Glossary of Nautical Terms
(I try to give the nautical meaning; many words have obvious
alternative, everyday meanings.)
- APPARENT WIND
- The wind felt aboard a moving vessel. It is the
combination of the true wind and the
boat wind. A
boat in forward motion always pulls the apparent
wind forward of the true wind.
- The wind is said to back when its direction changes in
a counter-clockwise direction. A wind that was blowing from
the south and shifts to the east is often said to be
"backing to the east."
Also see veer and haul.
- BOAT WIND
- The wind produced by the boat itself as it moves
forward. A boat powering forward at 5 knots in a dead
calm creates a 5 knot boatwind.
- COMPASS COURSE
- The course to be steered as indicated by the ship's compass.
This course takes into account the deviation from the Magnetic Course
that must be considered for a particular compass and its
environment aboard a particular ship, both of which influence its accuracy.
- DEAD RECKONING
- From "deduced reckoning": a technique of navigation
in which a plot is kept, starting at a known location
(a fix) and, by careful observation
of course and speed, the current position is deduced.
- An old log which has lost most of its bouyancy,
and now floats nearly vertical, with one end down, and
the upper end just at or below water level. Deadheads
are common in old harbors where logs were floated in for
loading on boats.
- the last fixing of position obtained from land or coastal references
prior to navigation on open water
- The correction applied to Magnetic Courses in order to
convert them to Compass Courses. It takes into account the
error of the compass, caused by both internal and external
influences on the compass. The deviation of a compass varies
with the heading of the ship..
- DR PLOT
- Deduced Reckoning plot: a charting of course and
speed by which one keeps track of ship's position. Positions
are usually calculated (deduced) once an hour, or more
often as needed. Whenever possible, the DR postion is
confirmed by a fix.
- DR POSITION
- The position of the ship according the navigator's
track of course and speed since the last fix.
- (1) The distance of open water over which a wind has blown before
it reaches your location.
(2) The ability to sail to windward with a resulting course
sufficient to carry you to a destination, e.g.,
"We can fetch the mark on this tack."
- A known position, obtained by sighting of objects of
known position and applying their bearings from your position,
or by close proximity to the known location itself, or
by application of other ingenious methods developed over
the centuries by sailors and mathematicians.
- A heard or school of whales; a social meeting, visit, or the like,
as between vessels at sea; [Nautical] (of the officers and crews
of two whaling vessels) to visit or converse with one another for
- Applied to the wind direction: to change in a clockwise fashion.
Also see veer and back.
- HOBBS TIME
- Elapsed time as indicated by a counter which is activiated by an
oil pressure sensor on an associated engine. Named after the first
manufacturer of such a device.
- One nautical mile per hour. A nautical mile is equal to one
minute of lattitude, or about 6076 feet. Hence, a knot is
about 1.15 statute miles. Often explained to landlubbers as
"a mile and an eighth."
- LOW WATER DATUM
- A plane of reference for measurement of water depth. For Lake Huron,
for example, charted depths refer to the level of the lake when the
water guage at Goderich reads 576.8 feet above sea level. During the
summer months, it is not unusual for the lake to rise three feet above
this level, and, during periods of extreme high water, the lake has
risen as much as five feet above the reference level!
- A concise weather forecast coded in strings of five numerals and
transmitted by radiotelephone.
- MAGNETIC COURSE
- The course to be steered as indicated by the reference to
Magnetic North instead of True North.
This course takes into account the variation from the True Course
that must be considered for a location on earth. A perfect compass
would point in reference to True North, but compasses must
often have a deviation applied to them to correct for errors.
- The line at the bow of a small boat, used to tow it or
to moor it.
- RHUMB LINE
- Technically, a course line that crosses all meridians
at the same angle, but casually used to mean the straight
line course between two points. On mercator projection
charts, rhumb line courses are straight lines.
- A Reversible Pilot Seat; first seen on early Boston Whaler boats.
- In the U.S., a prescription drug that suppresses
motion sickness. Usually taken via a trans-dermal
(through the skin) patch worn on the neck. It's
effective at suppresing nausea, but has side effects
in some people of drowsiness and hallucinations.
- The affect of winds and current on
a boat's progress, often in conflict with the
boat's intended course.
- SPEED OVER GROUND (SOG)
- The speed of the vessel relative to the bottom,
as opposed to the vessel's speed through the water.
The speed over ground includes
the negative or positive effects of the currents in the water.
- A freshwater predator gamefish. The hybrid offspring of a Lake Trout
and a Brook (or Speckled) Trout, it was introduced to Lake Huron
by Michigan and Ontario fisheries in an attempt to bolster
sport fishing. It is presently not reproducing well, and it
is maintained by stocking. The named "SPLAKE" was formed by choosing
the "Speckled" Trout name in favor of the "Brook" Trout; otherwise
the fish would be called a "Brake"...
- TRUE COURSE
- The course to be steered as measured from True North.
This course is calculated or measured from charts, then
converted to Magnetic Course or Compass course by the
application of variation and deviation respectively.
- TRUE WIND
- The true speed and direction
of the wind, not modified by the effects of
the boat's movement.The actual wind, i.e.,
not the apparent wind
felt on the boat.
- The correction to be applied to adjust reference bearings
and courses from True North to Magnetic North. It varies as
a function of one's location on earth.
- The wind is said to veer when its direction changes in a clockwise
direction. For example, a wind blowing from the south changes to the
west. This is described as "the wind veered to the west."
Also see back and haul.
- Progress in a westerly direction. In days prior to the determination
of longitude, a vessel navigated by sailing to a particular latitude, then
sailing due east or west as needed until reaching the desired destination.
A ship was said to be "running her westing down".
- Velocity Made Good, i.e., speed made good in the desired direction.
Distance gained towards destination versus time, as opposed to
simple speed through the water.
Portions Copyright © 1995, 1996, 1997 by James W. Hebert. All rights reserved.
Last modified: February 23, 1997