Future of Sailing? - Page 3 - SailNet Community
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post #21 of 61 Old 10-21-2006
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snip~

Still, why is this not the future of sailing?

~snip

Probably because it is too expensive, too complicated and probably provides little increase in efficiency. If we are talking about a motor-sailer/condo with washer, drier, big screen TV, dishwasher, etc., etc. then yes, maybe, but not for a sailboat.
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post #22 of 61 Old 10-21-2006
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energy efficiency and electric propulsion

disclaimer: I'm not an engineer. I hope one comments on this thread.
The problem I see with a boat equipped with a diesel reciprocating engine generator, battery bank, and electric propulsion motor is one of efficiency. Let's start with the premise that in using these devices, you are converting one form of energy into another, as in chemical to thermal to mechanical to electrical to mechanical to kinetic. Next, we must admit that each time a form of energy is converted, there is a certain loss of eficency. For instance, published efficiencies for diesel reciprocating piston engine generators is on the order of 25-40%.
The amount of energy that can be stored in diesel fuel can be calculated. For various diesel-powered propulsion systems, we can estimate a "miles per gallon" efficiency of propelling the boat. Comparing diesel propulsion with an engine coupled directly to a propeller shaft versus that produced by a diesel generator to batteries to electric motor to propeller raises the issue of efficiency loss at each conversion. The direct diesel propulsion has to be more efficient in moving the boat, thus more "mpg" as there are less steps of energy conversion. This is one of many reasons why I think electric boats are not yet commonplace. Now, of course if you add additional power generation capacity from generating power from boat movement via the propeller shaft while under sail, it gets more interesting. There are many intriguing possibilities for the future, including fuel cells as storage devices. I wait on the sidelines with interest
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post #23 of 61 Old 10-21-2006
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I guess the big question is, after ten years and a thousand boats like this on the water, how will they hold up.

Dual energy conversion (stored diesel to electric to electric motor) is almost always less efficient than single conversion, so I'd look askance at that. Using the props as water generators might work well in a cat, but in a keelboat I'd expect that much drag on the boat is going to be a meaningful speed change--which is why most sailboats aren't using water generators on their props already. How many sailors want a prop that will give them MAXIMUM drag while under way?

Don't get me wrong, the diesel-electric bit sounds interesting. It worked well in U-boats (for different reasons) and it runs the entire railroad industry (again for different reasons) but...in a boat...an awful lot centers on how well that electric propulsion motor is going to work. Are they willing to give it a warranty comparable to a combustion engine? Or the alternator and starter in a car? Five years and 50,000 miles?
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post #24 of 61 Old 10-22-2006
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prop drag

Hellosailor, you raised an interesting question about prop drag when a boat uses propellers to generate electricity. This subject seems complex to me. I have read diametrically opposed opinions about prop drag: assuming a fixed-blade prop, is the drag more or less when it is spinning/freewheeing compared to locked and stationary? Some claim that cavitation causes a stationary prop to lose drag with increasing boat speed. While it's intuitively obvious that a folding/feathering prop has less drag, there are probably more boats on the water with fixed props. How much loss in boat speed would there be for those boats if allowing the props to turn a generator? I'm sure there must be some, or everyone would have prop shaft generators!
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post #25 of 61 Old 10-22-2006
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I come from boats where we wanted to SAIL, and while we made the proper obeisances and blessings over "Our father who art in Evinrude" and left offerings at Herr Doctor Professor Diesel's gravesite, I don't think I've ever spent any long time on any boat with a 3-bladed prop unless it was a motorboat! So, whether a 3-blade should be locked or roll just doesn't matter much to me.

OTOH there's always been a mark on the prop shaft, so the folder can be folded properly, or the fixed 2-blade can be rotated vertical and set to minimize drag. I can't see dragging the water wheel as a routine procedure.

With one horsepower equal to about 750 watts, I'm told you can figure about 25A @ 14.4 per horsepower, allowing for a 50% loss. I don't swear by that, it is just what I've been told. So, a 50A charging rate from a water wheel would be like a two horsepower "drag" on the boat. Maybe no problem for a cat scudding along at 18 knots but for those of us who think moving from 5.1 knots to 6.3 knots is a Really Good Trick?

Dunno. That would take some getting used to.

I suspect the real answer and real numbers with whether to lock a 3-bladed prop are going to depend on a lot of particular design issues. Whether the prop is blocked by flow from the keel, is in an aperature, has other turbulence from the hull, etc. etc. If I have to spend time living with one, then I'll chase down the latest opinions on it, and see if they've changed over time. Or, lock and unlock the prop, and see what Mr. GPS has to say about it.
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post #26 of 61 Old 10-22-2006
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If this is to be the future of sailing (btw it makes no sense for non sailing vessels because it's too inefficient) there must be a way to generate power other than using the generator. The motion of the boat through the water to generate electric power is absolutely critical, but as mentioned pevious posts there is no such thing as a free lunch (except wind) The premise one has to make before purchasing one of these systems is that one will be doing alot more sailing than motoring and be willing to put up with the loss in speed due to drag. I really want a small nuclear generator...that is the future
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post #27 of 61 Old 10-22-2006
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folding props

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Originally Posted by hellosailor
Quetzal-
Or, lock and unlock the prop, and see what Mr. GPS has to say about it.
hellosailor,
I confess that my boat has a fixed 3-blade prop....Your GPS experiment is interesting, and I'd like to hear if you do it. I thought a fixed prop represented a loss of about a knot or so of boatspeed on average.
This thread interests me because it is related to the idea of self-sufficiency. If one has an all-electric system on a boat and enough power can be generated to run it without outside fuel sources, that would be very interesting indeed, particularly in this world of dwindling resources.
My goal is to live aboard a boat when I retire. Looking forward at what systems such a boat might be equipped with will require much thought.
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post #28 of 61 Old 10-22-2006
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power sources

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I really want a small nuclear generator...that is the future
ebs,
When someone is able to develop a "cold fusion" reactor small enough to power a boat, that will be a possibility. It's beyond our current technology.
Remember the "Back to the Future" films with a car powered by a blender-sized device called "Mr. Fusion"?
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post #29 of 61 Old 10-22-2006
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Q, I'll take one of them thar "Mr. Fusions", in the future of course. We do have the nuclear technology now - subs and aircraft carriers - just need to down size a tad for my sail boat
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post #30 of 61 Old 10-22-2006
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Quetzal-
See http://www.hollandamerica.com/cruiseships/Westerdam they use the "Azipod" propulsion system, which consists of industrial diesel-electric plants powering separate electric propulsion pods. Given solar deck tiles I suppose it could be used instead of diesel for commercial vessels.

The questions are, the economies of scale, and the quality of the goods being sold to the recreational marine market.

NewYouCleah plants, or whatever presidents from both parties seem to be calling them, are nothing new. Westinghouse's Reddy KiloWatt cartoon character promised us all grapefruit-sized nuclear plants powering our homes from safe economical plutonium balls all the way back in the 60's.

Puts a new spin on "Back to the Future", huh?
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