Suppose you have two ancient Greek triremes. One carries 170 men to pull the oars, in the traditional fashion. The other also has 170 men but has been modified: Instead of pulling an oar, each man pumps a pair of pedals like those on a bicycle; the pedals are connected to drive chain that turns a screw-propeller.
Set the two in a race. Which ship goes faster?
Tie the two ships stern to stern. Which proves to have more power?
I think it would be the pedal-driven ship in both cases; human legs are stronger than human arms.
Not only are legs stronger, but the application of power through a pedal system is more continuous than through an oar system. When those oars are out of the water, no power is being used to propel the boat.
On the other hand, I’m not a rower but I think it’s more than just arm power in rowing.
I’m not a rower by any means, but the limited amount I’ve done has taught me that rowing is definitely a full body experience. You brace your legs against something and pull; your legs, back, stomach, chest, arms, everything is working in concert to move the oar(s). I believe crew boats have sliding seats to better make use of leg power. Wiki confirms:
Seems like the oars might have an edge, by virtue of having more surface area in the water. 170 slaves, two men to an oar, that’s 85 oars in the water. I think you would have to have a pretty sophisticated transmission to efficiently convey the power of all 170 slaves to a single propeller.
Is there a history of pedal powered devices (using pedals on cranks) prior to the invention of the bicycle?
Seems to me that the 50% or so of the time the oars are not doing any work would make it pretty easy for the prop to come out on top, but rowers use their backs as well as arms to row-the peddle guys would have only their legs. The loss of any thrust 50% of the time and the efficiency of the oars compared to a prop that works all the time at what would probably be better efficiency than an oar would allow for drivetrain losses and still be better IMHO.
Prop design would make it easier to use the same power and make the ship go faster (smaller diameter/higher pitch) or more thrust for the pull-off (large diameter, shallow pitch) where the oars are just oars.
Dang it, there were no posts when I started typing this, but what Dag Otto said.
And as for surface area of oars vs surface area of the prop, you might not be able to drive a prop with exactly equal surface area as all the oars, but what is there will be working while the oars are in between strokes.
Just wanted to chime in to say that when rowing, the oars are not out of the water anywhere near 50% of the time. The oars swing forward through the air quite quickly, and then take a (relatively) long time to be pulled through the water.
If you google “human powered boats” you’ll discover a lot of links to people trying to set speed records with muscle power alone. Virtually every boat in these competitions is pedal-powered.
Here’s a competition in 1994 where a 58-year-old man and his son in a pedal-driven boat kept pace with Olympic athletes using traditional paddles and oars.
The challenge with the triremes would be figuring out a linkage that could transmit the force from so many different people efficiently. But in general, pedalling delivers more power than rowing.
Any galley intended for battle could not be rowed by slaves, since what do the slaves do when the galley gets boarded? They revolt and join the boarders. Or consider that one dropped oar can foul the entire bank. You would no more man your expensive war galleys with slaves than you would man modern tanks and bombers with slaves.
I don’t why you think the oars would have a larger surface area than a prop. Did the OP limit the size of the prop? I don’t care how big your oars are, a prop can be designed to have at least the same area if not more.
[old joke]
slave master to galley slaves:
“I have good news and I have bad news. First the good news, you all get an extra ration of rum at lunch. Now the bad news, the queen wants to go water skiing after lunch.”
[/old joke]
A large prop is better at absorbing and transmitting larger power loads. Better than spinning a small prop faster, which just churns the water.
Here is a discussion of propellors in modern ships.
Also, as mentioned above, the linkage of the pedalers to the drive system needs to be addressed. The right gearing could probably increase the efficiency significantly. One thing that occurrs to me is that although the rowers minimize the amount of return time on their backstroke, the propellor blade is transmitting power to water throughout its rotation. I just don’t know if this is a significant factor.
Here is a more basic essay on propellor design from the same website. Really makes me think that a properly design pedal system would be better than the rowers.
The main difference is how the power is transmitted to the water. Oars work by drag, pulling an object through the water. Propellors, on the other hand, work by lift, generating a force differential on the two sides of the prop.
Lift is more efficient than drag at transmitting the energy. This is why we don’t see side-wheeler or stern-wheeler ships any more, because the propellor (lift) is more efficient than turning a wheel with boards on it (drag).
As an aside, the Chinese “scull” with a single oar over the stern, moving it side to side to drive the boat forward. In this configuration, the oar is generating lift rather than drag … clever folks.
I dunno, but I’m sure there’s a good reason why powered boats use propellers instead of motor-driven oars. Or paddle wheels. In fact, I got the idea for the OP from the following passage from Part II of George Orwell’s 1941 essay “The Lion and the Unicorn: Socialism and the English Genius”:
On the validity of his judgment on capitalism I make no comment here, but the example used to illustrate it is an interesting one.
I remember when Allan Abbot was building pedal powered hydrofoils back in the 1980’s. He once held the human powered land speed record. The first hydrofoil he built was notable because the thing had to be launched from a catapult. The water had to be very flat, if I recall collectly. The second generation had a set of pontoons which allowed a water start. According to this site the Decavitator holds the world human powered water speed record of 18.5 knots (21.3 mph) over a 100 meter race course. Note that it has an air propeller to eliminate cavitation effects from a water propeller. Here’s an interesting page of human powered hydrofoils, most of which have conventional water propellers.
I’ve read some “Connecticut Yankee” stories like L. Sprague de Camp’s Lest Darkness Fall – or alternate-history stories like John Maddox Roberts’ The Seven Hills, where technologies familiar to us, such as the steam-powered boat, are invented in antiquity – and I’ve never read one where a character thinks of a pedal-powered boat (which would require fewer engineering breakthroughs than a workable steam engine).