End of this post

Weather Fronts at Sea: Warm, Cold and Occluded Fronts Explained

1 / 4

End of this post

MLC 2006 Legal Structure — Articles, Regulations, Standards & Guidelines

Ask SailRabout this topic

1 / 5

End of this post

Fixed CO₂ Fire Extinguishing System – Principles, Components & Safe Operation

Ask SailRabout this topic

1 / 4

End of this post

MARPOL Annex I & V Compliance Essentials

Ask SailRabout this topic

1 / 4

Keep what you read

You can save topics to revise later, sort them into your own collections, and pick up where you stopped in each.

Use email instead

By continuing, you agree to SailR's Terms and Privacy Policy.

End of the list

That's every topic for now

Browse the Playbook

Advection Fog vs Radiation Fog & Hoar Frost vs Rime — Know the Differences

2nd Mate

times asked: 10; times asked
questions: 4; questions
last asked: 2025; last asked

The slides, written out

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

Slide 1 · ADVECTION FOG,

ADVECTION FOG, RADIATION FOG, HOAR FROST & RIME Key Maritime Weather Hazards Every Watchkeeper Should Know FOG TYPES Formation, Conditions & Examples FROST & ICE Formation & Key Differences MARITIME IMPACT Risks & Watchkeeper Responsibilities

Slide 2 · FOG TYPES EVERY

FOG TYPES EVERY MARINER SHOULD RECOGNIZE ADVECTION FOG (SEA FOG) VS RADIATION FOG Warm, moist air moves horizontally over a colder sea surface. Common at sea, especially over cold currents. Can occur day or night, in any season. Often widespread and persistent. Visibility may remain poor for hours or days. Forms mainly over land due to rapid night-time surface cooling. Clear skies and light winds. Ground cools quickly, air reaches dew point, fog forms. Common in river estuaries, low-lying areas and harbour approaches. Often dissipates after sunrise, but may persist in winter. REAL-WORLD EXAMPLE GRAND BANKS OF NEWFOUNDLAND Warm Gulf Stream air flows over the cold Labrador Current — classic advection fog zone. REAL-WORLD EXAMPLE COASTAL HARBOUR APPROACHES AT DAWN Fog forms over coastal plains and drifts into harbour approaches at sunrise. WATCHKEEPER'S NOTE Fog reduces visibility and affects navigation safety. Radar, AIS and sound signals become critical — and remember, sound signals can be distorted in fog.

Slide 3 · FROST OR ICE?

FROST OR ICE? KNOW THE DIFFERENCE HOAR FROST VS RIME Forms by direct deposition of water vapour (sublimation) onto cold surfaces. Requires surface temperature below freezing and below the frost point. Occurs in calm to light wind conditions. Appears feathery, crystalline and delicate — like ice needles. Common on superstructure, rails, rigging, radar mast, and exposed fittings. Main hazard: slippery decks, ladders and reduced grip. Forms when supercooled water droplets freeze instantly on contact. Forms on surfaces below freezing in freezing fog, drizzle or low cloud. Usually occurs in windy conditions that bring supercooled droplets. Appears dense, opaque, white and granular. Builds up on windward sides — forecastle, anchor windlass, radar, lifeboats, aerials. Main hazards: heavy ice loading, radar blockage, equipment damage and breakage risk. WATCHKEEPER ALERT Rime accumulation can create significant topside icing hazards. Monitor weather reports and take preventive action. QUICK COMPARISON FEATURE HOAR FROST RIME FORMATION Water vapour deposits directly Supercooled droplets freeze on impact SURFACE CONDITION Below freezing & below frost point Below freezing WIND CONDITION Calm to light Usually windy APPEARANCE Feathery, crystalline Dense, granular, opaque MARITIME HAZARD Slips, reduced visibility Heavy ice loading, radar blockage

Slide 4 · QUICK COMPARISON

QUICK COMPARISON AT A GLANCE FOG COMPARISON FEATURE ADVECTION FOG (SEA FOG) RADIATION FOG CAUSE Warm, moist air moves horizontally over cooler sea surface. Surface cooling at night causes air to reach dew point. LOCATION At sea, especially over cold currents. Primarily over land and coastal approaches. WIND CONDITION Light to moderate winds (≈ 4–15 knots favorable*). Calm to light winds (< 5 knots). TIME Any time, day or night, any season. Night to early morning. PERSISTENCE May last for many hours to several days. Often dissipates after sunrise, may persist in winter. THICKNESS Can be deep (hundreds of metres). Usually shallow (tens of metres). WATCHKEEPER FOCUS Radar, AIS, sound signals – visibility can remain poor for extended periods. Expect improvement after sunrise, but stay alert during pilot operations. *Many marine forecasting references cite approximately 4–15 knots as favorable, but no universally accepted fixed wind range exists. ICE / FROST COMPARISON FEATURE HOAR FROST RIME FORMATION Direct deposition of water vapour (sublimation). Supercooled droplets freeze on impact. SURFACE REQUIRED Below freezing AND below frost point. Below freezing (droplet impact). WIND CONDITION Calm to light. Usually windy (brings supercooled droplets). APPEARANCE Feathery, crystalline, delicate. Dense, granular, opaque. MARITIME HAZARD Slips, reduced grip, reduced visibility. Heavy ice loading, radar blockage, damage risk. KEY TAKEAWAY Understanding how fog and ice form helps you anticipate visibility and icing hazards — protect your ship, your crew and the voyage.

In exams

Asked 10 times across 4 different questions, most recently in 2025. Asked most in 2nd Mate (10).

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

Spotted a mistake?

Ask SailR about this