ebb The tide A loose term applied both to the falling tide and to the outgoing tidal stream.
eddy. A circular motion in water; a horizontal movement in a different direction from that of the general direction of the tidal stream in the vicinity, caused by obstructions such as islands, rocks, etc, or by the frictional effects of beaches, banks, breakwaters, etc.
elbow. A change of direction in the contour of a submerged bank or shoal; a sharp change in the direction of a channel, breakwater, pier, etc.
elevation. That which rises above its surroundings, such as a hill, etc.
On a chart, the elevation of a feature is its height above the level of MHWS or MHHW. See also heights.
embankment. A sloping structure of stone, rubble or earth, raising the height of a river bank, or used as the foundation for, or strengthening of, a causeway or dyke.
embayed. To be in such a position, or under such adverse conditions, in a bay that extrication is difficult if not impossible.
entrance lock. A lock situated between the tideway and an enclosed basin when their levels vary. It has two sets of gates by means of which vessels can pass either way at all states of the tide. Sometimes known as a Tidal lock.
equilibrium tide. The hypothetical tide which would be produced by the lunar and solar tidal forces in the absence of ocean constraints and dynamics.
equinoctial spring tide. A spring tide (greater than average) occurring near the equinox (in March and September).
equinox. Either of the two points at which the Sun crosses the equator: or the dates on which these occurrences take place.
erosion. The wearing away of the coast (or banks of a river) by water action; the opposite of accretion.
escarpment. An elongated and comparatively steep slope separating flat or gently sloping areas.
estuary. An arm of the sea ??at the mouth of a tidal river, usually encumbered with shoals, where the tidal effect is influenced by the river current.
estuary port. A port built at the tidal mouth or estuary of a river. < br />
even keel. The state of a ship when her draught forward and aft are the same. Loosely applied when a ship is floating at her designed draught marks.
eyot. A small island in a river.
F fairway. The main navigable channel, often buoyed, in a river, or running through or into a harbour.
falling tide. The period between high water and the succeeding low water.
fan. A relatively smooth feature normally sloping away from the lower termination of a canyon or canyon system. Also termed a Cone.
fathom . A unit of measurement used for soundings. Equal to 6 feet or 1.8288 m.
fathom lines. Submarine contour lines drawn on charts, indicating equal depths in fathoms.

ferry. A boat, pontoon, or any craft, used to convey passengers or vehicles to and fro across a harbour, river, etc.
fetch. The area of ??the sea surface over which seas are generated by a wind having a constant direction and speed. Also, the length of the generating area, measured in the direction of the wind, in which the seas are generated.
fish aggregating device. A term used to describe a moored or floating object ranging in construction from a collection of buoys or rough bamboo rafts through to large rafts on which lights and radar reflectors are fitted.
All these devices have plastic streamers or palm fronds hanging below them, the purpose of the device being to attract algae and marine growths on which small fish feed and in turn attract shoals of larger fish.
fish haven. An area where concrete blocks, hulks, disused car bodies and similar items of scrap material are placed on the sea bed in order to provide suitable conditions for fish to breed in.
In Japanese waters, the term “floating fish haven” may be used instead of marine farm (qv).
Draught permitting, vessels may navigate over seabed fish havens, but they are hazards to anchoring or seabed operations.
fish pound. A barrier across the mouth of a creek placed to retain fish in a creek.
fish stakes. A row of stakes set out from the shore, frequently to a considerable distance; often terminating in a partly decked enclosure from which a net can be lowered.
fish trap. An enclosure of stakes set in shallow water or a stream as a trap for fish.
fish weir. An enclosure of stakes set in a stream or on the shoreline as a trap for fish.
fishing ground. Area wherein craft congregate to fish; most particularly those areas occupied periodically by the large fishing fleets.
fishing harbour or port. One especially equipped for the convenience of the fishing industry, the handling of fish and the maintenance of its vessels.
fitting-out basin. A basin in a shipyard sited and equipped, to accommodate ships to complete the installation of machinery, etc, after launching.
fix. The position of the ship determined by observations.
flat. An extensive area, level or nearly so, consisting usually of mud, but sometimes of sand or rock, which is covered at high water and is attached to the shore.
Sometimes called Tidal flats. See also ledge.
floating beacon. A moored or anchored floating mark ballasted to float upright, usually displaying a flag on a tall pole, and sometimes carrying a light or radar reflector; used particularly in hydrographic surveying.
floating bridge. A power -worked pontoon used as a ferry which propels itself across a harbour, river, canal, etc, by means of guide chains.
floating dock. A watertight structure capable of being submerged sufficiently, by admission of water into the pontoon tanks, to admit a vessel. The tanks are then pumped out, the dock and vessel rising until the latter is clear of the water, thus serving the same purpose as a dry dock.
flood channel. A channel in tidal waters through which the flood (incoming) tidal stream flows more strongly, or for a longer duration of time, than the ebb. It is characterised by a sill or bar of sand or other consolidated matter at the inner end , ie the least depth in the channel occurs close to the inner end. Ebb channels occur in close association with, and usually alongside, flood channels: they have a sill at their outer end.
flood-mark . A mark, consisting usually of a horizontal line and a date, sometimes found on riverside buildings, dock walls, etc, to mark the highest level reached by flood waters at the date indicated.
flood tide. A loose term applied both to the rising tide and to the incoming tidal stream. See also ebb tide.
flow. The combination of tidal stream and current; the whole water movement.
Also a loose term for flood (eg ebb and flow).
following sea. One running in the same direction as the ship is steering.
foraminifera. Single- celled animals consisting of a mass of jelly-like flesh with no definite organs or parts of the body; covered with a casing of carbonate of lime: common in the surface waters of the sea.
forced tide. A tide which exceeds its predicted height at high water.
foreland. A promontory or headland.
foreshore. A part of the shore lying between high and low water lines of Mean Spring tides.
form lines. Lines drawn on a chart to indicate the slope and general shape of the hill features; generalised contour lines which do not represent any specific or standardised heights. See also hachure.
foul area, foul bottom or foul patch. An area where the seabed is strewn with wreckage or other obstructions, no longer dangerous to surface navigation, but making it unsuitable for anchoring.
foul ground. An area where the holding qualities for an anchor are poor, or where danger of striking or fouling the ground or other obstructions exist.
foul bottom. The bottom of a ship when encrusted with marine growth .
fracture zone. An extensive linear zone of irregular topography of the sea floor, characterised by steep-sided or asymmetrical ridges, troughs or escarpments.
free port. A port where certain import and export duties are waived (unless the goods pass into the country), to facilitate re-shipment to other countries. See also transit port.
freshet. An abnormal amount of fresh water running into a river, estuary or the sea, caused by heavy or prolonged rain or melted snow.
fringing reef. A reef, generally coral, closely attached to the shore with no lagoon or passage between it and the land . furrow. Oceanographically, a fissure which penetrates, roughly perpendicularly to the run of the contours, into the continental or island shelf or slope. See also canyon.
G gangway. Similar to a brow (qv) when it is sometimes called a gangplank.
Also, the actual opening in the ship side by which a ship is entered or left.
Also, a passage-way in a ship.
gap. Oceanographically, a break in a ridge or rise.
gat. A swashway, gut or natural channel through shoals.
geodesic. The shortest distance between two points on the spheroid. It is equivalent to a great circle on the sphere.
geoid. An imaginary surface which is everywhere perpendicular to the plumb line, and which on average coincides with Mean Sea Level in the open ocean. Its shape approximates to that of a spheroid, but it is irregular due to the uneven distribution of the Earth mass.
gird. To gird a ship is to prevent her from swinging to wind and tide. Of a tug, to be towed broadside on through the water by her tow-rope.
Global Navigation Satellite System (GLONASS). The satellite navigation system owned and operated by the Russian Federation. Global Positioning System (GPS). The satellite navigation system owned and operated by the United States Department of Defense. globigerina ooze. Ooze which has the limy skeletons of foraminifera as its principal constituent, the dominant element being the calcareous tests of the globigerina (a spherical shelled organism).
godown. A term used in Eastern ports for a warehouse or store.
gong-buoy. A buoy fitted with a gong which may be actuated automatically or by wave motion.
gradient currents. Currents caused by pressure gradients in the water.
gravel. Coarse sand and small water-worn or rounded stones; varying in size from about the diameter of the top of a man thumb to the size of a pinhead. See also sand, pebbles.
graving dock. Another name for a dry dock. To grave is an old term meaning to burn off the accretions on a ship bottom before tarring, etc.
grid. A systematic rectangular network of lines superimposed on a chart or map and lettered and numbered in such a way that the position of any feature can be defined with any required degree of precision.
grid reference. The position of a feature given in grid letters and numbers.
gridiron. A flat framework, usually baulks of timber placed parallel with each other, erected on the foreshore below the high water line, and in such a position that a vessel can be moved over it at high water and left dry and resting on it at low water.
< br /> ground. A portion of the Earth crust which may be submerged or above water, eg spoil ground, middle ground, swampy ground, landing ground.
to ground. To run ashore or touch bottom.
ground speed. The speed of a vessel over the ground.
ground swell. A long ocean swell; also this swell as it reaches depths of less than half its length and becomes shorter and steeper; ie influenced by the ground.
groyne. A low wall-like structure, generally of wood or stone, usually extending at right angles from the shore, to prevent erosion. Frequently erected in estuaries and rivers to direct the flow of the water and prevent silting or encourage accretion.
gulf. A portion of the sea partly enclosed by land; usually of larger extent and greater relative penetration than a bay. < br />
gut. A natural narrow inlet of deep water in a bank or shoal, sometimes forming a channel through it. It may also refer to the main part of a channel.
H
hachures. Shading lines sometimes used on charts and maps to indicate the general slope and shape of hill forms. See also form lines.
half tide. The height of the tide halfway between high water and low water. See also. mean tide level.
half-tide basin. A basin the gates of which are open for entry and departure some hours before and after high water.
half-tide rock. Formerly used to describe rocks which are awash at about mean tide level.
harbour. A stretch of water where vessels can anchor, or secure to buoys or alongside wharves, etc, and obtain protection from sea and swell. The protection may be afforded by natural features or by artificial works. See also artificial harbour, island harbour.
hard. A strip of gravel, stone or concrete, built on a beach across the foreshore to facilitate landing or the hauling up of boats.
harmonic analysis. An analysis of tidal observations, carried out to determine the harmonic constituents of the tide, as a basis for tidal predictions.
harmonic prediction. Prediction of the tide by combining harmonic constituents.
haven. A harbour or place of refuge for vessels from the violence of wind and sea. In the strict sense it should be
accessible at all states of the tide and conditions of weather.
head. A comparatively high promontory with a steep face.
An unnamed head is usually described as a headland.
Also, the inner part of a bay, creek, etc, eg the head of the bay.
Also, the seaward end of a jetty, pier, etc.
head sea. A sea coming from the direction in which a ship is heading; the opposite to a following sea.
heading. Synonymous with ship head.
headway. Motion in a forward direction.
Also, an obsolescent term synonymous with vertical clearance (qv).
heavy sea. A rough, high sea.
height. The vertical distance between the top of an object and its base.
On Admiralty charts, the term “height” (except in the case of drying heights) is used in the sense of elevation (qv) and unless otherwise stated, is expressed, in metres or feet as appropriate, above the level of MHWS, MHHW, or, in places where there is no tide, above the level of the sea. See also elevation, High Water Datum.
Also, the height of a vessel is the height of the highest point of a vessel structure (eg radar aerial , funnel, cranes, masthead) above her waterline.
height of the tide. The vertical distance at any instant between sea level and chart datum.
heights. A comparatively level plateau at the summit of a precipitous mountain.
high focal plane buoy. A light-buoy on which the signal light is fitted particularly high above the waterline. Used as fairway or landfall buoys. See also lanby.
High Water (HW). The highest level reached by the tide in one complete cycle.
higher high water. The higher of two successive high waters where diurnal inequality is present .
high water datum or datum for heights. The high water plane to which elevations of land features are referred.
On Admiralty charts this datum is normally the level of MHWS when the tide is predominantly semi-diurnal, or MHHW when the tide is predominantly diurnal.
high water stand. A prolonged period of negligible vertical movement near high water, this being a regular feature of the tides in certain localities while in other places stands are caused by meteorological conditions.
Highest Astronomical Tide (HAT). The highest tidal level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions. < br />
holding ground. The sea bottom of an anchorage is described as good or bad holding ground according to its capacity for gripping the anchor and chain cable. In general, clay, mud and sand are good; shingle, shell and rock are bad.
hole. A small area of ??considerably greater depths than those in the vicinity; of less area than a deep.
hollow sea. A very deep and steep sea.
hopper. A barge used in harbours, etc, for conveying sullage or spoil to a spoil ground (where it is discharged through the bottom of the barge).

horizontal datum. A reference for specifying positions on the Earth surface. Each datum is associated with a particular reference spheroid. Positions referred to different datums can differ by several hundred metres.
hydrography. The science and art of measuring the oceans, seas, rivers and other waters, with their marginal land areas, inclusive of all fundamental elements which have to be known for the safe navigation of such areas, and the publication of such information in a form suitable for the use of navigators.