USCG Master 100 key terms

The vessel required to keep its course and speed when two power-driven vessels meet in a crossing, head-on, or overtaking situation, unless a risk of collision requires action.

The vessel required to take early and substantial action to keep clear of the other vessel in a crossing, head-on, or overtaking situation, as required by the navigation rules.

A meeting between two power-driven vessels whose courses cross, where one sees the other on its own starboard side and must give way to the vessel on its starboard side.

A meeting of two power-driven vessels approaching on nearly reciprocal courses, where each must alter course to starboard and pass port-to-port.

A vessel approaching another from more than 22.5 degrees abaft its beam, which must keep clear of the vessel being overtaken until finally past and clear.

Conditions such as fog, rain, or smoke that reduce visibility, requiring vessels to proceed at a safe speed, sound fog signals, and use radar where fitted.

A waterway of limited width where vessels must keep as near the outer limit on their starboard side as is safe and practicable, and avoid crossing if it impedes others.

The speed at which a vessel can take proper and effective action to avoid collision and stop within a distance appropriate to the prevailing circumstances and visibility.

A situation where the bearing of an approaching vessel does not appreciably change, indicating that collision may occur unless one or both vessels take action.

A white light placed on the fore-and-aft centerline of a power-driven vessel, showing forward over an arc of 225 degrees, used to indicate the vessel's heading.

A red light on the port side and a green light on the starboard side, each showing over an arc of 112.5 degrees from ahead to 22.5 degrees abaft the beam.

A vessel that, through exceptional circumstances such as machinery failure, is unable to maneuver as required and therefore displays two red lights or balls at night or by day.

A direction measured clockwise from true north, expressed in degrees from 000 to 360, and used as the reference for chart work and position plotting.

The angular difference between true north and magnetic north at a given location, which changes slowly over time and is shown on nautical charts.

The angular error in a magnetic compass caused by the vessel's own magnetic fields and metal structures, varying with the vessel's heading.

A method of estimating a vessel's position by advancing the last known position using course and speed through the water, without correcting for current.

A vessel's position determined from two or more intersecting lines of position, such as bearings, ranges, or GPS, plotted on a chart.

A line on a chart along which the vessel must lie, derived from a single observation such as a bearing, range, or measured depth.

The direction toward which a current carries a vessel (set) and the speed at which it does so (drift), used to correct dead reckoning and plan courses.

A position obtained by advancing an earlier line of position along the vessel's track and crossing it with a later line of position taken on a different object.

The reference level, usually lowest astronomical tide, to which depths and drying heights on a nautical chart are referred so that charted depths are conservative.

The buoyage system used in North and South America and parts of Asia where, when entering from seaward, red buoys are kept to starboard and green buoys to port.

The vertical distance from the waterline to the deck edge or freeboard mark, indicating how much hull remains above the water to resist flooding and provide reserve buoyancy.

The vertical distance from the waterline to the lowest point of the hull or keel, which determines the minimum depth of water the vessel can safely navigate.

The weight of water displaced by a floating vessel, equal to the vessel's total weight including cargo, fuel, stores, and crew.

The difference between the forward and after drafts of a vessel, describing whether it floats level, by the bow, or by the stern.

A permanent or temporary tilt of a vessel to one side caused by off-center weight distribution, not by the vessel's designed trim.

The equipment used to anchor a vessel, including the anchor, chain or rode, shackles, and windlass, selected for holding power and bottom type.

The ratio of anchor line or chain paid out to the depth of water beneath the bow, typically 5 to 7 to 1 for chain in good holding ground.

A mooring line led fore and aft from a vessel to a dock or piling to prevent the vessel from moving ahead or astern along the berth.

A designated location on board where crew and passengers assemble during an emergency to be counted, briefed, and prepared for abandonment or other action.

The order and process of leaving a vessel that is in danger of sinking or fire, using lifeboats, liferafts, or survival craft after donning appropriate gear.

A full-body protective garment that reduces heat loss in cold water, designed to be worn during abandonment and to keep the wearer dry and buoyant.

A life jacket or buoyant vest approved for the wearer's size and activity, designed to keep the head above water and turn an unconscious person face-up.

An Emergency Position Indicating Radio Beacon that transmits a distress signal with the vessel's identity and position to satellites when activated in an emergency.

A Search and Rescue Transponder that, when interrogated by radar, displays a series of dots on the rescuer's radar screen to help locate a survival craft.

A fire involving flammable liquids such as fuel, oil, or paint, which is extinguished by smothering with foam, CO2, or dry chemical rather than water.

An emergency in which a person falls into the water, requiring immediate rudder and engine response, a lookout, and prompt recovery while maneuvering to keep the person in sight.