I am looking to design a water propeller to turn a small generator and
have some questions. First of all, I have some propeller design
programs for a "driving" propeller but was wondering which
characteristics are true (or approximate) in reverse. Of course, I am
assuming that the concave side of the propeller will be facing
upstream in the "driven" condition.
1) Given the same of amount of shaft torque (or horsepower), will the
drag on the prop in the driven state be the same as the thrust in the
driving state?
2) Related to the above, can the same slippage characteristics be
applied in the reverse state?
3) Are there different design features that should be considered for a
driven propeller in order to maximize efficiency?

Thanks for help with the above!
Bailey--

I can't help you much on the engineering part of your question..

However, I can tell you what I have used with some success for a tow/water
gen. My generator is a permanent mag. DC (computer tape drive)motor.

The propeller is a small outboard prop. I would guess it's between 5-8 hp..
It is mounted on the end of a chunk of 3/4"x 24" stainless round stock. On
the other end I have welded ring to shackle the tow line to. Actually I
ended up splicing the line, without thimble to reduce fouling in sea weed,
etc.

To be honest, it's been a few years since I last used it (Baja '89 trip) I
don't remember what type of line I ended up using since they all seemed to
twist up, but eventually they became taught enough that it couldn't twist
any more and turned the generator.

I tried putting the prop on frontwards and backwards and never really
noticed any difference. I'm sure they would be if you could compare in ideal
conditions, but..

I think the ideal prop would be like the ones used on the Walker Taff Rail
Logs. I have a pair with mine but wouldn't want to risk using them on the
tow gen. These have the blades in more of a spiral around a torpedo shaped
hub. Mine are on the boat so I can't verify, but I think they have three
blades and spiral nearly a complete turn/twist over about 3 inches. (I'll
verify that when I go to the boat today).

One of the more important elements that I found, was the 2 ft long shaft
that I had on the prop. it acted like a weight and also helped to keep the
the line taught when the going is very slow (even hanging straight up and
down.

If I remember correctly, I got about 3 amps once the boat speed got up to
about 3-4 knots. Nothing noticeable below that. But enough to stay ahead of
the autopilot or running lights.

--
My opinion and experience. FWIW

Steve
s/v Good Intentions

I don't have any answers for you, but what you are describing is really very
similar to the way a generator in a hydro-electric dam is driven. Instead
of a propeller, it's a turbine. Maybe you could do some research on the
characteristics of a hydro-power turbine?

Sounds like an interesting project; let us know what you come up with!

"MBS" wrote in message
om...
I am looking to design a water propeller to turn a small generator and
have some questions. First of all, I have some propeller design
programs for a "driving" propeller but was wondering which
characteristics are true (or approximate) in reverse. Of course, I am
assuming that the concave side of the propeller will be facing
upstream in the "driven" condition.

Hydro generators do use a propeller. They use a Peltier Bucket. Originally
designed for hydrulic mining in the California goldfields.
Bill

"Snafu" wrote in message
news
I don't have any answers for you, but what you are describing is really
very
similar to the way a generator in a hydro-electric dam is driven. Instead
of a propeller, it's a turbine. Maybe you could do some research on the
characteristics of a hydro-power turbine?

Sounds like an interesting project; let us know what you come up with!

"MBS" wrote in message
om...
I am looking to design a water propeller to turn a small generator and
have some questions. First of all, I have some propeller design
programs for a "driving" propeller but was wondering which
characteristics are true (or approximate) in reverse. Of course, I am
assuming that the concave side of the propeller will be facing
upstream in the "driven" condition.

On Wed, 05 Nov 2003 06:29:27 +0000, Calif Bill wrote:

Hydro generators do use a propeller. They use a Peltier Bucket. Originally
designed for hydrulic mining in the California goldfields.
Bill


Close. Hydro plants DO use "propellers" - it's called a Franklin Turbine.
And the "Peltier Bucket" is a Pelton Wheel. OP could google those and get
some good information.

Lloyd Sumpter, BC Hydro Engineering

"Lloyd Sumpter" wrote in message
...
On Wed, 05 Nov 2003 06:29:27 +0000, Calif Bill wrote:

Hydro generators do use a propeller. They use a Peltier Bucket.
Originally
designed for hydrulic mining in the California goldfields.
Bill


Close. Hydro plants DO use "propellers" - it's called a Franklin Turbine.
And the "Peltier Bucket" is a Pelton Wheel. OP could google those and get
some good information.

Lloyd Sumpter, BC Hydro Engineering


I knew the Peltier was wrong. Have been working on some Peltier coolers,
and just had a brain fart.

Are you overclocking your cpu or designing a beer cooler for
your boat? :^)

-JimL


Calif Bill wrote:
removed
Have been working on some Peltier coolers,
and just had a brain fart.

Did a beer cooler about 20 years ago. Then was too expensive and required a
fan. Biomedical application.
Bill

"JimL" wrote in message
...
Are you overclocking your cpu or designing a beer cooler for
your boat? :^)

-JimL


Calif Bill wrote:
removed
Have been working on some Peltier coolers,
and just had a brain fart.

On Wed, 05 Nov 2003 06:43:27 -0800, Lloyd Sumpter wrote:

On Wed, 05 Nov 2003 06:29:27 +0000, Calif Bill wrote:

Hydro generators do use a propeller. They use a Peltier Bucket. Originally
designed for hydrulic mining in the California goldfields.
Bill


Close. Hydro plants DO use "propellers" - it's called a Franklin Turbine.
And the "Peltier Bucket" is a Pelton Wheel. OP could google those and get
some good information.

Lloyd Sumpter, BC Hydro Engineering

No flame and I'm not trying to split hairs, but I always thought that
turbines were designed based on volume and head. High pressure, low volume
used Pelton Wheels which are essentially high pressure jets aimed
tangentially at flat bladed turbines, while conventional (high volume, low
to mid pressure) used propellers which more closely resemble what we think
of as propellers. Is a Pelton wheel the same as a Franklin turbine?
Thanks,
--

Larry
email is rapp at lmr dot com