Can anybody in the NG factually and authoritatively address the
relative physics and mechanical efficiency of paddlewheel vs. propeller
as propulsion sources for larger, displacement speed watercraft?

wrote:

Can anybody in the NG factually and authoritatively address the
relative physics and mechanical efficiency of paddlewheel vs. propeller
as propulsion sources for larger, displacement speed watercraft?



Yup, about a hundred years ago. Why do you suppose the screw
replaced the paddlewheel? If there were any means of propulsion
more efficient than the screw, either the military or the
commercial builders would have switched to it years ago.

-Raf

--
Misifus-
Rafael Seibert

http://www.ralphandsue.com

wrote in message
oups.com...
Can anybody in the NG factually and authoritatively address the
relative physics and mechanical efficiency of paddlewheel vs. propeller
as propulsion sources for larger, displacement speed watercraft?


It shouldn't be too hard, a little trig, a little physics. The main
detractor from paddlewheel seems to me to be that the force has an upward
and downward component that represents wasted energy. So the thrust
varies as the sine of the angle of the blade to the water. To get the
overall efficiency, integrate sine x from the point where the blade
enters the water to where it exits the water.

That what you are looking for?

wrote ...
Can anybody in the NG factually and authoritatively address the
relative physics and mechanical efficiency of paddlewheel vs. propeller
as propulsion sources for larger, displacement speed watercraft?



Sure. Go to the library and look for any marine engineering handbook
published prior to about 1910. They'll cover paddlewheels along with
Scotch boilers, contact condensers, walking beams, etc etc.

In WW2 the Brits built a series of paddlewheel propelled minesweepers,
but I don't know of any references specific to their power plants...
maybe you could ask the Admiralty?

The benefits of a paddlewheel are shoal draft and GREAT starting,
stopping, & low speed maneuverability (at least, for split wheels & side
wheels). A high speed paddlewheel ski boat would have an nearly
intantaneous hole-shot! The disandvantages are they're a bit less
efficient and much more draft sensitive (the later advanced ones had a
way of jacking the wheel shaft up or down to match the boat's lading),
plus the freewheel much more dramatically than a prop... if something
goes wrong, all the paddle machinery continues to whirl as the boat
coasts to a gradual stop, usually thrashing everything inside to a pulp
and occasionally punching holes in the bottom.

Some years ago I had the chance to inspect the power plant of a late era
yukon River paddle steamer, now in a park in Fairbanks. The boilers are
out, but everything else is in place. There was a generator (100V DC
according to the labels) on the stbd paddle shaft, electric or shaft
driven fuel pump, HP & LP cylinders on concentric shafts, etc etc. A
very pleasant afternoon for this old steam engineer but a very boring
one for my wife


Del Cecchi wrote:
It shouldn't be too hard, a little trig, a little physics.

You can get the basics pretty good, but have to keep in mind that
paddlewheels operate at much less slip than props (or at least, that's
what I've heard... never designed & sea trialed on myself)

... The main
detractor from paddlewheel seems to me to be that the force has an upward
and downward component that represents wasted energy. So the thrust
varies as the sine of the angle of the blade to the water. To get the
overall efficiency, integrate sine x from the point where the blade
enters the water to where it exits the water.

That what you are looking for?

You don't even need integration... the linear velocity of the inner edge
of the paddle blades would be a pretty close approximation, but it
wouldn't tell you how much HP you need to drive X tonnage at Y speed.

A big problem with paddlewheels is that the thrust is all radial to the
main bearings, and it needs more bearings too.

Lots of fun to read about, I'd like to try steaming a paddlewheeler but
not much interesting in building or financing one.

Fair Skies
Doug King