Modern paddlewheels

One of the more irritating qualities of water is its clinginess. Its tendency to attach itself to objects by 'surface tension' or some such thing. If it would only 'go its own way' once we were done with it, life would be so much simpler. Boats with bannana like profiles would be able to plane as well as move along nicely at displacement speed. But nooo.

Once the wheel got going fast, it would be more like a fly wheel (water ballasted) than a propulsion device. If you ever rode a bicycle through a puddle, you would know what I mean. I guess the secret of propellers is that they benifit from the very characteristic of water that bedevils paddle wheel design.

The clinginess is used to create 'lift' because the water on the low pressure side of the propeller blade insists on following the blades curve and, there by ends up being pulled along as well as pushed.

I suppose a really efficient paddle wheel would be a circular plate with blade plates atached to it at 90 deg angles. The circular and the blade plates would be as thin as practical. That way, all the surfaces moving through the water would be perpendicular to gravity and there would be little tangental surface for the water to 'ride' around the circle.

Another problem is that only 1/3rd the paddle wheels diameter is actually immersed in the water. For that reason, they have to be relatively huge to be really effective.

Bob

 

Fish tails act more like a oscillating paddelwheel than anything else. And now the USN is trying to find the eff. of that compared to screws.

 

A fishy auxilliary?

I bet fish would have propellers too. If they could.

The problem with that system is that you have to move the mass to one side, stop it, then move it to the other side. My guess that the biggest secret the fish have is that thier whole body flexes in a neat undualating curve. Quite hard and expensive to imitate, but easy for the fish to do.

Being a sailer myself, I have thought of the idea of adding a flexible plate to the trailing edge of my rudder blade so it could act as a 'fish tail' when the wind quit. I would have readily available auxiliary power at the end of my wrist. With no need for paddles or oars.

If I could re write sailboat racing rules, I would allow boat rocking, known as 'pumping', and tiller wagging, which I think is called 'ooching'. It would be interesting to see what design (and auxilliary propulsion) developements would come out of that.

Bob

 

edit: double post

 

This is a very interesting topic. I've always had a slightly irrational fondness for paddle wheels and thought there should be more of them about, but the technical problems are quite big.

From observation of the paddle steamer Waverley, the last remaining example of the paddle steamers which used to serve in the Firth of Clyde, the paddles kick up vast amounts of turbulence at low speeds, which then reduces as the vessel reaches cruising speed. The wake is very flat when cruising, but this may just be due to the narrow beam. The effect of water being drawn up into the paddle boxes is for some reason more noticeable on one side than the other, but is significant and must affect the efficiency. I don't however know any figures, and I believe the old Admiralty test was inconclusive. A "tug of war" does not prove anything as far as overall efficiency is concerned. It tests only bollard pull - i.e. the force exerted by the propulsion system when the boat is stationary. This is of importance to tugs, fishing vessels and other vessels used for heavy towing, but it has no bearing on efficiency at speed. Paddle wheels are naturally unsuited to bollard pull tests, as at low speed they kick up huge turbulence and so create losses. They are more efficient at higher speeds, which is what they were generally used for, in Scotland at least - the fast displacement passenger steamers mentioned above.

I would really like to know if anyone can point me to any research which has been done on the relative efficiencies of screws and paddles at a range of speeds, as I have been variously told that paddles are hopelessly inefficient, as efficient as screws, or that a well-feathered paddle wheel is more efficient than a screw. It is very difficult to know what the truth is as paddles are so rarely used these days, and where they still exist in old steam vessels the huge inefficiency of the expansion engine will make it very difficult to assess the efficiency of the paddles themselves.

Re: what some posters have been saying about using fixed paddle wheels, my understanding is that the feathering is critically important, as by reducing the angle at which the floats enter the water, it increases the "virtual diameter" of the wheels, meaning that a wheel as efficient as those used on the old stern-wheel steamers can be fitted into a far smaller paddle-box. The feathering mechanism used on the Scottish vessels did not involve weighting at all, it was an eccentric wheel with jointed arms which was connected to the top of each paddle float and aligned them as they entered and left the water (rather similar to the method used to align the blades on a Voith vertical-axis propulsion unit). It seemed to work very well but the mechanism was complicated, and that is a big barrier to modern manufacture.

Also, if you wanted to fit a large paddle wheel in a modern vessel with diesel engine, you would need a more complex gearing system than is used with a screw, as the wheel would have to be accelerated gradually to avoid extreme strain on the gearing and the feathering mechanism - unlike a screw, which can be started up at high speed when the vessel is still stationary, and the only penalty is slight loss of efficiency. This wasn't a problem in old paddle steamers, as the steam engines themselves started slowly and there was no gearing system at all, just a single large crankshaft.

 

2 PWC with the same everything originaly. 1 is now fitted with a snowmobile belt under it. Could be shortned for better performance. Who can carry more #'s at any speed? Sound like a contest?

 

Is there any point in trying to make a traditional paddle wheel efficient?It must be simply old technology which has had it`s day.A modern paddle wheel should look something like the images in post no 46.There must be a new ball game with such things as centrifugal forces playing a big part in how the water would behave.

 

You are right Tom. The shear number of gears, bearings. cranks, rods and weight of getting the power to the surface of the water, eliminates any efficiency to compete. It is the most non-efficient -surface drive- possible.

 

Without the steam engine a paddlewheel is lost.www.wanganui.org.nz/riverboats

 

Except for certain very specialised applications - for example a low-speed, shallow-draught vessel where the only alternatives are jets or pump-jets. In a case like that, where the alternatives are themselves inefficient, a paddle-wheel might compete; but I don't know the figures.

And don't forget pedaloes!

 

paddle boats alive and well in Austraila

In Goolwa a small town near the end of the Murray River, Peter Turner has built 2 paddles boats in the last 2 year of which one has feathering paddles which reduces the spalsh and lift accociated with fixed paddles. He has used the diff out of a ute and Kobota deisel engine fitted with a marine engine.
Part of the reduction has been achieved with rubber tooth belts 80mm wide with cast iron tooth pulleys

I beleive Australia has the largest collection of original paddle boats still in service. We celibrate 150 years of river trade in 2003

 

Lets really get specialized applications . Poling a Bonefish boat across the flats. Special odd balls do not address a type of propulsion compared to another in the same conditions. Both in +20' of water with 20 mph wind.

 

A goofy idea?

Just thought of an idea. What if the blades on the paddle wheel were half cylinder shaped. This design would be non feathering. the half cylinders would be oriented vertically with their open sides pointed aft. The idea being that some water would be pulled along with them as well as pushed. Nothing like a propeller, you understand, but much better than a flat plate. There would be eight of them on the wheel and they would be 3/4 as deep as the wheel's dip and half as wide as they are deep. With the eight blade configuration, there would always be either one and two halfs or two wholes completely immersed.

As the aft blade came out of the water, it would get an extra kick as the water ran out of it. Goofy idea I know. Couldn't help myself.

It would be an interesting diversion to have MIT kids design human powered boats that must use paddle wheels. These boats would later be raced. Maybe, to put the oness one wheel design, the hulls would be of standardized design. 'Six hour canoes' perhaps.

Bob

 

Just an addition to the collective wisdom about the use of high-speed wheels to create lift and thrust in boats.

This link is from an Icelandic motorsport where high-powered 4X4 cars are used in hillclimbs (near-vertical slopes of volcanic ash). Take a look at the video of the car driving on water. There is no doubt that the front wheels are providing lift - they are actually bouncing on the water!

The tread pattern is visible when the car is at rest. It is made up of individual grippers and not transverse cleats. That is, it is obviously made for gripping dirt and not for throwing water out the back. With deeper, continuous transverse treads, plus side ribs to prevent water exiting sideways, the lift and thrust would be much higher. It seems to me we have a propulsion method here that is better than foils and more efficient than slining surfaces.

http://www.creationnonstop.com/link...22&PHPSESSID=3afc584b84ed5301dbf06890ddb50bcb

 

Last word but one should be "sliding". Sorry.