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There is as a system of canals that connects a country, these canals are about 10 meters wide 15 meters deep. I am designing a ship that was built specifically to travel the canals. Its main purpose is maximum weight while maintaining a speed of 8 miles per hour or about 7 knots. The ship size should be enough for heavy transport so no small boats.

The question is what are some ways that I can achieve a 7 knots speed?

Some points to consider:

  1. The material that the ship is made of is wood and whatever metals used in building a ship, keep in mind that I can invent wood with some different properties if that would help.
  2. The ship transports people or animals or sometimes just cargo.
  3. Winds can't be considered because these ships need to move when needed and people can't just wait for the winds.
  4. There isn't a significant current or stream to use for the ship movement.
  5. There is a series of outposts all along the canals something like every 5 miles. I made these to serve as posts where profesional rowers await in case an urgent message needs to be delivered so that they can keep a fresh crew. These outposts can be developed further if needed to accommodate the cargo ships.
  6. There are animals that naturally dig canals that were domesticated and then used to dig the canals.

I know an obvious answer would be an engine of some sort but that would result in my world industrialization (I need it to remain medieval-like.) Rowing teams are also not ideal. An idea that I had was to use animals on both banks of the canal to pull the ship and replenish them at the outposts. That would work but I am looking for more of a mechanical solution.

I thought of using a rope that can be in reeled at each outpost but I can't just have a five-mile rope. I thought about using some form of stored power (other than a steam engine) - something like compressed gas that can be used to move the ship - but I doubt there was technology in medieval time that could compress large amounts of gas.

A steam engine would work but I would need a reason that those people don't just look at it and think of using it to build trains and cars (ruining the time period I'm looking for.)

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    $\begingroup$ Why animals on both banks? A single horse on a tow path next to a canal can pull a boat. Canals often only had a tow path on one side. For bigger boats you would need bigger draft animals, or more of them, but the vectors would be the same. You just need the draft animal(s) to walk far enough ahead that the direction of the rope is almost parallel to the boat's direction. $\endgroup$ – Patricia Shanahan Jan 26 at 3:18
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    $\begingroup$ Just a note. Canal barges were never ever rowed, they were always towed, either by people or by animals. And there is almost never any significant current in a canal. $\endgroup$ – AlexP Jan 26 at 9:39
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    $\begingroup$ @Trish Although many of us are using knowledge of real-world canals to inform our comments and answers, the OP is discussing 15 meter deep canals that must move boats at 8 mph by mechanical means but not anything that can be used for railways. That is fantasy worldbuilding, not real history. In e.g. British history railways replaced canals soon after steam engines for transport became practical. $\endgroup$ – Patricia Shanahan Jan 26 at 14:29
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    $\begingroup$ There is likely to be a lot of bank erosion from the wake at a speed of 7 knots. $\endgroup$ – Andrew Morton Jan 26 at 16:26
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    $\begingroup$ Note that even today, 7 knots is about twice the speed limit for canals. In a narrow passage like a canal, you can only go so fast before water resistance becomes a problem, and the likelihood of damage increases. $\endgroup$ – user3757614 Jan 26 at 17:42

12 Answers 12

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First, the dimensions of your canal are all wrong. It needs to be much wider than deep. Straight walls are a bad idea, too. With a cross section of 150 square meters, I would go at most for 5 m depth over a 20 m channel, with a total width of 40 m.

A boat with less than 10m beam and a draft of almost 15 m sounds impractical, too.

On both sides of the canal are roads for people who pull boats if you don't want animals. That means less than your seven knots, but any mechanical contrivance would need regular stops to hitch and unhitch ropes.

If you want a mechanical system, use something to turn a cable loop several miles long (hemp won't do, steel wire?) over rollers with hooks that can be "snatched" by a passing boat.

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    $\begingroup$ @PatriciaShanahan: They may make sense to minimize the cost of the land, but unfortunately they don't make engineering sense. The slope of the banks of the canal must be close to the natural angle of repose of the material, or else the banks will crumble. (A canal is an artificial cut; the natural tendency of the soil / mud / sand will be to close the cut.) The only situation where almost vertical banks may work is if the canal is dug through solid rock, like the Corinth Canal. $\endgroup$ – AlexP Jan 26 at 9:34
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    $\begingroup$ Actually, the depth makes sense if the boats in question are going to have deep keels (a vertical fin going deep into the water and giving a sail something to react against for tacking, also with a huge lead weight at the bottom for stability). Perhaps they go onto the open water and travel by sail. $\endgroup$ – Harper - Reinstate Monica Jan 26 at 10:42
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    $\begingroup$ @Harper-ReinstateMonica, if they are designed to tack, they're less than optimized for canal use. $\endgroup$ – o.m. Jan 26 at 10:57
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    $\begingroup$ @AlexP As a child living near real-world canals I was warned to be especially careful around them. The vertical sides made them hard for a child to escape if they fell in. The shallow depth, except at locks, meant an adult could often just stand up. $\endgroup$ – Patricia Shanahan Jan 26 at 13:50
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    $\begingroup$ This needs a picture of a horse pulling a boat. $\endgroup$ – Mazura Jan 27 at 0:04
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enter image description here

This is a fifteenth century conceptualization of a solution to your need. Please forgive the awkwardness of the picture as they hadn’t really gotten the hang of perspective, yet

Your canal boats could be powered by oxen or even cattle being delivered to market. They walk a tread mill, driving paddle wheels. I think wheels at the stern would be better than how they are depicted here. They would also probably need some sort of transmission or gearing to get the speed up to 8 mph (7 knots) since the typical walking speed of these creatures is closer to 4 mph (3.5 knots)

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    $\begingroup$ I have seen this solution used on the fanny in the discworld book snuff $\endgroup$ – Nullman Jan 26 at 9:19
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    $\begingroup$ This is extremely inefficient compared to just having the oxen walk on a towpath and draw the boat. Why would they do this? $\endgroup$ – AlexP Jan 26 at 9:37
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    $\begingroup$ @AlexP in that case becasue it was a river with many branches, so they would have needed to build hundreds of bridges to use animals on land. $\endgroup$ – John Jan 26 at 13:10
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    $\begingroup$ "Please forgive the awkwardness of the picture as they hadn’t really gotten the hang of perspective, yet" wish I could give an extra +1 for that $\endgroup$ – Renan Jan 27 at 21:18
  • $\begingroup$ @Renan wish granted $\endgroup$ – Jeutnarg Jan 27 at 21:36
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7 knots forces you into mechanization. That is out of the range of animals.

A Stevenson style steam engine running on a wood-and-strap-rail road

Essentially a primordial railway running along the far side of the tow path. Except built for tremendous side load, so possibly with the track canted or a huge thrust wall on the canal side. The track would be wood, with flat, wide rolling rails made out of strap iron. The wheels would not be train style wheels but wide, flat "roller" wheels running on the strap iron. Adhesion wouldn't matter; they will be a "rack" which engages gears powered by the steam engine, so a rack railway.

enter image description here

Compressed into two dimensions. The tow rope would be at a sharp angle, obviously, and the thrust rollers, rack and traction rollers would not be in the same plane. The boat would need to apply rudder to avoid being pulled into the bank, but that's normal for canal boats. The tow rope reaches across the regular tow path, so animals can still be used. The engine is quite light compared to the boat, so the track is canted and the boiler is mounted outboard, so tow-rope forces don't flip it over. The rack would keep a light locomotive from slipping outward. The locomotive cab isn't canted, because humans have to stand up in it.

*EDIT: As Patricia Shanahan points out, a long tow rope greatly eases thrust loads. As does having the locomotive closer to the bank. So let's make the animals reach across the trackway rather than the other way 'round. And move the thrust plate on the outward side, so it doesn't have to be held by tamped earth, and is held by the trackway itself, which also benefits from the weight of the locomotive. This is worth drawing: *

enter image description here

Again, the main thrust force the unit must contend with is from the boat; it has a side roller for that purpose. Side loads from just moving around "light" are handled by the rack gears.

There would be a ramp and bridge to allow light engines which have finished their run to climb over the canal and get on the other tow path, to haul a boat the other way. They would also be fully reversible and could use an escape track to run to the other end quickly.

The whole locomotive would weigh 10 tonne, towing a 5-tonne car behind carrying wood. Water reserves are small, because every mile there is 500 feet of trough right next to the track, fed from the canal, and the engine can dip a snorkel and pump up all the water it needs.

Using the railway straight up for direct haulage of freight is not practical, because a freight carriage that only carries 3 tonne is not nearly competitive with the canal boats, and heavier carriages are not feasible due to the wooden rail, carriage structure, bearings, draw bars, and brakes.

This needs a little elaboration. The core concept of "railway" is actually a great deal older than the 1820s. The 1820s is when the whole shebang came together to resemble the modern railway - recognizable track, 4' 8-1/2" gage, modernish inside-flange wheels, and a viable iron steam boiler and engines. (Literally. Rocket or John Bull would work on modern rails; John Bull did.) However, at least 50 years before that, there were things vaguely recognizable as railways, mainly used in specific industrial locations e.g. mining.

So this isn't even a proper railway: no flanged wheels, but instead, wide rollers on strap rail merely to support the weight (i.e. no adhesion). Thrust rollers to bear the sideways load and a rack to bear the forward/back load. The only technological fast-forward is a steam boiler-engine combo light enough to work, thus, out of the Stephenson camp more than the Watt camp.

Although if you're willing to build the wooden trackway strong enough to haul a 25-50 tonne machine (unlimited number of wheels since they aren't driven and aren't even braked), then yeah, a Watt style steamer would suffice.

The only purpose of weight for the locomotive is to keep it from flipping upward and inward from the tow rope's pull.

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    $\begingroup$ "A freight carriage that only carries 3 tonne is not nearly competitive with the canal boats": and yet in real history we have the example of England, which had an extensive canal network, and yet the railways took less than 50 years to out-compete the canals into irrelevance. (And a Watt steam engine presupposes that the industrial revolution is already in full swing. The Watt steam engine appeared long after the start of the industrial revolution.) $\endgroup$ – AlexP Jan 26 at 13:23
  • $\begingroup$ Seven knots is out of the range of animals? I can do seven knots for short distances. Many animals have greater strength, speed, and stamina. $\endgroup$ – WGroleau Jan 26 at 17:27
  • $\begingroup$ The benefit to a railway is a much higher maximum speed. A canal maxes out at around 4mph. Railways beat canals once you could get actual speed out of them. $\endgroup$ – user3757614 Jan 26 at 17:39
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    $\begingroup$ @WGroleau Not dragging a boat, you don't. $\endgroup$ – user3482749 Jan 26 at 19:12
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    $\begingroup$ @WGroleau Name one that can run at 7 knots for more than an hour while dragging a boat. Hell, name one that can even hit 7 knots while dragging a boat. $\endgroup$ – user3482749 Jan 26 at 21:05
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You could get all medieval on the Montech Water Slope idea.

enter image description here

Instead of repurposed railway locomotives on rubber tyres pushing the water, you could simply mount a trio of diminutive oliphants in each of a pair of heavy waggons driven by a treadmill. Straddling the space between the waggons is a kind of wooden dam. As the oliphants are set in motion upon their treadmills, the vehicles move forward, pushing the dam through the water of the canal. The wave thus generated shall push the canal barge forward.

enter image description here

Careful attention must be paid by the teams' Pilots and Beadles, who often use their wings as semafore signals, stationed along the length of the mighty engines. It's their job to coordinate the Gearsmen and Steersmen in their efforts to keep the paired engines going at the same speed and also guiding them so they won't plunge into the canal.

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    $\begingroup$ Why not oliphant-powered railways? $\endgroup$ – Patricia Shanahan Jan 26 at 14:31
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    $\begingroup$ Why do the oliphants have to be diminutive? $\endgroup$ – Spencer Jan 26 at 15:46
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    $\begingroup$ Wow, I had never heard of water slopes - amazing ! $\endgroup$ – Fattie Jan 26 at 17:27
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    $\begingroup$ I just do not understand how a seal can be maintained between the edges of the gate, and, the concrete ????????? youtube.com/watch?v=30mtcqRl2KY $\endgroup$ – Fattie Jan 26 at 17:33
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    $\begingroup$ @Fattie - it isn't a perfect seal, just "good enough". If you watch the video you'll notice that before the slope engine lowers its gate and begins moving up the slope, there's water flowing down the slope. The seal between the gate and the walls/bottom of the slope body needs to be just good enough that the amount of water flowing past the gate is less than or equal to the amount of water flowing down the slope from the top. $\endgroup$ – Bob Jarvis - Reinstate Monica Jan 26 at 20:55
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Windmill ships could be used.

If a large conventional windmill is positioned on board a ship it can turn to face which ever direction the wind is blowing from and the rotational power generated can be used to turn paddle wheels or better still a screw propeller.

The effectiveness of the windmill could be enhanced by using low friction hulls such as those of a catamaran or trimaran. Rowers would almost certainly still be needed to provide additional power as in case of a dead calm but a respectable speed might still be obtained and it would make the rowing easier.

enter image description here

enter image description here

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    $\begingroup$ Don't even pretend that catamaran was buildable with Medieval technology. $\endgroup$ – RonJohn Jan 27 at 0:53
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    $\begingroup$ @RonJohn Of course it was. The fact that catamarans were not built in the west does not mean that it is impossible using medieval technology. They were in use around Asia from the 5th century and possibly before that. Obviously they would not be using glass fibre, but wood works well. What aspect of having two hulls makes it impossible? $\endgroup$ – Slarty Jan 27 at 9:58
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    $\begingroup$ I wrote "**that catamaran". Not just the epoxy-fiber hull, but the (probably carbon fiber) monopole, and giant, lightweight (also carbon fiber) blades resting on ball bearings. And don't forget the gearing. While the Ancient Greeks had the skill to do it for small, hand cranked things like the Antikythera Mechanism, high speed gears were definitely beyond Medieval capabilities. $\endgroup$ – RonJohn Jan 27 at 10:57
  • $\begingroup$ Yes true it would have been a lot more primative, but still possible using flour mill technology $\endgroup$ – Slarty Jan 27 at 11:35
  • $\begingroup$ I'm more than dubious. That's ok, though, since none of my money, and little of my time is at stake... $\endgroup$ – RonJohn Jan 27 at 11:39
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Chain boat! https://en.m.wikipedia.org/wiki/Chain_boat_navigation

Although the method of generating the torque remains up to you, whether it's animals or slaves or an engine, chains laid on the bottom of the canals that are pulled by the craft can be much longer than 5 miles, they reached a few hundred in the past.

Or you can have the chain itself move with the craft clamped onto it, then you could maybe have water mills powering it, but they'll have to be huge.

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Each ship has two capstans, mounted on either side near the bow. There are a series of bollards along the sides of the canals.

The capstans can be driven by people or animals. They are designed with the right ratios to pull rope in at your target speed when turned at the natural walking pace of the drivers.

There are two teams of mounted rope movers, one on each bank. During phase 1, the end of the port rope is attached to a bollard on the port bank, and is being wound onto the port capstan to pull the boat along. Meanwhile, the starboard rope movers are unwinding the rope from the starboard capstan and carrying its end forward to the next starboard bollard. As the boat passes the port bollard, go to phase 2 in which the port and starboard roles are exchanged. The rope movers can trot, because they are not doing heavy hauling, allowing the required speed.

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I remember seeing a documentary about (real-world) canals where they mentioned that through tunnels, people would sometimes lie on their back on the highest deck, and and "walk" along the roof of the tunnels (the tunnels were standard height, and ships were made to match that).

You could extend this by having something over the top of the canals (from bank to bank) to grab on to, e.g. a rope or arch, a little higher than the tunnels (maybe 1 meter above deck?). You go to the bow (front) of the boat, grab on, and push it to the back of the boat. Then you walk back to the front and repeat the process. You only need to accelerate enough to compensate for friction, and slightly more. Wiki says: "Hire fleets on British canals usually consist of narrow boats in varied lengths from 30 feet (9.14 m) upwards", I think you could easily leave 45 feet (15 meters) between arches - this gives you 23 feet/7.5 meters of push as you walked bow-to-aft, then you would walk forward at the same speed as it glides forward, and you would meet up with next arch just as you got to the front.

In a small, flat body of water, with no water flow, it takes very little effort to start a ship moving, and it will keep moving for quite some time (depending on the size, of course, but then you're talking about a canal, so the ships won't be too big. I've towed a 6 tonne boat in a rowing dinghy (for a laugh, but it did work).

It might be worth breaking down the problem into sub-problems - energy source (steam, human/slave, animal, chemical, spring, weights, flywheel), propulsion (pushing against something: propeller, paddlewheels, ropes, wheels pushing against the side or bottom, top of tunnels). Mix and match the options to find one that suits.

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A hand-cranked propellor? The best image I can find is this article on the CSS Hunley.

CSS Hunley was manually powered. The crew (eight men) turned a crankshaft, which was connected to the submarine's propeller. Hunley's maximum speed, when the crew was working their best, was about 3 knots.

That speed is for a submerged metal vessel.
https://uboat.net/articles/63.html

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The 'most sensible' option would be to plan for more reasonable speeds of a traditional draft animal canal network. Humans can move a huge volume of material in a timely fashion even if only heading along at little more than a walking pace of draft animals towing a narrow boat.

However that's been done and is obviously boring, so...

If our goal is to establish reliable and speedy transport of large volumes of goods and materials without readily falling into building railroads, then we have a relatively simple option if we can stomach the cost...

Flash Lock Stairs:

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

If our society is in a location that can provide enough sources of water then we can harness that flow of water directly. Effectively we are building/rebuilding rivers in a controlled manner, then punting barges out into them to float down the line.

How fast we can allow them to go will depend on how much water we have on hand, how much engineering we're willing to invest, and possibly how brave your crews are... As we're basically building giant and stupidly long log flumes.

Quick travel is of course a one-way deal unless we want to get really creative with lock design, but otherwise we can overcome that with good loop designs. 'Flow' from point A to B down one stretch of canal, then ascend a lock-stair and flow back from B to A [Or from B to C, then another run from C to A] on a different canal.


To avoid excessive wear on the canals and improve control, you would likely want to have many very shallow 'steps', and probably send boats down in groups/trains. Skilled lock operators can then open and close their locks in series to maintain and control the speed of the boats, and ensure water levels don't drop too far in any given part of the system.

As a bonus you also naturally end up with stations potentially well suited for optical-telegraph... As each lock probably wants to be setup such that they can see the previous one so they can open or close as needed.

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


Geography wise, such a system would likely work best for a nation which has a long and relatively narrow section of moderately level land that fronts many long mountain/highland valleys that get plenty of rain. Your society is going to need to be experts at designing aqueducts and canals.

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Big flat spring that would power the propeller and could be changed to a fresh one at every post or just changed, given the ship can take lots of weight. Maybe even, when the ship's finally stopping, it could be re-winded by the force of the water pushing on the propeller. If not, then the spring mounted in different way could make the propeller help stop the ship.

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  • $\begingroup$ Springs don't have the energy density you need. $\endgroup$ – Mark Jan 28 at 21:12
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I would borrow an idea that I read about in Sir Terry Pratchett's book "Snuff".

The book at one point refers to a series of riverboats going up and down a river. The design is described to be somewhat similar to riverboats that once plied the Mississippi River, but they ran on Ox power rather than steam This wiki article contains references to animal powered paddleboats..

There is a paddle boat system with a paddle array on either side of the boat (like a Mississippi riverboat). This is geared and mated to a couple of large treadmills inside the hull. Oxen are on the treadmills and plod along driving the gear mechanisms, which turn the paddles and propel the boat. When an ox gets tired, harness up a rested ox and keep going. Dung is simply mucked out and tossed over the side.

This gets you moving up and down the mostly calm waters of the canal system. since you will have to dredge them occasionally, you will get a decent amount of fertilizer out of your canal system every year. It's a Win-Win! Navigability is not going to rely on current flow or wind power, and you aren't going to have to worry about animals following a footpath along the sides of the canals towing barges and such.

Just keep in mind that it's not going to smell nice.

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  • $\begingroup$ It's more efficient to just have the ox walk along beside the canal, pulling the barge behind it, which is what everyone did up until the invention of the steam engine. $\endgroup$ – Mark Jan 28 at 1:38
  • $\begingroup$ @Mark except that an ox walking along is not going to get anywhere near the speeds mentioned in the OP. a paddleboat may struggle to get that fast, but you can, with gearing, get better speed than you could with just an ox plodding along. $\endgroup$ – Paul TIKI -Monica come Home Jan 28 at 14:03
  • $\begingroup$ You're not going to get the desired speeds from animal power, period. Seven knots was a typical speed for a paddlewheel steamer of the mid-1800s, and these ships had engines of around a hundred horse (or ox) power. $\endgroup$ – Mark Jan 28 at 21:11

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