Navigation and Seamanship:
Synthesis of an article by the late Peter Whitlock
Navigational science of the period was a rather hit or miss affair, particularly out of sight of land, and was basically to remain so until the mid 18th century. The tools of the pilot or navigator in Tudor times were relatively crude. The spyglass, later to be called the telescope, did not evolve until the early part of the 17th century, and a means of scientifically anticipating the weather was not available until the arrival of the barometer in 1643. No adequate survey of the British coastline existed until the the end of the 16th century.
Nevertheless, the 16th century saw tremendous advances in the science of navigation. Seamen had evolved rule of thumb methods of using the sun, stars and moon for direction finding since time out of mind, but now the scholar and the pilot were to work in unison in Portugal. The pilot was taught to use instruments and it is interesting to note that Sir Francis Drake used Portuguese pilots.
One of the basic items of navigation was the lead and line, essential for letting the pilot know the water depth, and at the same time, the nature of the seabed.
latter information was useful in helping them to identify the section
of coast, the distance off shore and for locating suitable holding ground
to anchor in. This was achieved by sticking a pice of tallow in the
bottom of the lead, allowing sand, shingle and shells to adhere to it.
The lead weighed 7lbs or 14lbs, with 28lbs for a deep sea lead, weights that are still the same. The line was marked with pieces of cloth, rope and leather at certain fathom marks so that the leadsman could identify the nearest mark by sight during the day and by feel at night.
The "Log" was used to measure the speed of a ship through the water. A piece of wood with a "stray" line attached was thrown off the stern of the ship until it floated clear. This stray line was in turn attached to a rope reeled on a hand held drum. As the ship moved away from the floating log the reel turned and the rope was allowed to run off for a specified period of time measured by a sand glass. The line was marked by knots in the rope at proportionate distances and at the end of the specified period the number of knots to run off the reel was recorded. This gave rise to the term "knots" to express nautical miles per hour. The "league" was the common usage for expressing distances in Tudor times.