By Tullio Vidoni
PhD Dissertation, University of British Columbia, 1993
Abstract: Roberto da Sanseverino went on a pilgrimage to the Holy Land in 1458. He travelled from Venice to Jaffa on a galley and made his return, from Acre to Ancona, on a three-masted sailing ship. During both voyages he kept very accurate logs of distances, courses and wind directions. He described the sails employed for different modes of sailing and other activities pertaining to the safe operation of the vessels. These logs are contained in Sanseverino’s diary of his pilgrimage and are an essential part of an original manuscript kept at the University of Bologna. This diary is the first documentation, and the only one known to exist up to this time, which presents a complete description of the methods employed by medieval shipmasters to navigate and handle their ships overlong voyages.
The accuracy and reliability of the numeric data and of the other facts contained in the logs are such that, among other unusual findings, they make it possible to deter-mine the length of the Venetian sea mile, the angles of tack of medieval ships to windward and the speeds attainable under various conditions of sailing. Other original descriptions encompass the handling of ships in anchorages and some of the technical considerations that were essential to ensure ship seaworthiness under different conditions of cargo. Further reflections on all these data make it possible to arrive at certain conclusions about the economic constraints of sea ventures in different seasons of the year.