The following are some of the terms and definitions, which may prove helpful in the daily dealings with oil tankers. This list is compiled from various industry sources. While extensive, it should not be considered a complete list of all vessel and charter party related terms and definitions.


Accommodation Ladder - A term applied to a portable flight of steps suspended over the side of a vessel from a gangway to a point near the water, providing any easy means of access from a small boat. Accommodation Ladders are usually supplied with two platforms, one at each end. Sometimes called gangway ladder.

Adrift - Floating at random; not fastened by and kind of mooring; at the mercy of winds and currents; loose from normal anchorage. A vessel is said to be adrift when she breaks away from her moorings, wharfs, and so on.

Aft, After - Toward the stern or the back of the vessel. Between the stern and the midship section of the vessel.

Afterbody - The section of the vessel aft of amidships.

Aframax Carrier - A tanker of approximately 80,000 to 120,000 dwt..

Agency Fee - A fee charged to the ship by the ship's agent, representing payment for services while the ship was in port. Sometimes called attendance fee.

Air Draft - The distance from the vessel's water line to the upper most point on the vessel, usually the top of a mast or radar tower. When a vessel has to transit areas where there may be overhead obstructions (bridges, power lines, cranes, loading arms, etc.) it is vital to know what its air draft (draught) will be at the time of transit. The air draft of a vessel will vary depending upon the draft of the vessel and its trim.

Aloft - Above the deck.

Allowed Lay Time - The number of hours allowed for loading and discharging a cargo as stipulated in a Charter Party.

American Bureau of Shipping (ABS) - A Classification Society. Under the provisions of the U.S. Load-Line Acts - it has the authority to assign load lines to vessels registered in the U.S. and other countries.

Amidships (or 'Midships') - The middle portion of a vessel.

API - The American Petroleum Institute, founded in 1919, was the first oil trade association to include all branches of the petroleum industry. The API scale is a scale used to define the specific gravity of a cargo. It is mainly used in the crude trades, with the product trades preferring the metric SG scale.

API Gravity (Relative Density) - A means used by the petroleum industry to express the density of petroleum liquids. API gravity is measured by a hydrometer instrument having a scale graduated in degrees API. The relation between API gravity and relative density (formerly called specific gravity) is: API Gravity at 60 Deg. F. = 141.5 - 131.5\Relative Density 60F/60F

Articles of Agreement - The Document containing all particulars relating to the terms of agreement between the Master of the vessel and the crew. Sometimes called ship's articles.

Atlantic Basin - The Atlantic Ocean and the ports and seas surrounding it, including the eastern seaboard of the United States and Canada, the U.S. Gulf and Caribbean Sea, the northern and eastern coasts of South America, the North Sea, the Black Sea and the Mediterranean Sea.


Backhaul - A deviation to move cargo on the return leg of a voyage for the purpose of minimizing ballast mileage and thereby reducing transportation cost. For example, N. Europe/ E.Med./ USNH/ Carib., versus N. Europe./ Carib.

Ballast - Seawater taken into a vessel's tanks in order to submerge the vessel to proper trim. Ballast can be taken into cargo tanks, double bottoms, fore and aft peak tanks and/or segregated ballast tanks, (SBT).

Clean - Term applied to the seawater used for ballast when it is not contaminated by any oil and is carried in clean tanks.

Dirty - Term applied to the sea water used for ballast when it is contaminated with the remnants or residue left in cargo tanks that previously carried crude oil or heavy persistent refined oils.

Permanent - Ballast carried in ship's tanks that were designed to carry nothing else.

Segregated/Dedicated - Ballast kept in tanks segregated from cargo pipes and tanks.
Ballast Movement - A voyage or voyage leg made without any paying cargo in a vessel's tanks. To maintain proper stability, trim, or draft, seawater is usually carried during such movements.

Ballast Passage - The "ballast leg" of a voyage as differentiated from the "loaded leg."

Ballast Pump - A pump used for filling and emptying the ballast tank.

Ballast Tanks - The tanks used to carry the vessel's ballast. They may be permanent, dedicated, or cargo tanks.

Bareboat Charter - Bareboat charterers hire the vessel for a period of time, usually several years, and are responsible themselves for all operational matters including crewing, insurance and maintenance of the vessel.

Barge - Also lighter. A general name given to a flat-bottomed craft specially adopted for the transportation of bulk cargoes.

Barrel - A volumetric unit of measurement equal to 42 US gallons. There are 6.2898 barrels in one cubic metre. Note that oil tankers do not carry oil in barrels (although ships once did in the 19th century): the term is used to define the volume only.

Beam - The width of a ship at its widest part. Also called its breadth.

Berth - Dockage space for vessel. Sleeping quarters. Also slang for having a crew position on the vessel.

Bilge - The lower internal part of the hull where the vertical sides meet the bottom. This term applies to both the inside and the outside of the hull. The internal space can be the lower part of a ship's hold or the engine room and serves as a drainage area where accumulated water can run into and be pumped from.

Bill of Lading - A B/L is the basic document between a shipper and a carrier and a shipper and consignee. It represents the contract of carriage and defines the terms and conditions of carriage. It is the final receipt from the carrier for the goods shown on it and for the condition of the goods. It describes the nature, quantity and weight of the cargo carried. It is also the document of title of the goods shown.

BIMCO - Baltic and International Maritime Council

Bitts - Cast steel heads serving as posts to which mooring lines and cables are secured on a ship.

Boilers - Steam generating units used aboard ship to provide steam for propulsion or for heating and other auxiliary purposes.

Boiler Room - Compartment in which the ship's boilers are located.

Bonded Bunkers - Ship's stores that can be delivered under special arrangement direct from a bonded warehouse to the vessel without payment of the custom duties.

Bonded Stores - Ship's stores that can be delivered under special arrangements direct from a bonded warehouse to the vessel without payment of the customs duties.

Boom - A general name given to a projecting spar or pole that provides an outreach for handling cargo.

Boston Beam - Boston can only accommodate vessels with a maximum beam of 90 feet. Vessels which can comply with this (usually under 40,OOOmt dwt) are referred to as 'Boston Beamers'.

Bow - The forward most part of a vessel. This area usually houses gear lockers and is the end where anchors and mooring equipment are located.

Breadth - See Beam

Bridge - A general term referring to that area of a vessel where the wheel house and chart room are located. It is the navigating section of a vessel.

Bridge AFT - Vessels with no midship house. All quarters with Bridge are contained in one superstructure at after end of vessel.

Bulbous Bow - A large protruding bow section designed to break water friction allowing the vessel to make better speeds.

Bulk Cargo - Usually a homogeneous cargo stowed in bulk, and not enclosed in any container.

Bulkhead - A partition in a ship that divides the interior space into various compartments in the walls of a vessel's tanks.

Bum Boat - A small open rowboat employed in carrying supplies for sale to vessels in a harbor.

Bunkers - Fuel for a vessel. The type will vary depending upon the propulsion mode of the vessel. Steamships will use a heavy fuel oil, diesels use a range of fuels from heavy to light, and gas turbines generally use kerosene.

Buoy - A floating object employed as an aid to mariners to mark the navigable limits of channels, their fairways, sunken dangers, isolated rocks, telegraph cables, and the like.

Butterworth Tank Cleaning System - A mechanical device used for the purpose of cleaning oil tanks by means of high pressure jets of hot water. The apparatus basically consists of double opposed nozzles which rotate slowly about their horizontal and vertical axis and project two streams of water through all possible angles against all inside surfaces of the space being cleaned. The tank washing machines can deliver sprays of water at various temperatures and pressures that are dictated by the type of cargoes carried and the reasons for cleaning (Quick bottom wash through gas-freeing and tank entry for hot work).


Call Letters - The letters assigned to the ship's radio (station).

Camber - The arching of the deck upward measured at the centerline in inches per foot beam.

Calibration - The process of adjusting, or of measuring the performance of a device.

Calibration Tables (Gauge Or Tank Tables, Innage/ Ullage Tables) - Tables developed by recognized industry methods that represent volumes in each tank according to the liquid (innage) or empty space (ullage) measured in the tank. The tables are entered with linear measurements (for example, feet, inches, meters, centimeters) to obtain calibrated volumes (for example, barrels, cubic meters or cubic feet).

Canceling Date - A stated date after which, if a vessel is not ready to load, the intending charterers have the option of canceling the charter. The passing of the canceling date leaves the owner's obligation unimpaired unless the charterer releases him.

Cancellation Clause - A clause in a charter party whereby the charterer reserves the right to cancel the charter if the ship fails to arrive, ready to load, on a specified date at a named port.

Capacity - The volume of a container or tank filled to a specified level.

Capacity Plan - A general plan or inboard profile which gives all data relating to the capacity of cargo spaces, tanks, bunkers and storerooms.

Capping - Routing a vessel around the Cape of Good Hope, South Africa.

Cargo Hose - A hose usually of 6 to 10 inches in diameter used for the transfer of cargo from ship to shore and vice versa.

Cargo Plan - A plan giving the quantities and description of the various grades carried in the ship's cargo tanks.

Cargo Pump - Pump used on tankers for discharging cargo and loading or discharging ballast. Located, at the bottom of the pump room, these pumps are usually of the common duplex type, or turbine type of which the centrifugal is the most common.

Cargo Quantity Option Certificate - A certificate signed by vessel and shore representatives acknowledging the amount of cargo intended to load.

Catwalk - A raised bridge running fore and aft from the Midship House, and also called "walkway." It affords safe passage over the pipelines and other deck obstructions.

Centerline - A horizontal fore-and-aft reference line, dividing the vessel into two symmetrical halves.

Center Tanks - Cargo tanks located on the vessel's centerline.

Centrifugal Pump - A pump consisting of a shaft to which vanes are attached and which rotates in a circular casing. Water or liquid flows into the casing near the center of the rotating shaft and is propelled outward along the vanes by centrifugal force. It escapes through a discharge pipe at the circumference of the casing.

Chain Locker - The compartment for storing the anchor chains, located near the bow of the ship.

Charterer - The company or person given the use of the vessel for the transportation of cargo or passengers for a specified time.

Charter Party - A document of contract, or agreement, by which a ship- owner agrees to lease, and a charterer agrees to hire, an entire ship, or all or part of the cargo space to carry cargo for an agreed sum under certain conditions.
Bareboat Charter - Owner lets an unmanned ship for a long period at a rate that covers any depreciation and nominal return. Charterer mans the vessel and pays all operating expenses.

To Fix A Charter - To reach final agreement on the terms of a charter party.

Charter Rates - The tariff applied for chartering tonnage in a particular trade.

Disponent Owner - Charterer who has sublet the vessel and is acting as the owner per the terms of the contract.
Charter Types

Contract of Affreightment (COA) - A service contract under which a ship owner agrees to transport a specified quantity of fuel products or specialty products, at a specified rate per ton between designated loading and discharge ports. This type contract differs from a spot or consecutive voyage charter in that no particular vessel is specified. (Rates are usually discounted below other forms of contracts.)

Period Charter - Refers to consecutive voyage (C/V) exceeding four voyages, time charters (T/C) and bareboat charters. - Note: Loose term may have other connotations.

Spot (Voyage) Charter - A charter for a particular vessel to move a single cargo between specified loading port(s) and discharge port(s) in the immediate future. Contract rate (spot rate) covers total operating expenses such as port charges, bunkering, crew expenses, insurance, repairs, and canal tolls. The charterer will generally pay all cargo-related costs.

Time Charter (T/C) - A charter for varying periods of time, usually between two and ten years, under which the owner hires out the vessel to the shipper fully manned, provisioned, stored and insured. The charterer is usually responsible for bunkers, port charges, canal tolls and any crew overtime connected with the cargo. The charter rate (hire) is quoted in terms of a cost per month per deadweight ton.

Classification of Petroleum - Classes "A-C" of petroleum are considered flammable and have a flash point of 80° F or below. Examples of these classes range from very light napthas (Class A) to most crude oils (Class C). Class D cargoes such as kerosene and heavy crudes are considered combustible and have a flash point above 80° F but below 150° F. Class E cargoes are the heavier fuel oils and lubricating oils and have a flash point above 150° F.
Classification Society - The professional organizations which class and certify the strength and seaworthiness of vessel construction. Class and certification issued to each vessel may be required for insurance purposes. American Bureau of Shipping (ABS) and Lloyds Register of Shipping are two of the most well known classification societies in the world today.

Clean Service - Tanker transportation of products lighter than residual fuels, e.g. distillates, including No. 2 Heating Oil.

Clean Ship - Refers to tankers that have their cargo tanks free of traces of dark persistent oils that remain after carrying crudes and heavy fuels oils.

Clingage - The residue that adheres to the inside surface of a container, such as a ship's tank or shore tank, after it has been emptied.

Closed Gauging System - A method of obtaining measurements of the tank contents without opening the tank. This may be accomplished by using automatic tank gauges or by taking measurements through a pressure/vapor lock standpipe. This type of gauging is done extensively on vessels with inert gas systems. Such a system that allows no vapors to be lost to the atmosphere is a true closed system while other types that allow minimum vapors to be lost to the atmosphere are called "restricted systems."

Cofferdam - The narrow, empty space between two adjacent watertight or oiltight compartments. This space is designed to isolate the two compartments from each other and/or provide additional buoyancy. It prevents any liquid contents of one compartment from entering the other in the event of a bulkhead failure. In oil tankers, cargo spaces are usually isolated from the rest of the ship by cofferdams fitted at both ends of the tank body.

Coils - These are the heating elements in the cargo tanks which are used to heat DPP cargoes on the laden voyage so that the cargo is fluid enough to discharge efficiently at the discharge port. Alternatively, some vessels are fitted with heat exchangers.

Combined carriers, or combination carriers - Ships designed to be able to carry both oil cargoes or 'dry' cargoes such as iron ore or grain, in the hope that the vessel can maximise earnings by swapping between wet and dry cargoes and eliminate some of the time spent 'in ballast'. Note that the vessel alternates cargoes, and does not carry both oil and dry cargo at the same time.

Consignee - The person to whom cargo is consigned as stated on the bills of lading.

Consignor - The shipper of the cargo.

Contamination - The result from commingling of a grade of cargo with a sufficient quantity of another grade to destroy the characteristics of the cargo.

Contract of Affreightment, (COA) - A service contract under which a Ship owner agrees to transport a specified quantity of fuel products or specialty products, at a specified rate per ton, between designated loading and discharging ports. This type of contract differs from a spot or consecutive voyage charter in that no specific vessel is specified. (Rates are usually discounted below other forms of contracts.)

Controlled Fleet - All ships owned and period chartered by affiliate(s).

CPP or clean petroleum products - Liquid products refined from crude oil, whose color is less than or equal to 2.5 on the National Petroleum Association scale. CPP's include Naphtha, let fuel, Gasoline, and Diesel/Gasoil.
CST, or centistokes A measurement scale for the viscosity of a liquid.

Crosshaul - Two ships on intersecting trade routes. This voyage pattern may indicate uneconomic vessel llocation. For example; Aruba/Fawley and Puerto la Cruz/New York.

Crude Oil Wash (COW) - A method of cleaning tanks using oil from the ship's cargo. COW is normally used when a tanker is discharging. Oil is taken from the tanks and pumped through a special line to fixed or semi-fixed tank washing machines where it is sprayed against all inside surfaces of the tank. This procedure removes any cargo which is 'clinging' to the surfaces of the tank.

Cubic Capacity - The inside measurement of a tanker's cargo compartments or tanks, usually expressed in barrels or cubic feet/meters.

Cubic Limitation - Reaching cargo tank capacity before vessel sinks to its load-line. This is usually caused by loading a light crude (crude with a high API) or clean products.


Davits - A set of arms on a ship from which its lifeboats are suspended.

Deadfreight - Non-utilization of cargo carrying capacity on a vessel.

Deadweight - Deadweight Tonnage (DWT) - The lifting or carrying capacity of a ship when fully loaded. This measure is expressed in long tons when the ship is in salt water and loaded to her marks. When loaded to her summer marks the value is for her summer deadweight (SWDT). It includes cargo, bunkers, water, (potable, boiler, ballast), stores, passengers and crew.
1 Long Tons = 2,204.6 lbs.

Deadweight Scale - A table that is part of the vessel plans and indicates the draft the vessel will be down to at any particular phase of loading.

Deck - A platform or horizontal floor that extends from side to side of a ship. The main deck is the highest complete deck on a ship (the one which runs the full length of the ship).

Deck Log - Also called Captain's Log, scrap logbook or rough logbook. A full nautical record of a ship's voyage, written up at the end of each watch by the deck officer on watch. The principle entries are: course steered; distance run; compass variations, sea and weather conditions; ship's positions, principal headlands passed; names of lookouts, and any unusual happenings such as fire, collision, and the like.

Deck Officer - As distinguished from engineer officer, refers to all officers who assist the master in navigating the vessel when at sea, and supervise the handling of cargo when in port.

Deck Stores - The spare gear and consumable stores provided for the upkeep and safe working of the tanker and her cargo, excluding stores used in engine room.

Deep Water Route - A designated area within definite limits which has been accurately surveyed for clearance of sea bottom and submerged obstacles to a minimum indicated depth of water.

Demise Charter- Also called bareboat charter in which the bare ship is chartered without crew; the charterer, for a stipulated sum, taking over the vessel with a minimum of restrictions usually for 10 or more years. See Bareboat Charter.

Demurrage Amounts paid by charterers to the owners of a vessel under a spot charter for time used for charterers' business in port, over and above the amount allowed for in the Charter Party, according to the terms, conditions and exceptions laid out in the Charter Party. Demurrage calculations can often be very complex.

Density - The density of a homogeneous substance is the ratio of its mass to its volume. The density varies as the temperature changes and it is usually expressed as the mass per unit volume at a specified temperature.
Absolute Density - The mass of a substance per unit volume at a specified temperature.

Relative Density - The ratio of the mass of a given volume of fluid to the mass of an equal volume of pure water at the same temperature and pressure. Relative density replaces the term "specific gravity".

Relative Density At 60° - Fluid relative density measured against water with both materials at 60 degrees F and reference pressure of 14.696 psia (or equilibrium pressure). Equivalent to "RD 60/60".
Deviation - A departure from a voyage pattern on either the forward or return leg of a voyage.

Dirty Ballast - Applies to the seawater used for ballast when it is contaminated with the remnants or residue left in cargo tanks that previously carried crude persistent refined oils.

Dirty Ship - Refers to tankers that have been carrying crude oil and heavy persistent oils such as fuel oil and dirty diesel oils.

Dispatch - The function of issuing voyage instructions or sailing orders to vessels. Also an agreed amount to be charged by terminals for prompt vessel turn around.

Dispatch Days - Days saved in the loading and discharge of a cargo vessel within the (lay) time allowed under the charter party. Note: Dispatch is not usually applied in the tanker business.

Displacement Tonnage - Expressed in tons it is the weight the water displaced by the vessel which in turn is the weight of the vessel at that time. The vessel's light displacement is the weight of the vessel only and the vessel's loaded displacement is the weight of the vessel and all cargo, stores, fuel, water, etc. on board.

Disponent Owner - Charterer who has sublet the vessel and is acting as the owner per the terms of the contract.

DOC. Document of compliance - This is a certificate issued to the operating company to attest to its compliance to the ISM (International Safety Management) rules.

Double Bottom - A general term used for all watertight spaces contained between the outside bottom plating, the tank top and the margin plate. Double bottoms are usually sub-divided into a number of separate tanks and can be used to hold clean ballast, potable or boiler feed water, or fuel. They also provide a measure of protection for cargo tanks if bottom plating is damaged in the event of grounding. Chances of pollution may be diminished due to this protection.

Double Hull Often referred to as double skin - A design of tanker which has double sides and a double bottom. The spaces created in the double sides and bottom are used for ballast, and provide a protective distance between the cargo tanks and the outside world.

DPP or dirty petroleum products - Liquid products refined from crude oil, whose color is greater than 2.5 on the National Petroleum Association scale. DPP's will usually require heating during the voyage as their viscosity or waxiness would make discharge difficult at ambient temperature. DPP's include Fuel oil, Low Sulfur Waxy Residue (LSWR) and Carbon Black Feedstock (CBFS).

Double Sided - Hull construction design in which a tanker has an inner and outer side.

Draft - The depth of a ship in the water. This distance is measured from the bottom of the ship to the surface of the water. Draft marks are cut into or welded on the surface of a ship's plating. They are placed forward and aft on both sides of the hull and also amidships. At the midships draft we will also find the authorized Load Line markings which designate maximum drafts allowed for vessels under various conditions.


Dry Certificate - A document issued at the discharge port by a representative of the consignee indicating that each shipboard cargo tank has been completely discharged.

Drydock, or d/d - Periodically all vessels must enter a drydock as part of the vessel's maintenance procedures and survey requirements to allow for various inspections and maintenance work. This will usually be conducted every 2 2.5 years although some more modern vessels are designed to go 5 years between drydockings
DWT, or Deadweight The cargo carrying capacity of a vessel, in metric tonnes, plus the weight of bunkers, stores, fresh water etc.


Ensign - The flag carried by a ship as insignia of her nationality.

"ETA" - Estimated Time of Arrival.

Even Keel - The existing conditions of a vessel whose fore and aft drafts are equal.


Filling Density - The ratio of the weight of liquid in a tank to the weight of distilled water at 60° F. the tank will hold. It is expressed as a percent.
Fixing This is the term used for concluding a charter party negotiation. A charter party contract is often referred to as a 'fixture'. A vessel whose next employment has been arranged is referred to as 'fixed'.

Flag State - Any state that allows ships to be registered under its laws.

Flags of Necessity (or Convenience) - Flag states that provide lesser economic, financial, tax and/or regulatory burdens to ship owners registering their ships in those countries.

Flame Screen (or Arrester) - A device comprised of a fine wire gauze that is fitted into the discharge end of a vent line. It prevents the passage of flame, but will allow vapor to pass through. Flame screens are also fitted to removable ullage plugs used to cover ullage holes on cargo tank tops.

Force Majeure - Clause permitting contract to be broken in the event of uncontrollable events, e.g. war, strike government action, which preclude its fulfillment.

Fore, Foreward - Toward the stem or the bow. The section of the vessel between the stem and amidships.

Forepeak - The narrow extremity of the vessel's bow. Also the tank located in that part of the ship.

Frames - The ribs of a ship.

Free on Board (FOB) - Incoterm. The charterer is responsible for the cost of loading the cargo.

Freeboard - The distance from the water line to the top of the weather deck on the side.

Freight Rate - The charge made for the transportation of freight.

Fuel Oil - A name given to the heaviest grades of residual fuel used in marine oil burning boilers.


Gangway (Gangplank) - A device by which persons come on board or disembark the vessel.

Gas Free - An atmospheric condition in a tank when it is free from any concentration of inflammable, noxious or toxic gases and vapors.

Gas Free Certificate - A certificate issued by a chemist after sampling the air in a tanker's cargo tanks after the cargo has been pumped out. It is endorsed with one of the following notations: (1) Safe for men, (2) Not safe for fire, (3) Safe for men and fire, (4) Not safe.

Gauging - A process of measuring height of a liquid in a storage tank usually using a weighted graduated steel tape and bob.

General Arrangement Plan - A drawing of a ship which lists all necessary statistics and operating information such as LOA, SDWT, cargo, water, fuel capacity, etc. The deadweight scale is also contained on this important chart which is usually posted outside the ship's office or mate's cabin.

General Average - A general contribution of money paid by all parties concerned in a marine adventure in direct proportion to their several interests when a voluntary or deliberate sacrifice has been made of one or more of the party's goods in time of peril with a view to saving the remainder of the property.

Gross Tonnage (GT, or GRT) - A measurement of volume including most of the confined spaces on board a vessel. The figure is often used as a basis for calculating port charges.


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HW - High water in port as determined by tides which might affect the amount of cargo a vessel can load.

Handy Size - Tankers of about 12,000 to 25,000 DWT.
Handymax tanker Tanker of about 30 50,OOOmt dwt.

Harbor Dues - Various local charges against all seagoing vessels entering a harbor, to cover maintenance of channel depths, buoys, and lights. etc. All harbors do not necessarily have this charge.

Hawse Pipe, Hawse - The hole in the bow through which the anchor chain passes.

Hawser - A cable used in warping or mooring the vessel.

Heating Coils - Coils located in the bottom of cargo tanks that steam passes through to heat cargo. The heat lowers the viscosity of the cargo and permits easier pumping of the cargo at the discharge port. Vessels in clean service normally do not have or need heater coils as the viscosity of the clean products (with the exception of some lube oils) is high enough to permit easy pumping at atmospheric temperatures.

Hog (Hogging) - The condition of a vessel caused by the unequal distribution of cargo. When a vessel loads too heavily at the ends it causes an arching, or bending upward, of the hull at the midships area. This can also be caused by the vessel working in heavy seas with a large wave under the amidships section.

Hull - The body of the vessel not including its masting, rigging etc.


IMO - International Maritime Organization, a United Nations agency that issues international trade standards for shipping.

In Class - A vessel currently meeting all the requirements of its Classification Society is "in-class".

Inert Gas (IG) - A gas used by marine tank vessels to displace air in cargo tanks to reduce oxygen content to 8 percent or less by volume and thus reduce possibility of fire or explosion. The inert gas used is usually nitrogen, carbon dioxide or a mixture of gases such as flue gas.

Inert Gas System (IGS) - A mechanical method of introducing inert gas into a vessel's tanks. An inert gas is one which has little or no ability to react with other gases, or to heat. Examples of inert gases are nitrogen and CO2. Shipboard inert gas systems utilize CO2, either from flue gas sources or from inert gas generators.

Inerting - A procedure used to reduce the oxygen content of a vessel's cargo spaces to 8 percent or less by volume by introducing an "inert" gas blanket such as nitrogen or carbon dioxide or a mixture of gases such as flue gas.

Innage - The amount of space within a tank that is occupied by oil. Innages are sometimes called soundings or body gauges.

Inshore Traffic Zone - A designed area between the landward boundary of a traffic separation scheme and the adjacent coast intended for coastal traffic.

Inspector - A person assigned to determine the quantity and/or the quality of a commodity.
Company Inspector - A Company employee given the responsibility of determining the quantity and/or the quality of a volume of oil being moved or stored.

Independent Inspector (Cargo Surveyor) - A person or organization of persons acting independently, but on behalf of, one or more parties involved in the transfer, storage, inventory or analysis of a commodity for purposes of determining the quantity, and/or quality of a commodity. They may also be assigned to the calibration of various measurement instruments and/or storage tanks ashore or on vessels.

Intake Certificate - A document issued by the shipper indicating the amount of cargo loaded aboard the vessel as calculated from the shore tank gauges. Freight is paid on the basis of these figures.

Intermediate Fuels - Light, residual-type fuel oils with characteristics between bunker fuel and marine diesel fuel, typically used in motor ships. It is quoted in terms of Redwood per second.

International Loadline Certificate - A document issued by a classification society stating the minimum freeboard granted to a vessel and giving the position of the loading disc on the ship's side.

Intertanko - International Association of Independent Tanker Owners.

IP - Institute of Petroleum

ISGOTT - International Safety Guide for Tankers and Terminals

Isherwood System - A method framing a vessel which employs closely spaced longitudinals with extra heavy floors spaced further apart. Most tankers use this type of framing system.

ISM. International Safety Management - A set of regulations that operators of tankers must comply with, which aims to improve the safety standards of the tanker industry.


Jacob's Ladder - A rope ladder with wooden rounds used for getting on or off a vessel not at a berth. Also referred to as a pilot's ladder because of its extensive use by vessel's pilots.

Jettison - The act of throwing goods or pumping cargo overboard to lighten a ship to improve stability in an emergency.


Keel - The backbone of the ship. It is a longitudinal beam or plate in the extreme bottom of a ship from which the ribs or floors start.

Knot - A nautical mile (6,080 ft.).


Laden Loaded with cargo - The opposite is 'in ballast'.

Laden/ballast ratio - A comparison of the time the vessel spends employed compared with the time spent without a cargo, which is sometimes used as a management tool to assess performance.

Lay days - The period of time described in the charter party during which the owner must tender his ship for loading. The charterer is not obliged to start loading before the commencement of lay days. The charterer may cancel the charter if the ship does not tender prior to the expiration of lay days.

Laytime On a spot voyage - laytime is the amount of time in port granted by the owners of the vessel under the terms of the charter party for the charterers to arrange for the loading and discharging of the cargo. The usual amount of total time allowed to charterers in the tanker trades is 72 running hours. Any excess time used will be paid for at an agreed rate. This is known as demurrage. In the tanker trades, any time saved (dispatch) will not be credited to charterers, however.

Length Between Perpendiculars (LBP) - The length of the vessel measured between the forward part of the stem to the after part of the rudder post.

Letter of Protest or Notice of Apparent Discrepancy - A letter issued by any participant in a custody transfer citing any condition with which issue is taken. This serves as a written record that the particular action or finding was questioned at the time of occurrence.

Length Overall (LOA) - The extreme length of the vessel measured from the foremost part to the aftermost part of the

Lighter - 1) General name for a broad, flat-bottomed boat used in transporting cargo between a vessel and the shore. The distinction between a lighter and a barge is more in the manner of use than in equipment. The term "lighter" refers to a short haul, generally in connection with loading and unloading operations of vessels in harbor while the term "barge" is more often used when the cargo is being carried to its destination or over a long distance. 2) To load or discharge cargo to or from another vessel. VTBL vessel to be lightered.

Lighterage - 1) Fee charged for conveying cargo by lighters or barges. 2) Area where vessels normally lighter.

Lightering - Conveying cargo with another vessel known as a lighter from a ship to shore, or voyage.

Lightweight - A measurement of mass representing the weight of the ship when completely empty. Usually expressed in long tons (22401bs).

Limited Liability - The law that permits a shipowner to restrict his liability to the value of this vessel after the accident plus the earnings for the voyage.

Limber Holes - Holes in the bottoms of stringers through which cargo flows through to the suction strums. List - The leaning of the vessel to the port or starboard.

Lloyd's Register of Shipping - British classification society.

LOA - Length overall The length of the vessel from stem to stern. A handymax may have an LOA of 180m, a modern panamax 225m, a VLCC over 300m.

Load Displacement - The displacement of a vessel when it floats at its loading draft.

Load Line - The maximum draft to which the vessel may load. The line on a vessel indicating the maximum depth to which that vessel can sink when fully loaded with cargo. Also known as its marks.

Load on Top (LOT) - is defined as both a procedure and a practice.
Procedure: Load on top is the shipboard procedure of collecting and settling water and oil mixtures, resulting from ballasting and tank cleaning operations (usually in a special slop tank or tanks), and subsequently loading cargo on top of and pumping the mixture ashore at the discharge port.

Practice: Load on top is the act of commingling on-board quantity with cargo being loaded.

Loaded Passage - The passage during which the tanker is carrying cargo.

Log - An apparatus for measuring the speed of a vessel through the water. Also, an entry made in a logbook to record any event e.g. to enter in the logbook the name of a seaman and his offense and the penalty attached to it.

Long Ton - A unit of weight = 2,240 pounds or 1,106 kilos.

LOOP - The Louisiana Offshore Oil Port, a 19 mile-long underwater pipeline connecting Louisiana with offshore tankers. The LOOP provides VLCCs and VPLUSs with an alternative method of delivering crude oil to port rather than Caribbean transshipments and lightering.

LRi and LR2 - Size of clean vessel equivalent to panamax and aframax, which see. LR stands for Long Range.

LT - or long ton Imperial weight measurement equal to 22401bs. A long ton is 1.6% heavier than a metric tonne.

Lumpsum - The alternative to fixing on a'Worldscale' basis for spot charter parties, is to fix an agreed lumpsum freight amount for a specific voyage. Lumpsum fixtures are more common in the products trades than in the crude oil markets.


MARPOL regulations - A series of internationally ratified IMO regulations pertaining to the marine environment and the prevention of pollution.

Marine Surveyor - A duly qualified person who examines ships to ascertain their condition, on behalf of owners, underwriters, etc. Also called "ship surveyor" or simply "surveyor".

Maritime Law - That system of jurisprudence that prevails in courts having jurisdiction of marine causes. Also called marine or admiralty law. It is a branch of both international and commercial law.

Mean Draft - The average of the drafts measured at the bow and the stern.

Metric Ton - A unit of weight 2,204.6 pounds (1,000 kilograms).

Midship Draft - The draft read at the midship markings. This draft can, and often does, differ from the Mean Draft due to hogging or sagging.

Molded Breadth - The breadth of the hull at the widest part, measured between the outer surfaces of the frames.

Molded Depth - The depth measured between the top of the keel, or lower surface of the frame at the center line, and top of the upper deck beam at the gunwale.

Mooring Line - Any hawser by which a vessel is secured to a dock or mooring. It may be made of natural materials (manila), synthetics, (polypropylene), or wire. Under certain circumstances the anchor chain is detached from the anchor and a section of that is used to secure the vessel.

MR - Another term for a tanker of around 25 50,000mt dwt (see handymax). MR stands for Medium Range.

MT, or metric tonne - A unit of weight, one tonne being 1000kg. Note that one cubic metre of fresh water (SG 1.00) at 15C will weigh exactly one metric tonne.


N/B - New building.

Net Capacity - The number of tons of cargo which a vessel can carry when loaded in salt water to her summer freeboard marks. Also called cargo carrying capacity, cargo deadweight, and useful deadweight.

Net Registered Tonnage - The internal capacity of a vessel measured in units of 100 cubic feet less the space occupied by boilers, engines, shaft alleys, chain lockers, officer's and crew quarters and other spaces not available for carrying passengers or freight. Net registered tonnage is usually referred to as registered tonnage or net tonnage.

Net Tonnage - The volumetric cargo capacity of a ship expressed on the basis of 100 cubic feet to the ton. On passenger vessels it also includes space used by passengers.

Norske Veritas - Norwegian classification society.

Notice of Readiness (NOR) - Notice served by the Master to inform the terminal/charterer the vessel is ready in all respects to load or discharge cargo.


OBQ (On Board Quantity) - The material remaining in vessel tanks, void spaces, and/or pipelines prior to loading. On-board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.

OCIMF - The oil companies' international marine forum is an organization of oil companies that own or operate ships.

Off-Specification Product/Cargo - Refined products or other cargo that does not meet normal quality requirements and therefore require special handling and restraints to assure separation from specification products/cargo.

Off-Hire Day - Each day, or part thereof, during which a tanker is not earning revenue from the charterer.

OPA90, or US Oil Pollution Act of 1990 - Legislation passed in the USA which details, amongst other things, certain regulations regarding the age and hull type of tankers, and vessel operators' liabilities and responsibilities with regard to the US marine environment.

OPEC - Organization of Petroleum Exporting Countries. Members include Algeria, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates and Venezuela.

Operating Costs - The costs incurred by the shipowner during a voyage or time charter, and by the charterer in a bareboat charter. Comprised mainly of: crew wages and associated costs; insurance (hull and machinery, and protection and indemnity premiums); cost of lubricants and spare parts; repair and maintenance (routine maintenance, dry-dockings and classification fees).

Outage (Ullage) - The depth of the space in a tank not occupied by oil. Same as ullage. It is measured from the flange of the ullage hole to the surface of the oil. Also the space left in a petroleum product container to allow for expansion as a result of temperature changes during shipment and use.

Out-Turn Certificate - A document issued by the receivers of cargo indicating the amount of cargo discharged.


Panamax - The maximum size ship that can fit through the Panama Canal in terms of width, length and draft generally about 80,000dwt.

Passage - A journey from one port or place to another, as distinguished from the term "voyage" which refers to a ballast and loaded passage. Also sometimes called trip.

Peak Tank - Tanks in the forward and after ends of the vessel. The principal use of peak tanks is in trimming the ship.

Per Calendar Day (Month/Year) Costs - Vessel's costs expressed as $ per day (month/year) for a calendar period during which the vessel was in service. The number of calendar days (months/years) are divided into the total costs incurred during the period.

Per Operating Day (Month/Year) Costs - Vessel's costs expressed as $ per day (month/(year) during which the vessel actually operated. It includes the costs incurred while the vessel was idle for repairs or other non-operating reasons. The number of operating days (excluding non-operating delays) are divided into the total costs.

PCNT - Panama Canal Net Tonnage A measurement based on volumes in accordance with the Panama Canal Authority rules, which is used to calculate the charges for transiting the Panama Canal.

Pilot House - The enclosed space on the navigating bridge from which a ship is controlled when underway.

Plating - The steel plates which form the shell or skin of the vessel.

Plimsoll Mark - The mark on the side of a classed vessel which indicates its safe load lines at varying seasonal conditions.

Port - The left side of a vessel when an observer is facing forward looking toward the bow. Also a door on a ship.

Port Charges - General term which includes charges and dues of every nature assessed against the vessel or its cargo in a port. It usually includes harbor dues, tub boat charges, pilotage fees, custom house fees, consular fees, etc.

Port of Registry - The port at which a vessel is registered and to which she is considered to belong. The port of registry is shown on the stern below the name of the vessel.

Port State - A state that has ports to which ships call. The port state makes regulations the calling ships must adhere to. The port state control is the controlling authority of the port state on shipping such as the coast guard or naval authorities.

Port Time (Two Types) - 1) Seabuoy to Seabuoy - The time elapsed between the vessel's passing the port's seabuoy upon entrance to re-passing it upon exit. It includes time for steaming in and out of berth, delays, hose connections, anchorage time, clearing and loading or unloading time. 2) Port to Port - Includes only time for delays, hose connections, anchorage time, clearing and loading or unloading time. Use must be consistent with voyage mileage basis.

Portable Measurement Unit (PMU) - A device designed to measure the ship's cargo when its tanks are closed to the atmosphere. It is used in conjunction with a vapor control valve.

Portable Sampling Unit (PSU) - A device designed to sample the ship's cargo when its tanks are closed to the atmosphere. It is used in conjunction with a vapor control valve.

Position Report (Position Sheets) - A summary of worldwide movements for vessel prepared by the Fleet Coordinators.

Posted Price (Contract Price) - The price for marine fuel oils which appears on a price list published by marine fuel oil (bunker) brokers.

Pour Point - The lowest temperature at which oil will remain liquid.

Premium - Surcharge over general market rate level to compensate the vessel's owner for an unusually difficult trade, e.g. Lake/Aruba, or to correct for an imbalance in supply/demand conditions in a given area.

Pressure/Vacuum Valve (P/V Valve) - An automatic dual purpose valve, commonly fitted in the vent lines of tankers. When in the closed position, the function of this valve is to relieve either pressure or vacuum in a tank. When in the open position it allows the passage of air or vapor into and out of the tank.

Pressure - The amount of force exerted on a unit of area by a fluid.
Absolute Pressure - The pressure referenced to a perfect vacuum as zero pounds per square inch absolute.

Atmospheric Pressure - The pressure exerted by the atmosphere. Although this pressure varies with altitude, barometric pressure and humidity, the atmospheric pressure can be defined in custody transfer contracts, or by state and federal authorities. Atmospheric pressure is most often stated as 14.696 pounds per square inch absolute.

Back Pressure - The operating pressure level measured upstream from a control valve.

Gauge Pressure - That pressure measured relative to atmospheric pressure as zero, usually designated psig.

High Vapor Pressure - A fluid which, at the measurement or proving temperature, has a vapor pressure that is equal to or higher than atmospheric pressure.

Low Vapor Pressure - A fluid which, at the measurement or proving temperature, has a vapor pressure that is less than atmospheric pressure.

Reid Vapor Pressure - The vapor pressure of a fluid at 100 degrees Fahrenheit as determined by test method ASTM D 323-58.

Static Pressure - The pressure in a fluid that is exerted normal to the surface. In a moving fluid, the static pressure is measured at right angles to the direction of flow.

Protest, Notice of - A letter issued by any participant in a voyage citing any condition with which issue is taken. This serves as a written record that the particular action or finding was questioned at the time of occurrence. For example a declaration made by the Master before a notary public or consular official when through stress of weather, there has been or the master fears that there might have been, damage to the vessel or cargo. Copies are frequently demanded by insurance underwriters in the event of a claim.

Protection & Indemnity Insurance - Mutual protection provided by an association of shipowners against liabilities not covered by insurance.

Pumproom - An enclosed area on a tank vessel which houses main and stripping cargo pumps, ballast pumps, educators and the associated piping and valves necessary for their operation.


Quarter - A side of a ship aft, between the main midship frames and stern. Also a side of the ship forward, between the main frames and stem.


Rate - The cost, or revenue, for a particular voyage based on a standard of reference, e.g. Worldscale, INTASCALE, ATRS.

Reducer- A short section of pipe, having one end of smaller diameter than the other and having a flange on each end, for connecting a smaller hose or pipe to a pipe of constant diameter.

Registry - A duty imposed on shipowners in order to secure to their vessels the privileges of ships of the nation to which they belong.

Re-Positioning - The movement of a vessel in ballast to shift it from one trading pattern to another.

Restricted Measurement System - A measurement system designed to measure the ship's cargo when its tanks are closed to the atmosphere. During measurements a minimum amount of cargo vapors might escape to the atmosphere

Relative Density - See DENSITY

ROB (Remain on Board) - The material remaining in vessel tanks, void spaces, and/or pipelines after discharge. Remaining on board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.

Rogue Wave - An ocean wave much larger than the current wave sequence. This wave may also be outside the current wave direction and may be 100 feet or more in height

Route - See Deep Water Route, Traffic Route, Two-Way-Route. Means Whichever type is appropriate in the context unless otherwise specified.

Routing - A complex of measures concerning routes aimed at reducing the risk of casualties; it includes traffic separation schemes, two-way routes, tracks, areas to be avoided, inshore traffic zones, and deep water routes.

Rudder - The flat or shaped frame hung to the sternpost of a ship, which is used to steer the ship.

Rules of the Road - The rules and regulations accepted by international agreement and enforced by law in marine countries which govern the movements of ships when approaching each other under such circumstances that a collision may possibly ensue.


Safe for Men - A term signifying that the vapor content of a space so certified is less than 0.1 on a gas indicator.

Safe for Men and Fire - A term signifying that the vapor content of a space so certified is 0.1 or less on a gas indicator and that the space contains no oil or sediment which could produce vapors.

Sag (Sagging) - The condition of a vessel caused by the unequal distribution of cargo. When a vessel loads too heavily in the center it causes a bending downward of the hull at the midships area. This can also be caused by the vessel working in heavy seas with large waves under each end and no support under the center of the ship. Sag is the opposite of Hog.

Sampling - The process of obtaining a sample of the material in the tank, container or pipeline to use for testing or other purposes. This can be achieved by automatic or manual means. The following are the most common types of samples taken:
All-Levels Sample - A sample obtained by lowering a weighted, stoppered bottle or beaker or bottle to a point 1 foot (0.3 meter) above the free water level and then, with a sharp jerk of the line opening the sampler and raising it at a rate that it is about 75% full (a maximum of 85% full) as it emerges from the liquid.

Automatic Sample - A sample taken by automatic means. The two basic types of automatic samples are:

Flow-Proportional Sample - A sample taken by an automatic sampler from a pipeline at a rate that is proportional to the liquid flow rate.

Time-Proportional Sample - A sample taken from a pipeline at regular intervals during a batch transfer period.

Bottom Sample - A spot sample taken from the material at the bottom of the tank.

Lower Sample - A spot sample obtained at the midpoint of the lower third of the tank contents.

Middle Sample - A spot sample obtained at the midpoint of the middle of the tank contents.

Running Sample - A sample obtained by submerging an unstoppered beaker or bottle from the surface of the liquid to a point as near as possible to the shore tank draw off point or about one foot above the level of the free water in a ship tank, and then raising it without letting it rest, at a rate so that it will be about 75% full as it emerges from the liquid.

Spot Sample - A sample taken at a specific "spot" within a tank using a stoppered bottle or beaker and lowering it to the level of desired sample then opening it and allowing it to remain at that level until full. A thief or a zone sampler may also be used to obtain spot samples.

Tap Sample - A sample taken from a valve or connection on a tank or pipeline.

Upper Sample - A spot sample obtained at the midpoint of the upper of the tank contents.

Upper, Middle, Lower Samples - Spot samples taken from the upper third, the middle and lower thirds of the liquid in the tank. The samples so taken may then be composited or analyzed separately.

Salvage - The property which has been recovered from a wrecked vessel, or the recovery of the vessel herself.

Scupper - Any opening or tube leading through the ship's side to carry water away from the deck.

Sea Trials - A series of trials conducted by the builders during which the owner's representatives on board act in a consulting and checking capacity to determine if the vessel has met the specifications.

Seaworthiness - The sufficiency of a vessel in materials constructions, equipment, crew and outfit for the trade in which the it is employed. Any sort of disrepair to the vessel by which the cargo may suffer; overloading; untrained officers; may constitute a vessel unseaworthy.

Seaworthiness Certificate - A certificate issued by a classification society surveyor to allow a vessel proceed after she has me with a mishap that may have affected its seaworthiness. It is frequently issued to enable a vessel to proceed, after temporary repairs have been effected, to another port where permanent repairs are then carried out.

Separation Zone or Line - A zone or line separating traffic proceeding in one direction from traffic proceeding in another direction. A separation zone may also be used to separate a traffic lane from the adjacent inshore traffic zone.

Ship's Agent - A person or firm who transacts all business in a port on behalf of shipowners or charterers. Also called shipping agent; agent.

Shipbreaker - A company that demolishes or cuts up vessels which are obsolete or unfit for sea. The steel is used for scrap.

Ship Chandler - Particular merchants handling ship's stores, supplies, and sundries, etc. Sometimes handles spare parts as accommodation to ship operators.

Shipper - The person for whom the master of a ship agrees to carry cargo. Also called consignor.

Short Ton - A unit of measurement equal to 2,000 pounds.

Sister Ships - Ships built on the same design.

Skin - The plating of a ship.

Slops - A mixture of petroleum and water normally arising from tank washings.

Sludge - A mixture of petroleum and water, usually semi-solid, frequently containing sand and scale.

SOLAS - Safety of Life at Sea Convention.

Sounding - See GAUGING

Special Survey - The survey requirement of a classification society that usually takes place every four years. At the special survey vital pieces of equipment are opened up and inspected by the classification surveyor.

Spill - Oil getting into the sea in any amount for any reason.

Spot Charter - See Voyage Charter.

Spot Market - The market for the immediate charter of a vessel.

Starboard - The right side of a vessel when an observer is facing forward looking toward the bow.

Stern - The after most part of a vessel. The stern will house the steering gear room and various stowage areas. It is that section of a vessel over the rudder and propeller.

Stem - The upright post or bar of the bow.

Stores - A general term for provisions, materials, and supplies used aboard ship for the maintenance of the crew, and for the navigation, propulsion and upkeep of the vessel and its equipment.

Submarine Loading Terminal - A terminal where loading is carried out by means of an offshore hose run along the sea bottom.

Suezmax Carrier - The maximize size ship that can sail through the Suez canal generally considered to be between 120,000-199,999 DWT depending on ships dimensions and draft. See also Vessel Sizes.

Superstructure - Any structure built above the uppermost complete deck such as a pilothouse, bridge, accommodation house etc.


Tackle - Any combination of ropes and blocks that multiply power. The equipment on a vessel used to perform working tasks on the vessel.

Tank Washing - The cleaning of a vessel's tanks. It is divided into two types of activities:
Water Washing - The use of a high-pressure water stream to dislodge clingage and sediment from the bulkheads, bottom, and internal tank structures of a vessel.

Crude Oil Washing - The use of a high-pressure stream of the crude oil cargo to dislodge or dissolve clingage and sediment from the bulkheads, bottom, and internal tank structures of a vessel during the discharge operation.

NOTE: Regulatory agencies require that a vessel's tanks be inerted before this tank cleaning method is used.

Tender (TO) - A master tenders his vessel when he advises the charterer or supplier that he is ready to load.

Time-Charter - The hiring of a tanker from a shipowner for a period of time. As operator, the shipowner is paid on a per-day basis and is responsible for providing the crew and paying operating costs. The charterer is responsible for paying the voyage costs, save for certain specific exceptions such as loss of time arising from tankers breakdown and routine maintenance. See "Voyage Charter" and "Bareboat Charter".

Thieving - Determining the amount of water at the bottom of a tank of oil.

Ton - Typical unit of weight measurement used on tankers. See Long Ton, Metric Ton, Short Ton.

Tonnage - See Deadweight, GRT and NRT.

Tonnage Tax - Taxes, fees, harbor dues etc. paid on the vessel based on a tonnage calculation.

Tonne - Metric ton.

Tons Per Inch Immersion (TPI) - The number of tons required to change a vessel's draft one inch in the water. TPI varies with the draft and it's values can be found on a vessel's deadweight scale. The metric equivalent is known as TPC (Tons per Centimetre)

Tonne- mile - Quantity transported multiplied by average voyage distance. Also Ton-mile.

Topping-Off - 1) the operation of completing the loading of a tank to a required ullage. 2) Filling up cargo tanks which were only partially filled at the loading port because of port or canal draft restrictions. The filling up occurs outside the loading port via lightering activities, or at another loading port.

Trim - The condition of a vessel with reference to it's longitudinal position in the water. It is the difference between the forward and after drafts expressed in feet/inches or meters/centimeters. Trim forward is called 'by the head' and trim aft is called 'drag'.

Trim By The Head (By The Stern) - A vessel is said to trim by the head (or stern) when its draft forward (or aft) is greater than aft (or forward).


Ullage - See Outage

Ullages - Measurements taken with a steel tape from the lip of the ullage hole to the to the surface of the liquid; usually read to the nearest 1/8 inch.

Underwriter - In marine insurance one who subscribes his name to the policy indicating his acceptance of the liability mentioned therein consideration for which he receives a premium.

Unseaworthiness - The states or condition of a vessel when it is not in a proper state of maintenance, or if the loading equipment or crew, or in any other respect is not ready to encounter the ordinary perils of sea.

U.S. Calls - Letter begin with "K". Liberian begin with numbers "A" or "E" or a numeral. Call letter must be used in cables after a vessel's name.

US Gulf - The Gulf of Mexico.

Used Laytime - The amount of lay time that was taken by the vessel for loading and discharging on a voyage.

VPLUS - Ultra Large Crude Carriers of above 320,000 DWT. See also Vessel Sizes.


Vapor Control Valve (VCV) - This valves is used in conjunction with closed and restricted measurement equipment to allow measurements in ship's tanks that are closed to the atmosphere. Once a portable measurement unit (PMU) is attached to the VCV, the valve is opened and the PMU's probe is dropped into the tank to perform the required measurements.

Vapor Recovery System (VRS) - Procedures and equipment for the collection of hydrocarbon vapors from vessel's tanks and the transfer to shoreside recovery equipment.

Vessel Experience Factor (VEF) - A factor based on the compilation of the history of the total calculated volume (TCV) vessel measurements, adjusted for on-board quantity (OBQ) or remaining on board (ROB), compared with the TCV shore measurements. This factor if developed according to the latest industry standards may be used to obtain a better ship shore comparison of volumes.

Vessel Sizes and Uses
Tankers and barges come in all sizes from the small harbor/lake variety to the biggest things ever built by man that move. The size of any particular tanker depends on many factors. Use, cargo type, amount and demand, passage length and port restrictions at both loadport and the discharge port are among the most important of these. Tankers were generally classified as follows:
Clean Tanker categories

Under 16,500 DWT - Coastal, Small, Harbor/Lake Tankers

16,500 - 24,999 DWT - General Purpose Vessels

25,000 - 49,999 DWT - Medium Range Vessels

50,000 - 79,999 DWT - LR1 (Large Range 1)

80,000 - 159,999 DWT - LR2 (Large Range 2)

Crude Tanker Categorie

55,000 - 79,999 DWT - Panamax Crude Carrier

80,000 - 119,000 DWT - Aframax Crude Carrier

120,000 - 199,999 DWT - Suezmax Crude Carrier

200,000-- 319,999 DWT - VLCC (Very Large Crude Carrier)

320,000 DWT & above - VPLUS (Ultra Large Crude Carrier)
Coastal, Small, Harbor/Lake Tankers - Under 16,500 DWT

These small ships supply terminals with a variety of products from heating oils gasolines and kerosene, to more exotic fuels and chemicals. They are predominantly product carriers and are also are used extensively for bunkering service in harbors and busy ports.

General Purpose Vessels - 16,500 - 24,999 DWT

On a worldwide basis, this class of vessel probably covers the largest range and variety of cargoes carried. This class of ship includes chemical carriers, special service product and crude oil vessels and serve mostly coastwise terminal trades.

Medium Range Vessels - 25,000 - 49,999 DWT

Medium sized tankers cover a broad range of vessel types. Ships of this size category are capable of carrying almost any kind of petroleum product. The smaller group will usually carry gasolines, jet fuels, chemicals and heating oils. The larger size of the group will carry heavier fuel oils and crude oils.

LR1 (Large Range 1) - 50,000 - 79,999 DWT (Clean Products)
LR2 (Large Range 2) - 80,000 - 159,999 DWT (Clean Products)

Vessels in this class that are less than 100,000 dwt are divided into two basic categories namely, "Dirty " and "Clean". The "dirty" vessels carry the "black" or dirty cargoes such as crude oil , heavy fuel oils, asphalt etc. The "clean" vessels carry the refined "white" clean products such as gasoline, jet fuels, kerosene etc. Chemical carriers would also fall into the "clean" category. Because of the strict tank inspection requirements for clean products, most proprietary vessels or those on long term charter or do not routinely change their trading patterns from clean to dirty or vice versa. However market requirements and charter economics do require vessels to sometimes slip in and out of these clean and dirty trades. Vessels in this class that are over 100,000 dwt tend to be crude oil carriers only.

Panamax - A tanker whose dimensions enable her to transit the Panama Canal where lock width is the determining factor. Ships are approximately 55,000 to 79,999 dwt.

Aframax - A tanker of approximately 80,000 to 120,000 dwt.

Suezmax - A tanker whose dimensions enable her to transit fully loaded through the Suez Canal. Ships are approximately 120,000 to 199,999 dwt.

VLCC (Very Large Crude Carrier) - 200,000-320,000 DWT

VPLUS (Ultra Large Crude Carrier) - 320,000 DWT and above

Because of their huge sizes these vessels have been almost exclusively only used for the carriage of crude oils. Only the smallest of this category has carried any type of refined products. Several of these VPLUS classed vessels were over 500,000 and the biggest of these ships had a deadweight of 564,939 tons.
Vetting - The general process of approving a vessel for use. (From old English "To Vet" - to look at or review again.) Note: actual procedure varies from company to company.

VLCC - Very Large Crude Carrier of 200,000 - 319,999 DWT. See also Vessel Sizes.

Volume - The amount of space occupied by a fluid at certain conditions of temperature and pressure. Various types of VOLUMES used in marine custody transfer are defined as follows:
Gross Observed Volume (GOV) - The total volume of all petroleum liquids and sediment and water, excluding free water, at observed temperature and pressure.

Gross Standard Volume (GSV) - The total volume of all petroleum liquids and sediment and water, excluding free water, corrected by the appropriate volume correction factor (Ctl) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60°F or 15°C and also corrected by the applicable pressure correction factor (Cpl) and meter factor.

Indicated Volume - The change in meter reading that occurs during a receipt or delivery.

Net Standard Volume (NSV) - The total volume of all petroleum liquids, excluding sediment and water and free water, corrected by the appropriate volume correction factor (Ctl) for the observed temperature and API Gravity, relative density, or density to a standard temperature such as 60°F or 15°C and also corrected by the applicable pressure correction factor (Cpl) and meter factor.

On Board Quantity (OBQ) - The material remaining in vessel tanks, void spaces, and/or pipelines prior to loading. On-board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.

Remaining On Board (ROB) - The material remaining in vessel tanks, void spaces, and/or pipelines after discharge. Remaining on board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.

Total Calculated Volume (TCV) - The total volume of all petroleum liquids and sediment and water, corrected by the appropriate volume correction factor (Ctl) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60°F or 15°C and also corrected by the applicable pressure factor (Cpl) and meter factor, and all free water measured at observed temperature and pressure (gross standard volume plus free water).

Total Observed Volume (TOV) - The total measured volume of all petroleum liquids, sediment and water, and free water at observed temperature and pressure.

NOTE: Where the term 60°F or 15°C is used, it is referring to two different reference standards and does indicate that the two temperatures are equal.
Voyage Charter - A contract in which a charterer pays a shipowner for the use of a ship's cargo space for one, or sometimes more than one, voyage. The shipowner is the operator, responsible for paying both operating costs and voyage costs. Also Spot Charter.

Voyage Costs - Fuel costs, port charges and canal dues (or tolls) incurred during the course of a voyage.


Wall Wash Test - The procedure of introducing an appropriate liquid into a vessel's tank to test for hydrocarbon, color and other contaminants. This test is done by physically pouring the liquid down vessel's tank bulkheads and trapping a portion on filter paper. This test is also done on vessel's steam coils and sumps.

Watertight Door - A door so constructed that, when closed, it will prevent water under pressure from passing through.

Water/Cut Measurement - The procedure of locating the oil/water interface for the purpose of determining the volume of free water in a shore tank or vessel compartment. It is also used to refer to the line of demarcation of the oil/water interface.

Wedge Formula - A mathematical means to approximate small quantities of liquid and solid cargo and free water on board prior to loading and after discharge based on cargo compartment dimensions and vessel trim. The wedge formula is to be used only when the liquid does not touch all bulk heads of the vessel's tanks.

Wedge Table - A pre-calculated vessel table based on the wedge formula and displayed much like the vessel's usual innage/ullage tables. These tables, however, are for small quantities (on- board quantities, remaining on board) when the cargo or free water does not touch all bulkheads of the vessel tank.

Wing Tanks - Vessel tanks located to the port or starboard of the centerline and designated port or starboard wings or wing tanks.

Wipe Test - The procedure of physically wiping random interior areas and steam coils of vessel's tanks with absorbent white rags. This procedure is used to test the tank's coating for possible color contamination.

Worldscale - The New Worldwide Tanker Nominal Freight Scale is a catalogue of theoretical freight rates expressed as US dollars per tonne for most of the conceivable spot voyages in the tanker trade. The final rate agreed will be determined as a percentage of the 'Worldscale' rate, based upon a guaranteed minimum quantity of cargo. This allows for charter parties to cover a wide range of possible voyage options without the need to calculate and negotiate each one separately.