That is something we can’t know. (Read the theories about how he might have navigated with or without instruments elsewhere on this website.) Nor does the Sea Stallion project give us any clues, because only modern navigation instruments are used on board. But let us simply reflect over how someone in Viking times might have thought when trying to find a route across the open sea without a magnetic compass. These thoughts are partly based on experience from practical experiment with empirical and low-technological navigation.
We will get help from Morten and Gudmund. They are two young men who sailed to the Faroe Islands for the first time with their crew. Gudmund lives in Viking times, Morten more than 1,000 years later. They represent two different points of view on navigation:
All available knowledge or sufficient knowledge
There is a lot that Morten can read about the waters around the Faroe Islands. The more he reads, the more confident he feels. Gudmund does not know nearly as much about what to expect. But others have been there before, so he thinks their usual good seamanship will see them through.
Today’s sailors have access to an abundance of information, of which only a part is necessary for sailing safely. The Viking navigator’s knowledge was limited but relevant and directly usable, since it was built on his own experiences and those of others. So we can call his navigation method empirical.
Objective and abstract sea charts or a subjective and concrete picture of reality
By buying sea charts, Morten is paying for knowledge that Gudmund gets by talking to others who have already sailed to the Faroes. The sea chart gives Morten a bird’s-eye view that he tries to transform into a picture of what will come up over the horizon. Gudmund gets a concrete description of what he can expect to see when he arrives at a location where another skipper has been before. The skipper also tells about sounds with strong currents, mountains that can give falling winds, and other important things that he has seen and heard about.
"Leidarmaðr" was the man who found the way in Viking times and he was an important man on board. He could at least partly compensate for the lack of sea charts and written sources with good memory techniques. His subjective knowledge could be an advantage in such cases, as it was a combination of facts and useful experiences.
Morten uses his sea chart for calculating how far it is to the Faroes measured in nautical miles. Gudmund has asked experienced navigators how many days it usually takes.
Today we state a distance in nautical miles, i.e. an objective unit of length. In Viking times, it would be stated as the number of days it would take to sail, i.e. a subjective unit of length.
Position or course
Both Morten and Gudmund live in the area called Egersund. Morten plots a course towards the Faroes directly from home, while Gudmund will first sail a little north. He wants to start from somewhere that is on the same degree of latitude as the Faroes. This means he only needs to see the sun at the same height in the sky at noon every day to be on the right course.
Viking Age descriptions of sail routes did not state where an island was, but gave the course and the number of days normally required to sail there from a given place. It must have been vital to keep to the given course towards the target as neither one’s own exact position nor that of the target were known. To sail direct west as Gudmund did was the easiest – as long as one was east of the target, one would reach it sooner or later. But the Viking navigator was occasionally forced to diverge from the course because of contrary winds. In these circumstances, it was probably easier to continue relating to the course by crossing close to it with short tacks, than to leave the course and have to work out a completely new course to the target when a favourable wind returned.
Position on a grid or relative position
Morten can calculate exactly where he is by giving the coordinates in a fictive grid, i.e. his latitude and longitude. Gudmund has more of a feeling of the direction in which certain islands, points and mountains lie in relation to places he knows.
Without a sea chart and a grid in the form of latitude and longitude, one cannot give an exact position. When the merchant Ottar described how one sailed along the Norwegian coast, he did so by referring to islands that he could not see during the voyage itself, and by relating how much time it took to sail between known places. One thus had a mental chart that built on various known places’ relations with each other.
Exact or approximate position
Morten is accustomed to always knowing his exact position. So when he loses his GPS in the sea without the Faeroes in sight, he suddenly feels very small... Gudmund, on the other hand, feels quite confident – out here there are no rocks or areas with dangerous waves that he must pay attention to. As long as he keeps to his westerly route he does not need exact knowledge of where he is, because he will get there sooner or later.
On the open sea, a position is used primarily as a starting point for setting a course. An approximate starting point gives an erroneous course, but the North Atlantic’s large and high islands were also relatively easy to find. When one has seen and recognised the island, one could adjust course to the harbour or fjord one was going to. An imprecise navigation method might have been more time-consuming, but need not have been more dangerous assuming one did not meet a storm while sailing a longer stretch. One could partially compensate for uncertainties about e.g. dangerous shoals in the vicinity of land through double look-outs, sailing more carefully, lying to at night, having a good "leidarmaðr" on board, etc.
But it did happen that a Viking crew became “lost at sea”, if they could not see the sun for several days. Then they needed plenty of food and especially water, in order to be able to search for the island they were going to, perhaps in another week or so.
Exact or average calculations
Morten often calculates how much time it will take to reach the Faeroes by dividing the remaining distance by the speed in knots. Gudmund does not calculate in knots. He makes an assessment, based on his experience of the boat’s movements at various speeds, of how far they have sailed and thus how much there is left to sail.
No matter whether one had an instrument for measuring speed or not in Viking times, one can do without. Experiments show that it is possible to assess speed with neither log or instrument with less than 5% error on average, because the errors tend to cancel each other out over time. Assessing the course with or without a sun compass, according to the same experiments, can be done with an average error rate of about 10°, and assessing the time is often with no greater error than an hour.
Instruments or senses
The instruments in Morten’s boat can show course, speed, wind velocity, heeling, the altitude of the sun, etc. Gudmund gets the same information mainly from what he can see, hear and feel.
Today, the navigator registers part of what happens through figures that he processes mathematically. In Viking times, the navigator received information directly from his senses and processed it using a combination of experience and intuition.
Navigation – a matter for discussion?
Morten’s crew often asks, “Where are we?” and “When will we get there?” Gudmund’s crew observes the same things that Gudmund himself observes and they can make their own judgements about where they are going.
Most navigators since Viking times have had various instruments to help them. The instruments gave answers in the form of unambiguous numbers (though with varying degrees of error), which only the navigator had access to. It was not so important to discuss position with the crew.
Navigation in Viking times was more a matter of assessing positions than an exact reading of numbers or calculations. So it may have been natural for the navigator to confer with experienced crew members who had the same information as the navigator. Decisions taken on board might have been more up for discussion in those days, as is shown by an episode in the Greenland Sagas, in which Leif Eriksson’s crew wondered why he was steering so close to the wind when in reality they had a following wind. (The purpose of the voyage obviously affected how decisions about navigation were taken on a vessel. There are differences between e.g. war activity and a trading journey.)
To relax or to be attentive
Morten’s GPS always shows him what course he needs for the Faroes. He is also told by his other instruments when it suits him, so Morten does not think so much about the navigation. Gudmund, on the other hand, must think more for himself and he accepts the information that nature has to offer. So he is constantly attentive to the boat’s movements, wind changes, the swell, the flight of the birds, the position of the sun, and other clues about the boat’s course and speed.
A modern navigator has access to the same information as a navigator in the tenth century. But he often chooses to ignore some parts because he doesn’t need them, e.g. the flight of the birds and the position of the sun in the sky. Other parts he gets in an easier form, e.g. from weather reports and his navigation instruments. Not needing to be so attentive is relaxing – but he also runs the risk of disengaging the whole of his contact with the nature surrounding him.
P.S. Why did Leif steer an erroneous course? He had seen some men stranded on rocks, and he wanted to rescue them.
Lena Lisdotter Börjesson teaches courses in square-rig sailing and low-tech navigation at Fosen Folk High School in Norway. She has conducted experimental voyages of about 2,000 nautical miles with Viking Age navigation methods.