Navigation is the scientific approach to finding your way, used mainly at sea in low-tech societies. The skill of determining a ship’s position or of setting its course on a map or a chart – or in geometrical coordinates, such as latitude and longitude – is Navigation (Sea); see p. B211. Coastal and open-sea navigation use this skill somewhat differently.
Few TL0 societies use abstract concepts of location. Instead of Navigation, they rely on Area Knowledge (pp. B176-177) – that is, personal familiarity with a specific body of water. (River and harbor pilots in present-day societies still employ this skill!) This can’t substitute for all applications of Navigation. Notably, it’s seldom useful out of sight of land; thus, most TL0 societies avoid such voyages. Treat TL0 peoples with long-distance seafaring, such as the ancient Polynesians, as “advanced in a science” for this purpose.
A ship’s navigator may have to deal with four different questions:
1. Where are we? A ship’s location can be defined either by its visible surroundings (“San Francisco Bay”) or in terms of map coordinates (“37°46’ N, 122°14’ W”). Area Knowledge can substitute for Navigation in the first case but not the second. This roll is most often needed when a ship has sailed off course (e.g., during a storm).
2. Where are we going? If a ship’s voyage has a known destination, a navigator can identify this. Doing so depends on the available reference materials, not on a Navigation roll. Navigational information for an obscure destination may require a Research roll – or be the starting point for an adventure!
3. How do we get there? Plotting courses is a navigator’s primary job. If the point of departure and the destination are both known, a successful Navigation roll identifies the fastest route. Add 10% to travel time per point of failure. Critical failure means the ship encounters a navigational hazard or gets lost.
For an unknown point of departure or an unknown destination, make a Navigation roll at -4 to guess the best heading. Success means the ship ends up in a known or worthwhile location (e.g., it makes landfall after being lost at sea); critical success may send the ship to a rich port, an island paradise, or a hidden pirate haven, if the GM wishes! Failure indicates the ship gets nowhere in particular.
Critical failure means it encounters a hazard – or gets lost, if it wasn’t already. If the ship starts at an unknown point, any success also identifies its location.
The basic difficulty of these Navigation rolls depends on the voyage’s hazards:
Weak opposing current; single rock or shoal: 0
Strong opposing current; weak current carrying you toward a hazardous shore; several widely spaced rocks or shoals: -1
Strong current carrying you toward a hazardous shore; multiple closely spaced rocks or shoals; narrow passage between bodies of open water: -2
Multiple closely spaced rocks or shoals; narrow passage with weak currents carrying you out of the safe channel: -3
Multiple closely spaced rocks or shoals; narrow passage with strong currents carrying you out of the safe channel: -4
In unknown waters, extra care must be taken to identify hazards. If this isn’t done, double these penalties!
In all cases, coastal navigation is easier than open-sea navigation, as there are only two headings to choose from. Make these rolls at +2.
4. Are we on course? Normally this requires no skill roll; any trained navigator can answer this automatically. If a ship has no trained navigator, roll against Seamanship. There are several methods of performing these tasks. Equipment modifiers often apply to these.
This is the oldest form of Navigation, practiced since TL1, and the only one for which Area Knowledge can substitute at TL0. Position is identified by landmarks, usually visually. Such Navigation is often Per-based, and Vision modifiers – including the use of a spyglass (p. 42) – can aid or hinder it. While normally limited to coastal navigation, it can be applied to open-sea navigation if there are predictable currents, winds, or changes in the water.
Landmark recognition involves only rough measurement of distances (by days of travel) and headings (from the sun, stars, or prevailing winds). Courses can’t be charted with any precision; Navigation is at -3, and has no Astronomy default. If the sky can’t be seen at all, Navigation is at -5.
Merkhet (TL1). An ancient Egyptian device, made from a slitted palm-leaf. Used in good weather to observe the pattern of stars moving across a plumb line, it reduces the Navigation penalty to -2 by determining direction more accurately. $10, neg. Easily broken (DR 0, HP 1, and Fragile), it’s normally carried in a hardwood case: $10, 1 lb.
Windrose (TL2). A rectangular box with 30 compass points around its exterior, each corresponding to the rising or setting of one of 15 fixed stars. Different models are required for the northern and southern hemispheres. Reduces the Navigation penalty to -1 in good weather. $25, 1 lb.
Sunstone (TL(3+1)). The Viking expansion (700-1100 A.D.) relied on extraordinarily skilled navigation. Some readers have interpreted a few lines from the sagas as hints at an unusual technology: use of the naturally polarized mineral cordierite to determine the sun’s location on cloudy or foggy days, or when the sun is just below the horizon (for about a quarter-hour after sunset). The Navigation penalty under these conditions is -3 rather than -5. $30, 1 lb.
Stick Chart (TL1). Developed in the Marshall Islands by the ancient Polynesians, these charts used curved and diagonal sticks to represent currents, and cowry shells to signify islands. They weren’t actually taken to sea, but were used to train navigators in memorizing vital information. Studying one reduces the penalty for an uncharted destination to -2. For a navigator with Eidetic Memory, there’s no penalty. $300, 10 lbs.
Periplus (TL2). Used by the Phoenicians, Greeks, and Romans, this is a scroll that describes destinations and landmarks, and approximate distances between them, along a shore. A rutter (TL3) is similar, but in the form of a bound book. A typical periplus or rutter reduces the penalty for an uncharted destination to -2; one of good or fine quality makes that -1 or 0. As with all books, price and weight are variable.
Used in ancient Egypt, the sounding pole provides a way to judge depth in shallow waters. It’s thrust into the water at the prow of a boat to feel the depth of the bottom. This avoids the doubling of hazard penalties – but only in shallow rivers and lakes. It remains useful in more-advanced forms of navigation. A 12’ pole: $40, 4 lbs.
Developed in the ancient Mediterranean, this is a 50- yard line with a wax-coated lead weight at the end. It’s thrown over the side to determine depth by length markings along the rope. Together with keeping a lookout, this avoids doubled hazard penalties in unfamiliar waters. The wax coating sticks to the bottom material, bringing up samples; examining these gives +1 to Navigation to identify a vessel’s location, if references describing bottom materials are available. It remains useful in more-advanced forms of navigation. $175, 30 lbs.
Dead reckoning (short for “deduced reckoning”) is the first quantitative navigation method. It becomes possible at TL2 and is in general use by TL3. It allows Navigation rolls with no penalty for lack of precision, and can be used to identify a ship’s position on a grid of latitude and longitude.
Dead reckoning requires keeping track of a ship’s heading and speed, and the duration of each leg of a voyage, and figuring out how far it traveled and in which direction. This information is used to plot its position on a chart. There’s still no Astronomy default.
Basic equipment for dead reckoning includes a reliable timekeeping device (usually a sandglass; see Timers, p. 45), a compass, a chip log, charts (like the portolan, below), and a set of dividers.
A “compass” in the geometer’s sense: two rods connected by a stiff elbow joint at the top, held at a specific angle and used to trace circles and arcs. In navigation, it’s used to calculate distances on a chart. It’s part of basic equipment for dead reckoning. $5, neg.
First developed in China and later introduced to the Near East and Europe, a compass has a magnetic needle that points to magnetic north (or, in China, magnetic south). There are two versions:
It’s possible to judge headings astronomically without a compass, if the sky is visible: -1 to Navigation to steer by the pole star, or -2 by other stars or by the sun.
Developed in medieval Europe, a portolan is a large, bound reference book holding not only descriptive text, but charts of coasts with cities marked on them (see Maps and Globes, p. 45). From each city, lines marked with compass headings go out to other cities; thus, use requires a compass (above). A typical portolan eliminates the penalty for an uncharted destination; one of good or fine quality gives a bonus of +1 or +2. Many navigators treated their portolans as secret documents, not wanting to share the information with rivals. Without one or more such charts, dead reckoning can’t be used to sail to a known destination, although it can still be used to chart a voyage to an unknown one (-4 to Navigation). As always for books, price and weight are variable.
Invented around 1500, this is a long cord on a reel, with knots every 42’ and a wooden float at the end that’s weighted with lead so that it always floats the same way up. The float is tossed off the stern and the cord is allowed to unreel. The number of knots that unreel in 30 seconds is the ship’s speed in nautical miles per hour, or “knots.” Used to estimate speed; forms part of basic equipment for dead reckoning. $175, 55 lbs.
As early as TL1, cruder measurements were made by throwing a piece of wood off the stern and estimating its distance by eye. This is free but less accurate: -1 to Navigation.
Celestial navigation uses precision instruments to determine a ship’s exact position by observing the sun and stars. This is Navigation as defined on p. B211, with a default to Astronomy-5. It emerges at TL3 with the development of instruments to measure latitude – although it isn’t fully developed until TL5, when invention of the ship’s chronometer allows precise measurement of longitude (see GURPS High-Tech for relevant gear and rules).
The limited form of celestial navigation used at TL3 is “running down the line.” If the ship’s current location and destination are known, the Navigation roll is at +2 because – as with coastal navigation – there are only two directions to choose between. If either is unknown, the penalty is -2, not -4, for the same reason, and a successful roll determines the ship’s exact latitude as well as setting a course. The navigator requires the equipment for dead reckoning and one of the following instruments, which further modifies the roll:
Astrolabe (TL3). See p. 43 Used with a cross-staff (p. 43). Gives -1 (quality) to skill for celestial navigation. Kamal (TL3). See p. 43. Gives -1 (quality) to skill for celestial navigation.
Sun Shadow Board (TL3). A crude version of a quadrant, developed by the Vikings (700-1100): a semicircle of wood mounted on a handle. Gives -2 (quality) to skill for celestial navigation. $20, 10 lbs.
Quadrant (TL4). See p. 43. Used as a navigational tool since the 1400s; Columbus’ log records using one. Counts as basic equipment for celestial navigation. (The sextant, which appears at TL5, gives +1 (quality) to skill.)