Conversion tables; used
units of one system to units in another.
astronomer credited with disproving the Ptolemaic System.
direction in which a
vessel is heading or is intended to be steered, the direction through
Course made good; the
which the vessel is actually traveling as opposed to the direction in
is pointing. Corrections;
alterations made to
charts to update
using LOPs from several
navigational aids or
marks to obtain a position fix.
Crux;the Southern Cross a
constellation seen in
the southern hemisphere.
celestial navigation it
is the point on the earths surface directly beneath the Zenith, and the
the surface you are standing on is your body’s Geographical Position or
the direction in which a
vessel is pointing,
as opposed to the course made good.
Eye; the height of a sextant user’s eye above
needed to add as a correction to a site reduction.
Height of tide;
a figure taken from the
tide tables indicating the depth
of water above the chart datum.
the apparent line, for
an observer where the
earth’s surface and the sky meet. Also a circle formed on the celestial
sphere by a plane tangent to a point on the Earth's surface.
Horizon Mirror half
clear glass half mirror, on a sextant it allows the observer to view
horizon at the same time as a reflection of whatever is showing in the
Mirror. Read more:
sideways movement of a
vessel usually caused by the
when taking a sun or
moon sight it is difficult to guess
where the center is so the observer aligns either the top edge (Upper
more usually the bottom edge (Lower Limb) of the object on to the
sight is then corrected using the appropriate correction tables.
line drawn on a chart on
which the position of the vessel must lie. The line deduced from either
compass bearing of a mark or a sight reduction. A minimum of two or
more are necessary to establish a fix.
the time when the sun
reaches its highest
altitude at your position and is directly north or south of you. it
be at your Zenith and its GHA will correspond to your longitude.
time at your
Angle, LHA; the angular distance
of an observed celestial object to the west of the observers meridian.
phenomena; alterations made to the
prevailing weather by local
an instrument used to
calculate speed and
distance travelled, through the water.
a book in which the
navigator records data
about the vessels progress
the angular distance
east or west from the
Greenwich or Prime Meridian (0⁰) on the earth’s surface.
see Limb. LOP; see Line
device used for
navigation which aligns with the earths magnetic field thus indicating
direction of magnetic north.
a LOP or
previous line of position forward to a current line of position. A fix
two separated bearings of the same fixed object and the distance run
which, indicates that
there is safe water for navigation is all around the mark
the Tide Tables
this is a port where the details have to be worked out in relation to a
emitted from a
single position which will show up as either red, white or green
the angle of the observer, designed to indicate a safe navigational
direction towards which a
Tide or Current is flowing.
an instrument used to
distances, like the altitude of the sun, moon and stars for navigation.
I am perfectly aware that the majority of Wooden Boat aficionados are sensible folk. However, I need to point out that I am an amateur wooden boat enthusiast simply writing in order to try to help other amateur wooden boat enthusiasts. And while I take every care to ensure that the information in DIY Wood Boat.com is correct, anyone acting on the information on this website does so at their own risk.