Safe harbour,  Safe water mark,  Sagging,  Sail,  Sail loft,  Sailor,  Sail plan,  Samson post,  Sand,  Sandwaves,  SAR,  SatNav,  Scaffie,  Scandalise,  Scantlings,  Scharnow turn,  Schooner,  Scope,  Screw, SCUBA,  Scull,  Scupper,  Scuttle,  Scuttle butt,  Sea,  Sea anchor,  Sea bed,   Sea boots,  Sea chest,  Seam,  Sea state,  Seasickness,  Seaworthy,  Sectored light,  Seize,  Sennet whip,  Sentinel,  Serve,  Set,  Settee,  Sextant,  Shallop,  Shackle,  Sheathing,  Sheave,  Sheer,  Sheet,  Ship,  Shoal,  Shoal draught,  Shore,  Shoulder of mutton,  Shroud,  Sic,  Sidewheel,  Sink,  Skaffie,  Skeg,  Skiff,   Skipper,  Skyscraper,  Slack water,  Slate,  Sling,  Slipway,  Slivit board,  Sloop,   Slush,  Slush fund,    Smack,  Snotter,  Snow,  Soft eye,  Soft shackle,  SOG,  SOLAS, Sole,   SONAR,  Sound,   Sounder,  Sounding the deep,  South,  Sou'wester,  Spanker,  Spar,  Special mark,  Spider band,  Spinnaker,  Spirit room,  Splice,  Splice the mainbrace,  Split lug,  Sponson,  Spray,  Spreader,   Spring,  Sprit,  Spritsail,  Squall,  Square,  Square meal,  Square-rigged,  Squared away,  SS,  SV,  Stability,  Staff,  Stain,  Stall,  Stanchion,  Standard port,  Standing lug,  Standing rigging,  Stand on,  Starboard,  Starter,  Stay,  Staysail,  Steaming light,  Stem,  Step,  Stern,  Stern post,  Sternway,  Stitch and glue,  Stiff,  Storm,  Stow,  Stowaway,  Straight,   Strake,  Stream,  Stretcher,  Strike,  Strip plank,  Studding sail,  STV,  Submarine,   Surge,  Sway,  Sweep,  Swell,  Swim,  Swing,  Swinging circle,  Swing the compass,  Swinging the lead,  Synoptic chart

S   Sierra

My engines are going full astern

Safe harbour

A haven.  A harbour which provides a refuge from bad weather.

Safe Water mark

A buoy which indicates the end (or the beginning) of a channel and the presence,  all round the mark,  of safe water.

The buoy has vertical red and white stripes;  its top mark is a red ball.   The light,  when fitted,  is white and may be Fl.Mo’A’,  or L.Fl.10s,  occulting or isophase.   See lights.

The concept of 'safe water' is relative,  not least to the size of the ship or boat,  and should be interpreted from the chart.   The tiny SWM placed in the river by the yacht club would have no relevance for the 600 ton freighter using the same river.

Trinity House says "Safe Water Marks may be used mid-channel, as a centreline or at the point where land is reached. These buoys indicate the presence of safe, navigable water all around the buoy".


When the peaks of two adjacent waves support the bows and the stern,  and the midships sections deflect downward.

A vessel with little resistance to leeway is said to sag to leeward when on a wind.


n   A sheet of flexible material used by a sailing vessel to convert the movement of the wind into motive force to drive the vessel through the water.
A sail is raised into position by a ha'lyard and (sometimes) brought down by a downhaul.   The angle of the sail to the wind is controlled by a sheet (line).   The forward,  more or less vertical,  edge of a sail is the luff,  the after edge is the leech*.   The bottom,  more or less horizontal,  edge of the sail is the foot.   The top edge of a four sided sail,  the head,  is usually attached to a gaff or a yard.
The forward lower corner of a sail is the tack,  the after lower corner is the clew.   The top corner of a sail is the peak.   The upper forward corner of a four-sided sail is the throat.
The tension in the luff of a sail is a balance between the ha'lyard,  pulling upward,  and either a kicking strap or a tackline (or both),  pulling downward.

The tension in the foot is controlled by an outhaul line at the outboard end of the boom and the attachment of the sail to the mast or the inner end of the boom.


Sails are not parachutes.

The wind flows along both sides (windward and leeward) of a sail from luff to leech.   Because of the angle of the sail to the wind (the angle of attack) and the different speed of the wind on the two sides of the sail the air on the leeward side is at a lower pressure than the air on the windward side:   the sail is drawn (or pushed) toward the lower pressure.   The balancing resistances and forces of the hull and keel result in the boat moving forward.

If the angle of attack is too small there is no pressure difference between the two sides of the sail.

If the angle of attack is too great the wind on the leeward side becomes turbulent,  and the sail stalls.

Crab claw sails and lateen sails are exceptions:  their power depends upon vortex turbulence on the leeward side of the sail,  with a large angle of attack.

Sails are not simple flat,  two-dimensional,  sheets of material;   they are constructed of panels of material joined together so that the sail has a three dimensional shape.   When filled with wind  a sail becomes an aerofoil.

See also Balanced lug,  Bermudan,  Crab claw,  Dipping lugGaff,  Gunter,  Jib,  Lateen,  Leg-o’-mutton,  Raffee,  Settee,  Shoulder o' mutton,  SkyscraperStanding lug,  Spinnaker,  Split lug,  SpritsailSquareStaysail.

*Falconer (in 1815) referred to our luff as a 'foreleech' and to our leech as an 'afterleech',  probably because the two vertical edges of the sails of square-rigged vessels were interchangeable and depended on the tack:  the tack and the clew were also interchangeable.

v   To sail;  to operate a sailing boat;  to use the wind to move a vessel through the water.

More generally,  to operate any vessel.


Sail loft

A large open space,  usually above the workshop,  where sails can be laid out on the floor to be measured,  cut and sewn.   See Loft.

Sail Plan

A set of drawings showing the arrangement of the sails.


Someone who sails;  who travels by water,  or works aboard water-borne vessels.   The vessel need not be powered by sails.   There is an implication of seafolk who are not officers.   See Mariner.


Samson Post

A vertical post set in the centreline of the fore deck used for belaying anchor rodes or mooring warps.

Named after the Biblical strong man betrayed by Delilah.

Not a sampson post.

The workboat Provider is moored to a floating pontoon at Westminster Pier:  the bowline is attached to a metal samson post

Samson post

Small particles of rock composed mostly of silica commonly found on the bed of the sea and on the seashore.

Sand is used in the building industry mixed with cement to form concrete.


Large ripples,  up to several metres in height,  formed in the sand of the seabed by currents (often tides) flowing at right angles to the long axis of the ripple.

In shallow seas,  such as the North Sea,  large sandwaves can significantly reduce the depth available for vessels.

The largest sandwaves,  tens of metres high with wavelengths of hundreds of metres,  occur outside San Francisco Bay;  they are caused by the huge tidal outflow through the narrow entrance to the bay.


An acronym for Search and Rescue.

Both the Royal Air Force and the MCA operate SAR aircraft,  both fixed wing and rotary wing.   They are used to locate vessels which need help and to rescue mariners from stricken vessels.


An abbreviation for Search and Rescue Transponder,  a device for signalling distress and to guide search and rescue teams.

Examples include EPIRB,  PLB.



Satellite Navigation.   The terrestrial equivalent of GNSS (Global navigation and satellite systems)

  1. A Scottish fishing vessel (link).   See fifie,  baldie,  zulu.

  2. A 15ft sailing dinghy with a long keel and two bilge keels and with a single standing lug sail



A way of reducing the effectiveness of a sail quickly.

A Bermudan sail can be scandalised by hauling the topping lift.

A gaff-rigged sail can be scandalised by lowering the peak of the gaff,  or by tricing up the tack.

Brailing a sprit-sail is a form of reefing.


The dimensions of a vessel's individual components.

Scharnow turn

Used by power driven vessels to turn onto a reciprocal course when the point to turn toward (the MOB) is significantly further astern than the radius of the turning circle.

  1. Put the rudder over hard toward the MOB.

  2. After deviating from the original course by about 240 degrees, shift the rudder hard to the opposite side.

  3. When heading about 20 degrees short of the reciprocal course, put the rudder amidships so that vessel will turn onto the reciprocal course.

See also Anderson turn,  Williamson turn,  crash stop.


Originally a two-masted vessel carrying fore-and-aft-rigged sails. The foremast was the shorter of the two. Later, three or more masts were the pattern, with one or more square-rigged topsails added.



The length of rode paid out between the boat and its anchor.

Where the rode is all chain,  the RYA tells us that the scope should be at least  four times the depth of water.  Where the rode is mostly line the scope (it says) should be at least six times the depth.   When deciding the scope attention should be paid to the swinging circle of the boat around its anchor and to the proximity of other boats.

“Chain in the locker is wasted chain”



Slang for propeller.



Self Contained Underwater Breathing Apparatus



n   An oar used over the stern of a boat.

v   To scull.   To move a boat using an oar over the stern.

n   A special type of oar used  by recreational oarsmen in long narrow boats.

Often,  the long narrow boat itself.


Holes in the bulwark or toerail through which water runs overboard from the deck.

Large scuppers may have freeing ports,  which are hinged plates which prevent water boarding the ship but allow it to drain away.



n   A small circular aperture in a deck or bulkhead not intended for the passage of people,   through which powder, etc., may be passed from one deck or compartment to another.

v   To scuttle a vessel is to open holes in the hull so that she sinks.   In wartime,   ships may be scuttled to prevent them being used by the enemy or to block the entrance to a harbour.   In peacetime,  redundant ships may be scuttled to form artificial reefs to provide breeding grounds for marine life and to provide 'wrecks' for recreational diving.


Scuttle butt  

Drinking fountain.

Originally,  a cask (specifically,  a butt) of water on deck,  with a scuttle in the lid and a pannikin,  from which the crew could help themselves.   In relaxed moments,  the crew might gather around the scuttlebutt to gossip and yarn.

A butt (or a pipe) is half a tun,  or two hogsheads:  108 Imperial gallons for ale,  128 Imperial gallons for wine (see cask).

coll:   Shipboard gossip;  "Have you heard the scuttlebutt about the new First Officer?".


n   The water which covers most of the earth,  being salt at about 3.5%.

n   A body of saline water largely surrounded by land.   the Atlantic Ocean is too big to be a sea.   The North Sea is too small to be an ocean.

Sea anchor

A kind of parachute,  deployed from one of the bows of a boat into the water,  which holds the head of the boat to windward.

A drogue is deployed from the stern and is used to slow the boat when running downwind.

See Anchor,  Heave to.

Hove to with a sea anchor from the port bow
Sea bed

The bottom of the sea.

The nature of the sea bed is described on charts as abbreviations;  eg cS means 'coarse sand';  S sh means 'sand and shell'.

Sea boots

High,  waterproof boots,  worn by sailors.

Sea chest

A box with a hinged lid in which a seaman kept his personal effects.

See also Chest.


The line along which two materials are joined,  often by means of a needle and thread or yarn.

Primitive craft such as coracles and curragh were made of animal skins sewn together at the seams with ligaments or skin,  sometimes with vegetable fibres.

The planks of clinker-built craft are joined at the seams with clench nails or copper nails and roves.

The planks of carvel-built boats are not sewn together;  each plank is nailed to a rib or frame close to the next plank.   The gaps,  or seams,  between the planks were once caulked with wax and moss,  then with cotton and now with plastic.

The planks of strip-planked boats were once nailed together,  and to the ribs,  with iron nails.   The seams might now be closed with plastic nails or with glue.

Fibreglass boats have few seams,  typically between the hull moulding and the deck moulding;  these are closed and sealed with synthetic resins.

The panels of sails are sewn together at the seams with modern plastic-derived threads.

Sea state

The general appearance of the surface of the sea.

The sea state is affected by several things.

  • The strength of the wind:  the stronger the wind the higher the waves.   The higher the waves the more likely they are to break.   Strong winds blow the crests of the waves over,  causing them to break and creating "white horses".   Very strong winds blow the tops of the waves into spray.

The Beaufort scale of wind strength was devised to measure the strength (not speed) of the wind in the sails of square-rigged ships.   In the early 20th Century it was changed to be a measure of the sea state.

Force 1 (light airs) cause ripples on the surface.

Force 2 (Light breeze) causes small wavelets.

Force 3 (Gentle breeze) causes occasional breaking crests (white horses).

Force 4 (Moderate wind) causes frequent white horses (breaking crests).

Force 5 (Fresh breeze) causes moderate waves with many white crests.

Force 6 (Strong breeze (a yachtsman's gale)) cause large waves with white foam crests.

Force 7 (near gale) causes the sea to heap up with spray and breaking waves with foam blowing in streaks.

Force 8 (Gale) gives moderately high waves with breaking crests.

Force 9 (Severe gale) gives high waves with spray reducing visibility

Force 10 (Storm) gives very high waves with long breaking crests.

Force 11 (Violent storm) gives exceptionally high waves with continuously breaking crests and spray severely reducing visibility.

Force 12 (Hurricane)

  • The fetch of the wind (the distance it has travelled over the sea):   the longer the fetch the higher the waves.

  • Change of wind:  a strong wind for a period of time will raise waves (a swell) proportionate to the strength and the fetch,  with the 'wave train' at right angles to the direction of the wind.   If the wind changes direction a new wave train will develop in a different direction from the original:  the sea will become confused and irregular.

  • The depth of water:  as the wave train approaches a lee shore and the depth of water decreases to become about equal to the wave height,  the waves begin to break.   On a gently sloping beach this can result in the curling,  overarching breakers which surfers enjoy.   In shallow seas,  such as the North Sea,  as waves increase in height they become shorter in wave length and their faces become steeper.

  • The tide:  wind in the same direction as the tide causes smaller waves and a smoother sea.   Wind against the tide causes a short,  steep sea;  the wavelength is shorter,  the waves are higher and the faces are steeper.



Nausea and vomiting induced by the movement of a vessel at sea.

There are many folk and patent remedies for seasickness;  different remedies seem to work for different people.


Capable of sailing safely at sea.

Certificated for sailing.

Sectored light

A sectored light,  of a lighthouse, shows different colours of light in different directions.

See chart.



v  To bind two lines together with many turns of small stuff.

The seizing may be frapped with two or more turns of the same small stuff at right angles.

The photograph shows a thicker line whipped with small stuff and a thinner line turned into an eye,  the two parts being seized together with small stuff and frapped.

Whipping and seizing
Sennet whip

A sennet is a plait or weave of cordage or rawhide with three,  four or more strands.

A sennet whip was usually of plaited rawhide.



A hook invented by Mr. W Etty Potter for attaching a weight (a chum,  kellet or angel) to an anchor rode.   The diagram by Francis B Cooke shows the principle.

Ancor sentinel

vb   To place something before someone.   Food is placed on a plate in front of a restaurant diner.   A shop assistant might place requested items on the counter in front of a customer.

vb   To wind small stuff tightly around a line or a wormed line or splice to hold the worming in place.   The small stuff might once have been tarred marline but is now more likely to be waxed nylon thread.   The serving may be parcelled with canvas.



n   The direction of the tidal stream,  which may be found from a table of tidal diamonds or from a tidal stream atlas.   Measured in degrees True.

The table of diamonds and the tidal atlas are arranged in 1-hour periods either side of the High Water hour of the reference port.   The figures imply that the set and drift are constant during each tidal hour and that they change abruptly at the end (and beginning) of each hour;  in fact,  there is a progressive change from one hour to the next.

The course which a vessel makes over the ground is the resultant of its heading,  speed and leeway,  and the set and drift of the tide.

See Stream.

vb   To set the sails is to unfurl them from the yards or booms,  to raise them with the ha'lyards and to adjust them with the sheets so that they move the vessel efficiently.


A sail similar to a lateen,  with its long,  angled yard and long,  boomless foot,  but with a significant vertical luff unsupported by a spar.


An instrument comprised of mirrors and a graduated scale,  used to measure the angle of the sun or a star above the horizon.

In conjunction with an accurate timepiece and tables of the positions of the sun and stars it can be used to calculate a vessel's position.

Sextant & Octant

A device for linking two parts,  such as links of a chain,  a cringle and a sheet,  a stay and a stemhead fitting,  together.

Shackle between anchor and chain

Referring to a rig,  rather than a vessel.

There are two masts,  both with sprit sails,  the after mast being taller than the forward mast.

The picture is taken from  'Wooden Boat' 60,  p 70

Shallop rig.png


A covering of material (originally lead,  then copper, felt, etc.,  but now more probably fibreglass) placed over a portion of the ship’s surface to protect it. Copper sheathing covered the immersed part of a wooden ship to protect it from fouling with marine growth.   Lead and copper (and silver!) are toxic to living things and kill worms,  barnacles and weeds.   Modern antifouling paints consist of epoxy resin and finely-divided copper.

When tarred or varnished canvas,  or similar,  is wrapped tightly around a wire or rope stay it is known as 'parcelling'.


The grooved wheel around which the rope moves in a pulley block.

See Heart,  Dumb sheave.


The junction of the deck and the topsides.

The sheerclamp is a timber piece linking the inside tops of the frames together,  from stem to stern,  and supporting the deck beams.

The sheerstrake is the topmost run of planking from stem to stern.

A sheerwale is a strake,  thicker than the rest of the planking,  at the sheerline.

'Sheer' is often used to describe the curvature of the sheerstrake or gunwale of a vessel.


A line which controls the clew of a sail.   Joshua Slocum referred to Spray's sheets as 'sheet-ropes'.

The sheet-line of a square-rigged sail is attached to a cringle at the lower,  aftermost (for the time being) corner of the sail.   On all sails except the course it runs to a block near the end of the yard below,  along the yard to the mast and down the mast to the fife-rail.

When the ship is put onto the other tack the erstwhile sheet-line becomes a tack-line holding the luff of the sail taut.

The course sail sheet-line runs from the aftermost lower corner of the sail to a block near the rail or the side-deck.   The corresponding line at the forward end of the foot of the course sail is tacked down to a block on the beam forward of the mast.

(Also attached to the clew and the tack of a square' sail are clewlin’s which are used to haul the clews up to the yard above when the sail is furled or handed.)


A staysail or jib has two sheet-lines (or sheets),  both attached to the same clew cringle.   The one to leeward is hauled taut by a block (or,  more usually,  a winch) near the leeward beam.   The other is loose and idle.


A boomed fore-and-aft mainsail has an outhaul (line) (used to increase the tension on the foot of the sail) attached to the clew cringle and passing through a block near the end of the boom.   The sheet is attached (often by a complex system of pulley blocks) to the boom,  not the sail.   In this respect the sheet (line) of a fore-and-aft mainsail is more akin to the brace of a square-rigged yard,  or perhaps to a vang.

A boomless fore-and-aft mainsail has its sheet attached to the clew cringle.



A large sea-going vessel.

Coll   A vessel which carries one or more boats.

alt   A three masted sailing vessel with square-rigged sails on all three masts.

See Brig,  schooner,  sloop.


There are,  and have been, very many types of ships,  such as galleys,  galleons,  destroyers,  frigates . .

It’s not always clear how the names arose,  and the definitions have never remained constant.   A sailing frigate was simply a small fast ship with few guns,  quite different from a 21st Century frigate.   The best definition of frigate might be that such ships mounted their principal armament on a single continuous upper deck.   It seemed that the type name stuck while the ship itself evolved through the centuries.

v  To ship something is to deploy it.   An oarsman would ship his oars ready to move his boat.



A shallow area of water,  presenting a hazard to navigation.

See Horse.

Shoal draught

Shallow draught,  so as to sail in shoal (or shallow) waters.


n   The land next to the sea;  the beach.   The edge of the land.

n   A stout post used as a temporary support or brace.

v   To prop up or support (a boat) using shores.


Shoulder of mutton

A triangular sail attached at its luff to a mast.   The angle of the tack is not square,  as a Bermudan sail's is,  but acute,  so that the clew is higher than the tack;  the foot and the leech may be of equal length.   The clew may or may not be extended by a sprit-boom,  controlled at the mast by a snotter.   The sheet is attached either to the clew or to the tip of the sprit-boom.   See Leg of mutton.



A stay which supports the mast laterally.



Latin:  sic erat scriptum:  “thus was it written”.

It usually means “The chap who wrote this spelled it this way,  but I don’t agree.”


The paddle wheels at the sides of a paddle steamer.

Typical Missisipi paddlesteamers had a single large paddle wheel at the stern.

The paddle ships which plied the British Isles had one sidewheel on each side of the vessel.


v   To sink a vessel is to fill it with water so that it falls to the sea bottom.   Vessels are sunk (caused to sink) by striking rocks and becoming damaged or by enemy action.

Deliberately to fill one's own vessel with water so that it sinks to the bottom is to scuttle it.

n   The round or rectangular container where dishes,  hands and vegetables are washed.   A sink usually has one or more taps providing water (sometimes hot and cold) and a drain.


A vertical fin below the keel,  at the stern,  in front of the rudder.   It might form an attachment for rudder mountings,  or it might form the third 'leg' of a tripod for a twin-keel vessel to take the ground.   On a dinghy,  a skeg provides directional stability.   Its area contributes a little frictional resistance to the flow of water so that the stern trails behind the stem.


Falconer,  in 1815, defined a skiff as "a small light boat resembling a yawl,  also a wherry without masts or sails,  usually employed to pass a river".

Falconer's yawl had four to six oars and no sails.

Now (early 21st century) it is a small light rowing boat,  sometimes with sails.



A person (not necessarily qualified) in charge of a boat.

Any person in charge of a small group of people.   Scoutmasters are called 'skipper'.



According to Falconer,  "a small triangular sail . . . sometimes set above the royal."

Slack water

Slack tide.   When the tide is neither rising nor falling,  for a brief period at high water and at low water.   When the drift of the tidal stream is minimal,  perhaps before it reverses its set.

In sounds such as the Menai Straights there is a period of slack water,  when the streams from East and West meet and the level is still rising or falling.



A piece of slate upon which the skipper's instructions to the helmsman are written with a chalk.   A modern boat might use a small whiteboard and marker.

A modern equivalent is the slate of the clapper-board used to identify a scene in a film. 

At the end of a watch the details would be entered into the logbook and the slate would be wiped clean.  Each watch would start with a "clean slate".


n   A bight of line passed around an object to raise or lower it.

The slings of a square-rigged ship support a yard so that it remains horizontal (square to the mast).

v   To use a sling to hoist or lower something.

coll   A sailor might sling his hammock,  that is,  suspend it from the hooks,  in the 'tween decks.

Someone asked to leave might be told to "sling yer 'ook";   'hook' being slang for an anchor.



A slope,  or ramp,  into the water for launching and recovering small boats.

The slope,  often with a railway and slides,  for launching newly-built ships.

Slivit board

A plank or board hung from the boat outside its fenders to keep the boat away from widely spaced piles.


Sailing boats are now (early C21) defined by their rig.   In earlier centuries they were defined more by their purpose or size.   As the purpose,  size and rig evolved over decades and centuries names tended to linger,  so that in two different centuries boats with the same type-name might be very different.


A 21st Century sloop has two fore-and-aft sails.   The mainsail is usually Bermudan,  but may be gaff or gunter,  occasionally a sprit-sail.  The foresail is hanked to a forestay between the stemhead and the mast.   The foresail may be small,  in that it barely fills the fore triangle between the mast and the forestay,  or its clew may extend well abaft the mast.

The mast is usually supported by Marconi stays.

Sloops often deploy a spinnaker or cruising chute when sailing downwind.


In 1867 a sloop was a vessel similar to a modern-day cutter,  with the bowsprit fixed,  not running,  the jib set on a stay with hanks and a gaff mainsail.

A sloop of war is not to be confused with a sloop.

In the Royal Navy the rating of a ship depended on the rank of the officer in command:  the frigate Blossom was rated a ship when commanded by a captain and,  on her next cruise,  was rated a sloop when commanded by a commander.   A sloop of war carried 10 to 18 guns and might be rigged as a ship,  or a brig,  a schooner or a cutter;  Blossom was ship-rigged. 

Gaff-rigged sloop


The grease and fat left from boiling meat;  used for greasing running rigging.

Slush Fund

The cook (and the boatswain) would sell the slush ashore and use the money for the benefit of the crew.


A cutter-rigged fishing vessel,  with a long wide counter used on the East coast of England.   Most smacks have now (early C21) been converted into pleasure yachts.

CK363 (on the right) has reeved her bowsprit inboard so as not to inconvenience other vessels in the roadstead;  as a result,  her forestay,  bobstay and whisker stays are slack.

East Coast smack at West Mersea

A wire or line which supports and controls the inboard (mast) end of a sprit or sprit-boom.

The spreet of the Thames barge Hydrogen (on the left) is supported by a snotter consisting of a large chain painted white.

The sprit of the SOF dinghy (on the right) is supported by a short length of line.

Spreet & snotter on a Thames barge
Sprit snotter

n   A brig with an extra mast (the snow mast) behind the main mast to carry the spanker.

n   Water which precipitates from clouds in the form of grouped hexagonal crystals,  and which forms white layers of crystalline water on exposed surfaces.

The delight of children;  the bane of travellers.

Soft eye

An eye splice without a thimble.

Soft shackle

A shackle made of braided line,  spliced.

Soft shackle
Soft eye


Speed over the Ground.   Measured in knots (nautical miles per hour).

The ship’s log measures speed through the water;   SOG must be calculated using set and drift of the tide,  and leeway.

A chartplotter,  or GNSS instrument,  measures SOG directly.



International Convention for the Safety Of Life at Sea:  a document which recommends  and mandates safety procedures for ships and boats.

Chapter V,  Annexe A23 is relevant to yachtsmen,  although the RYA has negotiated a watered-down version for pleasure craft in the UK.


n   The 'floor' of the cabin or cockpit of a small boat.

n   A kind of flatfish,  prized for its delicate taste.



SOund Navigation And Ranging.   A transceiver in the hull of a vessel sends sound signals into the water and detects the echoes which return.   An electronic device measures the time taken for the echo to return and displays the answer as range,  the distance of the object which caused the echo,  and direction.

See Echo Sounder.

The SONAR of a submarine sends sound signals in all direction and detects both the distance and the direction of the echo.


n   A noise.   What is heard.

n   A narrow channel of water (across which one might swim) from the sea,  separating two islands.   From the Old Norse 'a straight' or 'swimming'.   The Sound of Mull is a narrow channel of sea between the island of Mull and the mainland of Scotland.

adj   Perfect.   Without defect.

vb   To make a noise,  as in speaking,  playing music or using an echo-sounder.

vb   To fathom,  probe,  measure the depth,  especially of the sea,  from the Old English 'sund',  meaning 'water' or 'sea'.



A device for measuring the depth of water.

See also Echo sounder,  Lead line,  Fish finder.

Sounding the deep

Measuring the depth of the sea,  or 'plumbing the depth'.

The 'deep' was sounded with a lead-line,  or sounding-line,  from at least the time of St Paul in the 1st century AD (Acts xxvii)   The depth of water is now measured with an echo-sounder.

An echo sounder sends a short duration of noise down to the sea bottom,  and detects the echo which is returned.   The time between sending the sound and receiving the echo is proportional to the depth of water;  this is calculated by the electronics inside the instrument.

The word 'sound'  has had,  and has,  several meanings,  two of which are:

n   A noise,  as heard by the ear.

vb   From the old Germanic source that yielded the Old English 'sund',  meaning 'water' or 'sea'.

'The deep',  in Medieval times,  was 'unknown',  'mysterious'.   The concept of depth,  being the distance from the sea surface to the sea bottom,  was equally mysterious.   The word (and the concept) was also applied to the points on a lead line where there was no mark.   See Marks and deeps.



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

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

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


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

It follows that a magnetic compass points to magnetic South and not to true South;  the variation* between true South and magnetic South 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 concept.

South magnetic Pole

A waterproof hat,  with a gutter around the brim and a long brim behind to drain water away from the wearer's head and neck.

A southwesterly storm;  a strong wind from the South West.



A fore-and-aft,  usually gaffsail set abaft the mizzen mast of a square rigged vessel.   Most useful when steering,  tacking or wearing ship.   Also known as a driver.



A pole,  such as a yard,  mast,  sprit or boom to which a sail is attached.

Spider band

An iron band around a mast to carry the belaying pins.

Special mark

A yellow buoy used to mark features not marked by other buoys.   These include administrative areas,  anchoragesmoorings,  water skiing areas,  bathing areas,  marine farms,  pipelines,  outfalls,  cables.

The buoy is yellow and the top mark is a yellow diagonal cross.   The light is yellow and may flash any sequence not used by white lights.



A large,  lightweight triangular sail,  with a significant bunt,  used by modern sloops to sail downwind.

The head (peak) of the sail is hauled to the top of the mast by the spinnaker ha'lyard.   The tack and the clew are interchangeable.

With the wind on the port side of the boat (the port tack),  the wind flows across the the sail from the luff,  on the port side,  to the leech,  on the starboard side,  creating a low-pressure area ahead of the sail.   The spinnaker pole,  from the mast to the tack of the spinnaker,  extends the foot of the sail to windward,  and is held by a guy-line (a brace?) to the port quarter.   The clew is held and controlled by a guy-line (a sheet) to the starboard quarter.

The tack is difficult to change by turning the boat head to wind:  the sail tends to wrap itself around the forestay and become uncontrollable.

The tack is changed by gybing the boat and by moving the spinnaker pole from the previous tack to the previous clew.

A spinnaker behaves in much the same way as a square-rigged sail.   It is physically different in that there is no yard at the head (which is peaked rather like a skyscraper or raffee);  where a course sail might have a cro'jack yard from tack to clew a spinnaker has a boom from the tack to the mast.

Cooke suggests that the sail derived its name from the yacht Sphinx,  which the crew called "Spinks": its sail became known as a 'spinker' and then a 'spinnaker'.   Before that,  in a slightly different form,  and abaft the forestay rather than before,  it was known as a 'balloon sail'.


Spirit room

The purser's storeroom.

Originally the room where the spirits (mostly rum) were stored.


A method of weaving,  or interleaving,  the strands of a rope to join two ropes or to form a loop or an eye.

Splice the mainbrace

A brace is a line from a yardarm to a point on the sheer further aft;  it is used,  in conjunction with those of other yards and the other ends of the yards,  to alter the angle of the square yards when trimming sails.

The braces might need to be spliced (repaired,  rejoined) when they have been shot through in battle.

It was a colloquial expression,  used as an order to issue the rum ration,  or perhaps an extra ration as a reward.

Split lug

There are two four-sided sails,  one before the mast,  the other abaft the mast.   Both sails are held aloft by the same fore-and-aft,  oblique yard.

The fore-sail is tacked down to the stemhead or one of the bows.   Its clew has two sheets,  one leading aft to each beam.   It may or may not have a boom along its foot.

The after-sail is laced along its luff to the mast and tacked down to the heel of the mast.   Its clew may or may not be extended by a boom with a gooseneck or jaws at the mast.   The sheet is attached to either the clew or to the tip of the boom.

Folkard suggested that the split lug sail was created by a young lieutenant from a balance (what we would now call a dipping) lug sail by cutting a sail close to the mast,  attaching a sheet to the fore part and lacing the after part to the mast.   He did so because changing the tack of his balance (our dipping) lug was difficult for a novice crew.


Extra flotation at the side of the hull to carry equipment or to provide additional buoyancy.

See Camel.


Drops of seawater blown by the wind from the crests of breaking waves or when the water is pushed violently upward by the stem and bows of a vessel.


A spar on a sailing ship used to carry the shrouds outward to a better angle to support the mast.


n   Spring tide:  the highest range of tide within a fortnight.   The lowest range of tide within the fortnight is a Neap tide.

n   A line from a quarter or a bow to a shore-side bollard amidships to prevent the boat surging fore and aft. If the boat has a centre cleat amidships then the mooring springs may run from the centre cleat to shore bollards forward and aft.   In the diagram below,  3 and 4 are springs.

n   A line from a quarter to the anchor rode to enable the boat to be turned across the wind or tide.

n   A season of the year including (in the Northern hemisphere) March,  April and May.


A spar (other than a mast,  boom or yard) which extends a sail.

A sprit-boom carries the clew of a sail out horizontally,  in much the same way as a boom,  except that a spritboom is held to the mast by a snotter and a boom is attached to the mast (or even the deck) by a gooseneck or by jaws.

A bow-sprit carries the tack(s) of one or several sails forward ahead of the stem.

A sprit (or spreet) carries the peak of a four-sided sail above and abaft the mast head.

A boomkin might be acknowledged as a form of sprit which carries the braces further outboard,  or the mizzen sheet further aft.

Thames sailing barge with bowsprit and spreet

This Thames sailing barge,  moored at West Mersea without her sails,  has her bowsprit steeved up at a steep angle and her spreet rigged.

Thames sailing barge

This Thames sailing barge,  moored alongside at Maldon,  has her bowsprit steeved almost vertical.

Her brailed mainsail is held upward and outward by her spreet.   A pair of vangs can be seen extending from the top of the spreet to the quarters.


n   A square-rigged sail on a yard below the bowsprit.

n   A four sided sail extended by a sprit (or spreet).

This sailing boat carries a spritsail supported at the luff by the mast.

The sprit is supported at the heel of the mast by a snotter,  which also adjusts the tension,  and therefore the shape,  of the sail;  the sprit extends the peak of the sail upward and aft.

A spritsail rarely has a boom along its foot and is therefore difficult to set well on all points of sail.   Without a vang the peak of the sprit may sag to leeward.

It is brailed with lines from the top of the mast to the clew,  or the leech.   The brail draws the clew up to the sprit and may then draw the sprit to the mast.


Spritsails evolved as working sails on oyster boats and Thames barges on the East coast of England.   The height of the sail was advantageous,  especially in the East Coast rivers,  by being above the banks and trees.     The huge power of the sail can be reduced to nothing in moments by brailing. 

Sprit-sail dinghy

This sprit-sail dinghy has her sail extended upward by a spreet held at the mast by a snotter.   This sail has no boom,  no vangs  and no brail.


A sudden,  possibly short-lived,  increase in wind strength often associated with precipitation and a change of wind direction.



adj   An adjective describing a geometric figure with four sides of equal length,  each connected to two adjacent sides at right angles.

n   A right angle (an angle of 90°),  or an instrument for measuring right angles.

As in square sail,  refers not to the shape of the sails (which are never square!) but to the fact that the yards (and therefore the heads of the sails) are at right angles (square) to the mast.   'Square sail' is a verbal contraction of 'square-rigged sail'.

Square meal

A good meal;  enough food.   During the Age of Sail (and since) food aboard ship was more plentiful (and possibly better) than food ashore.

Shipboard plates were square wooden plates.


Square rigged

A vessel is square-rigged when some or all of its sails are carried on yards at right angles (square) to the mast,  but not always square to the centre line of the vessel.

Chatterton wrote,  in 1909,  that "Manwayring,  who fought in the English Fleet against the Armada . . ." referred to 'square-rigged' as 'cross-sail'.

Squared away

Running downwind,  the yards of a square-rigged vessel would be held square to both the mast and the centre line.

Smart,  tidy,  correctly stowed.   All difficulties resolved.


Steam Ship.   A 'steamer'

A ship operated by high-pressure steam.

Water is boiled in a vessel (a boiler) constructed to withstand high pressures.   The steam drives pistons within cylinders or turbines.   The movement of the pistons or the rotation of the turbines rotates the paddle wheel(s) or propellers which move the ship.   The steam may also be used to drive electricity generators and other machinery.

The heat to boil the water was originally generated by burning wood and,  later,  coal.   Most 20th Century ships burned oil,  often heavy oil,  to boil the water.   Some modern ships and submarine (vessels) use nuclear power to boil water.


Sailing vessel.   A vessel which is moved through the water by the force of wind acting on its sails.



The tendency of a vessel to become upright when heeled.

Measurements of static stability assume the boat to be stationary in calm water & no wind and relate the boat's centre of gravity (CG) to its centre of buoyancy (CB)   The Angle of Vanishing Stability (AVS) is the angle of heel (at rest in calm water and no wind) at which the boat shows no tendency either to right or to capsize:  its CG and CB are vertically exactly in line.

Measurements of dynamic stability,  with the boat moving through waves and wind,  are more difficult.



A post which supports the guardwires.

Originally the posts which supported the deck beams in the centre line.


n   The group of people which operates a unit,  such as a ship or company or office.


n   A pole or stick which carries a flag.



n   A dye used to add colour and a degree of waterproofing to wood.


To stop,  or to become ineffective.

A sail stalls when,  at a high angle of attack,   the wind on its leeward face becomes turbulent and the pressure difference between the two faces is insufficient to drive the boat.

A rudder stalls when,  at a high angle of attack,  the water on its leeward face becomes turbulent and the rudder becomes ineffective.

A rudder can also stall at low angles of attack if the flow of water across its surface is too slow.   This can happen when the speed through the water is very slow;  when the propeller is not turning or when running downwind the water in a wave overtakes the boat.


Standard Port

A port for which there are tide tables.

A secondary port does not have tide tables,  but has a table of differences from a nearby standard port.

Standing lug

The four-sided sail is bent to a yard which is fore-and-aft,  and oblique,  not square to the mast.   The tack (or fore-clew) is tacked down close to the heel of the mast or to the boom.   The clew (after-clew) may be extended by a boom held at the mast by a goose-neck or jaws.   the sheet is attached to the clew or tip of the boom.   See Lugsail.


Standing rigging

The stays and shrouds which hold up the masts and spars.

See Running rigging.

Stand on

v   To maintain the same course and speed.

Where there is potential for a collision between two vessels the IRPCS provides rules (Rule 11 to Rule 18) for which is the 'stand on' vessel and which is the 'give way' vessel.   It also provides rules (Rule 16 and Rule 17) for the action to be taken by the stand on vessel and by the give way vessel.



The right hand side of the boat,  looking forward.

Viking long-boats were pointed at both ends,  so the steering oar was mounted on the right hand side (because most men were right-handed) near the stern:  this side became known as the steering board,  or st’(a)r’board.

A vessel on the starboard tack has the wind on its starboard side.

On a square-rigged vessel the starboard clew of the course sails becomes the tack,  and is tacked down to a bow.


A length of knotted line carried by petty officers on ships of the line to persuade the men to work;  to 'start' them moving.



n   The wire or line between the stem,  stern & the sides of the boat and points high up the mast which support the mast.   Those at the sides may be called shrouds:  those at the stem or from the foredeck are forestays:  those at the stern are called backstays.   Adjustable backstays may be preventer backstays or running backstays.

v   To stay a vessel is to change from one tack to another.   A vessel 'in stays' has come to the eye of the wind but has failed to fall onto the new tack;  in irons.   a vessel which fails to tack, and falls back onto the original tack,  has 'missed stays'.



Stays'l:  a sail which is carried on a stay,  very rarely on a backstay.   Jibsgenoas,  are stays’ls carried on a forestay.

Flying jibs and cruising ’chutes are carried,  not on a stay,  but on their own ha’lyard and luff wire,  as are spinnakers.


Steaming light

The masthead light of the IRPCS.

IRPCS,  Rule 21 "Definitions" says:

   "(a)   "Masthead light" means a white light placed over the fore and aft centre line of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either (both;  each) side of the vessel."

IRPCS,  Rule 23 "Power-driven vessels under way" says:

   "(a)   A power-driven vessel under way shall exhibit:

          (i)   a masthead light forward;

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

A power driven vessel of less than 50m in length need carry only one masthead light.

A masthead light is not at the top of the mast,  but ahead of it.   It is not an anchor light or a tricolour light.   "Steaming" refers to the power driving the vessel which would,  originally,  have been high-pressure steam in an external combustion engine.

A vessel with sails set and its engine running is to be thought of as a power-driven vessel (see Rule 25 (e)).



The most forward part of the boat,  from the deck to the water line and below,  between the bows.

The structural member which links the bows together and to the keel.



The specially strengthened and shaped part of the deck,  keel or keelson on which the heel of the mast rests.



The back of the boat.   The end farthest from the stem.

Stern post

The more-or-less vertical post at the stern which links the keel to,  and supports,  the transom.


A boat has 'way' when it is moving through the water.   When it is moving astern,  it has sternway.

Not to be confused with the IRPCS definition of 'under way'.

See Clubhaul.



A vessel is stiff when she can carry a lot of sail without heeling too far.

See tender.

Stitch and glue

A method of building small boats in which the (plywood) planks are temporarily sewn together with copper wire or cable ties and then glued together with epoxy resin.


Winds of Force 10.


v   To put away;  to secure;  to make tidy.

n   Sometimes used as a noun in the context of a sail stowed (furled) onto a yard or boom.   A sea-stow is not as tidy or tight as a harbour-stow.


Someone who hides aboard a vessel in order to be carried to another port without authority or payment.


A narrow channel of water (perhaps from the sea) (across which one might swim).   From the Old Norse and Old English 'sund',  'swimming (across a narrow channel)'.



Or Streak.

A continuous run of planking from stem to stern.

The individual planks of a strake may be joined together with butt joints or scarph joints.

See Wale.



A flow of water,  as in a river or tideway.

The flow of the tide,  as distinct from the rise and fall of the tide.

The tidal stream has direction and rate.   The direction in which the tidal stream flows (the set of the tide) is measured in degrees True.   The rate of flow (the drift of the tide) is measured in knots.

Values for tidal streams are shown in Tidal Stream Atlases and in the Table of Diamonds on Admiralty charts for one-hour periods relative to the Reference Port of the chart or atlas.   It is assumed (although it is not true) that the stream remains constant during the hour and changes abruptly at the cusp.

The High Water hour is the hour either side of the time of High Water at the Reference Port (The HW hour begins 30 minutes before the time of HW and ends 30 minutes after the time of HW).   The previous hour is the -1 hour:  the following hour is the +1 hour,  and so on.

In the stream atlas,  the set of the tide for the hour is given as the direction of an arrow which can be measured with parallel rules or a plotter:  the drift is given as two numbers,  in tenths of a knot.   The first number is the drift at the neap tide,   the second at the spring tide;  the dot (or comma) is not a decimal,  it is the point where the stream is measured.

In the Table of Diamonds on the chart,  the set for the hour is given in degrees True,  the drift is two numbers;  the first is the drift at the Spring tide,  the second is the drift at the Neap tide.

There are more dots than diamonds,  but each diamond represents a dot.



n   A batten running along inside the hull,  on which rests a thwart.

n   A sloping,  athwartships batten on which a rower might rest his or her feet.

n   A flat,  horizontal device,  with handles at each end,  for carrying an unconcious or incapable person.


To haul down one's flag as an act of surrender.

To strike a tent is to take it down and pack it away;  there is no suggestion of surrender.

Sailors hand sails;  they do not strike them.

Strip plank

A method of building boats where the planks are thin strips,  often less than an inch wide,  glued together.   The planks are usually sheathed with fibreglass and epoxy resin.


Studding sail

Stu’n’s’l.   Sails carried on booms which were extensions to square-rigged yards.   Such booms are not yardarms.


Sail Training Vessel.


An adjective describing anything below sea level,  such as a submarine cable or pipeline.

The adjective has become nominalised when used to describe a submarine vessel,  which is specialised for working under water for extended periods of time.   Most submarines have been used for warfare but many are now used for exploration and for working with submarine equipment such as oil and gas rigs,  pipelines and cables.


A transient,  horizontal movement.

Springs are used on a moored vessel to prevent surging fore and aft.


To lift something aboard with a line and tackle.


n   A long oar used to move an unpowered vessel,  such as a lighter.

v   To remove dust or small debris from a surface with a brush or broom.

coll:   Waves might 'sweep' over a vessel during a storm,  especially if items stowed on deck are swept away.



The up-and-down movement of the sea:  waves which do not break.


vb   to move through the water by moving of arms and legs.

n   a length of river bank allocated to a coarse angler during a fishing competition.

n   the underwater part of a narrow boat from the aftermost width of the beam aft to the narrow point at which the propeller shaft emerges.



To move backwards and forwards at the end of a line (like a pendulum) under the effect of gravity alone,  or in combination with a regular impetus such as a clock escapement or a person's arm.

A leadsman swings the lead at the end of the leadline before casting it into the sea to 'plumb the depths'.

A criminal might swing at the end of a rope whilst being hung for murder (this no longer happens in most civilised countries).

A vessel might swing (horizontally) at the end of its anchor rode under the effect of a tidal stream.


Swinging circle

When a vessel swings to its anchor rode it describes an arc of a circle over the ground.   When the tide turns this arc may become a full circle with a radius only slightly less than the scope of the rode.

Swing the compass

"Swing (the vessel) for the compass"

To measure the Deviation of a ship's compass,  and to prepare a Deviation Card.

Deviation changes with the vessel's heading;  it is normal to measure at five or ten degree intervals.   The vessel is sailed or sprung in a circle (swung) and the steering compass is compared with a hand-held compass or with a gyroscopic compass.

The deviation card is unique to the vessel measured,  in the state in which it was measured.   Changes to any electronic equipment or ferrous metal objects (like engines) will alter the deviation.

Strictly speaking,  it is the ship which is swung,  not the compass.

See McGregor

Swinging the lead

Plumbing the depth with a lead line.

Leadsmen stood on the channels,  leaning outward and held in place by a light line or belt.   The bitter end of the leadline was attached to the ship;  the rest was coiled into the leadsman's hand,  with the lead hanging on about a fathom of line.   He would swing the lead in a vertical circle,  to gain momentum,  and,  at the top of the arc,  release the line so that the lead fell into the sea well ahead.   As the lead fell to the sea bed the leadsman would let the line run through his fingers (feeling the marks and deeps) until it touched the bottom.   He would then call the mark.   The skill lay in casting the lead far enough ahead so that when it touched the sea bed the line was vertical.   When the lead was recovered the sailing master,  or the officer of the watch,  would examine the tallow.

Those sailors who had not done the job thought of it as a light duty;  leadsmen were 'swinging the lead';  escaping from hard work.

In fact,  swinging the lead was skilled,  hard,  dangerous work.   Leadsmen were frequently soaked with spray or immersed in waves.   The safety of the ship and the lives of the crew depended on their skill.

Synoptic chart

A synoptic chart describes the atmospheric pressure systems for the area covered by the chart,  typically 1,000km or more across.   The Meteorological Office (MetOffice) provides daily synoptic charts (and predictive charts for 72 hours) of the North Atlantic to include the Eastern seaboard of North America,  Greenland,  Iceland and the Western seaboard of Europe,  including the British Isles.


Synoptic charts are useful for predicting the weather.

North Atlantic Synoptic Chart


John Starkie

March 2020

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