{"id":5397,"date":"2025-03-06T21:20:08","date_gmt":"2025-03-06T20:20:08","guid":{"rendered":"https:\/\/www.yamana.ch\/2025\/03\/06\/long-or-short-waves-heres-how-to-evaluate-sea-conditions\/"},"modified":"2025-03-06T21:20:08","modified_gmt":"2025-03-06T20:20:08","slug":"long-or-short-waves-heres-how-to-evaluate-sea-conditions","status":"publish","type":"post","link":"https:\/\/www.yamana.ch\/en\/2025\/03\/06\/long-or-short-waves-heres-how-to-evaluate-sea-conditions\/","title":{"rendered":"Long or Short Waves? Here’s How to Evaluate Sea Conditions"},"content":{"rendered":"

What does it mean when we read forecasts predicting 3-meter waves with a 12-second period?
\nIs it a dangerous or manageable wave? Let’s see how to interpret the data we’re given! <\/strong><\/em><\/p>\n

Sea State<\/strong><\/h2>\n

When we read weather forecasts from various apps or weather sites, we are provided with the following parameters:<\/p>\n

    \n
  • \n

    The significant wave height (Hs)<\/strong>, which is the vertical distance between the crest and trough of the wave. The significant wave height represents the average height of the highest third of waves.<\/strong> <\/p>\n<\/li>\n

  • \n

    The period<\/strong> is the time in seconds (s<\/strong>) between the passage of two successive crests at a fixed point. The average period<\/strong> is the arithmetic mean of the periods of all waves. <\/p>\n<\/li>\n<\/ul>\n

    Wave Height<\/strong><\/h2>\n

    When sailing, we’ve surely observed an anomalous<\/strong> wave, higher than those indicated in the forecasts. This phenomenon is related to the concept of significant wave height,<\/strong> which represents the average height of the highest third of waves<\/strong>. Consequently, it’s entirely normal to occasionally encounter waves higher than this value. But to what extent can they exceed the predicted height? <\/p>\n

    There are statistical relationships that allow us to estimate the probability of encountering waves of different heights compared to the significant wave height. Below, we’ll look at these relationships to understand how frequently and to what extent we can expect higher waves: <\/p>\n

      \n
    • Hmax = 2 \u00d7 Hs<\/strong> \u2192 occurs approximately every 2000 waves<\/strong><\/li>\n
    • H\u2081\/\u2081\u2080\u2080 = 1.67 \u00d7 Hs<\/strong> \u2192 occurs approximately every 100 waves<\/strong><\/li>\n
    • H\u2081\/\u2081\u2080 = 1.27 \u00d7 Hs<\/strong> \u2192 occurs approximately every 10 waves<\/strong><\/li>\n<\/ul>\n

      Practical Example<\/strong><\/h4>\n

      If a forecast indicates rough seas with 3-meter waves (Hs)<\/strong>, even higher waves might occur at sea:<\/p>\n

        \n
      • 1 wave every 2000<\/strong> (Hmax<\/strong>) could reach 6 m<\/strong> (if the period is 8s, this happens about every 260 minutes).<\/li>\n
      • 1 wave every 100<\/strong> (H\u2081\/\u2081\u2080\u2080<\/strong>) could reach 5 m<\/strong> (if the period is 8s, this means one every 13 minutes).<\/li>\n
      • 1 wave every 10<\/strong> (H\u2081\/\u2081\u2080<\/strong>) could reach 3.8 m<\/strong> (if the period is 8s, one every 80 seconds).<\/li>\n<\/ul>\n

        Long or Short Waves: How to Distinguish Them?<\/h2>\n

        Now that we know waves can be twice as large as predicted, we can continue our reasoning and delve into other aspects of waves.<\/p>\n

        Waves can be categorized into two main types:<\/p>\n

          \n
        • Long waves,<\/strong> where the distance between two successive crests is much greater than their height. They are gentler and less steep, thus more manageable for navigation. <\/li>\n
        • Short and steep waves<\/strong>: the distance between crests is closer to the wave height, making them steeper and more difficult to handle, especially with headwinds.<\/li>\n<\/ul>\n

          A wave is considered long and navigable if its wavelength is at least 10 times its height<\/strong>. Let’s look at two examples: <\/p>\n

            \n
          • A 3-meter<\/strong> wave with a wavelength of 30 meters<\/strong> or more will be gentler and more manageable in open seas.<\/li>\n
          • A wave of the same height, but with a wavelength of only 15 meters<\/strong>, will be steeper and potentially breaking.<\/li>\n<\/ul>\n