|Tudor Navigation and
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. This 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.
Finding the ship's position when in sight of land wasn't too difficult, except when exploring uncharted waters. Pilots became familiar with land marks, water colour, scend of the sea, tidal stream lore, even the smell of a certain area. This led to the sensible policy of employing pilots for a specific area, as with Trinity House pilots today. It is noteworthy that the Trinity House for the Advancement of Navigation and Training in Pilotage was formed by Henry VIII in 1514. Thomas Spert, Master of the Mary Rose in 1513, was appointed master of Trinity House at its inception.
The pilot was directly concerned with the science of astronomy, he needed to know the "age" and bearing of the moon for the purpose of tidal prediction. Tide tables were already in being, although the true cause of tides was not yet understood.
The measurement of North - South movement (latitude) and East - West movement (longitude) presented another set of problems. Latitude was measured by taking a "sight" of the altitude of a heavenly body, usually the altitude of the midday sun, or a star, primarily the Pole Star in Northern latitudes. The instrument used for this purpose in the period of the Mary Rose would have been either an astrolabe or more likely, a cross staff. In conjunction with astronomical tables published in Lisbon in 1509, the latitude of a ship could be reasonably accurately determined.
Longitude was another matter entirely. At the time of the Mary Rose this was achieved by "dead reckoning", a form of guesstimate of distance and direction over a given time. The log and sand glass combination gave the speed of the ship, with the course being obtained from the compass. This information was plotted on the "traverse board", a form of peg board on a compass rose. Pegs were inserted every half hour of a four hour watch to show course and estimated distance covered. This information would be interpreted by the pilot and transferred to his "portolan chart" using his dividers for the plotting. The pilot could now estimate his east - west distance travelled to give him longitude. His cross staff would give him a latitude check. So far no traverse board or cross staff have been identified on the Mary Rose.
There were of course considerable errors, the roll of the ship could impede the flow of sand in the glass and bad weather could make sun or star sights impossible for days on end. The measurement of time was assisted by the use of pocket sundials. These gave the local time by the sun at the particular latitude they were set for. Nine pocket sundials were found aboard the Mary Rose. The sun dials' built in compass needle enabled them to be orientated to magnetic north. Really accurate measurement of longitude had to wait for the development of a reliable ship born clock, the Harrison Chronometer of the 1770s finally allowed navigators to do so.
The chart had existed since the middle of the thirteenth century. These were called "portolans" and probably originated in Venice or Genoa. This sheep or goatskin chart gave coastal outlines with the positions of ports marked on them. Compass roses featured all over these charts to enable courses to be plotted. By the 16th century, these charts were in common use by the Portuguese.
The existence of dividers on the Mary Rose may indicate that the ship carried charts. The pilots of the period also had a "portolano", a form of sailing directions that went with such charts. This described coasts and ports, anchorages, rocks, etc. The successor to the portolano, the routier or "rutter," was becoming popular in the 16th century. These followed the format of present day sailing directions, giving tidal information and views of the coast as seen from seaward. In 1541, "The New Rutter of the Seas for North Partes" was published for circumnavigation of the British Isles.
By the 16th century the compass was becoming an essential aid for the navigator. The compasses on the Mary Rose were mounted on gimbals in a bowl to compensate for the movement of the ship. The compass bowls had glass tops and were set in wooden boxes for protection.
The pilot also needed a lodestone, a piece of magnetic oxide of iron. (The Pole Star was often referred to as "The Lodestar"). This stone was used to stroke, and thereby magnetise, the compass needle. The compass needle points not to true north, but to magnetic north, a wandering point in the Canadian Arctic. The angular difference between true north and magnetic north on any part of the earth's surface is known as "variation". By 1530, the Portugese had the means of measuring and tabulating variation. Another error of the compass is caused iron fitting and items within the ship. This causes a deflection of the needle known as "deviation".
Contemporary usage of words and expressions relative to navigation.
1557: It floweth a shoare at this place at an E. moone full
sea, and the shippe lay thwart to wend a flood, in the off, at a
S.S.E. moone. So that... when it is full sea on the shoare, it is two
points to ebbe, before it be lowe water in the off.
1576: I found our compasse to be varied by 11 deg. and one
part to the westwards, which is one point.
1538: The wind arose at North and by East enforcing us to
weigh... now the wind is come 3 points more being North-North-East...
1497: ...a Straunger Venisian, by which a caart made hym
self expert in knowying the world...
1574(1577): They hale the logge or piece of woode again,
and looke how many fadome the ship hath gone in that time.
1514: To Thomas Metford of Rye for lodesmanship for ij hoyes.
E 36/5. f.261
1512: 2 lodesman alias pylotts
1514: A balynger of Rye of xx tonne... with a master,
lodisman, v men and a lad... for waftyng of ij hoyes
1513: Master Tresorer wyl yt ye delyver Woodles the lodes
man for tarrying wt hys boot & 3 men wt hym by the spaas off 8
hoole weekes... to weche uppon the bringyng in off all the kynges
shippes thorowgh the blak deppes hys coosts £6 13s 4d
1472... a marvelous blasynge steere... and then it
compassede round about the lodesterre...
Lead and Line: 1495: The Regent: Sowndyng leddes of
xiiij lb, j; of xij lb apece, ij.
1387: First instance noted of the office of "Pilot of the Black Deeps".
1512: The Regent's charges... pylotts at 20s. a man a
1513: Master Tresorer pay the pylot of the Gabriell after
eyght ducats le month and this billl shall be yr discharg by me
1587: A Traverse-Booke made by M John Davis in his third
1635: The quartermasters... have a care to look to the steerage and