I   India

I am altering my course to port


International Association of Marine Aids to Navigation and Lighthouse Authorities.

IALA-A: Region A Covers Europe,  Africa,  Asia,  Australia

IALA-B:  Region B covers the Americas and Japan.

IALA regions A and B


n   Frozen water.

Pure water (with no solutes) freezes at 0°Centigrade.   Sea water freezes at about -2°C,  depending on the amount of dissolved salt.

Ice is less dense than water,  and so it floats on the surface.

Being less dense ice occupies more space than the same weight of water:  it expands as it freezes and tends to burst the pipes in which it flowed.

At sea,  ice is a danger to shipping.   In the form of icebergs (mountains of ice) it can tear holes in the hulls of ships.   In the form of sheet ice it can trap vessels of any size,  and crush them.

n   An acronym (ICE) for Internal Combustion Engine.


Crew not required to serve watches.   They include specialists such as the cook,  the carpenter,  the sailmaker.


A rotor or blade in a turbine or pump.   The engines (including outboard engines) of yachts and power boats have impellers which drive cooling water through the engine.   The impeller is often made of rubber which perishes and disintegrates over time and needs to be changed.



v   To compel someone by force to join the Navy.

It doesn't happen anymore.

v  To do something which causes other people to admire one.


adj   Describing the inside of a ship.


adj   Describing an engine fitted inside a small boat with only the end of the shaft and propeller on the outside of the hull.   To be distinguished from an outboard engine.


The propeller shaft of an inboard engine is mostly within the boat:  only a small part of the shaft and the propeller are outside.

An outboard engine,  together with its gearbox,  shaft and propeller,  is entirely outside the boat,  usually mounted on the transom with the engine high and the propeller immersed in the water.   The entire unit can be steered:  it can also be removed from the boat.

An inboard-outboard arrangement has the engine entirely within the boat.   The shaft emerges from the transom well above the waterline and enters an outboard gearbox with a vertical shaft to the propeller below the waterline.   The vertical shaft and the propeller can be steered in much the same way as an outboard engine.

Inflatable boat

A small boat made substantially of fabric that can be inflated with air under pressure.   See RIB.



A line used to haul something in.   A jib-boom extends the bowsprit,  and can be hauled in alongside the 'sprit when not in use.   The tack of a jib,  or flying jib,  may be attached to a traveller on the bowsprit and can be hauled in toward the stem to reef or furl the sail.

See Outhaul,  Downhaul.   An 'uphaul' is a haulyard (ha'lyard or halliard)

Inglefield clip

A clip used to attach a flag to a flag halliard.

Inglefield clip


An international corporation which regulates and provides satellite communication (including 'phones).

The word has become generic for satellite telephones.


Close to the shore,  within the national boundary or 12 mile limit.

The original national boundaries were set at 3 miles,  which was long cannon shot and the distance which could be seen from a land based fort and could be protected by shore based batteries.


n   A device for measuring.   The word implies a degree of manual control of the instrument and dexterity by the operator;  a gauge requires no manual control or dexterity (although the gauges on an aircraft are known as instruments).

A rule measures short distances (millimetres to metres).

A micrometer measures short distances very accurately.

A sextant measures the angle of a star above the horizon.

A pair of dividers measures distance on a chart.

A Portland plotter,  or parallel rules,  measures angles on a chart.

Pens and pencils are often known as writing instruments.

n   A device for making music.

n   A legal document.


A contract of indemnity.

The insurer agrees to pay for the total or partial loss of a vessel,  or damage to other vessels or people under certain specified conditions.

If your uninsured vessel causes damage or loss of life you might be sued for damages amounting to thousands or millions.   If your vessel is insured,  the insurer agrees to pay the damages provided the specified conditions have been met.


A through-hull fitting mounted below the waterline in a vessel to draw seawater inboard for engine cooling, or for flushing.   Such fittings are protected on the inside of the hull by seacocks.

A fitting in the side of a power vessel,  well above the waterline,  for drawing in large amounts of air for the engines.


International Date Line

Originally a meridian at 180°East and 180°West.

Because the earth rotates from West to East,  the sun appears to rise in the East and cross the sky toward the West.   When the sun is overhead the Greenwich meridian it is midday (say,  Tuesday) in Greenwich and midnight at the IDL.   As the sun continues to move West a new day (Wednesday) starts at the IDL and progresses Westward.   When the sun becomes overhead the IDL it is midday Wednesday at the IDL and midnight Wednesday at Greenwich.  When the sun is again overhead Greenwich it is midday Wednesday at Greenwich and a new day (Thursday) starts at the IDL.

Voyagers travelling Eastward across the IDL appear to lose a day by moving immediately into tomorrow.

Voyagers travelling Westward across the IDL appear to gain a day by moving immediately into yesterday.

A number of Pacific Island states have preferred to be in either yesterday or tomorrow,  and the IDL has been moved to accommodate their wishes:  it is now a convoluted zig-zag line up to two time zones from the meridian at 180°East and West.


Intertidal zone

The land between High Water and Low Water.


A mechanism used to change Direct Current (from a battery) into Alternating Current suitable for powering equipment.


The inner strake of the gunwale.   See Wale.

A whale is very different.



A metal used,  among very many other things,  for making the nails which sometimes hold the planks of a boat to its frames.

Iron expands as it rusts,  and nails become loose in the planking.   The oxide encourages rot in the timbers,  which become iron-sick.

See Copper.

Iron is sometimes used as ballast for sailing vessels.   Its advantage over lead is that it is cheaper:  its disadvantages are that it rusts and makes a mess in the bilges;  it is less dense than lead and so occupies more space for the same weight.

Irons,  in

When the boat is head to wind and will not fall off onto either tack.

Iron topsail,  Iron wind

Slang for an auxiliary engine.


International Regulations for Preventing Collisions at Sea.

Commonly known as the CollRegs,  or The Rules of the Road,  this document prescribes how mariners should behave in the presence of other vessels.

The Regulations are not necessarily easy to read,  so attempts have been made to interpret,  summarise and simplify them.   Any such change of words necessarily changes the meaning and is dangerous.


A body of land smaller than a continent, surrounded by water.

An island is not necessarily one country.   The mainland island of Britain is part of one nation (the United Kingdom of Great Britain and Northern Ireland) but has several countries (England,  Scotland and Wales).   The island of Ireland has one nation (The Republic of Ireland) and part of another nation (Northern Ireland is part of the UK).


Continuous lines,  drawn on a chart,  linking points of equal atmospheric pressure.   Where the atmospheric pressure is measured in millibars,  isobars are drawn on a synoptic chart at intervals of 4 millibars.

On this synoptic chart there is a region,  over the British Isles and France,  of atmospheric pressure higher than 1024 millibars bounded by an isobar at 1024 millibars.

To the S'East of Greenland there is region of atmospheric pressure lower than 976 millibars bounded by an isobar at 976 millibars.

Isobars on a synoptic chart

If the Earth were not rotating,  air (winds) would move directly from the high pressure region to the low pressure region and the two would tend to become equal at about 1013.25 millibars:  with the same atmospheric pressure everywhere there would be no isobars.

But,  with some parts of the Earth being warmer than others,  warmer,  less dense air rises.   The rotation of the Earth,  and the resulting Coriolis force,  causes air (wind) to rotate anticlockwise (North of the Equator) within rising air masses around low pressure centres.  The winds (moving air) tend to follow the isobars,  but angled about 15° inward to fill the low pressure.

Where there is a great difference in atmospheric pressure over a short distance (at the S tip of Greenland on this chart) the isobars are closer together and the wind,  attempting to move from high to low,  is stronger.

The colder,  more dense air falling onto the British Isles and France (on this chart) rotates clockwise,  following the isobars but angled about 15° outward to fill the lows;  the pressure gradient is smaller,  and so the isobars are further apart and the winds are lighter.

'Warmer' and 'colder' are relative terms.   The 'colder' air mass falling onto France and the British Isles might be at 25°C,  but colder than surrounding air masses:  the 'warmer' air rising to the SE of Greenland might be at 15° to 20°C,  but warmer than the surrounding air masses.

Isolated Danger marker

Indicates a danger to shipping,  such as an isolated rock.   The mark is often a post mounted on the isolated danger,  rather than a buoy.   The buoy or post has bands of black,  red and black with a topmark of two black balls.   Its light is white,  Fl.(2).5s

An isolated danger
Tidal power turbine is an isolated danger

Refers to the lights of buoys or lighthouses where the length of light is equal to the length of darkness within the period stated.

Iso.5s means that the light is on for 2.5 seconds,  off for 2.5 seconds, in each 5 second period.



A narrow land feature connecting two larger land masses.   The Isthmus of Corinth links two otherwise isolated parts of Greece


John Starkie

March 2018

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