Question 1

As Chief Mate on watch, visibility reduces to 200m in fog. You detect a radar contact 6nm ahead and 2° on the starboard bow. Describe your response under COLREG Rule 19.

Accepted Answer

RULE 19 (RESTRICTED VISIBILITY) — CHIEF MATE RESPONSE: COLREG RULE 19 REPLACES RULES 11-18 IN FOG: in restricted visibility — none of the visual sight rules apply. All vessels are on Rule 19. RULE 19 REQUIREMENTS: (a) All vessels must proceed at SAFE SPEED enabling proper manoeuvring; (b) Vessels must have radar and use it; (c) Any vessel that detects another vessel by radar only (without visual or sound contact) must act to avoid close quarters in ample time; (d) If a close-quarters situation develops: (i) if the other vessel is forward of the beam — avoid altering to PORT; (ii) if the other vessel is abeam or abaft the beam — avoid turning to the other vessel. CONTACT AT 6NM, 2° STARBOARD BOW: (1) CALL THE MASTER: immediately — approaching close-quarters situation developing with restricted visibility. This is not solely the OOW's decision; (2) REDUCE SPEED: safe speed must be appropriate for the fog and distance to the contact. Reduce to manoeuvring speed; (3) SOUND FOG SIGNAL: one prolonged blast every 2 minutes (Rule 35a — vessel making way); (4) MAINTAIN RADAR WATCH: track the contact on radar — determine: (a) CPA (Closest Point of Approach); (b) TCPA (Time to CPA); (c) bearing trend (bearing maintaining — collision risk); (5) RULE 19(d)(i) CONSTRAINT: the contact is FORWARD OF THE BEAM — if alteration is needed, DO NOT alter to PORT. Alter to STARBOARD only, or reduce speed; (6) VESSELS IN FOG RULE: there is no requirement to alter in fog before you detect the other vessel's fog signal. But by radar — you should act in ample time. Rule 19 vs Rules 11-18: COLREG Rule 19 applies "in or near an area of restricted visibility" — not just when you cannot see. Even if you can see a little, once visibility is significantly restricted, Rule 19 governs. The rule explicitly applies when vessels cannot "see each other" — which is the case in 200m visibility unless the other vessel is very close. Rule 15 in fog (option D): Rule 15 (crossing situations) applies when vessels "are in sight of one another." COLREG Rule 3(k) defines "in sight": when "one can be observed visually from the other." In 200m visibility, a vessel 6nm away cannot be observed visually — therefore Rule 15 does NOT apply. In fog, Rule 19 governs — not crossing/overtaking/head-on rules. The Rule 19(d)(i) constraint: this is the specific restriction in fog — when a contact is FORWARD OF THE BEAM and close-quarters is developing, avoid altering to PORT. The rationale is that altering to port in fog could swing the bow into the other vessel's path. Altering to starboard is the preferred manoeuvre (consistent with the general COLREG bias toward starboard alteration). Maintaining course and speed (option C): Rule 19 does NOT require maintaining course and speed. In clear weather, the stand-on vessel maintains course and speed — but Rule 19(b) requires all vessels to take action to avoid close-quarters "in ample time" — which means acting early, not waiting. The risk of action in fog is creating confusion — which is why actions must be SUBSTANTIAL (large alteration or significant speed reduction, not small adjustments).

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.