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Beaufort vs Douglas Sea Scale: Application
Before we dive into the scales, first let me point out what the difference is between waves and swell. They’re two distinct types of water movement, each shaped by different forces.
Get in the spirit by visiting my RIBs ONLY YouTube channel, where, guided by this overview, switch your focus on the unique settings and conditions of each action video instead of the RIB.
Waves
- What They Are: Waves form due to local wind blowing across the water’s surface.
- Features: These waves tend to be shorter, choppy, and irregular, shifting quickly with changes in wind direction and speed.
Their size and pattern are directly influenced by the strength of the local wind. - Look and Feel: When the wind is strong, waves can become steep with breaking tops, resulting in rough, unpredictable conditions.
- Lifespan: Waves are temporary and subside once the local wind decreases or stops.
Swell
- What It Is: Swell is created by winds from distant storms or strong weather systems and can travel over long distances.
- Features: Swell consists of smooth, evenly spaced waves with longer wavelengths.
It moves independently of local wind and maintains a steady rhythm. - Look and Feel: Unlike the sharpness of waves, swell appears as gentle, rolling waves that don’t break as often and have a more relaxed shape.
- Lifespan: Swell can persist even when local winds are calm, often traveling for days across the ocean.
Scales Explained: One Doesn’t Exclude the Other
Beaufort Scale
Origin: The Beaufort Scale was created in 1805 by Admiral Sir Francis Beaufort of the British Royal Navy.
Initially, it served as a standardized way for sailors to estimate wind conditions based on the effects of the wind on the sea surface and ship behavior.
Before widespread meteorological instruments, this observational scale allowed sailors to gauge wind strength more reliably.
Purpose and Structure: The Beaufort Scale primarily measures wind force, with a focus on the wind’s impact on the sea state.
- Bft 0: Calm — Wind speed under 1 knot; sea like a mirror.
- Bft 1: Light Air — 1–3 knots; ripples on the water, no crests.
- Bft 2: Light Breeze — 4–6 knots; small wavelets, crests with no breaking.
- Bft 3: Gentle Breeze — 7–10 knots; large wavelets, crests begin to break.
- Bft 4: Moderate Breeze — 11–16 knots; small waves with whitecaps.
- Bft 5: Fresh Breeze — 17–21 knots; moderate waves, many whitecaps.
- Bft 6: Strong Breeze — 22–27 knots; large waves, foam streaks.
- Bft 7: Near Gale — 28–33 knots; sea heaps up, white foam streaks.
- Bft 8: Gale — 34–40 knots; moderately high waves, foam blown in streaks.
- Bft 9: Strong Gale — 41–47 knots; high waves, dense foam, spray.
- Bft 10: Storm — 48–55 knots; very high waves, rolling sea, reduced visibility.
- Bft 11: Violent Storm — 56–63 knots; exceptionally high waves, heavy spray.
- Bft 12: Hurricane Force — 64+ knots; air filled with spray, extremely dangerous conditions.
Applications: The Beaufort Scale is widely used in meteorology, maritime navigation, and by seafarers to assess wind-related sea conditions, crucial for navigation and safety.
Douglas Sea Scale
Origin: The Douglas Sea Scale was introduced by British Navy Captain H.P. Douglas in the 1920s and adopted by the British Navy in 1944.
Unlike the Beaufort Scale, which focuses on wind force, the Douglas Scale was created specifically to describe sea state conditions based on wave height from local and distant winds. Here’s how wave height is measured.
Swell Scale Levels (0–9): These levels describe the height of swell waves generated by distant winds, with a similar range as the sea state but focused on swell rather than wind-driven waves.
Structure: The Douglas Scale has two parts:
Sea State Scale: Categorizes wave conditions from local wind, with levels from 0 to 9.
Swell Scale: Describes swell conditions from distant winds, also with levels from 0 to 9.
- Sea State 0: Calm (Glassy) — Wave height under 0.1 meters.
- Sea State 1: Calm (Rippled) — 0.1–0.5 meters; small ripples with no crests.
- Sea State 2: Smooth (Wavelets) — 0.5–1.25 meters; wavelets with barely breaking crests.
- Sea State 3: Slight — 1.25–2.5 meters; small waves.
- Sea State 4: Moderate — 2.5–4 meters; moderate waves, whitecaps form.
- Sea State 5: Rough — 4–6 meters; larger waves, whitecaps and some spray.
- Sea State 6: Very Rough — 6–9 meters; high waves, extensive foam.
- Sea State 7: High — 9–14 meters; massive waves, large areas of foam.
- Sea State 8: Very High — 14 meters and above; very large waves, long crests.
- Sea State 9: Phenomenal — Waves exceeding 14 meters; extremely large and dangerous waves.
Douglas Swell Scale
Here are the levels of the Douglas Swell Scale (0–9), which describe the height of swell waves generated by distant winds. Each level corresponds to specific swell height ranges, which help mariners understand long-distance wave effects, separate from immediate, wind-driven waves.
- Swell Level 0: No Swell
- Description: No noticeable swell waves; the sea is smooth.
- Swell Height: 0 meters.
- Swell Level 1: Very Low Swell
- Description: Very slight, small, undulating waves.
- Swell Height: Up to 0.5 meters.
- Swell Level 2: Low Swell
- Description: Small but visible swell waves.
- Swell Height: 0.5 to 1.25 meters.
- Swell Level 3: Slight Swell
- Description: Moderate swell waves, noticeable but not large.
- Swell Height: 1.25 to 2.5 meters.
- Swell Level 4: Moderate Swell
- Description: Clearly defined swell waves, more significant in size.
- Swell Height: 2.5 to 4 meters.
- Swell Level 5: Rough Swell
- Description: Larger, rougher swell waves.
- Swell Height: 4 to 6 meters.
- Swell Level 6: Very Rough Swell
- Description: Large swell waves that can be challenging for smaller craft.
- Swell Height: 6 to 9 meters.
- Swell Level 7: High Swell
- Description: Very large swell waves, making navigation difficult.
- Swell Height: 9 to 14 meters.
- Swell Level 8: Very High Swell
- Description: Extremely large swell waves, hazardous for most vessels.
- Swell Height: 14 meters and above.
- Swell Level 9: Confused Swell
- Description: Swell waves from multiple directions, creating chaotic conditions; swell height varies greatly.
- Swell Height: Varies; typically associated with highly turbulent seas and crossing swells.
Application: The Douglas Scale is widely used in weather reporting, scientific research, and maritime industries to assess wave dynamics and swell conditions, providing mariners with valuable information on both immediate and distant influences on sea state.
Key Differences
- Focus: The Beaufort Scale gauges wind force and its effects on the sea, while the Douglas Scale assesses sea and swell conditions based on wave height.
- Measurements: The Beaufort Scale connects wind strength with sea conditions, whereas the Douglas Scale independently categorizes sea state and swell height.
- Range of Descriptions: The Beaufort Scale runs from 0 to 12, while the Douglas Sea Scale uses 0 to 9 for both sea state and swell.
Conclusion: Beaufort vs Douglas Sea Scale
Together, the Beaufort and Douglas scales offer complementary information on marine conditions.
Give It a Try!
Use these training videos to practice attributing the Douglas Sea Scale rather than focusing on the RIB.
Credits
Photo Beaufort: By Stephen Pearce – Royal Museums Greenwich, Public Domain, wikimedia
Photo Douglas: By Walter Stoneman(Life time: 1876–1958) – Original publication: National Photographic RecordImmediate source: www.npg.org.uk/collections/search/portrait/mw96139, PD-US, wikipedia
