Medieval Navigation, III: Captain’s Log

St. Brendan's ship on the back of a whale, and his men praying, in Honorius Philoponus' Nova typis transacta navigation 1621; image from Sea Monsters on Medieval and Renaissance Maps by Chet Van Duze. This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 70 years or less. {{PD-US}} – published in the U.S. before 1923 and public domain in the U.S

Over the last several posts, we have discussed how navigators and sailors ventured out into the open sea, and how they located their positions. Now I want to discuss how this information was recorded and saved for future sailors.

Back in Medieval times, being a navigator was a trade. You may have worked on a ship, and worked yourself up to a navigator, or, as a young man you were assigned as an apprentice to a master navigator. 

We have been using the word navigator, however, there was also a sailor is known as a pilot. A pilot is external from the crew, but is responsible for the navigation of that vessel. In modern terms, it is usually someone who takes over the navigation of a vessel when they are entering a port, channel, or harbor. In ancient times, a pilot was attached to a warship, or other vessel. The captain, or master of the ship, maintain the discipline and maintenance of the vessel, while the pilot performed the navigation. This pilot knew the routes to a specific destination. A person could also become an apprentice to a pilot in medieval times.

Back then, as any trade, it had its trade secrets. These secrets were also well kept in the profession. The information about sailing to one port or to another was passed down orally from the master to the apprentice. They were rarely written down, so this information could not be easily stolen or learned by someone else.

This passing of information works well if you are the navigator of a ship that went to one or two ports. But soon there was a need to expand outward across the vase oceans. If someone ventured to a far-off land, they needed to, or someone else needed to, repeat that voyage. Remember, people did not just become adventurers to discover the world. These sailors went across oceans for profit, or to establish colonies in their countries names.

One of the first navigation documentation in Europe was the rutter (aka periplus, derroterro). This was a form of written directions before the common use of charts and maps. It was a written description of the heading of the ship, points of interests, or ports to stop for supplies. It was a detailed description of the voyage through the point of view of the pilot.

If anyone was a fan or saw the TV miniseries “Shogun” (1980), you will remember after being shipwrecked in Japan, Pilot-Major John Blackthorne, was constantly looking for his stolen rutter. This was because, even if he could find a ship, he would have no idea how to navigate back to Europe without it. The TV show was based on a book of the same name by James Clavell. This book in fact was based on the real-life exploits of William Adams. Adams was one of the first Dutch sailors to reach Japan, and having served the emperor faithfully, one of the few Non-Japanese ever to be given the rank of Samurai.

So the rutter would describe how a ship would reach a destination. It became a guarded secret, the information inside would only be given to others in their trade who were from the same country or firm (as in the Dutch East India Company). 

If you are a port, you depend on the income from trade. If only a handful of navigators had the information on how to navigate to your port, your income would suffer. To increase the trade to their ports, they themselves started publishing their own rutters. This would allow anyone who possessed the skill of navigation to find their way to their ports and increase wealth there with their trade.

We still use something similar to the rutter today. The United States Coast Pilot® (USCP) consists of a 9-volume series of nautical publications broken down by geographical areas of the United States. New editions of The U.S. Coast Pilot are published annually throughout the year. It is a written narrative of what to see and expect when you navigate in and out of these waters.

Simple charts (basic terms for a map on water) appeared B.C., but their complexity was rudimentary. When sailors began to move out into the world, their charts had to become more complex.

Charts began to have not only coastlines, but information from previous voyages by other sailors. Information such as height of objects on land, depth of water, navigational hazards, even average sea temperature was beginning to appear on charts and of course the compass rose showing north, south east and west, and the angles between. Later, they would include lighthouses, buoys and other markers placed their as navigational aids. The person who creates these charts are called a cartographer. 

We all have seen a version of an ancient chart, where there were painted or drawn numerous sea monsters (see picture above). These paintings, like the charts themselves they appeared on, evolved over time. Initially, some of these monsters represented unknown points on a chart, places where few sailors had been and little information about the area was gathered. The monsters were painted there to indicate it was an unknown area. Many of these charts were also created not for sailing, but for personal use. Royalty in Europe would often have maps adorning their libraries, and the creatures painted on them were just for decoration.

Later, fruits, animals were drawn on the land mass of charts to show where there might be food. Also, fish and wales were drawn on the charts to show good fishing grounds or for whaling (this was during the time when wale oil fueled the lights of the world). 

After knowledge of the seas increased the monsters disappeared. They however were replaced with countries maps, or persons of royalty. These figures represented the areas that these countries controlled. European countries were constantly trying to control the shipping in different waters, it was valuable for a vessel to know if they were heading into waters controlled by an ally, or an enemy.

Notice on the chart how northern, or southern areas are larger than those near the equator. The latitude lines get wider apart as you leave the equator and head toward the poles.

This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license

There are several things you must remember in terms of charts and maps, they are inherently misleading. You must remember the earth is round, and you are taking this round object and making it flat. Look at a flat chart or map of the world, the latitude lines are closer together nearer to the equator than at the poles. So, distorted are these maps that it appears that Greenland is larger than Africa. One much remember this, since it is these lines that you can measure distance from. 

Knowing the earth is round, can benefit the person doing the navigation. We all are taught the shortest distance between two lines is a straight line, this is not true on the earth. The Great Circle or orthodromic navigation takes the curvature of the earth into effect when plotting a course across great distance. Plotting an arc is a shorter distance, than a straight line then to your destination. 

The reasoning for this, is if you plot an arc, you are removing some of the surface of the earth by going north (applies in northern hemisphere), and removing some of the earth surface because of the curvature of the earth. This may not seem possible, but you can relate to this information in daily terms. If you are like me, you have a thick stomach so it is semi round. Every so often I have to pull my pants back up, why? Because my belt slips off because is tighter around my waist then below it: Same concept.

Several types of charts were developed, but the Mercator Projection which I described above has been the standard for charts. The other forms of charts or maps of the earth, are for the most part for educational purposes or reference material.

The captain would draw his course on the charts and would refer to them during his trip, marking his position along the way, correcting the heading of the vessel if needed. Like the rutter, at one time, they were also kept secret.

An item I have taken care of for many years. A set of navigational dividers given to me from the Quartermasters of the Coast Guard Cutter Madrona and Cowslip when I left the Coast Guard.

Also, with the creation of the chart the captain need tools (called plotting tools) to help him mark his course, or location, on his vessel. Such common plotting tools as the divider, rulers, protractors. Later, other instruments were created such as the Nautical Slide Rule, a device which helps with common speed/time/distance problems used in navigation.

Besides charts, the Captain, or those on watch would keep a log, referred to as a Ship’s Log. These logs could have simple occurrences, such as course changes, or major items the ship encountered on their voyage. The information would later be used to help create the navigational charts above, or for a record for future sailors. Logs appeared over other parts of the ship. Deck hands who later were called Boatswains Mates, would keep a vigil on the deck, checking for water leaks, or maintaining ropes tied on the vessel. They would keep a log indicating the times they made a round on the vessel. Later, when engines powered the ships, the engineering staff would also keep a log about the functions of these engines.

Today, computers and GPS helps ships travel throughout the world, with little human interaction. We must look back at the ancient sailors with respect and admiration; many of them, using only skill, talent and determination, ventured out into unknown waters sometimes for years, some never returned. There is an old saying about these sailors: “Wooden ships and Iron Men”.

Thanks for reading my series of post on the history of navigation. I hope you enjoyed them, please leave a comment.

W.A. Rusho is a professional wrestler, author and historian. You may reach him via his website or his email.

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