Considering a sailing adventure to Mexico? Just look at how engrossed that guy is in the book! Grab a copy of the Unauthorized Guide to Sailing in Mexico, and you too can find yourself sitting on a Mexican dock with an oversized (but very attractive) hat.

Unauthorized Guide to Sailing in Mexico

test
« this internet connection sucks, my torrent won't download fast enough | Main | weak el nino year possible for 2014 »
Sunday
Feb162014

hydrogenerator sea trials: completed

I've been reluctant to write about my hydrogenerator for two primary reasons. First, it's hardly a new idea. There are commercial versions (that cost a grand or two) and hundreds of sailors have built DIY versions for decades. Second, I hadn't tested my little creation yet so it seemed a little presumptuous to wax on about something that might not work at all. 

But today, halleluiah, I sea trailed the whole mess in the dinghy with great results.

Essentially you toss the black prop (connected to the stainless shaft there) into the water. It's connected by a shackle to some single braid line, and then goes taught, the other end of the line being secured to a shackle on an Electro-Craft E722 permanent magnet motor's axle.

At 300 RPMS, which seems to happen around ~4.3 knots, the motor makes about 12.5 volts. The faster it goes the more amperage and voltage it creates. I'm not worried about a voltage regulator because the amperage is low (about 5 amps at 12.5 volts, to maybe 12 amps at 90 volts), but to reach the upper threshold of voltage we would be doing double our hull speed so at that point over charging our batteries will be the least of my concerns. 

I had a local machine shop drill a hole through the generator's shaft so I could put a shackle through it.I only lost about 1/4 of a knot in my testing, so if I double that (to be a pessimist) and do some math it means a 20 day passage would now take 22 days. But that's 22 days of making 5 amps continually, which means we don't need to haul as much gasoline or diesel. And as anyone who's sailed downwind knows, it literally stinks to run the engine because the exhaust fumes blow into the cockpit and cabin. 

For the motor I had a few criteria. One, it had to be a permanent magnet motor. Two, it had to be fairly low horsepower because I wouldn't have a lot of rotational torque (generated by the prop) to work with. Three, it had to hit charging voltage (> 12.5 volts) at a low RPM. The Ametek models are definitely the most popular, but I re-read the specs on the Electro-Craft E722 and felt it would do the job as well if not better. Both of these motors were originally designed to spin large disk drives around and as such are frequently found on Ebay. The good news is that a lot of people are building wind generators these days, the bad news is that it's raised the price considerably on the motors. I was lucky and got mine for $50 but $100-$200 seems a bit more common.

The other thing I had the machine shop do was build a shaft for the prop with an eyelet on the end.For the prop I'm sure there are better options than what I got, but I was pressed for time and saw a $400 prop on sale at West Marine in San Diego for $40. I figured that was better than whatever else I'd be able to find so I tossed it in my checked baggage and called it good. 

I had a machine shop drill a hole through the motor shaft that would accept an 8mm shackle so I could secure that to a thimble in the tow line.

I also had the machine shop use a solid stainless rod, thread it, and pop a nyloc nut on for the prop. Also, they put an eyelet on the end that I could likewise shackle to a thimble on the end of the tow line.

When testing I was happy to see that the line doesn't kink at all: the rotational twist builds up in a few seconds and then starts happily spinning the motor. The drag on the prop causes the line (at least my single braid) to not kink, and any twist is transferred as kinetic energy to the motor's shaft. 

The only other thing you want to make sure to add is a blocking diode. Otherwise when there's more voltage in the batteries than the motor is making, either because the boat is slow or possibly because your solar panels are putting out a lot of juice, the motor will start consuming electricity rather than generating it, and you can watch the prop as it tries to spin itself away from your boat.

My machinist showing me the fastener assembly he built for the prop shaft.All in, rounding up, I spent $50 on the motor, $8 on a blocking diode, $40 on the prop, $100 at the machine shop, and $40 worth of line and thimbles. So that's $240 and possibly another $30 for a soft shackle to make a fairlead, call it $300 all in to hopefully have a sizeable heap of clean energy for our passages. I'll report back with more info but I've got high hopes that in addition to being quieter and more environmentally friendly it will also end up being cheaper as $300 worth of gas and diesel really doesn't go that far.  

Regarding fish eating it. Personally I think that's cruiser-folklore (a.k.a. "sea stories"). The stainless steel shaft is two feet long and it's 1/2" single braid which is pretty tough to slice unless you hack it to death in multiple attempts. I'm of the personal belief that the loss of towed props is due much more to common and less dramatic reasons like forgetting to mouse a shackle. Either way though, the electrical connections and line that secures the motor to the boat will be sufficient but intentionally the weakest link so that if a school-bus sized sea monster bites hard it wont rip the transom off.

Reader Comments (4)

I'm impressed it worked ! I would never have guessed that the line would not kink.

How did you measure the amperage in the dinghy test ? 60 continuous watts at just over four knots is great !

BTW, thanks for the Merle recommendation. He's coming over in the AM with a Xantrex charger that we'll let run at 15.5 V for 8 hours. If the house bank doesn't explode that should take care of any sulphation (sp ?) according to Lifeline tech support.


-Sven

February 16, 2014 | Unregistered CommenterSven

Congratulations Eric on your new clean power toy. Additionally, I award you +5 nerd points for using an analog multimeter for testing in this digital age.

February 16, 2014 | Unregistered CommenterNate Kraft

Sven - I'm glad Merle worked out for you, he's been a great guy to know here in La Cruz. I'm stoked the line didn't kink as well. I picked the least-kinking line I know of (single braid) that would also be easy on the hands for hauling in. I have a voltage/amperage chart for the motor so that was guide for the current.

Nate - That's my original Navy model; I had that stuff since the mid 90's when I was sitting in a classroom learning basic DC circuitry. Based on what you're saying though it sounds like things have changed a bit in twenty years.

February 17, 2014 | Registered CommenterEric

I had a commercial one of those, years ago, and loved it. Except for the noise.

Be careful pulling it in! I tried it once, wearing gloves, when we were going ahead slowly. The line kinked in my hands and pinched me hard through the gloves, cutting my palms. Which is awful at sea-- they took forever to heal since I still had to pull on wet salty ropes, which would open up the cuts again and get them salty. My hands didn't heal until we arrived in Galapagos.

For me, the only safe way to retrieve it was to heave to and stop the boat completely. Even a little bit of forward motion would cause it to kink in the hands as I pulled it in. Maybe there is a better way...

Have fun! I'm a bit jealous you are heading that way so soon. You guys will have such a blast.

February 20, 2014 | Unregistered CommenterMatt Sponer

PostPost a New Comment

Enter your information below to add a new comment.
Author Email (optional):
Author URL (optional):
Post:
 
Some HTML allowed: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <code> <em> <i> <strike> <strong>