Travel: Water

Traveling over land is familiar. Many of us do it every day (even if we don’t do it as part of an army or with pack animals), but travel over water, though vital to the modern economy, isn’t part of daily life for most of us. Sometimes, though, the characters in your stories or games need to ride a raft downriver, strike out across the ocean in an outrigger canoe, or hoist the sails of a ship of the line. In this installment of the travel series, we look at types of pre-industrial water transport, the speeds and distances ships can travel, how much cargo ships can carry, and what it takes to make a successful voyage over water.

Speed

Ship speeds are conventionally measured in knots, equivalent to 1 nautical mile (1.151 statute miles or 1.852 km) per hour. 1 km/h is equal to 0.54 knots. In this post, I have given all speeds in terms of km/h for consistency with the other travel posts.

Types of transport

There are many different types of watercraft, from one-person rafts to massive cargo ships, but one essential way of distinguishing them is by means of propulsion. Pre-modern vessels had four basic options for propulsion: current, wind, paddles/oars, or draft.

Current

Rafts and boats meant to travel downstream on a river can simply ride the current. Current-carried boats still need human attention to keep them away from shallows, snags, eddies, and other hazards, but it is a very cost efficient way of moving people and goods. Of course, it’s only a one-way trip. Getting the boat back upriver again requires a different means of propulsion. River boats in ancient Egypt, for example, could ride the current downstream and sail back upstream under the prevailing winds off the Mediterranean sea. Sometimes the boats don’t go back up the river at all but are broken up and carried overland or just sold off for scrap. (Herodotus 1.194)

The speed of a current-carried boat depends on the speed of the river it rides. The speed of a river depends on many factors, including the volume of water, the width and roughness of the channel, the slope of the land, and season of the year. A small river on a gentle slope in a wide bed may seem to be barely moving, while a large river rushing downhill through a narrow gap may go incredibly fast. Different parts of a river move at different speeds. As a general guide, average speeds for navigable real-world rivers range from less than 1 km/h to around 5 km/h, but in building your world you can more or less make a river flow at any speed you like. (Schulze, Hunger, and Döll)

Wind

Just about every people who live near the sea have learned to harness the wind for sailing. From the massive Chinese treasure ships of the middle ages and stout European ships of the line of the age of sail to nimble Polynesian sailing canoes, sailing ships come in all shapes and sizes.

Over most large bodies of water there are winds that blow on relatively predictable daily or seasonal patterns. Some important wind patterns for travel are relatively stable, like the trade winds that create large loops over the oceans converging on the equator. Others are seasonal, like the Indian Ocean monsoon winds that blow from the southwest in summer and northeast in winter. Along most shores, local breezes blow from water to land during the day and the other way at night. At the local scale, of course, winds can be unpredictable, changing direction with the movements of high and low pressure systems.

It was once thought that early sailing ships could only run with the direction of the wind, but modern experiments with replicas has shown that ancient ships were capable of working to windward by tacking across the direction of the wind. (Palmer) Refinements in hull and sail design made close-hauled sailing (sailing within 30-50 degrees of directly into the wind) more viable over time. Chinese, Arab, and Viking sailing ships all developed some of these refinements between 700 and 1600 CE, but western European designs of the early 1700s were the first to combine effective sails and hulls for dependable close-hauled sailing. (Unger 80)

The speed of a sailing ship depends on wind speed, currents, the load the ship carries, and the design and condition of hull and sails, but also in great measure on the direction of the wind. When running before a favorable wind, ancient sailing ships could travel at speeds of 8 to 11 km/h. When tacking across an unfavorable wind, even fast-moving ships might make only 2 to 6 km of forward progress in an hour. (Casson 139-43; Irwin 18) The clipper ships of the eighteenth and nineteenth century age of sail could reach speeds over 40 km/h in exceptionally good conditions, but top speeds around 30 km/h were more typical. (Lyon 138)

Paddles/oars

Paddling or rowing a ship is useful on a small scale over fairly short distances. It has the advantages of being able to travel in any direction at a controllable speed without depending on wind or current and of precise navigation around hazards. Canoes, kayaks, and rowed boats have been used in many parts of the world for river and coastal travel, cargo transport, and fishing. The large sailing ships of Europe and China were often accompanied by small human-powered craft as tenders. Native North Americans made canoes ranging from one-person lake craft to large ocean-going vessels carrying dozens of people.

On a larger scale, human-powered ships are expensive to operate because they require so much labor. Ships like ancient Greek triremes and early modern Venetian galleys required hundreds of rowers. In most cases, despite popular myth to the contrary, rowers were paid laborers, but even when they were prisoners or slaves, they still had to be fed enough to keep them fit for hard work. Large oar-driven merchant ships would have been economically unfeasible in most circumstances; it was only worth the cost of crewing a large oar-powered ship when maneuverability was at a premium, so most such ships were warships.

The speed of human-powered ships depends on many factors, but the strength and coordination of the crew are key. Experienced canoe crews can maintain a speed of 5 km/h for up to eight hours a day. (Horvath and Finney 271) The reconstructed trireme Olympias recorded a sustainable speed of 10 km/h, with 17 km/h possible in a short burst, as for ramming. (Morrison, Coates, and Rankov 264)

Draft

Small barges in rivers and canals can be pulled by animals led along the shore. The speed of these craft depends on the speed of the animal. (And the conscientiousness of the driver: the Roman poet Horace recounts an overnight barge trip to nowhere when the drunken bargeman tied the mule to a rock and slept all night.) (Horace 1.5.17-23)

Carrying capacity

One of the big advantages to waterborne travel is carrying capacity. Water transport is vastly more efficient than land transport.

A ship’s carrying capacity is expressed in tonnage. Tonnage was originally calculated by the number of tuns (a measure of wine equal to 252 gallons) a ship could carry. Over time, more complex calculations have come into use to measure the volume and mass of cargo that a ship can handle. Modern calculations of tonnage use the metric ton (1,000 kg), but before later twentieth century, the long ton (1,016 kg) was widely used. To add to the confusion, tons (of both kinds) are also used to indicate the sizes of ships (as a measurement of the weight of water they displace). When researching historical ships and finding mentions of, say, a ship of 40 tons, it is vital to get as clear as possible what exactly is being measured and in what terms. (Lane)

The actual calculations of ship capacity (and their variations over time) are more complicated than most of us land-bound writers will ever need, but some points of reference are useful. The largest claims of ship capacity are made for the Chinese treasure ships of the Ming dynasty. It is unclear whether the descriptions of the largest ships are realistic, but ships capable of carrying 500 tons are reliably documented. (Church 10-11) A sample of eighteenth-century merchant vessels operating in the Caribbean ranges from 124 to 408 tons, with the average at 300. (French 438-9) A similar sample of eighteenth-century ships in Virginia finds a range of 41 to 213, with the average at 100. (Walton 394-6)

It is worth noting that in cases of national pride, like the Chinese treasure ships, there was incentive to overstate cargo capacity, while in the case of private merchant vessels, which paid taxes and docking fees based on their tonnage, the incentive was to understate. As always, use due caution with the sources.

Making the journey

Lots of things contribute to a successful journey over water: weather, the condition of the vessel, the skill of the crew, the amount of cargo loaded and people carried, and so on. A few points are worth special mention.

Labor

Small craft need only a few people to operate them, but larger ships take an experienced crew. The exact numbers required to operate a sailing ship depend on the size and rigging, but as a very general rule of thumb, you can estimate one sailor for every four tons of displacement. (Note that this is a different measure from cargo capacity.) (Church 9-10) For large sailing ships, crews of 100-200 sailors would be typical.

Large oar-driven ships require lots of muscle power. A classical Greek trireme took a crew of 200. The quinqueremes favored by the Roman and Carthaginian navies took 420, and even larger vessels with larger crews were also built.

Food and water

Apart from fish and rainwater, both of which can be unreliable, food and fresh water are not available at sea. Any ship traveling long distances must either stock enough of each for the passengers and crew or make regular stops for supplies. This issue is especially acute for large oar-driven ships. Although a rowing crew could eat (and even sleep) on board in extreme circumstances, it was normal for such ships to put in to shore each night for food and rest. (Thucydides 3.49) Sailing ships, with their smaller crews, could stay at sea longer, but when stores ran out there was no alternative to putting in to shore for resupply. Long voyages required careful planning and the stocking of food that could be kept a long time without spoilage.

Navigation

When traveling on rivers or in sight of land, you can rely on terrestrial landmarks, but traveling in open water requires a different set of skills. Much long-distance sailing in the pre-modern world depended on making several legs from one known landfall to another, relying on the experienced captain’s ability to recognize ocean currents and wind patterns, the movements of fish and birds, and the weather patterns created by landmasses out of sight over the horizon. Much of this information was imparted by oral tradition or recorded as descriptions of conditions observable from sea level. Sightings of the sun and known stars provided reasonably accurate indications of cardinal directions and latitude, although longitude could not be accurately determined without good clocks.

Many peoples recorded navigational information of this kind in forms as varied as the stick charts of the Marshall Islands representing patterns of currents, winds, and swells, and the narrative account of the coast of northwestern Africa given by the Carthaginian navigator Hanno. (Davenport; Hanno) Bird’s-eye-view maps of the kind we are familiar with today were of relatively little value in comparison and were not widely used until the age of global sailing when ships regularly traversed areas of the sea that their captains did not have extensive previous knowledge of.

Thoughts for writers

There is a long history of writers telling stories about life on the water, from the oceanic wanderings of Odysseus, Sindbad, and Norse adventurers to the riverine exploits of Huckleberry Finn and coastal shenanigans of the Pirates of Penzance. A strictly accurate portrayal of waterborne travel is rarely essential to telling a good tale, but there are times when getting the details right matters. I hope this post, like the others in the travel series, is useful in helping you figure out your own sea stories and river tales.

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