Hi, Kriss, you have some good innovative thinking, thanks for that.
Thanks also for the R/C prop link too, that site also has largish 3
bladed pusher props that might be a good fit for my mini-wind turbine
ideas for safe unattended use.
I suspect that the reason for the large diameter that you suggest, is to
create torque?
Maybe this could also be done using multiple blades, again, I see that
you are thinking that way, but would it not be better to have a blade
setup like an old style water pumping windmill, giving easy starting,
but limited in RPM, which in the case of regen for sailboats is not a
problem. You suggest 4 blades, how about 12 or more? Obviously, the
pitch would be set up for less drag that the pitch on the ones driven by
wind.
I suspect that the whole dual purpose need is a difficult problem that
might, due to the low power application and lack of reserve power, be
impractical to easily overcome. On one hand, we have a propulsion prop
that has slippage that increases like crazy with the speed, and on the
other hand, a turbine that needs low speed torque, low slippage, and
preferably can feather when the boat is not sailing above maybe 50% of
hull speed.
This again will bring up the old statement, "It depends what you are
doing". It might be possible for an ocean crossing, to have just the
multi-bladed prop, as there will be little if any motoring.
But I have a gut feeling that the most practical method would be a
"lift-out-able" regen prop.
I suspect that those right angle drill units would have insufficient
durability, same with a small angle grinder gearbox, but a (home-made?)
belt drive can twist around 90 degrees quite well, I suspect even narrow
width toothed belts could do so, provided that the pulleys had side
cheekplates and the pulley to pulley distance was large enough. Another
method from a previous century is a metal disc, with a rubber wheel
pressed against the face of it, this also allows variable speed, of
course.
As far as curved weedwhacker shafts go, the one I recently tested has
too much internal friction, being a crude form of speedometer cable
setup, and in use as a weedwhacker, actually warms up, it is harder to
tell when it is used with a prop fitted, due to water splashing, but
there is more loading, so it follows that there is more side friction in
that application, too.
The best setup, especially for removal from the water when appropriate,
might be like the Thailand 'long tail' outboards.
Overall, though, if the power production figures are too low, it might
make more sense to go with none-cogging mini turbines, as they have the
benefit of producing power when moored, as well as when underway, and
possibly less drag, dependent upon wind direction.
John
1.4. Re: actual test data for prop regen?
Posted by: "Femm" femmpaws@yahoo.com femmpaws
Date: Sun Oct 2, 2011 12:57 pm ((PDT))
Okay I'm going to sound off here.
The first thing you have to take into account is your brake out speed as
in how fast does the water has to be moving before it can over come the
mass and drag imposed on the prop and shaft...
Next you need to look at prop pitch... The more pitch the wheel has the
more speed it's going to take to get to your brake out speed. So a fine
pitched prop is going to work better. Two reasons, the fine pitch get's
better bite in the water, and the water doesn't have to move as far to
make one turn with the prop.
Because you are working at such low speeds the drag on the wheel is
almost the same as the power you are getting out of it. using your
numbers you are getting around 25 watts of power.... In my book that is
a very poor return.
Now if you built something that was set up just for charging would have
a different wheel design. With towed charging systems they have found a
helix to work the best at low speeds. But there is another way to do it
as well, by using a high aspect ratio prop.
What would you be looking for first, a large disk area so a 18 to 24
inch diamator would be a good start, then something with a fine pitch,
my guess would be 6 to 10 inches of pitch.
Next where to find them? A hobby shop!
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCGK5&P=0
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHMK6&P=0
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXFGV4&P=0
Or
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ993&P=0
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ994&P=0
Now any of these props will absorb over 3 to 5 horse power in the air.
If you take two of them and make a four bladed prop by stacking them on
the same shaft you should have the blade area needed to pull 400 to 500
watts of power at your 6 or so knots. I would say that's a lot better
output them 20 watts. These props are going to have less drag then a
boat prop at this speed and that means you should be able to get more
power out of them.
Now you are doing the how do I hook it up? Well the first thing that
come to my mind is a curved shaft weed-eater setup. Better yet would be
a straight shaft with a fairing pod over the little gear box. A prop
spinner may be the slick ticket for your nose cone.
Now you could get fancy and get some streamlined tubing and use a right
angle drill gearbox and a shaft up the tubing with some UHMW blocks to
act as bearings so the shaft will not whip in the tube. You could also
set it up so the water lubed your bearings and cooled them at the same
time.
You can get replacement stators for the GM altanators that will put out
48 volts.
Kriss aka femm
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