USCG Barge Supervisor key terms

The vertical distance measured from the waterline to the deck line at the side of the vessel. It indicates how much reserve buoyancy remains and decreases as the barge is loaded deeper.

The vertical distance from the waterline to the lowest point of the hull. It increases as cargo is loaded and is used to calculate displacement and verify available water depth.

The difference between the forward and after drafts of a vessel. A barge trimmed by the stern or bow affects pumping, cargo distribution, and handling characteristics.

A permanent or temporary tilt of a vessel to one side, measured in degrees from vertical. It results from off-center weight and must be corrected before transfer operations begin.

The point at which the total weight of the vessel and its contents is considered concentrated. Its vertical and transverse position determines stability and list.

The geometric center of the underwater hull volume, where the total buoyant force acts. It shifts as the vessel heels or changes draft.

The point about which a vessel rotates when inclined through small angles, found where the vertical line through the new center of buoyancy crosses the vessel's centerline. Its height above the center of gravity indicates initial stability.

The distance between the center of gravity and the metacenter, abbreviated GM. A positive value means the vessel is stable; a large value means stiff and quick-rolling, while a small value means tender.

The horizontal distance between the center of gravity and the center of buoyancy when a vessel is heeled, producing the moment that returns it upright. Often plotted as the GZ curve.

The loss of effective stability caused by liquid moving freely in a partially filled tank or hold. It raises the apparent center of gravity and worsens as tank breadth increases.

A tank that is not filled to the top or completely emptied, leaving a liquid surface free to shift. Slack tanks reduce stability and should be minimized during cargo operations.

The total weight of water displaced by a floating vessel, equal to the vessel's total weight including cargo, fuel, and stores. It is expressed in tons and read from a hydrostatic table or deadweight scale.

The total weight a vessel can carry when loaded to its assigned load line, including cargo, fuel, water, and stores. Cargo deadweight is deadweight minus non-cargo weights.

A mark on the side of a vessel showing the maximum permitted draft under various water and seasonal conditions. It is assigned by a classification society and enforced by port state control.

A measurement of the depth of liquid in a tank, taken with a sounding tape or float gauge. Soundings before and after transfer verify tank contents and detect leaks or valve errors.

The empty space between the liquid surface in a tank and the top of the tank, expressed as a depth or volume. Adequate ullage allows for expansion and prevents overflow during loading.

Water or other weight taken aboard to improve stability, control trim, or submerge the propeller. Ballast must be managed to avoid introducing invasive species and to maintain stress limits.

A flexible line connecting the barge manifold to the shore or receiving vessel for transferring liquid cargo. It must be pressure-tested, inspected, and supported to prevent kinking or strain.

The arrangement of valves, flanges, and piping on a barge where cargo hoses or loading arms connect. Correct lineup of manifold valves prevents cross-contamination and uncontrolled flow.

The final stage of loading a tank at a reduced rate to bring the liquid level to the desired ullage without overflow. It requires close communication between the barge and the loading facility.

The volume of cargo moved per unit time during a loading or discharge operation. It is agreed in the transfer plan and limited by hose size, pump capacity, and venting capability.

A closed transfer system in which displaced vapors from the receiving tank are returned to the supplying tank rather than released. It reduces air emissions and fire risk from volatile cargoes.

The lowest temperature at which a liquid gives off enough vapor to ignite briefly when exposed to an ignition source. It is the primary basis for classifying flammable and combustible cargoes.

The minimum concentration of vapor in air, expressed as a percent by volume, that will support combustion. Below this level the mixture is too lean to burn.

The maximum concentration of vapor in air above which the mixture is too rich to burn. Between the lower and upper limits lies the flammable range.

The pressure exerted by a vapor in equilibrium with its liquid at a given temperature. High vapor pressure cargoes require closed systems and careful venting to prevent tank overpressure.

A gas, typically cleaned flue gas or nitrogen, with low oxygen content introduced into a tank to keep the atmosphere below the flammable range. It prevents explosions during cargo operations.

The condition of a tank or compartment after removing flammable, toxic, or inert gases so that it contains breathable air suitable for entry. Certification is required before personnel enter.

Entering an enclosed space such as a tank, hold, or cofferdam with limited access and poor ventilation. It requires a permit, atmospheric testing, a standby person, and rescue equipment.

Any operation producing sparks, flame, or high heat, such as welding or grinding. It requires a permit, gas-free certification, fire watch, and removal of combustible material before starting.

A person assigned to monitor an area for fire during and after hot work or hazardous operations. They maintain firefighting equipment, sound the alarm, and watch for re-ignition after work stops.

The three elements needed for combustion: fuel, oxygen, and heat. Firefighting removes at least one element by cooling, smothering, or starving the fire.

A fire involving flammable or combustible liquids such as fuel, oil, or solvents. It is fought with foam, carbon dioxide, or dry chemical rather than a solid water stream.

An extinguishing agent that blankets a burning liquid surface, smothering the fire and preventing vapor release. It is the preferred agent for large Class B fires on barges.

Permanently installed equipment such as a deck foam system, CO2 system, or water spray used to fight fire without manual hose handling. It must be inspected and tested on a schedule.

A vessel-specific document describing procedures, equipment, and contacts for responding to a discharge of oil or hazardous material. It is required by regulation and drilled periodically.

A required log recording all transfers, discharges, and disposals of oil and oily mixtures on the vessel. Entries must be complete, timely, and signed by the person in charge.

The International Convention for the Prevention of Pollution from Ships, which regulates oil, chemical, sewage, garbage, and air pollution from vessels. Annexes set discharge limits and equipment requirements.

The amount of a hazardous substance release that must be reported to authorities. Notification is required immediately when a discharge reaches or exceeds this threshold.

A floating barrier deployed around a spill or vessel to contain oil and keep it from spreading. Correct anchoring and overlap at connections are essential for effectiveness.

A device that removes oil from the water surface by adhesion, weir, or suction. It is deployed with booms during spill recovery operations.

The international and inland navigation regulations governing vessel conduct, including right-of-way, lights, shapes, and sound signals. They determine which vessel must give way in a meeting or crossing situation.

The vessel required to keep clear of another under the navigation rules. It must take early and substantial action to avoid collision and avoid crossing ahead of the stand-on vessel.

The vessel with the right of way that must hold its course and speed. It may still take action to avoid collision if the give-way vessel fails to do so.

Lights displayed by a vessel at night or in restricted visibility to indicate its type, heading, and status. They include sidelights, masthead lights, stern lights, and special lights for towing or restricted maneuverability.

A rope or wire used to secure a barge to a dock, buoy, or another vessel. Lines must be sized for the load, inspected for wear, and tended as tide and draft change.

The wires, shackles, and fittings connecting a tug to its tow, including the tow wire and bridle. Regular inspection and proper sizing prevent breakage and loss of the tow.

A systematic examination of hull, tanks, piping, and equipment to verify condition and regulatory compliance. Findings are logged and deficiencies corrected before operations continue.