Chapter briefs for OOW.

What the paper asks

Position fixing by bearings, ranges and transits; running fixes; course to steer with current and leeway; the sailings; tidal height and tidal stream calculations; chart symbols and datums; and the practical judgement of when a fix is not to be trusted.

The concepts, in order

A fix has a quality. Three position lines crossing in a small cocked hat is a good fix; two lines at a fine angle is a poor one however neatly drawn. Bearings taken 60° to 120° apart cut cleanly. Always cross-check the fix against the echo sounder and against your own dead reckoning before believing it.

Dead reckoning and estimated position are different things. DR uses course steered and distance run only. EP applies the known set and drift, and leeway. Plotting one and calling it the other is a common examination slip.

Course to steer. Draw the intended track, lay off the current vector from the start, and swing the ship's speed as an arc onto the track. What you get is a course, not a heading — apply leeway on top, and then compass error to get what the helmsman is given.

Tides. Height of tide is interpolated between high and low water using the standard curve; clearance is height of tide plus charted depth minus draught, and a safety margin. The rule of twelfths is a rough check, not a substitute for the curve.

Datums matter. Charted depths are below chart datum, drying heights above it, and vertical clearances are above highest astronomical tide. Mixing them up is how bridges get hit and rocks get found.

Where marks are lost

• Using a compass bearing as a true bearing. Apply variation and deviation every time — CADET, compass to true add east.
• A cocked hat that closes too well. Suspiciously perfect fixes usually mean one bearing was adjusted to suit the other two.
• Forgetting leeway direction. Leeway pushes the ship downwind, so the correction is applied into the wind.
• Reading vertical clearance from chart datum. It is from highest astronomical tide, which is the pessimistic case for air draught.

What the paper asks

Sight reduction to an intercept and position line; meridian altitude for latitude; amplitude and azimuth for compass error; sunrise, sunset and twilight times; and the corrections applied to a sextant altitude.

The concepts, in order

The method in one line. Measure the altitude of a body, work out what the altitude would have been from an assumed position, and the difference — the intercept — tells you how far towards or away from the body your true position lies.

Corrections, in order. Index error first, then dip for height of eye, then the main correction combining refraction, semi-diameter and parallax. Getting sextant altitude to true altitude right is where most marks are won or lost.

Meridian altitude. At the moment a body bears due north or south, latitude comes straight from the altitude and declination with no sight reduction at all. It remains the simplest reliable observation at sea.

Compass error from the sky. Amplitude at sunrise or sunset, or azimuth at any time, gives a true bearing to compare against the compass. This is the practical reason celestial navigation survives — the gyro must be checked once a watch.

Where marks are lost

• Applying index error the wrong way. On the arc, subtract; off the arc, add.
• Forgetting dip. It is always subtracted, and it grows with height of eye.
• Confusing intercept direction. Toward if the calculated altitude is less than the true altitude.
• Using zone time when GMT/UTC is required. Every almanac entry is in UTC.

What the paper asks

Steering and sailing rules, particularly 5 to 19; lights and shapes for every vessel type; sound and light signals; conduct in restricted visibility; and the practical application to a described situation.

The concepts, in order

Rules 5, 6, 7 and 8 come before everything. Lookout, safe speed, risk of collision and action to avoid collision apply in all conditions of visibility, to every vessel, at all times. A candidate who jumps straight to give-way and stand-on has missed the structure.

Risk of collision exists if the compass bearing does not appreciably change. That is the test, and it applies to a radar plot as much as to a visual bearing. In doubt, assume risk exists.

Action must be positive, made in ample time, and obvious to the other vessel. A series of small alterations is specifically deprecated. Alteration of course alone is usually preferred to speed change, because it is visible.

Restricted visibility is a different regime. Rule 19 replaces the give-way and stand-on relationship entirely — there is no stand-on vessel in fog. Avoid an alteration to port for a vessel forward of the beam, and reduce to bare steerage way if a close-quarters situation cannot be avoided.

Where marks are lost

• Applying Rule 15 crossing rules in restricted visibility. Rule 19 governs, and there is no stand-on vessel.
• Forgetting Rule 2, the rule of good seamanship. Nothing in the rules exonerates a vessel from the consequences of neglecting an ordinary precaution.
• Paraphrasing a light configuration. Examiners want the exact arrangement, arcs and ranges.
• Treating stand-on as a duty to hold course regardless. Rule 17 permits, then requires, action when collision cannot be avoided by the give-way vessel alone.

What the paper asks

Radar and ARPA plotting, limitations and errors; ECDIS setup, safety settings and alarms; GNSS accuracy and failure modes; gyro and magnetic compass errors; AIS limitations; and echo sounder and speed log principles.

The concepts, in order

Radar plotting is still examined by hand. From the relative motion line you extract CPA, TCPA and the target's true course and speed. ARPA does it automatically — and inherits every error in the input data, particularly a wrong speed input or an unstabilised heading.

Radar has real limits. Minimum range from pulse length, blind and shadow sectors, sea and rain clutter, and targets lost in the sea return close in. A small wooden boat in a swell may not appear at all, which is why radar never replaces a lookout.

ECDIS is a system, not a chart. Its safety contour, safety depth and shallow/deep contours must be set for the ship, and the alarms are only as useful as those settings. Route check before departure, and understanding what an under-scale or overscale display hides, are the examinable points.

Every sensor has a failure mode. GNSS is vulnerable to jamming and spoofing and gives no warning of a wrong datum. Gyro settles slowly and has speed and latitude error. AIS shows what the other vessel has entered, which may be wrong, and is not a collision-avoidance device.

Where marks are lost

• Treating AIS data as reliable for collision avoidance. It is an aid to identification, not a substitute for radar plotting.
• Leaving ECDIS safety settings at the default. They must be set for the ship's draught and the passage.
• Forgetting gyro speed/latitude error. It is a real correction on high-speed vessels at high latitude.
• Confusing true and relative vectors on ARPA. The display mode changes what the vector means entirely.

What the paper asks

Stowage factor and broken stowage; securing and lashing calculations; general cargo, bulk, containers and dangerous goods; ventilation and sweat; cargo documentation; and the master's responsibility for a safe stow.

The concepts, in order

Stowage factor is volume per unit weight. Multiply by the cargo weight and add broken stowage to get the space required. Whether a ship fills up by weight or by volume — deadweight cargo or measurement cargo — decides the whole loading plan.

Securing is a force calculation. Lashings resist the inertial forces from rolling, pitching and heaving, which depend on the ship's motion and where the cargo sits. The Cargo Securing Manual is ship-specific and approved, and departing from it is a reportable matter.

Ventilation prevents sweat. Ship's sweat forms when warm moist air meets cold structure; cargo sweat when warm cargo meets cold air. The rule is to ventilate when the outside dew point is lower than the hold dew point, and not otherwise.

Dangerous goods run on the IMDG Code. Classification, packing group, segregation, documentation and stowage position all follow from it — and segregation between incompatible classes is the part that is examined.

Where marks are lost

• Ignoring broken stowage. It can be 25 % or more for irregular cargo and it decides whether the cargo fits.
• Ventilating on temperature rather than dew point. That is how a cargo gets wet.
• Overlooking tank top strength. Load density per square metre matters as much as total weight.
• Treating the Cargo Securing Manual as advisory. It is approved and mandatory.

What the paper asks

Displacement from draught survey; KG and GM by taking moments; free surface correction; angle of list from a transverse shift; trim by change of draught; and reading and applying the stability information booklet.

The concepts, in order

Everything comes from a moments table. List every weight with its distance from the keel and from the centreline, sum the moments, and divide by the total weight. That gives KG and the transverse offset of G in one operation.

GM is the margin. KM comes from the hydrostatic tables at the working draught; KG comes from your table; the difference is GM, and it must clear the required minimum after free surface is deducted.

Free surface is a virtual rise of G. It depends on the tank's surface dimensions, not on how much liquid is in it — and it goes as the cube of the breadth, so a full-breadth slack tank is the worst case there is.

Trim and list are different problems. Trim comes from the longitudinal distribution and is worked about the centre of flotation; list comes from the transverse offset of G and is a simple tangent relation with GM.

Where marks are lost

• Reading KM at the wrong draught. KM changes with draught and must be taken at the working condition.
• Omitting free surface for a nearly empty tank. The correction does not depend on the quantity.
• Working trim about amidships. The ship trims about the centre of flotation.
• Ignoring the effect of consumables burnt during the voyage. A departure condition that just passes may fail on arrival.

What the paper asks

Hull structural terms and their function; framing systems; watertight subdivision and closures; anchors and cables; mooring arrangements and rope handling; corrosion protection; and routine maintenance.

The concepts, in order

Longitudinal framing resists hull girder bending; transverse framing resists local and racking loads. Most large ships are longitudinally framed in the deck and bottom and transversely framed in the sides, because that is where each system does most good.

Local strengthening exists for named loads. Panting structure forward for pressure fluctuation, pounding structure for slamming, and web frames and bulkheads for racking as the ship rolls.

Anchoring is about catenary, not weight. The holding power comes from the anchor digging in with a horizontal pull, which requires enough cable out — commonly a scope of six to eight times the depth. A short scope lifts the shank and the anchor drags.

Mooring lines fail dangerously. Snap-back zones, mixed line materials on the same service, and lines led over sharp edges are the recurring causes. Synthetic ropes store far more energy than wire and recoil further.

Where marks are lost

• Confusing sheer, camber and rise of floor. Sheer is longitudinal, camber is transverse, rise of floor is the bottom slope.
• Quoting anchor scope as a fixed number of shackles. It depends on depth, holding ground and weather.
• Mixing wire and synthetic on the same bollard. They share load unequally and the stiffer line takes it all.
• Calling all corrosion protection painting. Anodes and impressed current do the underwater work.

What the paper asks

Pressure systems and fronts; wind circulation and Buys Ballot's law; tropical revolving storms — recognition, avoidance and the dangerous semicircle; ocean currents; ice; fog formation; and weather routeing.

The concepts, in order

Wind blows along the isobars, not across them. Buys Ballot's law: face the wind in the northern hemisphere and low pressure is on your right. Close isobars mean strong wind; the spacing is the forecast.

Fronts are boundaries between air masses. A warm front brings a long slow deterioration with drizzle and poor visibility; a cold front brings a sharp squally clearance and a marked wind veer. Knowing which is passing tells you what comes next.

Tropical revolving storms are avoided, not weathered. Falling barometer, long low swell from an unusual direction and a wind that will not shift are the warning signs. Plot the storm centre by the wind, identify which semicircle you are in, and act — the dangerous semicircle is on the side where the storm's translation adds to its own wind.

Fog has causes. Advection fog forms when warm moist air moves over cold water and is the common sea fog; radiation fog is a land phenomenon that drifts out. Knowing the mechanism tells you whether it will lift.

Where marks are lost

• Reversing Buys Ballot in the southern hemisphere. Low pressure is then on your left.
• Confusing veering and backing. Veering is clockwise, backing is anticlockwise, in both hemispheres.
• Running before a TRS without plotting the centre. That is how ships end up in the dangerous semicircle.
• Reading a falling barometer alone as a storm warning. The swell and the steady wind direction complete the picture.

What the paper asks

Sea areas A1 to A4 and the equipment each requires; DSC distress alerting and acknowledgement; distress, urgency and safety priorities; EPIRB and SART operation; MSI reception; and false alert procedure.

The concepts, in order

Sea areas define the equipment. A1 is within VHF DSC coverage, A2 within MF DSC, A3 within Inmarsat coverage, and A4 is everything else — the polar regions, where HF is the answer. The carriage requirements follow from where the ship trades.

The three priorities are distinct. Distress means grave and imminent danger; urgency, the pan-pan, is a serious situation short of that; safety, securité, is navigational or meteorological warning. Choosing the right one is examined constantly.

A DSC alert is only the alert. It is followed by a distress call and message on the associated voice or radiotelex frequency. A DSC alert alone tells a rescue coordination centre almost nothing beyond position and identity.

False alerts must be cancelled immediately. Cancel on the same medium, on all frequencies used, and inform the coast station. Switching the set off and hoping is a serious and reportable failure.

Where marks are lost

• Using pan-pan for a genuine distress. If there is grave and imminent danger, it is a mayday.
• Failing to follow a DSC alert with the voice message.
• Not cancelling a false alert. It is an offence in most jurisdictions and it degrades the whole system.
• Confusing an EPIRB with a SART. The EPIRB alerts by satellite; the SART shows on radar to home rescuers in.

What the paper asks

The principal IMO conventions and what each governs; the ship's statutory certificates and their validity; flag state, port state and coastal state jurisdiction; survey and certification cycles; and the officer's role in a port state control inspection.

The concepts, in order

Name the instrument before quoting the rule. SOLAS covers safety of life, MARPOL pollution, STCW competence, Load Line reserve buoyancy, Tonnage measurement, COLREGs collision avoidance, and MLC seafarer employment. Half the mark is in getting that right.

Three jurisdictions, three roles. The flag state has primary responsibility and issues the certificates; the port state inspects ships visiting its ports; the coastal state exercises rights in its waters under UNCLOS. They overlap, and knowing which is acting matters.

Certificates come from surveys. Annual, intermediate and renewal surveys on a five-year cycle, often delegated by the flag to a recognised organisation. An expired or improperly endorsed certificate is a detainable deficiency in its own right.

Port state control follows a pattern. Certificates and general impression first; clear grounds lead to a more detailed inspection; deficiencies are coded, and serious ones lead to detention. The best defence is that the certificates match the ship and the records match reality.

Where marks are lost

• Attributing oily water separation to SOLAS. It is MARPOL Annex I.
• Confusing the Safety Equipment and Safety Construction certificates.
• Assuming the flag state does its own surveys. Most delegate to a recognised organisation.
• Thinking a detention is about one deficiency. It is about whether the ship should proceed to sea.

What the paper asks

Man overboard manoeuvres; fire on board; abandon ship; collision and grounding; search and rescue patterns and the IAMSAR framework; muster lists and drills; and the structured answers an oral examination expects.

The concepts, in order

Answer in a structure. Raise the alarm, inform the master and the bridge, muster and account for people, contain the situation, then act, then report and record. Nearly every emergency answer fits that order, and the order is what is being marked.

Man overboard has three cases. Immediate action, delayed action and person missing — and three manoeuvres: Williamson turn for immediate return in poor visibility, Anderson turn for the fastest recovery, Scharnow when time has passed. Know which suits which case.

Search and rescue is coordinated. IAMSAR sets the framework, the rescue coordination centre coordinates, and the on-scene coordinator runs the search. Expanding square, sector search and parallel track each suit a different uncertainty.

Drills exist to build the sequence. Muster list, station bill, drills at the required intervals, and the record of them — an examiner will ask what your muster list says your own station is.

Where marks are lost

• Starting an answer with the machinery instead of the people.
• Forgetting to inform the master. It is an early action in almost every scenario.
• Giving a manoeuvre without saying why that one.
• Inventing a regulatory figure. Say you would verify it, and where.