Navigation in John Cabot's Time
In the 1500s, navigation was described as the art of steering
a ship by the shortest good way, by the most appropriate
direction and in the shortest time. The principle of modern
navigation is not any different. Yet, navigators at the time of
John Cabot had only a few tools to work with: the magnetic
compass, the log, the lead line, the quadrant or astrolabe, and
for a trans-oceanic crossing, a navigator sailed south or
north to the latitude of his target and then headed east
or west until his destination was reached. By using
either a quadrant or astrolabe to measure the angle above
the horizon of Polaris (the North Star) at night, or the
sun at noon, he could determine his latitude (the
distance in degrees north or south of the equator).
The quadrant was a heavy metal plate graduated in degrees -
like a protractor in a student's geometry set with a
plumb-bob (lead weight on a string) marking the angle.
Hanging the quadrant in the rigging, the navigator
sighted along the protractor's edge at the Sun or North
Star and used the plumb-bob string to mark the angle.
The astrolabe was similar. Descended from a far more complex
Arabian instrument, the astrolabe was suspended from a
cord to hang perpendicular to sea level, while the
navigator sighted the sun or a star through two small
holes in the plates on its moveable vane. The altitude
of the celestial body could then be read from the
graduated scale around the rim (The Explorers 94). If the
navigator made sightings on the sun, he had to allow for
its angle above or below the equator. In June the sun is
almost 23° north of the
equator and in December almost 23°
south of it.
|A 16th century brass astrolabe.
From Richard Humble and the editors of Time-Life Books, The Explorers
(Alexandria, Virginia: Time-Life Books Inc., ©1979) 94.
Photo courtesy of the Istituto e Museo di Storia della Scienza, Florence, Italy.
The cross-staff was an early navigational instrument for
measuring latitude. Also called a fore-staff, it consisted of a
square-shaped staff marked off with a scale, and fitted with a
sliding cross-piece set at right-angles to the staff. One end of
the staff was held at the navigator's eye. The cross-piece
was then slid forward or backward until its upper edge lined up
with the sun or polar star and the lower edge with the horizon.
The point at which the cross-piece cut the scale on the staff was
noted and converted into degrees by referring to a table.
Illustration by Duleepa Wijayawardhana.
The navigator of a vessel close to the equator saw the polar
star close to the northern horizon. When taking a measurement
from such a latitude he used a short cross-piece positioned close
to the edge of the scale away from his eye. As a vessel sailed
north and Polaris rose higher in the night sky, he moved the
cross-piece further down the staff toward his eye. When it
eventually went off the scale, he fitted a larger cross piece and
repeated the process.
|16th century illustration of a man using a cross-staff.
Plate XVII. "Taking a pole-star sight with a cross-staff," 1545, from
Pedro de Medina's Arte de Navegar, Valladolid. In David W. Waters, The Art of
Navigation in England in Elizabethan and Early Stuart Times (London: Hollis and Carter,
© Henry C. Taylor 1958) between pages 56 and 57.
He followed the reverse process when taking a position from
the sun. At noon near the equator the sun is nearly overhead in
which case the navigator used the largest cross-piece. As a
vessel sailed into more northern latitudes, the sun moved lower
toward the southern horizon, requiring the use of a smaller
piece. Each cross-piece had its own set of tables.
The back-staff was a similar instrument for measuring
latitude. However, it had the advantage of having the sun at the
navigator's back rather than in his line of sight. The
back-staff also consisted of a graduated staff. However, rather
than a cross-piece, it had an arc shaped part attached that cast
a shadow along the edge of the staff. To find the latitude, the
navigator at noon stood with his back directly to the sun and the
staff to his eye. Aiming for the horizon, he slide the arc-piece
along the staff until its shadow touched the far end. The point
at which the arc-piece cut the scale on the staff was noted and
converted into degrees by referring to a table.
The nocturnal, or night disc, was an early sea-faring navigational
instrument of unknown origin. First described in 1272, it was improved upon
in the early sixteenth century as a means of calculating the time at night (Clissold 236).
It consisted of two concentric circles of different sizes, made of
either wood or brass. The larger was divided into twelve sections to
represent the months of the year; and the smaller was divided into twenty-four
sections to represent the hours of the day. There was an index, or pointer, on
the smaller circle which pivoted from the centre of disc. The instrument was
placed at arm's length with the Polaris star clearly visible through a hole in
the centre. The index or pointer was then calibrated to "rest" on an imaginary
line connecting two stars in either of two orbiting star groups - the pointers
of Ursa Major or the guards of Ursa Minor. The readings taken from these calibrations
gave the hour of night (Kemp 599-600).
|A nocturnal from H.M.S. Sapphire sunk in the harbour of
Bay Bulls, Newfoundland.
The Sapphire was a 32 gun, 5th rate, frigate that was in Newfoundland to protect
the English migratory fishery. However, the vessel was trapped in Bay Bulls by four
French naval vessels, and to avoid capture was scuttled in 60 feet of water on September
11, 1696. The nocturnal was excavated in 1977 by Parks Canada.
Courtesy of the Department of Canadian Heritage, Parks Canada,
Federal Archaelogy. ©Her Majesty the Queen in Right of Canada. Reproduced
with the permission of the Minister of Public Works and Government Services, Canada.
This instrument allows a navigator to establish true north or
magnetic north. There is not an appreciable difference between
the two in Europe, but explorers discovered that the difference
increased in other parts of the world.
Europeans had known for a long time that the lodestone had
magnetic qualities. Initially a piece of the stone was floated on
wood in a pan of water. This was followed by a magnetized needle
floating on a straw in water, and then by a needle resting on a
pivot point - much like the modern compass.
The compass provided mariners with a rough or coarse
direction, which they could supplement by noting the direction of
the North Star, and of the sun at noon (south), and at sunrise
(east) and sunset (west).
|Remains of a Spanish compass, ca. 1565. Found during the
archaeological excavation between 1978 and 1985 at Red Bay Harbour,
Courtesy of the Department of Canadian
Heritage, Parks Canada, Federal Archaelogy. ©Her Majesty the Queen in
Right of Canada. Reproduced with the permission of the Minister of Public
Works and Government Services, Canada.
||16th century Spanish compass in case.
An artist's reconstruction of the compass found at Red Bay Harbour, Labrador.
Illustration by Duleepa Wijayawardhana. Based upon a Carol Pillar sketch
courtesy of Parks Canada from James A. Tuck and Robert Grenier, Red Bay, Labrador:
World Whaling Captial A. D. 1550-1600 (St. John's, Newfoundland: Atlantic
Archaelogy Ltd., ©1989) 30.
The navigator also needed to know the speed of his vessel. It
is likely that this was first done by measuring the time that a
piece of wood tossed overboard near the bow would take to reach
the stern. Later sailors dropped overboard a small sea-anchor - a
wooden triangle weighted on one side, with a rope attached to all
three corners. The rope had knots in it, and it would be paid out
for a fixed length of time as measured by an sand-glass. Speed
was gauged by the number of "knots" that went out
during that time. Eventually, the term "knot" came to
mean one nautical mile per hour.
|| Drawing of a 16th century sand-glass.|
Illustration by Duleepa Wijayawardhana. Based upon a Carol Pillar
sketch courtesy of Parks Canada from James A. Tuck and Robert Grenier, Red Bay,
Labrador: World Whaling Captial A. D. 1550-1600 (St. John's, Newfoundland:
Atlantic Archaelogy Ltd., ©1989) 31.
Some people consider that this term originates from
"Deduced Reckoning" which really means that the
navigator figured out the ship's position from its speed and
direction rather than from direct measurements. Navigators
devised a simple peg board so that for each turn of the
hour-glass, the helmsman marked off the direction (one of the
eight cardinal points of the compass) and the speed during that
The 15th century mariner lacked accurate
positioning tools. Explorers such as Cabot had no charts. Those
that followed him had inaccurate charts because the longitudes of
the various points were largely inaccurate. Mariners much
preferred navigating within sight of land, even if the trip was
longer. Then they had points of reference. It called for great
courage to navigate so close to land because the ship was in
constant danger of wrecking on rocks and shoals.
The Lead Line
The fourth dimension of navigation (after latitude, longitude
and time) is depth. Depth measurements probably predate any of
the others. A navigator cast a lead weighted rope forward of the
ship, allowed it to sink and when it touched bottom took up the
slack. The length of a rope was measured by tying markers often
at arms length called fathoms. Navigators calculated the water
depth by identifying the point where the rope exited the water
and counting the markers. The piece of lead tied to the end of
the rope was often indented on the bottom and the indentation
filled with tallow or fat. Small fragments of the bottom such as
clay, sand, gravel, etc. would stick to the tallow. By examining
sea bottom samples, navigators could often determine where they
Would you consider taking a trip of several thousands of miles
without a map? Cabot did that. Even in the world he knew, charts
were unavailable. Printing presses were not known, so maps were
individually drawn. Map makers were unable to relate correctly
the relative position of distant geographic features. Instead,
directions to get from place to place took the form of written
The ancient mariners did not sail in warm, dry wheelhouses 100
feet above the water, but on the open deck just a few feet above,
and sometimes, in the waves. They became acutely aware of their
surroundings. Land birds foretold of land nearby; swarms of fish
and kelp identified shallows. The usual direction of winds and
cloud types were all part of their intuition.
Navigation in John Cabot's time was very coarse by today's
standards. But his awareness of his surroundings, his prudence,
and his courage allowed him to traverse the Atlantic and explore
the island of Newfoundland and its rugged shoreline.
©1997, Newfoundland and Labrador Heritage Web Site Project