Paddle Wheels Question

[Bierjunge]

Hello ophicleide,

I appreciate your calculations and fully agree to them.
If you mention scaling factors (as in the model aircraft article), it might be interesting for you to know that we have had a very similar discussion here some time ago, leading to the identical results:
http://www.paddleducks.co.uk/smf/index.php?topic=3262.0
I do not say that your posting is redundant, far from it! I think it is quite important to bring these facts back in mind from time to time.

Moritz

[kazarka]

Ophicleide's most enlightening post was based upon work carried out by Denny's of Dunbarton. The Lucy Ashton also featured in Denny's research work:

Something like 16 steamers for the Clyde or the Scottish Lochs were built at Rutherglen. In 1888, as a subcontract, Seath constructed the hull of a paddle steamer for the North British Railway. On completion, the new ship entered service causing little stir or sensation but 60 years later, when retired from the fleet, the Lucy Ashton had earned affection from the Clydesiders for her regular and dependable functioning in all conditions and weather. Her story did not end there.


A wonderful opportunity presented itself in 1949 to the British Shipbuilding Research Association (BSRA). They had been anxious to carry out full-scale systematic resistance tests on a ship hull, and preferably without the water being disturbed by propellers, paddles or even a tug nearby. Such experiments had not been carried out in Britain since the tests on HMS Greyhound in 1874 and scientific reasoning had come a long way since then.


In 1949 British Railways decided to dispose of their oldest Clyde steamer, the PS Lucy Ashton. She was purchased by BSRA and stripped down, engines and paddles removed, and just abaft of midships a bridge fitted by Denny of Dunbarton on which were placed four Rolls Royce Derwent jet engines for propulsion. During 1950, with ear-piercing screeches, the Lucy Ashton ran on the Gareloch mile during which time information was amassed on speed, power output and, by deduction, considerable information on the resistance of ships underwater skin to motion through the water.


Six exact scale models or 'geosms' were manufactured correct down to the 5.75-in. sag on the Lucy Ashton's keel, and these were tested in various ship-model tanks. When T. B. Seath built this fine little steamer at Rutherglen in 1888 and when the North British Railway bestowed the name Lucy Ashton taken from Scott's novels, little did they anticipate the fame she would eventually acquire in the world-wide technical press!!

Ref: Song of the Clyde
A History of Clyde Shipbuilding
FRED M WALKER

[kazarka]

Ophicleide has, with his most interesting and enlightening post, now caused me a bit of a problem. To recap, I currently have fixed paddle wheels which 'flop about a bit' and run at a maximum 80rpm via a reduction gearbox and motors running off a 6v battery.

So far I have resolved to re-build the gearbox installing 5mm drive shafts, source and fit feathering paddle wheels and fit decent bearings on the inside of the paddlebox.

If I 'up' the drive voltage (providing the motors will accept 12v) I'm going to get around 160 rpm, to get any more would involve altering the current reduction gearing which will obviously impact upon the power of the drive. I can't help thinking that on an 8 float feathering wheel there are 32 pivots all producing drag  . . . anybody care to comment upon how substantial this is ?'