I – India

As a single-letter signal in the International Code it means, ‘f am altering my course to port’, and as such is more often given by sound than by any other means. It is two dots in the Morse code, and India in the phonetic alphabet.

IALA buoyage system

The initials stand for International Association of Lighthouse Authorities, and ‘the’ buoyage system is one result of this group’s efforts to reduce the thirty or so buoyage systems of the world to one uniform pattern. Fully titled IALA Maritime Buoyage System ‘A’, being one of several considered over a period of years, this system is an amalgam of the Lateral and Cardinal systems which were in use by various European countries. System A follows the ‘red to port’. System B has red to starboard, as in (e.g.) US waters. This dictionary is not the right place to give a complete description of the systems – Almanacs and most books on navigation contain full information.


International Certificate of Competence. A certificate that converts many national boating qualifications, such as Dayskipper, into an internationally recognised document.


In weather forecasts this means that the expected conditions will arrive in the specified area within six hours. Soon means within twelve hours, and Later means beyond twelve hours.


International Maritime Organisation. An agency of the United Nations that maintains a regulatory framework for shipping including safety, environmental, legal and technical and security cooperation.


International Measurement System – racing handicap system.

In irons

A sailing boat is in irons when she comes head to wind and fails to Pay off on either tack. The answer is to make a Stern board, to let the wind push her backwards and then to use the rudder to throw her stern off to one side or the other.

In stays

A sailing boat is in stays when she is going from one tack to the other, and in the arc when her sails are not drawing. She must always be in stays before she can get In Irons, though the one condition does not necessarily follow the other – indeed, it should be a rarity.

In-boom reefing

See roller reefing.

In-mast reefing

See roller reefing.


Within a vessel, or nearer amidships. E.g. to bring a sheet lead further inboard is to pull it closer to the vessel’s centreline.


As a comparative of position it indicates that a thing is nearer the cen¬tre of the ship than another. As an absolute term it means anything within the shell of the ship, as Inboard motor, whereas a bathing ladder would be Shipped outboard.

Index error

Of a sextant, is simply a misalignment of the index or pointer ¬that’s to say, when the mirrors are parallel, the index shows an angle whereas it should show zero.


A current setting into a bay or a sound.


The commonly-used abbreviation for inflatable boat. (Though since it is a boat only when inflated, I sometimes wonder if the word should not be ‘deflatable’.) Inflatables are light, stable and popular as yachts’ tenders. But they are no cheaper than rigid dinghies of the same carrying capacity, and they wear out in ten years or less whereas a rigid boat should last you a lifetime.

Inglefield clips

Interlocking C-shaped metal clips used for attaching signal flags to a halyard or to each other.


A rope used to haul the jib in from the bowsprit end, or any rope doing a similar job. Downhaul is equally obvious.

Initial stability

Like a flat-bottomed vase, some hull forms are stable to a certain angle of heel, and will return to the level if released. But, like the vase, if pushed too far they go right over. They have only initial stability. The round¬bottomed toy clown who comes up from any angle has more than initial stability – his is ultimate. Beamy flat-bottomed boats have high initial stability, and so do catamarans, but neither type has the ultimate stability of the boat with a deep ballasted keel which will pick herself up even if knocked flat. (The beamy barge-type boat should not be knocked flat, of course, nor should a catamaran. That would be carelessness and poor seamanship.)


As a comparative, towards the shore, or nearer the shore than the ob¬server. As an absolute, that region of sea which is, broadly speaking, where the land is in sight from a small boat. The region where many of us do most of our sailing. (Please see Offshore.)

Internal halyards

Halyards which run down the inside of a hollow mast (usually aluminium alloy) to emerge near deck level. They reduce windage and save you the trouble of Frapping them to avoid the abominable and slovenly clatter which characterises so many moorings and marinas nowadays.

International Code of Signals

A system of standard signals using mainly two letters (three for medical messages) in place of certain phrases and sentences.

Interrupted quick flashing light

A light which flashes at a rate of more than 60 times a minute, but with periods of darkness at regular intervals.

Intumescent paint

A paint which protects glass-reinforced resin (‘fibreglass’) against fire. The polyester resin of which most modern boats are built will burn merrily, so it is wise to protect the galley and engine areas with intumescent paint. When heated, this paint swells up into a crust, not unlike meringue, cutting off the oxygen supply to the resin, and to some extent insulating it from heat.


Converts DC to AC current to power household items such as microwaves, toasters, computers, etc.


The upper edge of a wooden hull may have a strake inside the top ends of the frames. This is the inwale. The strake outside is commonly called the Gun¬wale. (Neither has anything to do with whales. Please see Wale.)


International One Design.


International Offshore Rule.


Racing handicap system.

Irish pennants

Tatty ends of frayed rope flying in the breeze.

Iron topsail

In the past, when the wind fell light a gaff-rigged boat would set her topsail. Nowadays someone just presses the starter button of the diesel, otherwise known as the iron topsail.


An ironbound coast is a rocky one without anchorage or haven.


International Sailing Federation. Formerly IYRU.


A line on a weather map connecting places where atmospheric pressure is the same. Isobars are closely spaced around depressions, but widely spaced around anticyclones. The more closely spaced the lines, the greater the difference in pressure and the stronger the winds.


A line drawn on a chart to link places of equal depth.


A line drawn on a chart to link places of the same magnetic Variation.

Isophase light

A flashing light with equal durations of light and darkness.


A type of polyester resin that provides greater resistance to water absorption than orthophthalic resin and, as a result, is often used in the outer layers of a hull laminate


International Yacht Racing Union. Now renamed ISAF.