BD Deck Officer Class 2 (Chief Mate) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Great-circle distance formula

The great-circle distance D satisfies cos D = sin φ1 sin φ2 + cos φ1 cos φ2 cos Δλ, where φ is latitude and Δλ is difference of longitude.

Mercator departure formula

Departure in nautical miles equals difference of longitude in minutes multiplied by the cosine of mean latitude; this approximates east-west distance on a Mercator chart.

Sextant intercept

Intercept equals observed altitude minus calculated altitude; it is plotted toward the geographical position if observed altitude is greater, and away if smaller.

Rule of twelfths

During a six-hour tide, the rise or fall is divided into twelfths: 1, 2, 3, 3, 2, and 1 twelfth in successive hours.

Stowage factor

Stowage factor is cargo volume in cubic metres divided by cargo mass in tonnes; it indicates the space one tonne of cargo occupies.

Broken stowage

Broken stowage is the unused space in a cargo hold caused by shape, packaging, or dunnage; it is expressed as a percentage of available volume.

Cargo sweat

Cargo sweat is condensation on cargo when warm moist air meets a colder cargo surface; ventilation and dew-point control reduce its formation.

IMDG segregation code

The IMDG segregation code ranges from 1 to 4: away from, separated from, separated by one compartment, and separated by two compartments.

Metacentric height GM

GM equals KM minus KG, where KM is height of metacentre above keel and KG is height of centre of gravity; positive GM gives initial stability.

Free-surface correction

Free-surface correction equals free-surface moment divided by displacement; it reduces effective GM when a tank is slack.

Angle of loll

Angle of loll is the heel at which a ship with negative initial GM has zero righting lever; the vessel is unstable upright and may flop to either side.

Floodable length

Floodable length is the greatest compartment length that can be flooded without submerging the margin line, given the ship's subdivision and permeability.

STCW rest hours

STCW requires at least 10 hours rest in any 24 hours and 77 hours in any 7 days, with rest split into no more than two periods.

MLC work limits

MLC 2006 sets maximum work at 14 hours in 24 and 72 hours in 7 days, or minimum rest at 10 and 77 hours respectively.

Enclosed space entry

Enclosed-space entry requires risk assessment, atmosphere testing, a permit, a standby person, communications, and rescue equipment before entry.

Territorial sea width

Under UNCLOS the territorial sea extends up to 12 nautical miles from baselines; the coastal state exercises sovereignty subject to innocent passage.

MARPOL Annex V

MARPOL Annex V regulates garbage discharge from ships; discharge is generally prohibited except for specified food waste and outside special areas under set conditions.

General average

General average is a deliberate sacrifice or extraordinary expenditure incurred for the common safety of ship, cargo, and freight; all contributors share the loss.

Bill of lading title

A bill of lading is a receipt, evidence of the carriage contract, and a document of title; possession can transfer rights to the goods.

Fire tetrahedron

The fire tetrahedron consists of fuel, oxygen, heat, and an uninhibited chemical chain reaction; removing any component stops combustion.

Fixed CO2 release

Before fixed CO2 release, all persons must be accounted for, the space sealed, and ventilation stopped; re-entry requires atmosphere testing and ventilation.

SART frequency

A search and rescue radar transponder responds to 9 GHz radar signals, producing a series of blips that help locate the survival craft.

Williamson turn

The Williamson turn is a man-overboard manoeuvre: hard over one side, then hard over the other after about 60 degrees, to return on a reciprocal track.

GMDSS sea area A3

Sea area A3 is within Inmarsat coverage but outside A1 and A2; carriage requirements include Inmarsat or HF equipment for distress and safety communications.

NAVTEX frequency

International NAVTEX broadcasts maritime safety information in English on 518 kHz; 490 kHz carries national-language broadcasts and 4209.5 kHz is used for HF.

ECDIS safety contour

The ECDIS safety contour separates safe from unsafe water and is set by the navigator to exceed the ship's maximum draught plus under-keel clearance.

Buys Ballot's law

With back to the wind in the Northern Hemisphere, low pressure lies to the left; in the Southern Hemisphere, low pressure lies to the right.

Spring tides

Spring tides occur near new and full moon when solar and lunar tidal forces align, producing the greatest tidal range; neap tides occur near quadrature.

Advection fog

Advection fog forms when warm moist air moves over a colder surface and cools to its dew point; it can persist over sea areas.

Pivot point

The pivot point is the position about which a ship turns; with ahead power it is near the bow, and with astern power it shifts near the stern.

Squat effect

Squat is the reduction in under-keel clearance caused by water flow around a moving ship; it increases in shallow water and at higher speed.

Closed-loop communication

Closed-loop communication requires the receiver to repeat an order and the sender to confirm it, reducing misunderstanding during bridge or engine-room operations.