Old Wood and Rusty Iron by Mike Creasy
Screwed..... a feeling we've all had from time to time, whether looking at the restaurant receipt or thinking about what the nice salesman said. Feelings aside, the screw itself is actually a very useful thing, both for hanging up mirrors and for moving boats through the water. It seems that, back before the time of Christ, Archimedes drew up some plans for a screw-type water pump. And Archimedes may have borrowed the idea from some even earlier scientist. So why were early steamships driven by paddlewheels instead of screw propellers????
One good reason is that, unlike the screw, paddlewheels had been in common use for centuries, even before Archimedes had his bright idea about the screw. Ancient Chinese and Roman civilizations used paddlewheels to drive everything from grist mills to trip hammers, making the wheel itself a standard part of the engineering scene. These were, of course, paddles driven by the passage of water rather than the other way around, but when steam began to make a source of driving energy available, it was only reasonable to connect a steam engine to a paddlewheel.
Mind you, all of human history could have turned out much differently if the Romans had pursued their idea of building a modern warship propelled by paddlewheels turned by oxen. Now, if you've ever been around a cattle barn, you know there's a certain "by-product" which could have been shovelled into a Roman catapult for disposal on the head of an enemy, changing the face of warfare forever! The Ancient Chinese also had a go at paddlewheel warships, but they didn't seem interested in dung-battles, using slave-power instead.
In any event, after steam began to provide a source of reliable energy, it was harnessed to the most obvious drive system available - the paddlewheel. The Pyroscaphe was launched in France in 1783, powered by a single cylinder horizontal steam engine it managed 15 minutes of motion before the engine (not the paddlewheel) failed. In 1802, a barge-hauler was built for the Forth and Clyde Canal Company. The steamer Charlotte Dundas was possibly the first commercial use of steam and paddle in a boat, and proved the viability of steam coupled with the wheel.
There were many attempts made during the late 1700s to use an Archimedean screw to move a boat, mostly ineffective largely due to a lack of understanding of how the screw interacted with water. Gradually, as the new field of fluid dynamics became better understood, screw propellers became better able to transmit power from the steam engine to water, thereby driving a ship forward.
Screws quickly became more efficient at providing thrust than the paddlewheel, as proven by the famous "tug-of-war" between two ships in 1848. British Admiralty brass had the propeller-driven HMS Rattler and the paddlewheeler HMS Alecto tied stern to stern. Both ships were of the same class, the only difference being their propulsion systems. When they began pulling, Rattler easily dragged Alecto backwards, and the
age of screw propellers began.
Steam engines and screw propellers both developed at a remarkable rate in the late 19th century, probably reaching a peak with the development of huge (150,000 hp plus) steam turbines driving equally massive (40' diameter) propellers. Even as steam began to be replaced by other engine types (diesel, gas, electric, etc) the screw propeller continued to be the preferred means of turning engine power into thrust through the water. Even today, the propeller is almost a universal item among watercraft of all sorts, with only such rarities as the Voth-Schneider vertical-blade thruster making an appearance on specialized craft.
Paddlewheels are seldom seen anymore, especially since the development of the water-jet system for shallow water - itself simply a type of enclosed propeller.
So, next time you think that you've been screwed, just imagine that you're on the deck of your own Roman paddlewheel battleship, and fire a few smelly loads on a well-deserving head!
Bibliography
The Advent of Steam, Dr Basil Greenhill et al, Chartwell Books, 1993
Wkipedia