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Galley was a widely used type of ship in the Mediterranean sea. It was propelled by rowers and sails.

Supposing the ship builders at the time of the Punic wars got the right "inspiration" (how they get the "inspiration" is out of the scope of the question) to use a propeller and power it by using the leg power of the onboard men, would have this been technologically feasible for those times?

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  • $\begingroup$ Are you looking for a feasable and effective way to transform slave (or animal) muscle power into a rotating propeller? $\endgroup$ – Guran May 31 '17 at 8:51
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    $\begingroup$ Hellenistic (including Roman) galleys were lightweight ships, relying on speed and maneuvrability. They were not propelled by oars over long distances. And in the classical antiquity the rowers were soldiers, free people. $\endgroup$ – AlexP May 31 '17 at 9:11
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Bronze and iron would be sufficiently strong to take the force produced by a galley full of fit humans, and the level of skill necessary to fabricate and balance a propeller is not actually that high. Especially for one that's only going to be powered by people. (A fit man can only deliver about 1/5th of a horsepower for an extended period.)

The problem you run into is efficiency. With an engine turning the screw, the higher efficiency of the propeller makes it a better option than paddle wheels or oars. But when you add in the necessary bearings to support a crankshaft that can be used by a large number of men simultaneously, and whatever packing or gearing mechanism you're going to use to keep the water out of the boat, your friction losses start to add up. It's likely to end up coming out a wash compared to the cheap and easily-replaceable oars, especially at that level of technology with the crude, natural organic lubricants that would have been available.

Human-powered propellers were a feature of early submarines though. The engines of the time required too much air, and waterproof oarlocks would be enough more complicated than a single screw's packing that it made sense to just have the men turn a crank.

One option that was actually used on larger boats just prior to the commercialization of the steam engine though was to have the power delivered by horses on treadmills. It was generally confined to river boats since horses really don't like lack of fresh air for extended periods, and really, really don't like rough seas. But maybe they've been breeding some other large draft animal to tolerate being in a rocking boat and walking all day. If you're going to mechanize them, go for the gold medal. Human-powered boats are silly if there are other options.

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  • $\begingroup$ "the higher efficiency of the propeller" - NO. "Propulsive Efficiency of Rowing Oars", by Cabrera&Ruina - "best marine propellers have efficiencies of about 80%" "0.84 for a sculling oar" $\endgroup$ – Vashu Apr 9 '18 at 0:19
  • $\begingroup$ "Bronze and iron would be sufficiently strong to take the force produced by a galley full of fit humans" Correct. For some ten hp even wood would suffice. $\endgroup$ – Vashu Apr 9 '18 at 0:19
  • $\begingroup$ @Vashu That set of calculations only counts the power stroke. It doesn't factor in the energy required to return the oar to the starting position. I would expect that for equally efficient blade designs the propeller would have a slight advantage due to continuous momentum rather than the reciprocating motion of a set of oars. Single-oar sculling with a well-designed oar could be more efficient than a screw due to similar continuous application of force, but the mechanics of attaching a large crew to one oar likely eat up the gains. $\endgroup$ – Perkins Apr 10 '18 at 3:00
  • $\begingroup$ @Peskins And 80% for propeller do not factor shaft seals friction. I agree on detrimental effect of big crew. But this is the same as losses in gearing for propeller case - they are not about efficiency of propulsion, they are more about efficiency of power source. Take very little difference in efficiency between single propeller and oar, add technology limitation(is it simpler to make near ideal oar or near ideal propeller? I would bet on oar) and you cannot just assume "higher efficiency of the propeller". They are about the same. $\endgroup$ – Vashu Apr 11 '18 at 0:50
  • $\begingroup$ Anyway, I am just making a point about the fact that efficiency of screw and oar are comparable. Usually people are a little surprised by the fact. $\endgroup$ – Vashu Apr 11 '18 at 1:00
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An effective propeller needs good quality steel in large amounts. Roman metallurgy wasn't up to making an effective screw propellor. There is an alternative, and that is the paddlewheel.

In 1693 there are reports of M. du Quest making a paddlewheel man-o-war (see article in the Mariners Mirror behind paywall) which was reported to have matched a traditionally oared man-o-war in a race. Most of the carpentry techniques available to du Quest would have been known by the Romans.

The ancient Roman text De rebus bellicis describes an ox-powered paddleboat. The principal advantage seems not to have been speed compared to oars, but the possibility of using animal instead of human power.

I conclude that paddlewheel technology was known to the ancients, and could have been built with Roman techniques. However, the complexity, weight and possibility of breaking would not have given any overall advantage over oars, if human power was available.

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    $\begingroup$ Wouldn't bronze be a viable alternative to steel? $\endgroup$ – L.Dutch - Reinstate Monica May 31 '17 at 7:01
  • $\begingroup$ Bronze is very expensive. The limiting factor would be the cost of obtaining that much tin, when alternatives are available (copper is also not cheap). Bronze was used decoratively as, if you could afford it, you wanted to show it. $\endgroup$ – James K May 31 '17 at 7:06
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    $\begingroup$ A war galley wasn't cheap either. I think it should be feasible for someone who can afford a galley to find the funding for a bronze propeller. Yet i agree that the paddlewheel is much more likely, and cheaper. $\endgroup$ – Burki May 31 '17 at 7:17
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    $\begingroup$ Bronze statues weren't uncommon in ancient times, and there was enough bronze for several propellers. With the bronze of the Colossus of Rhodes you could have equiped a whole fleet. Expensive, yes, but so are today's aircraft carriers. War is a game where humans happily spend beyond sanity. $\endgroup$ – Rekesoft May 31 '17 at 8:39
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    $\begingroup$ @Burki the ease of replacing damaged oars compared to fixing a damaged paddle wheel far outweighs the paddle wheel not protruding so far. $\endgroup$ – Sarriesfan May 31 '17 at 11:13
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YES, the technology is feasible for the time.

Romans used hamster Wheels to build the Coliseum: See this clip from the Science Channel of one in action:

https://www.youtube.com/watch?v=eNccg6j1Dy0

One girl can use it to lift a 1200 lb block, and three students together raise a 5200 lb block off the ground. There is a drawing of such a wheel from Roman times; and the wheel and the compound pulley it uses were known to Romans (although the compound pulley may not be necessary for powering a ship).

Other examples are shown here, as cranes, plus examples proving the Romans knw how to use various forms of gearing.

https://en.wikipedia.org/wiki/Roman_engineering

Such a wheel is almost entirely powered by legs. Romans were very familiar with gearing as well; and were making both wrought iron and steel in the Noricum province (https://en.wikipedia.org/wiki/Roman_metallurgy).

The Hamster wheel creates power in a rotating axle; using simple gearing it could be used to turn a propeller. Note also, sealant is not necessarily a problem, the equivalent of an outboard motor propeller is easy enough to engineer: An outboard motor uses a propeller without piercing the hull of the ship; it is just mounted on the outside of the hull.

The Romans were extremely competent engineers and could have devised a system of gears, axles, pulleys, whatever to transfer the power generated by the wheel inside the boat to an underwater propeller that was outside the boat, and pushing the boat. (One simple idea: Turn the wheel 'sideways' so the axle is aligned with the long axis of the boat).

Multiple wheels could power multiple propellers; useful for steering or extra power when needed. Imagine 3 side by side: power the left wheel to turn right, power the right wheel to turn left, power left+right to go straight, power left+middle+right to go straight faster.

All the engineering skills and required materials for such a system were in place 2000 years ago; so the only missing pieces are inspiration and the power or money to turn inspiration into a working product.

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  • $\begingroup$ This has all the components of the answer I was considering, including turning the men at right angles to simplify power transmission. One could have a propeller for each man. The Romans easily had the metal tech and a propeller is at essence just an Archimedes screw. It would lower draft but greatly reduce the profile of the ship (see scene from Ben Hur where oars all get broken off, maiming rowers in the process) and the energy wasting step of lifting oars out of the water is eliminated. $\endgroup$ – Willk Jun 1 '17 at 0:37
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maneuverability.

Rowers make for a highly maneuverable craft, they can row at different speeds and even opposite directions to move the ship. This makes them far more maneuverable than any other ship on the sea. They also can operate in extremely shallow water, unlike a propeller which will make the draft of the ship deeper.

in Naval warfare maneuverability wins.

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Sure, but it's not a good idea.

Rowing uses your legs already, as well as the rest of your body. You're already getting the force a human can generate translated into forward acceleration as effectively as possible. Additionally, rowing is more efficient and responsive at turning and reversing than anything else the ancient world could have made. As 9ilsdx 9rvj 0lo aptly said, rowing is an Olympic sport, paddle-boating is not.

(This is not as true for most engines: you have to gear them down anyway, and the mechanism to make a rowing motion would be overly elaborate and lossy, so screws or paddle wheels are much more attractive)

If you're looking for an excuse to use capstans or giant hamster wheels, you might look at warping (drop an anchor far away, haul in the rope to move the boat to the anchor, move the anchor, repeat). Warping is slow going, and is absolutely not what you want to do in a fight, but is often the best way to navigate narrow or choked waterways (like rivers or rocky/sandbar-ey harbors).

If you absolutely had to get peddling to work, you're probably going to want a giant flywheel. The peddling drives the flywheel, probably with each seat or seat-pair driving a shaft with a wheel resting on the flywheel, and spinning it via friction. To disengage that seat, just lift their shaft off the flywheel. The flywheel would need to be really, really massive. Then you can run it through a clutch and a gearbox to a screw. Now you can have constant peddling work instead of sprints, and can get variable speeds out. You can probably even get very high speeds (with some hand waving) for a short time. You need a big flywheel, so the ship is likely pretty big too (which will make for interesting rotational inertia effects). You could even have multiple ways of charging it, like with a windmill on the deck.

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  • $\begingroup$ can you detail a bit more? $\endgroup$ – L.Dutch - Reinstate Monica May 31 '17 at 13:47
  • $\begingroup$ @L.Dutch he means that rowing utilizes much more power from single body than pedalling. The fatigue is less since you use muscles more endure, but it was not important how the rover (usually slave) felt after the whole day. Just notice, rowing is an olympic dyscipline, water biking not. $\endgroup$ – user21708 May 31 '17 at 14:49
  • $\begingroup$ @9ilsdx 9rvj 0lo: It kind of is important how the slave feels. If one technique makes the slave really tired but another technique does not, you can make him do the other technique 16 hours a day and get far more propulsion. You don't get unlimited slaves, you have to carry food and water for them which takes up space and makes the boat heavier. $\endgroup$ – James Hollis May 31 '17 at 15:43
  • $\begingroup$ @JamesHollis exactly, rowing utilizes slave power much better than pedaling. Well, probably. A good question for sports.SE to compare biker output with rower output. Well, you can't row on bike because you need to look forward constantly. $\endgroup$ – user21708 Jun 1 '17 at 7:33
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Yes and no. There would be no problem in making all the parts from wood. What would be the problem is:

  • the hole at the bottom of your ship. They would need to came up with a sealant that could keep the water from flooding the ship.
  • differential. Rowing slaves have one advantage if one of them is slower. He have no impact on the others as they are individual engines. With a propeller and a driveshaft you would loose power. Also it would be hard to spot and flog the lazy ones.
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  • $\begingroup$ The hole doesn't matter so much surprisingly, the Greeks already had access to the bilge pump $\endgroup$ – Separatrix May 31 '17 at 9:05
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    $\begingroup$ Roman (and in general, Greek and Hellenistic) galleys used free people (actually, not only free but freeborn, ingenui). Slaves do not generally make dependable soldiers. $\endgroup$ – AlexP May 31 '17 at 9:09
  • $\begingroup$ I think in a line of x rows it one goes out of pace it disrupt the entire flank, or not? $\endgroup$ – L.Dutch - Reinstate Monica May 31 '17 at 9:12
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    $\begingroup$ @L.Dutch: The rowers were soldiers, highly trained (and highly paid, for soldiers). They did not get out of sync unless something bad happened, such as an enemy galley ramming the side. $\endgroup$ – AlexP May 31 '17 at 9:14
  • $\begingroup$ Or you could mount it higher, on a long driveshaft. Like an ancient outboard. $\endgroup$ – Whelkaholism May 31 '17 at 9:25
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Weight would be a problem.

The little known fact is that typical galley (eg a trireme) couldn't stay in water for more than a day. Yep, that's right - those were not "ships" in today's meaning, but a large "boats". The largest distance they could be sailed was 1-day travel, because in the evening they had to be pulled on the shore to dry. They were also very light for the size, 140 men (out of a crew of 200) could pick it up and carry it on the shore. Ships were routinely transported over the land to the sea on the other side, with a kind of railway. I can't find the reference now, but I think there was an instance of carrying warships over land as a surprise maneuver, without the railway. The draft was mere 1m, so a galley could operate so close to the shore, where a bigger modern yacht can not.

As you see, the oars are actually the best choice of propulsion in those conditions - if you can train the oarsmen, that is. Because if you want to play out the fantasy of slave galleys then a mechanical propulsion becomes more viable by sole virtue of allowing unskilled workforce.

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Rowing uses your legs already, as well as the rest of your body. You're already getting the force a human can generate translated into forward acceleration as effectively as possible. Additionally, rowing is more efficient and responsive at turning and reversing than anything else the ancient world could have made.

in sport rowing, the shells have seats which move on wheels. If a galley had moveable seats which were physically joined, then they could be pushed forward and backward by special crew. Moveable seats would allow longer strokes with more power. Technology-wise the hardest thing would be the rollers and the axles between them. The rollers could be made of wood such as oak and the axles could be wrought iron.

Realistically, boat construction required great wealth. There was little tolerance for experimental designs. I am supposing in that environment, moveable seats could be developed somehow.

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Turn the wheel 'sideways' so the axle is aligned with the long axis of the boat).

I was thinking of a drive shaft the length of the galley. The shaft would be driven by bicycle-type gears. Like a drive shaft on a vehicle, there would be a universal joint to allow for flexing of the boat. The crew would sit perpendicular to the axis of the boat. They could be closely spaced and seated lower, so the boat would have a lower centre of gravity. The hull would protect them from enemy missiles and the hull could be higher to provide better sea-worthiness.

Realistically, the technology was not available: drive shaft, bicycle-type gears and universal joints require steel. By the time the technology was available so were steam engines.

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