Designations used on surveys and nautical charts to indicate the consistency, color, and classification of the sea bottom. Also called NATURE OF THE BOTTOM, CHARACTER OF THE BOTTOM.


Related Terms

ICE ISLAND

A large piece of floating ice showing about 5 meters above the sea surface, which has broken away from an ice shelf, having a thickness of 30 to 50 meters and an area of from a few thousand square meters to l50 square nautical miles or more; usually characterized by a regularly undulating surface which gives it a ribbed appearance from the air.

ICE FIELD

An area of pack ice consisting of floes of any size, which is greater than 10 kilometers (5.4 nautical miles) across. Ice fields are subdivided according to areal extent. A large ice field is over 11 nautical miles across; a medium ice field is 8 to 11 nautical miles across; a small ice field is 5.4 to 8 nautical miles across. uniform system of maritime

ICE PATCH

An area of pack ice less than 5.4 nautical miles (l0 kilometers) across.

SHIFT TIDES

Sighting the positions of the sun and moon using a sextant and using a nautical almanac to determine the location and phase of the moon and calculating the relative effect of the tides on the navigation of the ship

KNOT

A measure of speed equal to one nautical mile (6076 feet) per hour.

DECK LOG

A full nautical record of a ship's voyage, written up at the end of each watch by the deck officer on watch. The principal entries are: courses steered; distance run; compass variations, sea and weather conditions; ship's position, principal headlands passed; names of lookouts, and any unusual position, principal headlands passed; names of lookouts, and any unusual happenings such as fire, collision, and the like. Also called Captain's Log.

LEADING LINE

On a nautical chart, a straight line, drawn through leading marks. A ship moving along such line will clear certain dangers or remain in the best channel.

AIR ALMANAC

1. A periodical publication of astronomical data designed primarily for air navigation, but often used in marine navigation. 2. A joint publication of the U.S. Naval Observatory and H. M. Nautical Almanac Office, Royal Greenwich Observatory, designed primarily for air navigation. In general the information is similar to that of the Nautical Almanac, but is given to a precision of 1' of arc and 1s of time, at intervals of 10m (values for the sun and Aries are given to a precision of 0.1').

ALMANAC

A periodical publication of ephemeral astronomical data. If information is given in a form and to a precision suitable for marine navigation, it is called a nautical almanac. See also nautical almanac; if designed primarily for air navigation, it is called an air almanac. See also EPHEMERIS, ASTRONOMICAL ALMANAC.

ANCHORAGE CHART

A nautical chart showing prescribed or recommended anchorages

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