Question 1

As Chief Mate, list the IMO IS Code (Intact Stability) minimum stability criteria you check on the loadicator before departure.

Accepted Answer

IS CODE STABILITY CRITERIA — LOADICATOR PRE-DEPARTURE CHECK: The International Code on Intact Stability 2008 (IS Code, adopted under SOLAS/MARPOL by MSC.267(85)) specifies minimum stability criteria for cargo vessels. ALL must be satisfied before departure: (1) RIGHTING LEVER AREA 0° to 30°: the area under the GZ curve from 0° to 30° shall not be less than 0.055 m·rad; (2) RIGHTING LEVER AREA 0° to 40°: the area under the GZ curve from 0° to 40° (or up to the flooding angle if less) shall not be less than 0.090 m·rad; (3) AREA BETWEEN 30° AND 40°: the area between the GZ curve at 30° and 40° shall not be less than 0.030 m·rad; (4) GZ AT 30°: the value of GZ at 30° shall be at least 0.200m; (5) ANGLE OF MAXIMUM GZ: the maximum GZ lever should occur at an angle of heel greater than 25°; (6) INITIAL GM: the initial metacentric height GM₀ shall not be less than 0.150m. HOW TO CHECK ON LOADICATOR: enter all cargo, ballast, fuel, fresh water, and other consumables with their weights and vertical/longitudinal centres of gravity. The loadicator calculates: (a) final displacement and trim; (b) KG (centre of gravity); (c) KM (metacentre height); (d) GM = KM - KG; (e) GZ curve; (f) all IS Code criteria automatically. CHIEF MATE MUST: review the GZ curve display, confirm all six criteria show "PASS/OK", and the loadicator printout must be retained and signed. Load line compliance check also on loadicator. IS Code 2008 — mandatory for all ships: the IS Code 2008 applies to cargo ships of 24m and above (with some exclusions). The six criteria must ALL be satisfied. A vessel passing five of the six criteria fails the IS Code. The IS Code is mandatory under both SOLAS and MARPOL through various resolutions and amendments. The 0.15m GM minimum: this is the minimum — but it is very low. A vessel with exactly 0.15m GM is at the IS Code limit and would have poor motion characteristics in heavy weather. Professional seamanship requires assessing whether the GM is adequate for the anticipated voyage conditions — not just whether it meets the minimum. Rule of thumb: For general cargo vessels, GMs of 0.5-1.5m are typical. For container vessels, 1.0-2.0m+. For bulk carriers, can be very high when loaded. GZ at 30° criterion: this is often the most operationally useful indicator. A GZ of 0.2m at 30° means the vessel has meaningful righting lever throughout the range. Vessels with high centres of gravity (from car deck loading, deck cargo) can fail this criterion while still having a positive GM. The loadicator shows the GZ curve and the pass/fail status for each criterion. Chief mate vs office calculation: the chief mate must verify the loading on the vessel's approved loadicator — not rely on an office calculation that may not reflect last-minute cargo changes, late bunkering, or actual loading quantities. The chief mate's calculation is the authoritative pre-departure document and must be retained on board.

Question 2

You are in the Bay of Bengal in October. Barometric pressure has fallen 8mb in 4 hours and a heavy swell is arriving from the SSW despite a cloudless sky. As Chief Mate on watch, what do you suspect and how do you respond?

Accepted Answer

TROPICAL CYCLONE APPROACH — RECOGNITION: SIGNS: an 8mb pressure drop in 4 hours plus an anomalous swell from a different direction than the current wind — these are classic early warning signs of a tropical cyclone. October in the Bay of Bengal is the second peak of the cyclone season (post-monsoon, September-December). BAY OF BENGAL CYCLONES: rotate COUNTER-CLOCKWISE (Northern Hemisphere). A swell from the SSW suggests a system to the SSW generating that swell. LOCATING THE CYCLONE: using Buys Ballot's Law (Northern Hemisphere): STAND WITH YOUR BACK TO THE WIND — the low pressure centre is to YOUR LEFT. So if the current wind is from the NNE (facing SSW) — the cyclone centre is approximately to the LEFT (ENE). MANOEUVRING RULES: for a vessel in the DANGEROUS SEMI-CIRCLE (DSC — right-hand semi-circle in Northern Hemisphere): alter to STARBOARD and run with the wind on the starboard quarter to move away from the path. For a vessel in the NAVIGABLE SEMI-CIRCLE (NSC — left-hand semi-circle): bring the wind on the starboard bow and run at best speed. For a vessel ON THE TRACK: bring the wind on the starboard quarter and run. IMMEDIATE ACTIONS: (1) CALL THE MASTER; (2) Obtain the latest GMDSS weather broadcast/NAVTEX; (3) Plot the swell direction and barometric pressure trend on the chart; (4) BEGIN MANOEUVRING in accordance with the semi-circle rules; (5) Secure all deck equipment, hatches, and loose gear; (6) Commence ballasting if stability margin is low. Barometric pressure rate of fall: in tropical regions, the normal diurnal variation in atmospheric pressure is approximately 1-2mb. A fall of 8mb in 4 hours (2mb/hour) is far outside normal variation and indicates the approach of a significant system. This rate of pressure fall is explicitly used in seamanship as a criterion for a developing tropical cyclone. Bay of Bengal cyclones: the Bay of Bengal is one of the world's most active cyclone basins with peak activity in May-June and October-December. Bengali cyclones are noted for their rapid intensification and the shallow Bay of Bengal amplifies the storm surge to devastating heights (the 1970 Bhola cyclone killed 300,000 people partly due to surge). Swell without cloud: tropical cyclones generate long-period swells that travel far ahead of the system — typically 24-36 hours ahead of the centre. The swell arrives before the cloud cover and wind, which is why experienced mariners treat an anomalous heavy swell as a cyclone warning even in clear weather. Buys Ballot's Law: this rule for finding the low pressure centre from the wind direction works in both hemispheres (modified for Southern Hemisphere — centre is to the right when facing into the wind). Every OOW and CM should know this and be able to apply it immediately. Course into swell (option C): course selection in cyclone avoidance is NOT simply "head into the swell." The correct course depends on which semi-circle the vessel is in. Heading directly into the swell might take the vessel toward the cyclone track rather than away from it. Buys Ballot manoeuvre must override the simple "head to sea" instinct.

Question 3

As Chief Mate, you receive a NAVTEX synoptic chart showing a 968mb deep depression 400nm to your NW, moving E at 25 knots. Your position is to the S of the low track. Describe the expected weather sequence.

Accepted Answer

SYNOPTIC CHART ANALYSIS — DEPRESSION WEATHER SEQUENCE: WARM SECTOR DEPRESSION STRUCTURE: the classic mid-latitude depression has: WARM FRONT (ahead of the warm sector), WARM SECTOR, and COLD FRONT. The vessel to the SOUTH of the depression track is in the NAVIGABLE (or "safe") SEMI-CIRCLE and will experience: APPROACHING WEATHER SEQUENCE: (1) VEERING WINDS: as the warm front approaches (from WSW to W to NW) — south of the track; (2) WARM FRONT PASSAGE: (a) Clouds sequence: Cirrus → Cirrostratus → Altostratus → Nimbostratus (the "classical" cloud sequence of an approaching warm front); (b) Rain: continuous moderate to heavy rain with poor visibility; (c) Wind: south to SW, backs slightly as warm front passes; (d) Pressure: steady fall; (e) Temperature: rise; (3) WARM SECTOR: (a) Moderate SW winds; (b) Drizzle and low cloud (sea fog risk if warm, moist air moves over colder sea); (c) Pressure temporarily stabilises; (4) COLD FRONT PASSAGE: (a) Wind veers rapidly from SW to NW or N; (b) Heavy showers, squalls, possibly thunder; (c) Pressure rises sharply; (d) Temperature falls; (e) Visibility clears rapidly; (5) AFTER COLD FRONT: NW winds, showers, good visibility between showers, cumulus cloud. 968mb depression = strong system. At 400nm at 25kt movement = 16 hours to reach the vessel position. Wind force — from distance/isobar spacing on chart: calculate wind force from isobar spacing. 968mb depression = likely Force 9-10 on the south semi-circle at closest approach. 16-hour arrival time: 400nm ÷ 25 knots = 16 hours. This is a real operational planning figure — 16 hours is enough time to: (a) prepare the vessel; (b) ballast/secure; (c) brief the crew; (d) assess whether to divert to shelter or run clear of the track. A CM on watch who correctly identifies this timing gives the master critical decision information. The vessel south of the track: in a Northern Hemisphere depression moving east — the vessel south of the track is in the LEFT (navigable) semi-circle. The warm front WILL pass over the vessel south of the track. The warm sector and cold front will also pass. The CM who says "no warm front because I'm south of the track" is confusing the depression track with the location of the warm front (which extends south of the centre). Isobar spacing and wind force: on a synoptic chart, the spacing between isobars (drawn at 4mb intervals) gives a relative indication of pressure gradient and therefore wind speed. Closely spaced isobars = strong gradient = strong winds. At 968mb in a mid-latitude depression, the warm sector to the south typically shows 4-6mb spacing — equivalent to Force 8-10 (gale to strong gale). Uniform wind Force 12 (option D): incorrect. Wind in a depression varies with location — strongest winds are to the right of the track (dangerous semi-circle) and in the depression core (around the warm/cold front boundary). South of the track, the winds are typically Force 8-10 in a deep system. Force 12 is generally confined to the core of the strongest systems.