Ships and Shipbuilding: Sails and Rigging

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Michael includes masses of information about sails and rigging in his manuscript. He gives many details about the traditional lateen sails used on commercial and military galleys, as well as his nave latina. He also includes an extremely long description of the square sails associated with his nave quadra.

As with the hulls of his sailing ships, this text reflects the evolution of sail technologies in what has come to be called the "nautical revolution" of the Middle Ages.

Lateen rig

The traditional kind of sails used in the Mediterranean during the Middle Ages were large, triangular lateen sails. These were set on extremely long yards slung to one side of the mast. The yards were so long, they were actually made of two pieces. Michael does a good job of illustrating the arrangement in his drawing of the galley of Flanders at sea (page icon 145b). There he shows a lateen sail on a yard that is almost as long as the ship.

The lateen rig allowed a ship to sail closer to the wind than a ship equipped with square sails. If, for example, a wind was blowing directly from the direction a ship needed to go, most square-riggers of the time could sail no better than 90 degrees to this wind, making no headway at all. A lateen-rigged ship might be able to sail as much as 10 or 15 degrees into this wind and continue making headway by tacking back and forth.

But the lateen rig was difficult to operate. Since the yards were extremely long, they were also extremely heavy, and therefore difficult to move. They hung on the side of the mast, under a forest of shrouds and stays. When there was a change of course or of wind, the yards and sails had to be extracted from this forest of rigging and manhandled over to the other side of the mast. The procedure was quite complicated, as one can imagine from Michael's picture, and required a great deal of manpower.

Manpower, however, was no problem on a galley, where there were generally at least 150 oarsmen to do the heavy lifting.

Each of Michael's galleys carried two masts for lateen sails. His text includes details about the size of the masts and yards and a long list of the different shrouds, stays, halyards, and other rigging. Following Mediterranean tradition, almost all these lines used some combination of ropes and pulley blocks, as can be seen quite clearly in Michael's illustration (page icon 145b).

Michael only briefly mentions the sails carried on each of his galleys. Instead, he points the reader to a very lengthy section on sails inserted earlier in his manuscript (127a-129a). As Michael shows in several of his illustrations, each sail was made up of numerous smaller pieces of cloth which had to be sewn together and reinforced in a complicated manner. His section on sail making describes the cutting and arrangement of these pieces in great detail. The surprise in this section is that much of the discussion is mathematical. But sails were extremely expensive, so precision was essential.

Michael's nave latina carried lateen sails on both its masts. This was still a relatively new phenomenon for trading vessels. Northern Europeans had only just started to build ships with two masts. The nave latina would have been new technology to them.

Perhaps because of the novelty of the rig, Michael's description of the nave latina includes a long list of masts, yards, blocks, pulleys, and other parts of the rigging. Again, much of the discussion is mathematical and proportional. The forward mast is to be three times the ship's breadth. The yard is to be one-quarter the length of the mast above the deck. The length of numerous other lines are expressed as multiples of the mast, and so on. The text reflects the further penetration of mathematics into the world of the mariner.

Square rig

The second sailing rig described in Michael's manuscript is the square rig associated with his nave quadra. In this arrangement, the main sail is a large square canvas set on a yard that hangs horizontally from the mast at right angles to the keel. Most people are familiar with this arrangement from pictures of Viking ships or from images of sailing ships in such films as Mutiny on the Bounty.

In normal circumstances, ships equipped with square sails could not sail as close to the wind as ships with lateen sails. Square sails, however, required many fewer persons to manage, and were therefore cheaper to operate.

During Michael's lifetime, the sail plan of square-rigged ships was slowly evolving in ways that would eventually make sailing ships almost as maneuverable as galleys. Michael's nave quadra shows one step in this evolution. It carried a large square sail on the mainmast, but a lateen sail on its mizzenmast. Perhaps significantly, this innovation is described in Michael’s text, but lacking in the illustration that accompanies it. The square sail was imported from Northern Europe in the 1300s, where it was used on ships with only one mast. Shipwrights in the South added a second mast. Scholars believe they equipped this mast with a lateen sail to make the ship more maneuverable, rather than to add propulsion.

Ships with this kind of sail plan were still unknown in northern waters, where Michael's nave quadra would have represented the latest in sailing technology. It is for this reason, perhaps, that Michael's text devotes an extraordinary amount of space to a description of shrouds, stays, halyards, and myriad other parts of the rigging. As with the nave latina, the different pieces of the rigging are given dimensions that are proportional to the length and breadth of the ship, as well as the length of the masts.

It seems very likely that Michael used this proportional approach when rigging the lateen sails on his galleys for sea. It was well within his mathematical abilities.

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