MARINA OIC-NW Theoretical Exam cheat sheet

Latitude = angular distance north/south of the equator (0°–90°); longitude = angular distance east/west of the prime meridian (0°–180°). 1 minute of latitude = 1 nautical mile (1852 m).

Speed–distance–time: distance (nm) = speed (kn) × time (h); time = distance ÷ speed; speed = distance ÷ time. Use the 3-minute rule: distance run in 3 min = speed in knots ÷ 20.

Running fix: advance the earlier LOP by the course and distance steamed (using the log/speed), then plot the transferred LOP against a later LOP. Accuracy degrades with elapsed time and set/drift.

Doubling the angle on the bow: if the bearing of a fixed object doubles from the original relative bearing, the distance run since the first bearing equals the distance off the object at the second bearing (valid only with steady course/speed).

Set = direction toward which the current flows; drift = speed of the current in knots. Course to steer to counteract a current uses a vector triangle: water track + current = ground track.

Chart datum is normally Lowest Astronomical Tide (LAT); charted soundings are depths below datum, and drying heights are shown above datum. Height of tide + charted depth = actual depth.

Compass error: variation (from chart, magnetic) + deviation (from deviation card/table, magnetic) = total compass error. Convert with CADET: Compass + Deviation = Magnetic; Magnetic + Variation = True (reverse for True→Compass).

Passage planning per SOLAS V/34: appraise all information, plan the passage (including no-go areas, abort points, contingency anchorages), execute the plan, and monitor progress continuously.

Rule 13 overtaking: any vessel overtaking another must keep clear until finally past and clear, regardless of vessel type. Overtaking exists when approaching from more than 22.5° abaft the other vessel's beam.

Rule 14 head-on: both power-driven vessels alter course to starboard and pass port-to-port. Rule 15 crossing: the vessel with the other on her own starboard side is the give-way vessel.

Rule 16/17: give-way vessel takes early and substantial action; stand-on vessel must keep course and speed but may act when risk of collision exists and must act when collision cannot be avoided by give-way vessel alone.

Rule 5 lookout: proper lookout by sight and hearing, and by all available means appropriate to circumstances and conditions, to make a full appraisal of the situation and risk of collision.

Rule 7 risk of collision: assume risk exists if the compass bearing of an approaching vessel does not appreciably change; do not assume no risk from a large vessel or a bearing change at long range.

Rule 19 restricted visibility: safe speed, no assumed right of way; reduce speed to minimum steerageway if detecting a vessel forward of the beam; alter course to starboard if possible, avoid altering toward a vessel abeam or abaft the beam.

Power-driven vessel underway lights: masthead light(s), sidelights (red port, green starboard), sternlight; vessels under 50 m show one masthead light, 50 m and over show two (second higher and aft).

Sound signals in restricted visibility: one prolonged blast at intervals ≤2 min for power-driven vessel making way; two prolonged blasts (≤2 min) for power-driven vessel underway but stopped; one prolonged + two short for vessel not under command, restricted in ability to manoeuvre, constrained by draft, sailing, fishing, or towing/pushing.

Buys Ballot's Law (Northern Hemisphere): with your back to the wind, low pressure lies to your left and high pressure to your right; reverse in the Southern Hemisphere.

In the Northern Hemisphere, surface wind circulates counter-clockwise around a low and clockwise around a high; in the Southern Hemisphere the reverse. Wind blows slightly across isobars toward low pressure due to friction.

Isobar spacing indicates pressure gradient: closely spaced isobars mean strong winds; widely spaced isobars mean light winds.

Beaufort scale links wind speed to sea state: Force 6 (22–27 kn) = strong breeze, large waves, whitecaps; Force 8 (34–40 kn) = gale, moderately high waves, streaks of foam.

Tropical revolving storms (cyclones, typhoons, hurricanes) form over warm ocean waters (typically >26–27 °C), have a calm eye, and in the Northern Hemisphere circulate counter-clockwise, moving generally westward then recurving poleward.

Fog types: radiation fog forms over land on clear calm nights; advection fog forms when warm moist air moves over a colder surface (common over cold currents); frontal fog accompanies precipitation.

Sea breeze (daytime) blows from sea to land; land breeze (night) blows from land to sea. Both are local thermal circulations.

Swell is wind-generated waves that have propagated out of the generating area; it can arrive well ahead of a storm and indicates distant weather. Wave height depends on wind speed, fetch, and duration.

Archimedes' principle: buoyancy equals the weight of displaced water. Displacement = underwater volume × water density; in salt water, 1 m³ ≈ 1.025 t; in fresh water ≈ 1.000 t.

Metacentric height (GM) = KM − KG. Positive GM means the vessel is initially stable; larger GM means stiffer (faster roll) and smaller GM means tender (slower, larger roll).

Free surface effect reduces effective GM (GM_eff = GM − FSC). FSC = (sum of free surface moments) ÷ displacement. Keep tanks pressed or empty to limit it.

GZ curve (righting lever curve): area under the curve represents dynamical stability; the maximum GZ and the angle of vanishing stability define reserve stability.

Load line marks (Plimsoll): TF, F, T, S, W, WNA; the summer load line is the reference. Freeboard = distance from the load line to the deck line at the side.

Basic ship construction: keel (backbone), frames (transverse ribs), longitudinal stiffeners, floors, stringers, shell plating, bulkheads (watertight subdivision), decks, and hatch covers.

Turning circle terms: advance (distance ahead from the turn start to the point where the vessel is 90° from original course), transfer (distance sideways at 90°), tactical diameter (transfer at 180°).

Bank effect and squat: a vessel moving in shallow water squats (drops vertically and trims by the head) due to reduced under-keel clearance; squat increases with speed and with the square of the Froude number.

STCW watchkeeping: the OOW is responsible for the safe navigation of the vessel; the master may be called if in doubt, if visibility deteriorates, or if traffic/conditions become hazardous.

Handover checklist: confirm the vessel's position, course, speed, traffic, weather, machinery status, and any standing orders; never hand over without a proper briefing.

Bridge resource management (BRM): use closed-loop communication, challenge and response, and clearly delegated tasks. Avoid complacency and fatigue.

The official log book and deck log record courses, speeds, positions, weather, incidents, drills, and any deviations. Entries must be factual, timely, and signed.

Lookout: use all available means (visual, radar, AIS, hearing) and report contacts promptly to the OOW. A lookout has no other duties that interfere with lookout duties.

Underway in restricted visibility: keep the bridge manned, use radar and sound signals per Rule 19/35, reduce speed, and post a proper lookout.

Watch schedules under STCW: minimum rest periods apply; fatigue management is mandatory. The OOW must not be assigned duties that impair safe watchkeeping.

Bridge equipment checks: verify gyro/magnetic compass error, radar tuning and performance, ECDIS (position source, alarms), AIS status, and correct sound signal operation at the start of each watch.

Radar range: range (nm) = 1.23 × √(antenna height in feet + target height in feet). Higher antenna = greater detection range; the radar horizon is greater than the visual horizon.

Radar resolution: range resolution depends on pulse length (shorter pulse = better); bearing resolution depends on horizontal beamwidth (narrower beam = better).

Radar artifacts: sea clutter (near center, from waves), rain clutter (spread over precipitation), shadow sectors (blind areas behind masts/funnels), and false echoes (side lobes, multiple reflections).

ECDIS: must display chart data (ENC), own position, and alarms; the safety contour and safety depth must be set. Verify the position source and chart updates.

GPS accuracy: position error can increase from ionospheric/tropospheric delay, multipath, and satellite geometry (DOP). DGPS improves accuracy by correcting local errors.

Echo sounder: measures depth below the transducer; check the draft offset and the sound speed setting. Multiple echoes and aeration (from the propeller) can cause false readings.

Gyrocompass error: check against a known bearing or azimuth; magnetic compass error = variation + deviation. Deviation card must be current and posted.

AIS: transmits identity, position, course, speed, and heading; it does not replace radar or visual lookout. AIS can be absent, delayed, or erroneous - use it as an aid, not a sole source.

GMDSS: Sea Area A1 = VHF coverage (DSC); A2 = MF (DSC); A3 = Inmarsat coverage; A4 = outside A1–A3. Distress alert on VHF Ch 70 (DSC) or MF 2187.5 kHz (DSC).

Distress signal: MAYDAY (voice), repeated three times, on VHF Ch 16 or MF 2182 kHz. Include vessel name, position, nature of distress, and assistance required.

SOLAS: fire and boat drills at intervals not exceeding one month; abandon-ship drill and fire drill must be conducted. Life-saving appliances must be inspected and maintained.

MARPOL Annexes: I (oil), II (noxious liquid substances), III (harmful substances in packaged form), IV (sewage), V (garbage), VI (air pollution). Oil Record Book entries are mandatory.

MARPOL Annex V: garbage discharge restrictions; plastics are never to be discharged. Special areas have more restrictive rules.

SAR: the On-Scene Coordinator (OSC) coordinates search patterns; the Rescue Coordination Centre (RCC) coordinates the overall response. Common patterns: expanding square, sector search, parallel sweep.

Emergency position indicating radio beacon (EPIRB): 406 MHz transmits to the COSPAS-SARSAT system; a 121.5 MHz homing signal aids local search. Test only per manufacturer instructions.

Fire triangle: fuel, heat, oxygen. Fire classes: A (solid), B (flammable liquid), C (gas), D (metal), E (electrical). Use the correct extinguishing agent for the class.

Cargo stowage principles: distribute weight to avoid excessive stress on the hull and to maintain stability; keep the center of gravity low; avoid excessive list or trim.

Dangerous goods classes (IMDG): 1 explosives, 2 gases, 3 flammable liquids, 4 flammable solids, 5 oxidizers/organic peroxides, 6 toxic/infectious, 7 radioactive, 8 corrosive, 9 miscellaneous.

IMDG segregation: keep incompatible classes separated (e.g., away from, separated by a complete compartment or hold, or by a vertical separation). Follow the segregation table and the Dangerous Goods List.

Cargo documentation: bill of lading, manifest, dangerous goods declaration, and stowage plan. Verify labels, markings, and the UN number.

Hatch covers and cargo securing: ensure watertight integrity; lashings and securing arrangements must meet the cargo securing manual.

Cargo ventilation: ventilate to remove moisture and heat; avoid condensation (ship sweat and cargo sweat). Dew point control prevents cargo damage.

Bulk cargo: watch for liquefaction (cargo shift) in concentrates; avoid overloading and maintain adequate freeboard. Check the cargo's Transportable Moisture Limit (TML).

Container stowage: observe weight limits, stacking limits, and lashing requirements. Heavy containers low and central; verify the container's gross weight against the declared weight.

Knots: bowline (fixed loop), clove hitch (temporary securing to a post), reef knot (joining two ropes of equal size), sheet bend (joining two ropes of different size), round turn and two half hitches (securing to a ring).

Wire rope: 6×19 (general purpose, less flexible), 6×37 (more flexible), 6×12 (more flexible still). Lay length and construction affect strength and flexibility.

Anchoring: the scope (rode length) should be about 5–7 times the depth in good holding ground; more in poor holding or heavy weather. The anchor holds by its flukes digging in, not by weight alone.

Anchor types: stockless (Danforth, Bruce) for general use; stock anchor for older vessels; plow (CQR) for good holding. Use the correct anchor for the seabed.

Mooring: use spring lines to prevent fore-and-aft movement, breast lines to hold the vessel alongside, and head/stern lines to control position. Watch the tide and adjust lines.

Deck maintenance: keep surfaces clean and free of rust; apply protective coatings; inspect for corrosion, especially at welds, deck edges, and around fittings.

Rigging: standing rigging (stays, shrouds) supports masts; running rigging (halyards, sheets) controls sails and loads. Inspect for wear, corrosion, and broken wires.

Safe working practices: use personal protective equipment (PPE), inspect ropes and wires before use, and never stand in the bight of a line or in the snap-back zone.