Keep clear of me,
I am manoeuvring with difficulty
Daggerboard, Danbuoy, Davit, Davy Jones' Locker, Day, Day beacon, Dead in the water, Deadeye, Deadlight, Dead reckoning, Deadwood, Deal, Deck, Deckhead, Deck shoes, Deep, Degree, Depression, Depth, Derelict, Deviation, Devil, Dewpoint, Dhow, Diamond, Diesel, Differences, Dinghy, Dip, Dipping distance, Dipping lug, Dipping the eye, Direction, Directional light, Disembark, Displacement, Distress, Dive, Dividers, Dock, Dockyard, Dodger, Dog, Dogger, Dogvane, Dogwatch, Doldrums, Dolphin, Dorade, Dory, Douse, Dowel, Downhaul, Downwind, Drag, Draught, Drift, Drifter, Drink, Driver, Drogue, Drudge, Drydock, DSC, DUKW, Dumb sheave, Dunnage, Duty
A kind of adjustable underwater foil, for resisting leeway, which can be raised or lowered more or less vertically in a case. When beating to windward the daggerboard is lowered to resist leeway: when running before the wind it is raised to reduce frictional drag.
On these sailing dinghies, you can clearly see the difference between a centreboard and a daggerboard. Illustration Claudia Myatt.
In his 1906 treatise Folkard describes 'sliding keels', invented by Captain (later Admiral) Schank, as something we would now (early 21st Century) recognise as a dagger board: he reminds us that they had been " . . in use for centuries . . by the natives of Pernambuco in their catamarans." and that they were successfully tested by the Admiralty in 1791.
A locator buoy, with a float, a weight to keep it upright and a 2 metre staff with a flag. They are kept attached to the taffrail of the boat attached to one of the horseshoe buoys. They are thrown overboard if a crewmember falls in the water; the flag marks the position of the MOB.
They may also be used to show the location of a worksite, crab & lobster pots and the ends of a fishing net.
From Latin, the singular form of 'data': a single item of data, or information.
A reference baseline from which measurements are made.
An arbitrarily defined level.
A geodetic datum is a standard level from which measurements are taken for geographic surveys.
Ordnance Datum Newlyn (ODN) is the datum level for the Ordnance Survey of Great Britain, defined as Mean Sea Level at Newlyn, in Cornwall, between 1915 and 1921.
The Tunnel Datum for London Underground is Ordnance Datum Newlyn -100m.
The tunnel datum for the Channel Tunnel is ODN-200m
Datum line: see 'Direction'.
Davy Jones' Locker
Sailors who die, and are buried, at sea go down to Davy Jones' Locker.
Those who die ashore go to Fiddler's Green.
A crane made of a swinging boom together with blocks and tackle, which may be swung over the stern of a boat to lower and recover the dinghy. Sometimes davits are used for loading cargo, or lifting an anchor on deck. They are often mounted in pairs.
One of the two davits on the starboard quarter of the Thames Barge Hydrogen, out of Maldon, tending the ship's dinghy.
When related to a date, the twenty-four hour period between midnight and the next midnight.
The hours of daylight between sunrise and sunset.
Dead in the water
Under way (IRPCS Rule 3 (i)) but not moving through the water. There is an implication of loss of control and vulnerability (to an enemy).
A calculation (according to the RYA) of position using only the boat speed, the heading and the distance run, but ignoring the tide. It’s not clear whether it should be spelled ‘dead’, the meaning of which (in this context) is not clear, or ‘ded’, which might be a contraction of ‘deduced’.
Falconer (in 1815) thought it was "a judgement of the ship's position using the distance run and the course steered allowing for drift, leeway &c". The RYA would call this an Estimated Position.
Smyth (in 1867) used almost the same words as Falconer. They both used the spelling "dead-reckoning".
Planks of timber from the fir tree.
The floor beneath ones feet on the outside or inside of the boat. On a big ship the decks are equivalent to the storeys, or levels, of a house. One stands and walks on the deck, leans on the ceiling and looks up at the deckhead or headlining.
The overhead of a compartment. The underside of the deck above.
Deck shoes have 3 important features.
They must be smart and fashionable, with leather laces which stretch and break.
The soles must not slip on the deck.
The soles must not mark the teak or glass-fibre deck.
n To sailors, the original meaning of ‘deep’ was ‘hidden’, ‘mysterious’: in Medieval times sailors had no concept of deep, or depth, as we now understand the words. 'The Deep' was the dark, mysterious, dangerous place below the surface of the sea.
To measure (or plumb) the deep (hidden, mysterious) water a shaped piece of lead (Latin; Plumbum, Pb) was attached to a line and lowered to the sea bottom. The line had marks (of leather, calico, etc) at 2, 3, 5, 7, 10, 13, 15, 17, and 20 fathoms; at 4, 6, 8, 9, 11, 12, 14, 16, 18 and 19 fathoms were ‘deeps’, with no marks.
Plumbing the deep had more relevance to fixing a position than to knowing the depth of water.
See Marks and Deeps.
n A submarine trench or gulf, deeper than the surrounding sea bottom.
adj Deep water as opposed to shallow water. Deep is relative and subjective; if you can't swim, 3m is deep water. The ends of swimming pools are marked as 'deep end' and 'shallow end'; most people cannot stand on the bottom, at the deep end, with their head above water.
An angular measurement equal to one three hundred and sixtieth of a complete circle.
There are 60 (angular) minutes in a degree, and sixty (angular) seconds in a minute.
Directions at sea are now (early C21) measured in degrees clockwise from True North, and may be read directly from a gyroscopic or fluxgate compass adjusted to True North, or calculated from a magnetic compass.
Thus, from our position, North is 000°T, East is 090°T, South is 180°T and West is 270°T.
Degrees of Latitude are measured from a point at the centre of the earth: the equator is at 000°North and South; the North Pole is at 090°N; the South Pole is at 090°S; Greenwich (near London) is at 51.476852°N.
Degrees of Longitude are also measured from a point at the centre of the earth. Greenwich is at 000°East and West; Moscow is at 37.6° E; San Francisco is at 122.4194° W; The International Date Line would be at 180° East and West if small Pacific island states didn't keep changing their minds about which day is which.
One radian is 360° divided by 2 pi, or about 57.3°
Points are an earlier (and more or less obsolete) measure of angles; a point was 11.25°: one-thirtysecond of a full circle. An early (Age of Sail) compass showed thirty two points with names rather than degrees. Sailors were required to be able to 'box the compass'; ie, to name the points, in sequence, in a clockwise direction.
A region of low atmospheric pressure (normal atmospheric pressure is 1013 millibars), usually associated with warm and cold fronts. If points of equal pressure are linked by curved lines (called isobars) each isobar encloses an area of lower pressure. The synoptic chart on the right shows the distribution of isobars, 4 millibars apart, around a depression centred to the South East of Greenland, on a Polar chart. Winds blow around the depression clockwise in the Southern Hemisphere, anti-clockwise in the Northern Hemisphere. Winds do not blow parallel to the isobars, but are angled about 15° inward toward the lower pressure. Isobars are packed more closely where the winds are stronger.
Depth of water = charted depth + height of tide
The Deviation of the steering compass is unique to the boat on which it is mounted at the time it is measured. Any change to any electromagnetic structure on the boat (such as the engine, radar, radio or even the metal rim of spectacles placed close to the compass), or the position of the compass, will change the Deviation of the compass.
Deviation varies with the heading of the boat. For this reason the person who ‘swings the compass’ (or, more accurately, 'swings the boat for the compass') (see Annex 13 of SOLAS Chapter V) prepares a deviation table with three columns and a graph. The first column shows the ship's head in °C, the second shows the deviation and the third shows the ship's head in °M.
n A sort of priming made by dampening and bruising gunpowder.
Following some minor infringement of discipline aboard ship there would be the devil to pay. The unfortunate caulker involved would hang over the side of the ship between the devil and the deep blue sea.
Temperature at which moist air becomes saturated.
n All charts have tidal diamonds scattered over the chart. Each represents a point at which the tidal stream has been measured. Also on the chart is a table of tidal diamonds which lists the one-hour periods before and after the High Water hour of the reference port, together with the set and the drift of the tide, at that diamond, during each one-hour period. The set is expressed in degrees True. There are two values for drift: the first is the drift, in knots, at the Spring tide; the second is the drift, in knots, at the Neap tide.
See Tidal Stream Atlas.
n A gemstone of compressed carbon. "A girl's best friend" because it is valuable and saleable.
An adjective describing a liquid fuel or a type of internal combustion engine.
Petro-diesel (derived from mineral oil) is a mixture of about 75% paraffins with between 8 and 21 carbon atoms per molecule, and about 25% aromatic hydrocarbons. It also contains additives.
Biodiesel is obtained from vegetable oil or animal fats (biolipids) which have been transesterified with methanol.
Diesel fuel has a high flash point, and is difficult to ignite with, say, a match.
In a diesel engine, diesel oil is atomised to very small droplets, and mixed with air at a very high pressure (and temperature). Under these conditions it ignites and burns rapidly, further increasing the temperature and pressure of the gas and driving a piston to operate the engine.
In an almanac Standard ports have a complete table of tides, with times and heights of high and low water. Secondary ports do not have tide tables; instead, they have a table of differences from a nearby standard port. These tables of differences are a little tricky to use.
The UKHO website Easytide obviates these calculations by providing tide tables and curves for both standard and secondary ports.
n The two ends of the needle of a compass point toward the North and the South magnetic poles. The poles are usually below the horizon so that one end of a freely suspended needle would point downward.
The dip of special "dipping needles" (up to 2m long!) combined with tables of dip were used, at one time, to estimate latitude.
The distance, in nautical miles, at which a light just appears above, or disappears below, the horizon. The distance depends upon the height of the light and the height of the observers eye. There is a table in the almanac. The chart gives the height of the light (on a lighthouse) above Mean High Water Springs.
Dipping the eye
When passing the eye of a warp over a bollard it should be passed under warps already on the bollard and then up through their eyes before being dropped over the bollard. This ensures that any of the warps can be removed without disturbing the others.
For direction on the sea (or the surface of the earth) the datum line is between us and the true North pole.
The direction of a bearing; in practice, the datum line is from us to the magnetic North pole (eg NorthEast, or 045°M) as determined by a bearing compass. This must be converted to an angle with True North before plotting on the chart.
Refers to the light on a fixed structure, such as a lighthouse, which can be seen from only one direction. Directional lights are often placed near a bend in a channel: if a particular light (perhaps white) can be seen then the observer is in the middle of the channel: if a different light (perhaps red or green) can be seen then the observer is out of the main channel. Directional lights must be interpreted in the context of the appropriate chart.
v To leave a ship.
When an object is immersed or floated in water it displaces, or moves aside, the water.
The displacement of a floating object (like a boat) is the weight of water displaced by the object. The weight of water displaced is the same as the weight of the floating object.
Displacement is one of the ways in which a boat might be measured*.
Most boats displace more or less the same weight of water when moving as when stationary: they are displacement boats. Their maximum speed through the water is limited by the approximate equation
v ≈ 1.34√L
where v is the maximum hull speed
and L is the waterline length
By contrast, planing boats lift almost out of the water at speed and skip across the surface, displacing very little water.
Hydrofoil boats are lifted out of the water by their hydrofoils.
Wing-in-ground-effect vessels (which the drafters of the IRPCS erroneously call “Wing-in-Ground (WIG) craft”) are lifted above the water by short wings flying on a cushion of air (the ground effect) close to the water.
v To move beneath the water.
Submarine (vessels) are able to manoeuvre on the surface and under the water.
People swim under water (dive) for recreational purposes or to work.
v To move from a height to and below the surface of the water in a controlled way.
A person (or bird) who dives is a diver.
A facillity for building and repairing ships.
The folding canopy mounted over the companionway is a sprayhood, not a dodger.
n An iron hook with a sharp point and a handle or loop. Sacks or planks are pierced with the hook and dragged or lifted while manually loading and unloading a ship. Dogs (and their handlers) have been replaced by fork-lift trucks; the need for them has been replaced by containers.
n A bench dog is a wooden or metal pin which fits securely into a hole in a bench to restrict the movement of items being worked upon.
Navy watches are four hours long; but, if they were all four hours long the same people would be on watch at the same times every day. To vary this the First Dog Watch, from 1600 to 1800 (ship’s time) and the Last Dog Watch, from 1800 to 2000 (ship’s time) are each two hours long.
see also Bell.
n Nearly 40 species of marine mammal, of the Order; Cetacea, SubOrder; Odontoceti.
n A structure of several posts, lashed together and embedded in the seabed; used at one time for warping ships around the harbour.
n A species of fish (mahimahi, dolphin-fish or dorado) found worldwide.
These dolphins in Amsterdam harbour are no longer used to warp ships, but to moor and to protect the abutments of bridges.
Dorade is a sailing yacht designed in 1929 by Olin Stephens of Sparkman & Stephens and built 1929–1930 by the Minneford Yacht Yard in City Island, New York. The first vessel to use dorade ventilation boxes.
n A deck-mounted ventilation box which allows air below but not water.
Usually a rectangular box fixed to the deck, and fitted with vertical baffles. The baffles alternate to be free at the floor of the box, or free at the roof, forming a series of chambers.
Scupper holes perforate the wall of the box at the floor of each chamber.
Dorade boxes operate on the principle that air can pass freely through the chambers, yet rain or sea water will be trapped in successive chambers and will drain through the holes in the sides of the box. See Cooke, p483
n A species of edible fish; Sparus aurata, gilt-headed bream.
A solid cylinder of wood used to fasten two timbers together.
Treenails (trunnels, trennels, tr'n'ls) were solid cylinders of wood often several inches* long and an inch or more in diameter used to fasten planks to frames and the futtocks of frames together. The holes into which they were driven were almost exactly the same diameter as the treenail. The ends of treenails were slotted and fitted with wedges; the inner wedge expanded the treenail as it reached the bottom of the hole; the outer wedge was driven in later to expand the outer end of the treenail.
Common dowels are machine made from an inferior wood, such as birch, and are widely used in simple carpentry. Boatwrights prefer to make their own dowels (?treenails) from the same wood as the timbers to be joined.
* 1 inch ≈ 25mm
A line attached between the tack of a sail and the deck, used to tighten the luff, may sometimes be called a downhaul, but is more properly a tackline or tack purchase. In the words of Commodore Luce; "The yard of a lug-sail hooks to an iron traveler on the mast; the hauling end of the halliards should have an eye in its end, to be placed over the hook of the traveler before hoisting, and used as a down-haul." It's possible to see how this might have been misunderstood.
In the direction the wind is blowing.
Vessel A is said to be downwind of vessel B when the wind reaches vessel B before it reaches vessel A.
If you throw your hat into the air it will blow away downwind.
n a force acting against the relative motion of an object, such as a boat or a sail, moving in a surrounding fluid.
Both friction and turbulence contribute to drag.
The depth of water needed to float a boat.
The table of diamonds and the tidal atlas are grouped in 1-hour periods either side of the High Water hour of the reference port. The figures imply that the drift is constant during each tidal hour and that it changes abruptly at the end (and beginning) of each hour; in fact, there is a progressive change from one hour to the next.
n The difference between the size of a bolt and the hole into which it is to be driven. A bolt which is 1mm in diameter larger than its hole has a drift of 1mm.
n A metal rod which is driven tightly into a bored hole to join timbers together.
vb To drift is to allow a vessel to move with the wind and tide. A vessel may be intentionally adrift, perhaps when the occupants are fishing, or it may be adrift because it is not under command; in either case it is still under way according to the definition in the IRPCS.
A person with no clear objectives might be said to drift, perhaps from place to place or from job to job.
adj A drift net is one which, buoyed up by glass or cork floats, 'drifts' at the surface of the sea. In practice, they are usually anchored at one or both ends, or attached to the ship which has cast them.
n The water, overboard. An item lost overboard has fallen "into the drink".
n A potable liquid, often alcoholic.
A dock, closed by a gate (caisson) or lock, which can be flooded or dried. A vessel is floated into the drydock and shored. the gate is then closed and the water pumped, or drained, out. It allows the bottom of the ship to be cleaned or repaired.
A drydock is the modern equivalent of careening.
Digital Selective Calling (radio).
The DUKW (Duck) was a six-wheel-drive amphibious modification of a 2½ ton truck used by the U.S. military during World War 2 and the Korean War.
It was designed by a partnership under military auspices by Sparkman & Stephens and (GMC), and was used for the transport of goods and troops over land and water. It excelled at approaching and crossing beaches in amphibious warfare attacks, but was intended only to last long enough to meet the demands of combat. Surviving DUKWs have since found popularity as tourist craft in marine environments.
D: 1942; U: Utility (amphibious); K: all-wheel drive; W: two powered rear axles.
A dumb sheave has no pulley wheel; the rope moves in a groove in a block (usually of wood).
n Personal baggage.
Something which must be done.
It is the lookout's duty to look for and report other vessels.
It is the boatswain's duty to maintain the masts, spars and rigging.
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