm drop when the generator is connected to the batteries--loaded vs unloaded.

I'm also measuring about 50% slip when extracting 60 watts at 5 knots with the same prop on a Hamilton Ferris generator.

I discovered that I already had aboard the ability to generate nearly as much power from my outboard engine. I have a 6 HP Nissan with a 5 amp generator. It's obviously intended for powering navigation lights on small boats, but it's usable power - provided you use a charge controller to prevent overcharging your batteries (I have a simple relay that opens at 14.0 volts and closes at 13.5 volts). I'm able to get 3 amps at 5 knots using this procedure:

1) Remove the fuel connector and allow the engine to run out of fuel (so there's no fuel left in the carb reservoir). *
2) Put the transmission in neutral. Slow the boat to < 2 knots. *
3) Remove the plug from the safety cut-off switch to short the magneto (so there's no spark). *
4) Remove the engine cover. Remove the spark plug. Restore the engine cover.
5) Put the transmission in "forward."

Resume sailing.

* Safety related steps- don't skip these!

[capt-couillon]

Now that's an interesting concept.... My old suzy kicker has a light coil which I intended to use when under aux power. Have seen threads about the theory of using a trolling motor, but never considered using an outboard that a way....... Who said cruisers can't jury rig a solution.

Re prop rpm under load... Two observations in the same ballpark, may have to up the volt/rpm ratio for the initial tests. Thats more than I would have figured, but assume the worst hope for the best.

Tks
Cap' Couillon

[Triton318]

Thanks Cap' Couillon for sharing this information. It's given me the motivation to continue my efforts to build a DIY water-towed generator.

[capt-couillon]

Hope it helps some Jay..... You are just right around the corner. If I get anything together that is worth looking at I will let you know. Not far to Deltaville.

[goboatingnow]

water turbines would also benefit from a mppt style controller too, as the back emf plays havoc when the load is over demanded. The motor then spins at even lower revs then optimum.

DAve

[Cpt Pat]

Originally Posted by goboatingnow

water turbines would also benefit from a mppt style controller too, as the back emf plays havoc when the load is over demanded. The motor then spins at even lower revs then optimum.

DAve

I'm not sure about that. Solar panels have a "maximum power point" which for garden variety 12 volt systems is about 17 volts terminal voltage, declining in voltage as the panels heat up above 25 degrees C. Generators don't have the same characteristics: they don't have a "maximum power point".

Solar panels have a terminal voltage that when unloaded is above the battery voltage. That isn't the case with a generator, whose output starts at zero and rises with rotational velocity. The only load on the generator is its own internal friction until the terminal voltage is sufficient to forward-bias the steering diode. Once the generator reaches a terminal voltage that equals the battery terminal voltage, plus whatever series drop exists across the series steering diode (which is lost power - a good reason to use a Schottky diode), the "maximum" power is gained by taking everything the generator can output to the batteries - provided the propeller isn't so heavily loaded that it is operating in the "backside of its power curve" or even stalls. There is probably some efficiency to gain by keeping the water flow across the propeller at its optimum angle-of-attack (thrust to drag ratio) by reducing the load, but the gain would be low - and possibly lower than the losses in the MPPT controller. That goal would be better achieved with a variable-pitch propeller.

I did a search, and I was unable to find any of the MPPT controller manufactures that offer anything specific for PM generators. All the solar/wind power combination controllers were actually using pulse-width-modulation on the wind generator side. I've read some scholarly papers on the topic, but I still don't see a great deal of gain that can be achieved. Plus, you have to deal with all the RF interference generated by the MOS switching transistors in the controller - wiping out your SSB receiver.

On the comments about solar being a better buy: I completely agree. That is, until your deck is covered by solar panels, and you've even mounted them on your shrouds. At that point, the only option for increasing the solar panel capacity is to buy a bigger boat. I've run out of places to put panels that aren't under foot. See attached pic.