Yourbestsailvideo
Anchoring: wave diffraction
16 June 2026 · 12 min · 2K views
Man draws wave motion on whiteboard for sailing lesson
What this video covers
Wave diffraction causes swell to bend around headlands and into apparently sheltered anchorages — a phenomenon the video explains through diagrams and a personal experience. When a swell's wavelength (crest-to-crest distance) is comparable to or larger than the width of a bay entrance or the gap beside a promontory, the waves curve around the obstacle and penetrate the anchorage even when wind direction and fetch are favorable.7:43 When the wavelength is much smaller than that characteristic distance, waves travel in a straight line and the bay stays calm.10:44 The tutorial first reviews two core anchorage-selection criteria: anchoring in the lee of the coast to eliminate fetch and avoid a lee shore if dragging occurs, and separately checking swell direction — using apps such as Windy or Navili — because swell can arrive from a completely different direction than the current wind.3:28 Sandy bottoms are recommended for plow-type anchors (CQR, Delta, Rocna).5:20 Diffraction applies equally to a narrow-mouthed bay: if the entrance width is similar to the incoming wavelength, swell fans out across the entire interior.10:19
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