When a ship must travel great distances, a skilled navigator is required to make sure the journey happens quickly, easily, and effectively. No Profession (navigator) check is required to make simple trips; a simple trip involves traveling over short distances or along very obvious landmarks (visiting a city you just came from, following a distant mountain peak to find the monastery built at its summit, etc.). If such a check is required, the DC is 5.
Profession (navigation) truly comes into play when attempting to visit a new location, such as plotting a journey to a distant floating island, following a treasure map to a newly-discovered delve, or attempting to cross the Maelstrom to visit the worlds and planes on the other side. When making such elongated, detailed trips, someone in the party must pass a series of Profession (navigator) checks to keep the party traveling in the right direction. Someone can only gain aid from a single other creature when making Profession (navigator) checks, including someone using Profession (servant).
Note: While Survival and Knowledge (Geography) are useful when navigating an overland route or understanding landmarks, they do not equip a character for the intricacies of navigating planar space or an endless, uniform sea of green. In a pinch a character may make a Survival or Knowledge (geography) check in place of a Profession (navigator) check, but at a -5 penalty.
Plotting a Trip: In order to plot a trip to a destination without obvious landmarks, the navigator must first know where to go, often by purchasing a map from a dockside dealer. (Without a map or some other form of directions, there is little a crew can do but pick a direction and hope for the best). If the intended location is a floating isle, another plane, or some other location that moves, this map must be current to have value. If the map is particularly shoddy (or fraudulent and being pawned on unsuspecting PCs), it may not lead to the intended destination at all.
Every day, week, or month of the trip (as decided by the GM depending on the length of the journey), the navigator makes a Profession (navigator) check to stay on course. The target DC is 20 for a standard trip (on the same continent), 25 for long trips (across continents, under the ocean, etc.), and 30 for extremely difficult trips (journeys that cross planes and space). Particularly bad circumstances such as extremely cloudy weather applies a -4 penalty to this check (or worse, if dictated by the GM). In addition, maps of particular quality may add bonuses to this check, as outlined in Chapter 5: Equipment and under the Craft (cartographer) skill.
For every point a failed check falls short of this target DC, the party travels one mile off-course, multiplied by the number of days that check represented. Roll a d4 to determine the direction of the error (1=left, 2=right, 3=too far, 4=too short). If enough of these errors are made in the same journey, the party could end up grossly off-course, never knowing it until they reached a landmark, or arrived at where their intended destination was only to find it wasn’t there. At such times, the party may need to re-orient themselves via landmarks, begin exploring around them, or may even have to turn back.
Making Your Own Map: When a navigator has visited a location, they may make a note of it themselves with a successful Craft (cartography) check, using their own information when moving to and from that location in the future.
Old Maps: Destinations that move such as floating islands or planes require up-to-date maps in order to locate easily. For every month that passes after a map is made, the bonus it provides decreases by 1. If a map’s bonus ever reaches -4, it becomes useless.
Selling Maps: While old men in pubs might sell treasure maps, and the PCs might find someone willing to pay them for a special map to a secret location, generally the market for buying and selling navigational data is regulated by a cartographers guild, and the PCs will not be able to sell their own maps. The cartographers guild keeps their navigational information regularly updated, selling it to merchants and adventurers of all types, and few are willing to pay someone not in the guild for information they cannot know for certain is accurate (unless, of course, the buyer is a desperate PC who cannot afford better). As such, while the cartographer’s guild might employ adventurers to map dangerous areas, this is done as a service for a fee, rather than a chance to make and sell a map.