A Mariner's Knowledge

In his book, Michael recorded a broad selection of practical knowledge especially relevant to a mariner of the late Middle Ages. The manuscript is surprising in its breadth and covers four main subjects.

• Mathematics
  Michael loved mathematics and demonstrated how to solve many problems in several different ways. Mathematics is the first and longest section of his manuscript. It contains explanatory material on such topics as algebra, radicals, and fractions, as well as numerous practical commercial problems, complete with solutions.
• Ships and Shipbuilding
  Every year for more than four decades, Michael left Venice on long voyages aboard commercial or military vessels. His section on ships and their equipment is the second longest part of his manuscript. It contains a discussion of three kinds of galleys and two kinds of sailing ship.
• Navigation
  Michael's rise from an oarsman to higher positions on shipboard suggests that he had mastered the art of navigation. In his time many aspects of navigation were learned from practical hands-on experience rather than written instruction. However, Michael's manuscript contains a portolan, that is, a group of texts giving sailing instructions such as the distances and directions between ports in the Atlantic Ocean and in the Mediterranean Sea. The portolan also describes hazards and landmarks. Michael's manuscript also contains an explanation of a mathematical technique for navigating known as the marteloio.
• Time Reckoning
  When a ship left port, the crew had to keep track of time for itself. Michael included much material about time as it was understood and calculated in the late Middle Ages. The manuscript contains information relating to calendars, astrology, the phases of the moon, saint's days, and the date of Easter.