O   Oscar

Man overboard


Oakum is a preparation of tarred fiber used in shipbuilding, for caulking or packing the joints of timbers in wooden vessels and the deck planking of iron and steel ships, as well as cast iron pipe plumbing applications. Oakum was at one time recycled from old tarry ropes and cordage, which were painstakingly unraveled and taken apart into fiber; this task of picking and preparation was a common penal occupation in prisons and workhouses.

In modern times, the fibrous material used in oakum is derived from virgin hemp or jute. The fibers are impregnated with tar or a tar-like substance, traditionally pine tar (also called 'Stockholm tar'), an amber-colored pitch made from pine sap. Petroleum byproducts can be utilized for a tar-like substance that can also be used for modern oakum. White oakum is made from untarred material.”



A long thin,  often wooden,  device with a handhold (grip) at one end and a flat,  or shaped,  blade at the other.   They are used in pairs,  extending from the sides of a small boat,  to propel the boat through the water.   The loom,  between the handhold and the blade,  is held to the boat in a crutch or rowlock.

Occasionally,  a single oar may be deployed over the stern,  in a crutch in the transom and the boat moved forward by sculling.

Lin and Larry Pardey handled their heavy,  27' cruising yacht with a single sweep (a long oar) over one side,  adjusting the rudder and the stroke to keep the boat on course.

See Scull,  Ro,  Yuloh.


The North American word for rowlock or crutch.


On this synoptic chart of the North Atlantic there is a deep depression to the SE of Greenland which has three frontal systems:  The occlusions are blue lines with semicircles and triangles.

Occluded front

Cold fronts (blue lines with blue triangles) usually move around depressions faster than warm fronts (red lines with red semicircles),  and so overtake them.   Being more dense,  the colder air moves under the warmer air and displaces it upward:  the warm front and the cold front are then in roughly the same geographic location,  with the warm front at higher altitude.  

The weather around an occluded front shares the characteristics of both the warm and cold fronts.   It may be preceded by continuous rain and followed by cold,  clear air with heavy showers.

A synoptic chart showing two occluded fronts

Referring to the light on a buoy or lighthouse which is on except for short periods when it is off.   The periods of darkness are sometimes called ‘dark flashes’.

Oc G (2) 10s means a green light (and therefore a SHM in IALA-A,  a PHM in IALA-B) which is mostly on but occults (goes out) twice every 10 seconds.



A large body of saline water not surrounded by land.

The Atlantic is an ocean,  the North Sea is a sea.

The five oceans are the Pacific,  the Atlantic,  the Indian,  the Southern and the Arctic oceans


When a ship is abreast of,  or near something:  "We were off Cape Finisterre." means that the Cape could be seen on the beam.

A ship which is 'off and on',  beating to windward,  approaches the land on one board and moves away from it (making an offing) on the other.

"Nothing off" is an instruction to the helmsman not to allow the vessel to bear away or fall off the wind.



Some distance from the land.   Typically,  a ship is in the offing when it can be seen from the shore.   The skipper of a boat on a lee shore would be anxious to 'make an offing':  to get further from the land.


A person who has a position of authority in an hierarchical organization such as a navy.   An officer receives his or her commission from the Sovereign or head of state.

A flag officer is a commissioned officer in a nation's armed forces senior enough to be entitled to fly a flag to mark the position from which the officer exercises command.

The term is used differently in different countries:

In many countries, a flag officer is a senior officer of the navy, specifically those who hold any of the admiral ranks; the term may or may not include the rank of commodore.


An offset is a number in a table of offsets which describes the distance of a point from a reference line such as a centreline or waterline or baseline.   In the diagram the table of offsets gives the same information as the line drawings:  both describe the shape and dimensions of the Rushton catboat.

Lines plans with a table of offsets

n   More than 12 miles from the shore.   Outside the national boundary.

adj   An offshore wind blows away from the shore,  which then becomes a relatively safe weather shore (The shore is on the weather side of the vessel;  a lee shore is to leeward of the vessel).

See Onshore.

Off the wind

The wind is aft of the beam.


"Oilies",  "foulies".   A suit of waterproof clothing worn by sailors.   The original oilskins were oiled skins of,  e.g.,  seals.   These were replaced by oiled,  or tarred,  tarpaulin (canvas) and now (early C21) by complex,  petroleum derived fabrics.

Old Man

Crew slang for the Captain.

Old Salt

Slang for an experienced sailor.


adj   An onshore wind blows toward the shore,  which then becomes a lee-shore and,  in any strong wind,  a dangerous place to sail.

See Offshore.

On the wind

The wind is forward of the beam.


Officer of the watch.   The person for the time being in charge of the deck.


n   An instruction,  given by a more senior person in the armed forces,  which must be carried out.

n   A tidy arrangement of ideas or materials which thereby are readily accessible.


A general name for every kind of artillery used in war.

An ordinance is 'an authoritative order or instruction',  as might be issued by a religious order.


The East.

The countries to the East.


To align with.

To point in the correct direction.


The lowest deck of a (sailing) warship,  where the cables,  and belongings not often needed on the voyage,  were stored.


A mechanical device,  with spheres to represent the sun and planets,  to show the movements of the heavenly bodies.

Originally,  a planetarium.   Modern-day planetaria use instruments which project narrow beams of light onto the inside of an hemispherical dome representing the sky.



Outside the board;  outside the ship;  not within the ship.

Outboard engine (or motor)

A propulsion device which incorporates an engine,  gearbox,  shaft and propeller in one portable or transportable unit,  and which is designed to be clamped to the transom of a boat and which can, theoretically,  be removed or reinstated at will.   Typically,  the engine itself is located high,  at the level of the top of the transom.   The drive (propeller) shaft is vertical to a gearbox and propeller under water,  below the level of the transom.   The whole device can be tilted to bring the propeller clear of the water.   The boat is steered by rotating the entire outboard unit on its vertical axis,  rarely with a separate rudder.

Small outboard engines (up to about 5 horsepower) conveniently turn a small sailing or rowing dinghy into a powered craft.   This is useful for moving the boat into and out of a harbour or marina,  and for getting home when the wind fails.   At other times the engine can be removed from the transom and stowed aboard the dinghy or taken home for safe keeping and/or repair.

Larger outboard engines tend to have throttle and steering controls linked to wheels and levers within the boat;  they may be bolted to the transom rather than clamped:  removal of the engine is more complex and time consuming and such motors tend to be left in place. Outboard engines may be installed in a well within the boat.  

A large outboard engine has the single advantage over an inboard engine in that there is no need for watertight through-hull fittings for the propeller shaft,

Outboard engines may be fuelled with gas,  or petrol,  or petroil or electric batteries;  rarely with diesel oil.   The fuel tank may be mounted above the engine or it may be located remotely within the boat.

Electric outboard motor

The motor of an electric outboard is mounted underwater,  closely attached to the propeller

Petrol outboard motor

The 25 horsepower petrol outboard motor is bolted to the stern of FoolHardyToo.   The steering and throttle controls are routed to the wheelhouse.   The fuel tank is in the cockpit,  remote from the motor.

For all practical purposes 'engine' and 'motor' are synonymous.

Wordnet suggests that a motor converts energy into motion;  an engine converts thermal energy into motion.

Stackexchange is clear that motors run on electricity while engines run on combustion,  whether internal or external.

Wikipedia says that "an engine or motor is a machine designed to convert one [?any] form of energy into mechanical energy."

The Latin 'ingenium' meant 'talent,  device',  and used the same root as 'ingenious'.   Hence an 'engine' is a product of ingenuity;  a tool or a weapon;  later a large mechanical weapon (like a trebouchet).   The word was then used for 'steam engines' and 'internal combustion engines'.

The Latin 'movere' meant 'to move' and became the late Middle English 'motor';  a person who imparts movement.  In the 1660s it became an "agent . that produces mechanical motion".  In the mid 19th century it came to mean a device which imparts movement.

One might say that an engine converts energy into movement while a motor makes things move.


The outboard part of an inboard-outboard motor and propeller.   See Sterndrive.


Generally refers to a persons suit of clothes.

At one time meant the expenses of equipping a ship for sea.

To 'outfit' a boat is modern (American) slang for fitting out a boat;  arranging her rigging and furniture.


A line which leads from the clew of the sail to the end of the boom and is used to apply tension to the foot of the sail.

The outhaul often includes a purchase to increase the tension on the foot of the sail.   Not a clew-line (clewlin') which is a line used to haul the clew of a square-rigged sail to the yard above

Clew outhaul and purchase

n   A flotation device extended outboard of a canoe to provide stability.


n   A fitting used to extend a rowlock out beyond the side of,  for example,  a racing shell or eight.

At one time used to describe spars similar to modern-day spreaders.

Outward (bound)

Out of the port or the country.

A vessel 'outward bound'  is leaving the country bound for foreign parts.

Over a barrel

During the Age of Sail miscreant boys were beaten on the buttocks with a cane whilst bent over the barrel of a gun.

You have someone "over a barrel" if they must do your bidding without choice.



Out of the boat and into the water.   See MOB.


Cloudy,  dull weather.   Low level stratus cloud,  perhaps with nimbostratus.   More or less complete cloud cover.   Cloud 8 tenths to 10 tenths.


A series of standing waves which might break in unpredictable directions.

Overfalls typically occur where the tidal stream rises over an underwater ledge and then falls to the deep on the other side,  as off Portland Bill.


The flat surface above people's heads in a confined space below decks.   The underside of the deck above.

An overhead may or may not have a ceiling by having been ceiled.


v   Moving lines through a block by hand when there insufficient wind to pull them through.   In very light winds the friction in the mainsheet blocks may prevent the boom from moving out abeam;  the sheet may then be overhauled by manually pulling the lines through the blocks.

v   To overtake,  perhaps slowly,  another vessel.



Where one vessel  travelling faster than another moves from a position astern to alongside and then ahead.

IRPCS Rule 13 "Overtaking" says

"(a)    . . . any vessel overtaking any other shall keep out of the way of the vessel being overtaken.

 (b)   A vessel shall be deemed to be overtaking when coming up with another from a direction more than 22.5 degrees abaft her beam,  that is,  she would be able to see only the stern light of that vessel . . ."


John Starkie

July 2020

If you disagree,

or can't find a word

please let me know.