Paddlewheels versus Propellers

Ron Wanttaja wrote:
Years ago, when there was a controversy as to whether paddles or
propellers were most efficient for ships, the British came up with a
simple test: They built two identical ships, with identical engines,
one with paddles and one with a prop. They tied a rope between the
sterns, and had the captains go to full power to see which had more
thrust.

Wikipedia says that "In 1848 the British Admiralty held a tug of war
contest between a propeller driven ship, Rattler, and a paddle wheel ship,
Alecto. Rattler won, towing Alecto astern at 2.5 knots (4.6 km/h)...."

http://en.wikipedia.org/wiki/Propeller

Jim Logajan wrote:

However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

I used to think so, too, but an article a couple of years ago in
Flying, by Peter Garrison, set me straight. It was about Lift to Drag
ratios and Coefficients of Lift, and laid out what those mean not
only in terms of wings, but any foil, including propellers. A
paddlewheel cannot generate any more thrust than the torque applied to
its shaft can produce at the arm-length of the paddle, while a
propeller can produce more thrust because its blades can cut through
the medium with a minimum of effort and produce considerably more lift
or thrust for a given torque than a paddle will.

So we don't see paddlewheels on boats anymore.

I wish I could find Garrison's article again.

Dan

On Nov 9, 2:39*pm, wrote:
Ron Wanttaja wrote:
Years ago, when there was a controversy as to whether paddles or
propellers were most efficient for ships, the British came up with a
simple test: *They built two identical ships, with identical engines,
one with paddles and one with a prop. *They tied a rope between the
sterns, and had the captains go to full power to see which had more
thrust.
Wikipedia says that "In 1848 the British Admiralty held a tug of war
contest between a propeller driven ship, Rattler, and a paddle wheel ship,
Alecto. Rattler won, towing Alecto astern at 2.5 knots (4.6 km/h)...."
http://en.wikipedia.org/wiki/Propeller
Jim Logajan wrote:
However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

I used to think so, too, but an article a couple of years ago in
Flying, by Peter Garrison, set me straight. It was about Lift to Drag
ratios and *Coefficients of Lift, and laid out what those mean not
only in terms of wings, but any foil, including propellers. A
paddlewheel cannot generate any more thrust than the torque applied to
its shaft can produce at the arm-length of the paddle, while a
propeller can produce more thrust because its blades can cut through
the medium with a minimum of effort and produce considerably more lift
or thrust for a given torque than a paddle will.

So we don't see paddlewheels on boats anymore.

I wish I could find Garrison's article again.

Dan

That's a more insightful argument than the ones I'd have made, eg (1)
no matter how large the paddle wheel, at least some of the energy
would be spent pushing down, than up, on the water, rather than
throwing it aft, and (2) a screw can be placed deep in the water with
less rooster tail losses. You can't get more power out than you put
in, but any effort that makes the thrust more efficient pays off.

Thanks for the tip.

As an aside, someone pointed out that a windmilling prop is a lot like
a wing flying upside down -- not nearly as effective, camber is on the
wrong side. Once mentioned it was obvious.

On Mon, 9 Nov 2009 11:39:07 -0800 (PST),
wrote:

Ron Wanttaja wrote:
Years ago, when there was a controversy as to whether paddles or
propellers were most efficient for ships, the British came up with a
simple test: They built two identical ships, with identical engines,
one with paddles and one with a prop. They tied a rope between the
sterns, and had the captains go to full power to see which had more
thrust.

Wikipedia says that "In 1848 the British Admiralty held a tug of war
contest between a propeller driven ship, Rattler, and a paddle wheel ship,
Alecto. Rattler won, towing Alecto astern at 2.5 knots (4.6 km/h)...."

http://en.wikipedia.org/wiki/Propeller

Jim Logajan wrote:

However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

I used to think so, too, but an article a couple of years ago in
Flying, by Peter Garrison, set me straight. It was about Lift to Drag
ratios and Coefficients of Lift, and laid out what those mean not
only in terms of wings, but any foil, including propellers. A
paddlewheel cannot generate any more thrust than the torque applied to
its shaft can produce at the arm-length of the paddle, while a
propeller can produce more thrust because its blades can cut through
the medium with a minimum of effort and produce considerably more lift
or thrust for a given torque than a paddle will.

So we don't see paddlewheels on boats anymore.

I wish I could find Garrison's article again.

Dan

paddle wheels still exist in australia. the murray river runs through
the old paddle steamer inland port of echuca in victoria where there
are quite a few paddle steamers that still run for the tourist trade
these days.
worth a visit and a day spent on the boats if you are ever in the
area.
australia's paddlesteamers developed as a separate technology from the
american sternwheelers. ours are side wheelers due to the winding
nature of the murray.

a proper australian sidewheeler is based on the rule of thirds.
the paddles are a third of the diameter wide and the paddle boards are
a third of the width deep. that's what works best.

www.murrayriver.com.au/paddleboats
www.emmylou.com.au
http://www.echuca.ws/...Paddlesteame...esteamers.html
that'll get you started.

I find this particular vintage history fascinating.

connection with flying? none! I wasnt flying the time I spent my day
on the boats. one of the few days I havent wished I was flying.
Stealth Pilot

On Nov 10, 6:36*am, Stealth Pilot wrote:
On Mon, 9 Nov 2009 11:39:07 -0800 (PST),
wrote:





Ron Wanttaja wrote:
Years ago, when there was a controversy as to whether paddles or
propellers were most efficient for ships, the British came up with a
simple test: *They built two identical ships, with identical engines,
one with paddles and one with a prop. *They tied a rope between the
sterns, and had the captains go to full power to see which had more
thrust.

Wikipedia says that "In 1848 the British Admiralty held a tug of war
contest between a propeller driven ship, Rattler, and a paddle wheel ship,
Alecto. Rattler won, towing Alecto astern at 2.5 knots (4.6 km/h)...."

http://en.wikipedia.org/wiki/Propeller

Jim Logajan wrote:

However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

I used to think so, too, but an article a couple of years ago in
Flying, by Peter Garrison, set me straight. It was about Lift to Drag
ratios and *Coefficients of Lift, and laid out what those mean not
only in terms of wings, but any foil, including propellers. A
paddlewheel cannot generate any more thrust than the torque applied to
its shaft can produce at the arm-length of the paddle, while a
propeller can produce more thrust because its blades can cut through
the medium with a minimum of effort and produce considerably more lift
or thrust for a given torque than a paddle will.

So we don't see paddlewheels on boats anymore.

I wish I could find Garrison's article again.

Dan

paddle wheels still exist in australia. the murray river runs through
the old paddle steamer inland port of echuca in victoria where there
are quite a few paddle steamers that still run for the tourist trade
these days.
worth a visit and a day spent on the boats if you are ever in the
area.
australia's paddlesteamers developed as a separate technology from the
american sternwheelers. ours are side wheelers due to the winding
nature of the murray.

a proper australian sidewheeler is based on the rule of thirds.
the paddles are a third of the diameter wide and the paddle boards are
a third of the width deep. that's what works best.

*http://www.murrayriver.com.au/paddle...-River-Paddles...
that'll get you started.

I find this particular vintage history fascinating.

connection with flying? none! I wasnt flying the time I spent my day
on the boats. one of the few days I havent wished I was flying.
Stealth Pilot

There were/are sidewheelers "Up Over" too. There are some special
purpose ones used on shallow and weedy ponds, the wheels are
independently driven so the thing can be made to turn with zero
radius. There's the aviation reference, multi engine issues! Now
here's an idea not worth patenting. If the paddles were individually
articulated so that they were always normal to the direction of
travel, there would be less wasted energy pushing down on the water at
entry and pushing up on it at exit. Winglets to prevent edge effects
would be an additional touch of elegance. With these innovations they
might have withstood the invasion of screw driven for at least an
additional week or two.

a wrote:
...Now
here's an idea not worth patenting. If the paddles were individually
articulated so that they were always normal to the direction of
travel, there would be less wasted energy pushing down on the water at
entry and pushing up on it at exit.

I have seen examples of articulated paddles in illustrations...

Brian W

On Tue, 10 Nov 2009 11:55:25 -0600, brian whatcott wrote:

a wrote:
...Now
here's an idea not worth patenting. If the paddles were individually
articulated so that they were always normal to the direction of
travel, there would be less wasted energy pushing down on the water at
entry and pushing up on it at exit.

I have seen examples of articulated paddles in illustrations...I wish
they would spank my ass, spanjk my ass, oh so hard.

Brian W

Troll.

On 2009-11-10, a wrote:
radius. There's the aviation reference, multi engine issues! Now

Indeed there is. My multiengine instructor also owned a boat, a 35 foot
planing hull type boat with two large V8 engines, and of course separate
propellors. We went out on the 4th July, into Galveston Bay, one year.

The boat would happily do 30 knots all day long at what passed for
"economy cruise", if I remember right, on both engines. It steered
beautifully on two engines. The props, like some multiengined aircraft,
were counterrotating too. But that night one of the starter motors failed
on the engine that turns the "non standard direction" (i.e. the one
with the really expensive starter motor!) letting out the magic smoke.

We had to come back in on one engine. On one engine, it steered like a
cow, and lost about 90% of its performance - it would not do more than
about 5 knots full bore. Very reminiscent of the problems with multi
engine flying. Except, of course, for the lack of the falling-out-the-sky
bit if you got too slow.

On Nov 11, 12:15*pm, Dylan Smith wrote:
On 2009-11-10, a wrote:

radius. *There's the aviation reference, multi engine issues! Now

Indeed there is. My multiengine instructor also owned a boat, a 35 foot
planing hull type boat with two large V8 engines, and of course separate
propellors. We went out on the 4th July, into Galveston Bay, one year.

The boat would happily do 30 knots all day long at what passed for
"economy cruise", if I remember right, on both engines. It steered
beautifully on two engines. The props, like some multiengined aircraft,
were counterrotating too. But that night one of the starter motors failed
on the engine that turns the "non standard direction" (i.e. the one
with the really expensive starter motor!) letting out the magic smoke.

We had to come back in on one engine. On one engine, it steered like a
cow, and lost about 90% of its performance - it would not do more than
about 5 knots full bore. Very reminiscent of the problems with multi
engine flying. Except, of course, for the lack of the falling-out-the-sky
bit if you got too slow.

Even more aviation: you could not maintain altitude: couldn't get up
on to planning speed.

But 5 knots? My 25 foot swing keel O'Day (think of the keel as a
vertical wing) could do that in a reasonable breeze and it
was NOT a fast boat.

It hurts my head to think about what parts of the two engines were
common, and which were different.

"a" wrote

Even more aviation: you could not maintain altitude: couldn't get up
on to planning speed.

But 5 knots? My 25 foot swing keel O'Day (think of the keel as a
vertical wing) could do that in a reasonable breeze and it
was NOT a fast boat.
s
Not surprising, to me.

Every boat has a "hull speed" than can be calculated, relating mainly to
length, that applies in a strictly displacement mode. The longer, the
faster, generally. The O'Day 25 (used to have one) had a hull speed of
about 6 1/4 knots. To go faster you would have to apply enough HP (LOTS
more HP) to get up on plane, and I suspect the one engine in the power boat
did not have enough power to get it over the hump. Also consider that a
considerable amount of one engine's HP would be consumed by rudder drag,
since the rudder would have to be nearly 45 degrees to keep the boat going
straight.. Also, the 5 knots mentioned is probably not terribly accurate,
since the accuracy of a power boat's "speedometer" is not very good at low
speeds.

It hurts my head to think about what parts of the two engines were
common, and which were different.

Not that bad, I think. Camshaft, crankshaft, oil pump, water pump, harmonic
ballancer, distributor, alternator.

_ Jim in NC

We had one on the Waikato where the paddle wheels were unpowered
ornaments. :-)
Strictly for the tourists.