It was rarely possible for galleys to sail in a straight line to their destination. Normally, mariners had to tack back and forth in the face of contrary winds. Galleys, of course, had crews of oarsmen to allow them to proceed without favorable winds, but rowing was too strenuous to be continued for long stretches. All too often, ships were blown far off course in a storm or lost sight of land in a fog. In these cases, it was essential to have some method of recovering the course so that the galley could arrive safely at its destination. The Venetians had a mathematical technique for doing this known as the marteloio.
Michael calls the marteloio a technique for navigating mentally. A mariner using it did not need sea charts. All he needed was a special table committed to memory. With the help of this table and a few rules, he could easily plot and recover courses.
To understand this medieval technique, read our basic explanation; then follow Michael as he solves three different problems:
