Two hydrogenerators?

[valhalla360]

Originally Posted by GTom

And I suppose you are aware of the different optimized blade size for each speed class? And all this is from a "first gen" manufacturer, who didn't really do much more than use a standard prop, not a special design for power generation.

Yes, fully aware from my fluid dynamics courses in college.
but an optimized turbine will gain you a few percentage points increase in power. If you are running the power generation side of a dam, where the water supply is already optimized and very consistent getting a few percentage points more by tweaking makes a lot of sense. But on a sailboat where speed is often out of your control, going from say 3kts to 6kts will give you a 400% increase in power. It's a couple orders of magnitude difference what speed can do vs an optimized turbine. What you are seeing is mostly marketing. It's technically correct but in the big picture, optimizing the prop doesn't do a lot.

Wind is a valid point, solar - I don't know. Last time we did some 24 hour passages in Scotland, of which we had 10hours night and 14 hours overcast. Very good force 6 wind though!
Besides, I hope for a major improvement in solar tech in the next few years (at least in price...), thus a big investment is solar today would seem silly in 5 years. Meanwhile the sun-independent wind/hydro solutions of today will hold their value well. I do want solar, but not now.

Price is what makes solar so attractive NOW as power source not increases in efficiency per sqft. In the late 70's prices were on the order of $75/w. By the mid 90's it was down to $5/w and we've broken the $1/w range in recent years. Looking at the graphs, we are approaching the flat part of the curve as the economies of scale have largely been realized already. If the cost of a water generator is't scaring you away, there is no reason cost should scare you away from solar.

Even with misc hardware to install, $1000 and I could put in 400w and even on overcast days, I would expect to get some power out of them.

Ultimately it sounds like you are intent on getting a water generator and you are free to do so but there are better options out there and that's why you don't see many in use.

[GTom]

Originally Posted by valhalla360

Ultimately it sounds like you are intent on getting a water generator and you are free to do so but there are better options out there and that's why you don't see many in use.

I want a sun-independent option, because that "1000$" buys you 400w in the tropics, it gives you maybe 100W on an average N-Eu day and zero at night.

Originally Posted by valhalla360

...but an optimized turbine will gain you a few percentage points

My limited hydro class taught me that power is proportional to the wetted area, hence this has some founding:


Anyway, maybe on a slow vessel it's better to start with wind, as a night/overcast solution.

[valhalla360]

The graph demonstrates my point that it's all about speed. Go from 3kts to 6kts and you can drop down a size on the prop and still put out an order of magnitude more power.

As far as the cost of solar. $1000 was assuming everything to install 400w of panels. The panels themselves should be less than half that. The link you provided shows a 300w generator at $3800 before installation costs. There are cheaper ones. I found a 100w aquair for $1500. So even if you are only getting 100w on overcast days with solar, it's still doing better and you will get power reliably out of solar on far more days.

Again, you seem intent a towed generator, so I suggest getting them and putting a meter on it and letting us know in a year or two if we were wrong and how many days you got enough power to run an electric stove and such off the towed generators.

[GTom]

Originally Posted by valhalla360

The graph demonstrates my point that it's all about speed. Go from 3kts to 6kts and you can drop down a size on the prop and still put out an order of magnitude more power.

As far as the cost of solar. $1000 was assuming everything to install 400w of panels. The panels themselves should be less than half that. The link you provided shows a 300w generator at $3800 before installation costs. There are cheaper ones. I found a 100w aquair for $1500. So even if you are only getting 100w on overcast days with solar, it's still doing better and you will get power reliably out of solar on far more days.

Again, you seem intent a towed generator, so I suggest getting them and putting a meter on it and letting us know in a year or two if we were wrong and how many days you got enough power to run an electric stove and such off the towed generators.

Indeed, 3kts yields practically nothing, thus it would be a waste on a very clumsy vessel. Things start to be interesting around 6kts.

Once I get my boat I'll test a hydro generator, but not the overpriced ones, I'll most likely build one from a ~12"prop and a permanent magnet engine. This will take a bit of time... I absolutely agreed, that the price of 3-4ton fuel(!) is not realistic for such an installation. Quite typical though once you get a "for boats" stamp on it (same for wind generators)...