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Old 09-09-2016, 05:54   #31
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Re: Hydrogenerator for power

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Our cat is fitted with a Watt&Sea hydrogenerator with the new generation mounting bracket and we use it primarily on longer passages. We installed it in South Africa in January and used it 24/7 till we got to the Caribbean without any issues and will be down when we cross the Pacific next year. Our main reason for the purchase was to maintain the batteries during night passages for which it excelled at. We took the larger optional prop, 280mm if I recall, which drives more amps in to the batteries. Well recommended.
It makes me wondered why it wasn't as widely used as wind generators, at lease I hadn't personally know a boat that used one, the wind generator didn't produce as much power as I like, barely 100 watt.
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Old 09-09-2016, 06:06   #32
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Re: Hydrogenerator for power

You should know the yachties - they are waiting until the whole sheep crowd is running in the same direction....:-))
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Old 09-09-2016, 09:03   #33
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Re: Hydrogenerator for power

It has been a long time since I played with motors used as generators. Back then the motor from an exercise treadmill, or some of the variable speed home AC condenser fans were pretty efficient to use as generators.

There are still lots of wind power forums and groups with lots of info and helpful people.

Just a thought, if props are expensive, would it be cheaper to play with pulleys and belts at the generator to get the desired RPM range?
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Old 09-09-2016, 09:19   #34
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Hydrogenerator for power

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Just a thought, if props are expensive, would it be cheaper to play with pulleys and belts at the generator to get the desired RPM range?

The losses to friction on a simple v belt would pretty well render the device useless. And the cost of the pulleys and bearings would not be small.

At least when such arrangements are used on the main drive shaft there is plenty of torque available from the great big main engine prop which is big bit of drag many boats are stuck with anyway, either because of the cost of a feathering or folding prop or the practicalities of fitting one to the boat in question.

But Jim's solution is great and cheap. I was even able to source a super low pitch pusher prop for a 1960s 15 hp Evinrude many years ago for a tiny price from a few calls to various outboard wreckers.

Finally, after looking at those pictures in the document linked by Elpinguino, I am wondering if self fabrication of the prop may produce even better results.


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Old 09-09-2016, 10:13   #35
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Re: Hydrogenerator for power

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It makes me wondered why it wasn't as widely used as wind generators, at lease I hadn't personally know a boat that used one, the wind generator didn't produce as much power as I like, barely 100 watt.
I'd be worried about how much it slows you down
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Old 09-09-2016, 10:47   #36
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Re: Hydrogenerator for power

I used a commerical 200 watt towing generator, which was based on a 5-6 hp outboard prop and one of the old tape drive motors. It worked fine for me except for its propensity to leap out of the water in following seas at over 25 k windspeeds (probably 8-9 k boatspeed, but the determining factor is the size/steepness of the seas. It also fouled with sargasso weed in the Atlantic.

I was happy with 8 amps output (200 amp-hrs/day) at 7k boatspeed, and reckon that it slowed my 45 ft boat down by less than 0.2 knots when there was enough wind to drive me hull speed. If I was ghosting along in 5 knots of wind, it probably slowed me down half a knot and only put out 2 amps, so it generally got taken out of the water at that point.

When it was putting out over 100 watts, the generator case got quite hot to the touch--one time so hot that the magnets cracked. If I wanted to drive it at its rated power, I would have had to put cooling fins on it.
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Old 09-09-2016, 12:23   #37
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Re: Hydrogenerator for power

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I'd be worried about how much it slows you down

There is no noticeable reduction in speed. But then we have a 14m cat at some 18mt. The body is a slender 3cm and there is little resistance driving the prop. I can turn it easily with my pinky.
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Old 09-09-2016, 13:28   #38
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Re: Hydrogenerator for power

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I'd be worried about how much it slows you down
I was considering that factor as well, but it probably won't take more than half a knot and shouldn't be too bad if racing crowds are using it and may not matter as much for cruisers.
Wind aren't up to the power off shore and didn't work too well in the trade winds, they can charge on shore but there are more efficient way to charge on shore anyway, so maybe it's just the cost.
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Old 09-09-2016, 13:50   #39
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Re: Hydrogenerator for power

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I was considering that factor as well, but it probably won't take more than half a knot and shouldn't be too bad if racing crowds are using it and may not matter as much for cruisers.
Wind aren't up to the power off shore and didn't work too well in the trade winds, they can charge on shore but there are more efficient way to charge on shore anyway, so maybe it's just the cost.
Race boat that use them are different. The issue with hydrogenerators is that they really need an average speed thru the water of better than 5kn. That's pretty much the cut in speed. Off the wind with the waves and current pushing you figure you need 6kn SOG to get there, could be more, could be less. But that means if you aren't averaging 120-150nm days on a passage you simply aren't going fast enough to make them work well.

So what's the average passage speed of <40' cruisers...? About 130nm/day. So you get some reports that they work great, a lot of reports that the power is minimal, and a lot of frustration. The reality is that most boats cruising speed is right at the realistic cut in speed. Faster boats love them slower boats can't use them, and a lot of boats have flashes of brilliance followed by a lot of frustration.

Race boats on the other hand are just different. Consider average speeds of 10-12kn and all of a sudden the systems work like a charm. Sure you give up a little speed while charging, but it also means you can get away with carrying less fuel, battery bank size isn't at critical so you can save weight there as well. By the end of it boat weight is down a few hundred pounds, so whatever speed you loose while charging you get back the rest of the time by not having the weight aboard.

Bringing up the Dashew's is a good example of magical thinking... They generated massive amount of power, but they did it on a 70' boat known for high average passage speeds. Driven by two great sailors who spent a lot of money and time on making their boats go fast.

There is no good short answer other than if you aren't making 150nm days on average they probably won't work. If you are hitting 200nm days you should have one already.
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Old 09-09-2016, 14:26   #40
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Re: Hydrogenerator for power

In less than ideal wind condition many would run their motor and they get power from the catalyst, and lifted up when not needed for speed, I just don't know how easy it is to lift it.
10-12 knots are realistic for regular folks, but wind or solar doesn't produce sufficient power for the not so big mono hull, 5 knots is about realistic if it can produce twice the amount of wind and thrice the amount of solar.
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Old 09-09-2016, 14:39   #41
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Re: Hydrogenerator for power

Quite right, you need the speed to make them economical. Here's an output chart from watt and sea and its pretty much the results we record . Click image for larger version

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Old 09-09-2016, 20:16   #42
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Re: Hydrogenerator for power

With the bigger prop the wattandsea hydro gen is working fine from 6 knots on, but to use it efficent it's necessary that your boats energy consumption is downsized already. That means fist and most important thing is to reduce the use of energy as much as possible. This includes the nav equipement as well as the lights (led), fridge, and so on. Then the hydro gen is covering all your needs even by a lower boat speed. My experience is that the gen is not really slow down the boat - if yes - then we talk about 1/10 of a knot. But he is only working when you are under way....
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Old 10-09-2016, 00:54   #43
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Re: Hydrogenerator for power

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With the bigger prop the wattandsea hydro gen is working fine from 6 knots on, but to use it efficent it's necessary that your boats energy consumption is downsized already. That means fist and most important thing is to reduce the use of energy as much as possible. This includes the nav equipement as well as the lights (led), fridge, and so on. Then the hydro gen is covering all your needs even by a lower boat speed. My experience is that the gen is not really slow down the boat - if yes - then we talk about 1/10 of a knot. But he is only working when you are under way....
I agree, just having more power you will worry less, small things add up, computer, water maker etc. I just don't have to worry about how much power I use on the sea and for how long.
If the moving is unbearably slow, power from the engine, or on shore power of available at mooring.
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