N   November

No (negative)


National Advisory Committee for Aeronatics was a United States federal agency founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and Space Administration.   Among other things, NACA produced the NACA duct,  a type of air intake used in modern automotive applications, the NACA cowling,  and several series of aerofoils which are still used in aircraft manufacturing.   The aerofoil shapes are often used in hydrofoils,  including centreboards,  rudders and leeboards.



A solid metallic cylinder,  much longer than wide,  with a point at one end and a flat ‘head’ at the other.   Used to join two pieces of wood.   The point is placed on one piece of wood;  the head of the nail is struck with a hammer and the point is driven through both pieces of wood.   The friction of the nail in the wood holds the two pieces together;  the friction between the two pieces prevents them sliding upon one another.

Some woods split readily along the grain when nailed;  to prevent this a hole,  slightly narrower than the nail,  is bored through both pieces of wood and the nail is driven through the hole.

Traditionally,  nails, in preference to screws,  were used for joining planks to frames.


At sea,  a small passage between two lands.   See also straight.

The narrow parts of a navigable waterway,  especially a canal.

The English canals were built to a 7 foot gauge.   Most of the waterways were wider,  but the bridges,  tunnels and narrow locks were no narrower than 7 feet.   Fleets of 'narrow boats',  up to 70 feet long, were built to carry cargo and passengers along the waterways and through the narrows.

See Hadfield.


40 ft by 7ft steel narrow boat on the river Cam


Several narrow boats at Jesus Lock in Cambridge.   In the foreground Rosie is disembarking passengers

Nautical mile (nM)

In English usage a sea mile is, for any latitude, the length on the earth’s surface of one minute of latitude subtended at the centre of the earth.   It varies from about 1,855.3 metres (6,087 ft) at the equator to about 1,849.1 metres (6,067 ft) at the poles , with a mean value of 1,852.3 metres (6,077 ft).   

The international nautical mile was chosen as the integer number of metres closest to the mean sea mile,  ie 1852m.

American use has changed recently. The glossary in the 1966 edition of Bowditch defines a "sea mile" as a "nautical mile".   In the 2002 edition, the glossary says: "An approximate mean value of the nautical mile equal to 6,080 feet; the length of a minute of arc along the meridian at latitude 48°.".


When using charts based on Mercator’s projection,  one minute of latitude is close enough to one nautical mile to be useful.


Of,  or belonging to,  a navy.

Naval architecture is the art and science of designing and building ships.   A naval architect is a person who design (but not usually builds) ships.


n   The process and business of planning and following a route,  in this context,  by water.   The person who navigates is a navigator.

v   To navigate;   to plan and follow a route.

n   The British canals are known as navigations.   The men who dug the canals were known as navigators (or navvies).   Navvy is now a generic word for a labourer.

Navigation lights

All vessels should carry navigation lights for use at night or in reduced visibility.   They enable the vessel to be seen rather than to see.   They enable other mariners to identify some characteristics of the vessel.   Navigation lights are described in detail in the International Regulations for Preventing Collisions at Sea.   (Beware of summaries and interpretations (like Wikipedia) which change the meaning)


Rule 23,  “power-driven vessels underway” says “

(a)   A power-driven vessel underway shall exhibit;

  (i)     a masthead light forward

  (ii)    a second masthead light abaft of and higher than the forward one . . .

  (iii)   sidelights;

  (iv)   a sternlight. . . “  

 There are modifications and exceptions.

Rule 25,  “Sailing vessels underway . . .” says “

(a)   A sailing vessel underway shall exhibit;

  (i)     sidelights;

  (ii)   a sternlight.”   


There are modifications and exceptions.



Someone who navigates.

See also Navigation,  above.


The military ships and boats,  and the associated people,  equipment,  armament and stores,  of a nation.


Anything relating to sailors or sailing.


When the sun and moon are at a right angle to one another,  seen from the Earth,  the tidal range is at its lowest;   the tide with the lowest range in a fortnight is a neap tide.



When a vessel has gone aground at the top of the spring tide and must await the next spring before she can get off.   She must wait at least two weeks,  possibly several months.


A compass needle is (was) a strip of magnetized metal,  pointed at both ends,  and balanced on a pivot point at the centre.   One end points toward the North magnetic pole,  the other toward the South magnetic pole.


An orienteering compass.  The red needle points toward magnetic North,  the white toward magnetic South.

Needle,  compass.JPG


A sail needle is a small thin instrument with three flat sides,  sharply-pointed at one end and with an eye at the other end.   It is used to sew sails and to whip lines.


A point or promontory of land jutting out into the sea.   Eg Dungeness.



A grid of fibres linked together by knots.   Objects larger than the grid openings are contained by the net;  smaller objects pass through.

Nets are used to catch fish larger than a certain size while allowing the fry to pass through.

Fresh fruit is stored aboard ship in nets hanging from the overhead.



Short lengths of line,  in particular for tying in reefs.   See Knittle.


That part of the day when the sun is below the horizon,  and when vessels are required to show navigation lights.

Broadly speaking,  there are three watches at night:

The first watch is from 2000 (8pm) to midnight.

The middle watch is from midnight to 0400.

The morning watch is from 0400 to 0800.



Latin for 'dark cloud',  referring to rainclouds.

Nimbostratus clouds form a layer (stratus) along a warm or occluded front and precipitate rain as the warm  front approaches across the ground.

Convective Cumulonimbus clouds form at the cold front,  and are accompanied by rain and lightning.


n   Lengths of braided rope,  9 or 10 feet (2m) in length,  used to attach the messenger,  or voyol,  to the anchor cable.   The nippers were attached by the nipper-men (usually foretopmen) and held as the voyol pulled the cable.   (A modern equivalent might be the short length of line often attached between the anchor chain and a cleat to prevent the rode snubbing the windlass)   At the main hatch the nippers would be removed and the ship's children would carry them back to the manger board to be used again.


n   An affectionate term for a young child.



The abbreviation for nautical mile.




National Marine Electronics Association.

Shipboard electronic instruments,  such as echo sounders,  wind vanes,  AIS,  RADAR,  logs,  are linked together by electronic systems to standards set by the NMEA.

In contrast with computer standards,  such as USB,  NMEA equipment is waterproof and rustproof:  it is suited to a harsh marine environment.


From Falconer:  "A name given . . . to a tree-nail drove (sic) [driven] through the heel of each shore that supports the ship on the slip."

Modern boatyards and marinas use wedges between the shore and the ship and between the shore and the ground.

The act of securing the shores with tree-nails (or wedges) is 'nogging'.




When the sun is directly overhead.

Twelve o'clock.

Eight bells in the forenoon watch.



From any point on the Earth,  True North is the direction in which the North pole lies.

From any point on the Earth an imaginary line (a meridian) passes through that point and the North pole and the South pole.

The North and South poles are the tips of the axis on which the Earth rotates once every 24 hours.

From most points on the Earth,  Magnetic North is not in the same direction as True North.   The Magnetic North pole lies between Northern Canada and the True North pole,  and moves toward Russia at about 40 miles per year.

It follows that a magnetic compass points to magnetic North and not to true North;  the variation* between true North and magnetic North is different for almost every point on the Earth,  and must be taken into account when navigating with a magnetic compass.

* not variance,  which is a statistical value.


Not under command

IRPCS Rule 3 "General definitions" says

"(f)   The term "vessel not under command" means a vessel which through some exceptional circumstance is unable to manoeuvre as required by these Rules and is therefore unable to keep out of the way of another vessel."

A vessel which has lost steering or propulsion is not under command.



A conical red buoy marking the starboard side of a channel (when returning to harbour) in IALA-B.

In region A conical buoys are green and mark the starboard side of a channel when returning to harbour:  they are rarely called 'nuns'.

John Starkie

July 2020

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