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Maritime Fog Types

2nd Mate

times asked: 14; times asked
questions: 4; questions
last asked: 2026; last asked

The slides, written out

AI-drawn illustration. Simplified to explain the idea, not to scale.

Slide 1 · 01 UNDERSTANDING MARITIME FOG

01 UNDERSTANDING MARITIME FOG ADVECTION FOG (SEA FOG) FORMATION Warm, moist air moves horizontally over a colder sea surface and cools to its dew point. Condensation forms extensive sea fog. HOW IT FORMS WARM, MOIST AIR ADVECTS OVER SEA COLD SEA SURFACE COOLS AIR AIR REACHES DEW POINT CONDENSATION CREATES SEA FOG 1 2 3 4 CONDITIONS Warm, moist air Cold sea surface Light to moderate winds Stable marine boundary layer WARM, MOIST AIR COLD SEA SURFACE TYPICAL LOCATIONS Grand Banks of Newfoundland English Channel (spring and early summer) GRAND BANKS OF NEWFOUNDLAND ENGLISH CHANNEL WATCHKEEPER'S NOTE Often persistent and widespread. May remain for several days until weather conditions change. | |

Slide 2 · 02 UNDERSTANDING MARITIME FOG

02 UNDERSTANDING MARITIME FOG RADIATION FOG HOW IT FORMS (OVERNIGHT TO MORNING) EVENING LATE NIGHT PRE-DAWN MORNING Land cools by radiation as heat escapes to space. Surface cools the air above to its dew point. Fog forms near the ground as air reaches saturation. Sunlight warms the surface and the fog dissipates. 1 2 3 4 FOG USUALLY THICKER NEAR LAND MAY DRIFT A SHORT DISTANCE OFFSHORE FORMATION Occurs overnight when the land surface loses heat by long-wave radiation, cooling the air above it to its dew point. Fog forms near the ground. CONDITIONS Clear skies Light or calm winds Damp or marshy ground Long winter nights TIMING Forms overnight, is often thickest around sunrise, and normally dissipates after daytime heating breaks down the inversion. MARINE RELEVANCE Can drift a short distance offshore but is primarily a land-based fog. WATCHKEEPER'S NOTE Radiation fog is typically local in extent, forms in sheltered areas, and breaks up quickly after sunrise. DENSE AT SUNRISE, DISSIPATES AFTER SUNRISE | |

Slide 3 · 03 UNDERSTANDING MARITIME FOG

03 UNDERSTANDING MARITIME FOG ARCTIC SEA SMOKE FORMATION Very cold, dry air moves over relatively warmer water. Rapid evaporation saturates the cold air, producing steam-like fog. CONDITIONS • Very cold, dry air • Relatively warm water • Light winds • Strong evaporation COMMON AREAS • Arctic Ocean • Antarctic waters • Baltic Sea in winter • Open water within sea ice WATCHKEEPER'S NOTE Sea smoke usually appears as rising white steam over the sea surface. It is typically shallow but can reduce visibility. VERY COLD, DRY AIR WARMER WATER STEAM-LIKE FOG (SEA SMOKE) THE PROCESS 1 Cold, dry air moves over warmer water. 2 Warm water causes intense evaporation into the cold air. 3 Air becomes saturated; vapour condenses. 4 Sea smoke forms as steam-like fog above the water. QUICK FACTS Occurs when very cold air flows over significantly warmer water. Develops most readily in light winds. Typically shallow, but can locally affect visibility for navigational operations. | |

Slide 4 · 04 UNDERSTANDING MARITIME FOG

04 UNDERSTANDING MARITIME FOG SMOG A MAN-MADE FOG ENHANCED BY AIR POLLUTION FORMATION Smog is polluted air formed when atmospheric pollutants mix with moisture and, in some situations, fog. HOW IT WORKS Smoke and pollutant particles act as condensation nuclei, helping moisture condense into tiny droplets, which reduces visibility. WHERE ENCOUNTERED Industrial ports Large coastal cities Busy shipping approaches WATCHKEEPER'S NOTE Smog can vary in appearance from gray to brown and may cause strong odours in industrial areas. TYPES OF SMOG CLASSICAL (INDUSTRIAL) SMOG Caused by emissions from coal burning and industrial activities Rich in smoke, sulfur dioxide and other pollutants Occurs in cool, humid conditions, often in winter Associated with reduced visibility and poor air quality PHOTOCHEMICAL SMOG Caused by sunlight-driven reactions between nitrogen oxides and volatile organic compounds Common in sunny, warm conditions Forms a brownish haze Can cause eye irritation and respiratory discomfort OPERATIONAL IMPACT ON NAVIGATION REDUCED VISIBILITY Limits lookout effectiveness and increases collision risk. NAVIGATIONAL HAZARD Makes buoyage, landmarks, and other aids difficult to identify. INCREASED DEPENDENCE ON EQUIPMENT Greater reliance on radar, AIS, ECDIS and sound signals. PORT APPROACH RISK Poor visibility in port limits safe manoeuvring and berthing operations. SAFETY TIPS Maintain safe speed and enhanced lookout. Use radar, AIS and other equipment effectively. Sound appropriate fog signals as per COLREGS. Monitor weather and air quality reports regularly. Strengthen bridge team communication and vigilance. | |

In exams

Asked 14 times across 4 different questions, most recently in 2026. Asked most in 2nd Mate (14).

Drafted by SailR from our daily lessons. AI-drawn illustration. Simplified to explain the idea, not to scale. Last updated 19 Oct 2026.

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