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Sea vs Swell, Mist vs Fog & Coastal Weather Bulletin

2nd Mate

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

Slide 1 · SEA vs SWELL

SEA vs SWELL UNDERSTANDING THE DIFFERENCE SEA SWELL SEA Generated by local wind Short wavelength Steep & irregular Changes quickly Defines current sea state SWELL Generated by distant weather systems Long wavelength Regular wave pattern Travels long distances May exist even in calm weather QUICK MEMORY TIP Sea = Local Wind Swell = Distant Storm

Slide 2 · MIST vs FOG

MIST vs FOG IT'S ALL ABOUT VISIBILITY MIST FOG VS Visibility > 1000 metres (> 0.5 NM) Cause Fine water droplets suspended in air Navigation Possible with caution Visibility < 1000 metres (< 0.5 NM) Cause Dense suspended water droplets Navigation Restricted visibility procedures apply FOG CHECKLIST Safe Speed (COLREG Rule 6) Sound Fog Signals (Rule 35) 1 prolonged blast every ≤ 2 min Maintain Proper Lookout Use Radar & AIS Follow Rule 19

Slide 3 · COASTAL WEATHER

COASTAL WEATHER BULLETIN STRUCTURE THREE PARTS. ONE PURPOSE – SAFE VOYAGE. PART I WARNINGS • Gale Warnings • Storm Warnings • Tropical Cyclone Warnings • Other significant weather warnings issued by the Meteorological Service ↓ PART II SYNOPSIS • Position of Highs & Lows • Central Pressure • Fronts (Warm / Cold / Occluded) • Movement & Development of Pressure Systems • Associated Wave Conditions (if significant) ↓ PART III FORECAST • Wind (Direction & Speed) • Weather • Visibility (if < 5 NM) • Sea State (Wave Height & Total Sea State) • Ice Accretion (if applicable) • Outlook (Next 24 hours or more) Essential information for planning, monitoring and safe navigation at sea.

Slide 4 · QUICK REVISION

QUICK REVISION KEY POINTS TO REMEMBER 1. SEA vs SWELL SEA SWELL VS Generated by local wind Short wavelength Steep & irregular Changes quickly Defines current sea state Generated by distant weather systems Long wavelength Regular wave pattern Travels long distances May exist even in calm weather 2. MIST vs FOG MIST FOG Visibility > 1000 metres (> 0.5 NM) Fine water droplets suspended in air Navigation possible with caution Visibility < 1000 metres (< 0.5 NM) Dense suspended water droplets Restricted visibility procedures apply 3. COASTAL WEATHER BULLETIN STRUCTURE PART I WARNINGS PART II SYNOPSIS PART III FORECAST Gale Warnings Storm Warnings Tropical Cyclone Warnings Other significant weather warnings issued by the Meteorological Service Position of Highs & Lows Central Pressure Fronts (Warm / Cold / Occluded) Movement & Development of Pressure Systems Associated Wave Conditions (if significant) Wind (Direction & Speed) Weather Visibility (if < 5 NM) Sea State (Wave Height & Total Sea State) Ice Accretion (if applicable) Outlook (Next 24 hours or more) Essential information for voyage planning, monitoring and safe navigation. 4. COLREGS REMEMBER RULE 6 Safe Speed Proceed at a safe speed appropriate to the prevailing circumstances. RULE 19 Restricted Visibility Appropriate precautions and navigation rules apply in fog, mist, etc. RULE 35 Fog Signals One prolonged blast at intervals not exceeding 2 minutes for power-driven vessels making way.

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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