Maritime Dictionary – Everything That Starts with the Letter “J”

Jack – A national or variation of a national flag. 2. Crosstrees. 3. Instrument or machine for lifting heavy weights. 4. Colloquial name for a seaman.

Jack Block – Large wooden block used when hoisting or lowering a topgallant mast.

Jack Crosstrees – Iron crosstrees on a tall topgallant mast.

Jack in the Basket – Pole with basket, or basket-shaped, topmark. Used for marking a shoal or sandbank.

Jack Knife – Knife with a folding blade. Invented by Jacques de Liege in late 16^th century.

Jack Ladder – Ladder with wooden rungs, or treads, and rope sides.

Jack Nastyface – Nickname for an unpopular seaman. Originally, nom de plume of a seaman who wrote a pamphlet about conditions in Royal Navy in early years of 19th century.

Jack Screw – Large screw purchase used for lifting heavy weights, or for screwing, compressing or forcing. May be used for stowing cotton and similar cargoes.

Jack Staff – Flagpole at a ship’s bow.

Jack Tar – Former nickname for a seaman, now used by landsmen only. When used by seamen is a term of mild contempt for a man whose nautical knowledge is less than his knowledge of nautical terms.

Jackass Rig –  Name applied to a four-masted sailing vessel that is square rigged on fore and main masts, and fore and aft rigged on the two after masts.

Jacket – Doubling piece on outside planking of a wooden vessel. 2. Casing on a pipe or funnel where it passes through a deck. 3. Space between inner and outer walls of a steam cylinder.

Jackstaff – Small staff erected at stem head, or bowsprit cap, for flying a jack or other flag.

Jackstay – Iron rod, wooden batten, or taut wire on upper side of a yard, and to which the head of a square sail is bent. 2. Taut ropes that are stretched for a specific purpose; such as those extended between heads of davits; from head of davit to water line; between stanchions to take lacings of awings.

Jackyard Topsail – Yacht sail, with a wooden spar along foot, that is set above the gaff mainsail and extends beyond it.

Jacob’s Ladder – Jack ladder, particularly one going up a royal mast, or from a boat to a swinging boom. 2. A lightweight, portable ladder made up of wooden steps and manila rope.

Jacob’s Staff – Nickname given to ‘Cross staff’.

Jag Up – To stop up old rope in 5-fathom bights.

Jamb – The side members of a doorway’s frame.

Jansen Clause – Included in a policy of marine insurance to relieve insurers of liability for losses less than 3 per cent of insured value. Also called the ‘Franchise Clause‘.

Japan Stream – Alternative name for ‘Kuro Siwo’.

Jarrah – A durable Australian red hardwood with fire resisting properties.

Jarvis Brace Winch – Patent winch in later days of sail when ships were short handed.

Jason Clause – Usually inserted in maritime contracts that are subject to Harter Act. As a separate contract, it allows the owner of a technically ‘unseaworthy’ vessel to claim cargo’s contribution to General Average when he has exercised due diligence in making his ship seaworthy in all respects, and the ‘unseaworthiness’ was such that it could not have been avoided or discovered by any reasonable amount of forethought or care.

Jaunty – Nickname for a master-at-arms. Corruption of ‘gendarme’.

Jaw – Forked end of a gaff or boom. 2. Space between lugs of a shackle. 3. Distance along a rope from any one strand to the next appearance of the same strand in a straight line along the rope.

Jaw Rope – Rope by which jaw of a gaff is confined to mast. A parrel.

Jaws– The sides of the gooseneck at the inner ends of traditional booms or gaffs that hugs the mast. A popular movie.

Jears, Jeers – Tackles at bunt of lower yard, and by which it is hoisted or lowered.

Jehazi – Undecked coastal dhow of about 20 to 40 tons. Usually has matting bulwarks.

Jergue – Old form of ‘Jerque’.

Jerking Note – ‘Jerquing Note.’

Jerque – Search of a vessel, by Customs authorities, for unentered goods.

Jerquing Note – Certificate given by Customs searcher when ship has been searched and no unentered goods are on board.

Jet – Common name for a water jet propulsion system. Fine pipes in a carburettor for regulating the fuel supply available for vaporising and mixing with air. A high-speed jet and a low-speed jet are normally fitted to performance petrol motors.

Jet Foil – Hydrofoil propelled by waterjets situated in the foils upon which the vessel rides when at speed.

Jet Stream – Fast moving high altitude winds that equalise global atmospheric pressure. They can be harbingers of approaching storm systems.

Jetsam – Goods that have been cast out of a ship and have sunk.

Jettison – Deliberate throwing overboard of goods or fittings for the preservation of a ship in peril.

Jetty – Wharf, or other similar construction, that projects into the sea or harbour.

Jewel Block – Wood block, at yard arm, that takes a studdingsail halyard.

Jew’s Harp Shackle – Special bow shackle that formerly connected cable to anchor.

Jib – Triangular fore and aft sail set on a forward stay.

Jib Boom – Boom projecting forward from bowsprit, on which it is housed.

Jib Downhaul – Rope by which a jib is hauled down and inboard along jib boom.

Jib Frame – Vertical frame at side of a marine reciprocating engine.

Jib Guys – Rope stays leading inboard and downward from end of jib boom.

Jib Halyard – Rope by which head of a jib sail is hoisted.

Jib Headed – Said of any sail resembling a jib in shape. The forestay does not attach to the masthead, but at a point lower on the mast where the top of the jib meets the mast.

Jib Headed Sail – A Bermudan sail; a triangular sail with a pointed head.

Jib Inhaul – Alternative name for ‘Jib downhaul’.

Jib Iron – Iron hoop that travels along jib boom and carries tack of a jib (sail).

Jib of Jibs – Outermost jibsail when three or more are carried.

Jib Outhaul – Rope by which a jib tack is hauled out to jib boom when setting jibsail.

Jib Sheet – Rope by which clew of a jib is controlled.

Jib Stay – Stay to which luff of a jib is confined.

Jibe – ‘Gybe.’

Jigger – General purpose tackle consisting of single and double blocks, with standing part spliced to arse of single block. 2. After trysail of a four-masted barquentine. 3. After mast of a four-masted vessel.

Jimmy Bungs – Nickname for a ship’s cooper.

Jimmy Duck’s – Nickname for a ship’s poulterer.

Jimmy Green – Square sail set beneath bowsprit in later clipper ships.

Jingadah – Brazilian Indian seagoing bark outrigger.

Jockeying – Manoeuvring a yacht, in vicinity of starting line, with a view to getting a favourable position and a flying start.

Joggle – To adjust to fit.

Joggled Frame – Steel or iron frame having alternate raised and recessed portions—on outer edge—that are of same dimensions as depth and thickness of ship’s side plating. Allows plating to rest closely on frame and lap over plates above and below, without joggling plate edges.

Joggled Plate – Ship side plating so shaped that longitudinal edge of plate curves and overlaps plate next above or below it; the rest of the plate resting closely on the frame.

Joggled Timber – Frame, of a wooden vessel, so shaped that an attached strake has a clincher appearance, although there is no overlap or doubling. Joggle Shackle. Elongated and slightly bent shackle that can confine a link of chain cable. Has a quick-release pin.

John Dory – A spotted, flat (laterally) fish; European.

Joinery – The fine timber constructions of a vessels interior.

Joining Shackle – Flush shackle joining two lengths of cable.

Joint Rescue Coordination Centre (JRCC) – responsible for both aeronautical and maritime search and rescue incidents.

Jolly – Nickname for a Royal Marine.

Jolly Boat – General purpose boat of a ship.

Jolly Jumper – Square sail set above a ‘moonraker’. Was rarely carried.

Jolly Roger – Skull and crossbones flag of a pirate.

Jonah, Jonas – Old Testament character that is caste into the sea by his storm bound shipmates to quell the seas and is swallowed by a whale. Person whose presence on board is coincident with misfortune.

Joule’s Equivalent of Heat – Expresses the relationship between heat energy and mechanical work as 778-foot pounds; being equal to heat required to raise one pound of water through one degree Fahrenheit. The British Thermal Unit assumes 762-foot pounds.

Journal – Old name for a log book. 2. Book entered with day by day recordings. The section of a revolving shaft in contact with its bearing.

Judas – Said of any yam or rope end that hangs down and is at the mercy of the wind.

Julian Calendar – Devised by Sosigenes and inaugurated by Julius Caesar. Assumes a year to be exactly 365 1/4 days. Commonly used until 1582.

Julian Day – Figure that denotes the serial number of a day as reckoned from an epoch in 4713 B. C. The day begins at noon, G. M. T. Used by astronomers to avoid calculations for intercalary days, and for other factors. Introduced in 16th century by Joseph Scaliger, who named it after his father, Julius.

Jumbo Derrick – Heavy-lift derrick. Used when discharging very heavy items of cargo.

Jumboising – The conversion of a ship that increases its size, usually by inserting an additional central section.

Jump Ship – To desert a ship, or improperly leave her. To leave a ship without authority.

Jumper – Alternative name for a ‘Jolly Jumper’. 2. Blouse-like upper garment of R. N. seaman.

Jumper Guys – Additional guys for supporting jib boom.

Jumper Stay – Triatic stay. So called because used when jumping cargo.Wire stay between foremast and funnel.

Jumper Struts – Timber, metal or plastic rigging spreaders that are angled forward to increase mast support transversely and longitudinally. The stays they support are called jumper stays.

Jumping Ladder – Light rope ladder used for manning a lifeboat, or for men working over the side.

Jumpsurgee Strop – Exceedingly strong rope strop for a block. Made by taking enough rope to go three times round block and once round thimble. Each end is unlaid until there is enough unlaid rope to encircle block and thimble. Ends are then married and strands unlaid. Yarns are then made into nettles and grafted along unlaid rope.

Junk – Old and unserviceable rope used for making fenders, mats, swabs, oakum, etc. Originally was bulrush, from which the first ropes were made. 2. Large sailing vessel of China, Japan and Malaya. Sails are battened balanced-lug sails. Mast usually in one piece. The balanced rudder is suspended.

Junk Ring – Cast iron ring on upper part of piston. Is removable so that packing ring can be renewed when worn. Name is a relic of days when packing was of rope.

Jupiter – Largest of the planets, being 1300 times larger than Earth and 317 times heavier. Has at least nine satellites. Orbit lies between Mars and Saturn. Distance from Sun, 478, 000, 000 miles.

Jury Knot – Three bights of a rope so interlaced that when knot is shipped over head of a jury mast all parts encircle the mast and there is a bight on either side, a bight forward, and two ends aft. Fore stay and shrouds were attached to bights, the two ends being backstays.

Jury Mast – Temporary mast erected in place of a mast that is damaged or lost.

Jury Mast Knot – Shamrock knot. See Jury Knot. This knot can be difficult to make. Check out the easiest 10 most widely used knots on ships.

Jury Mat – Mat made by making bights in a length of rope, and then interweaving with bights and ends.

Jury Rig – Temporary and makeshift rig in place of rigging carried away or lost.

Jury Rudder – Makeshift rudder constructed in ship when proper rudder has been lost or damaged.Jury Steering Gear – Alternative steering gear for controlling rudder when usual steering gear cannot be operated.