Essential Chart Work - Tidal Stream Using Tidal Diamonds - RYA Yachtmaster Theory Training
February 23, 2024 · 4 min · 2K views
What this video covers
Tidal diamonds — the lettered symbols (A, C, D, and others) printed on a nautical chart — encode tidal stream data that can be read directly from a table printed on the chart's margin, without consulting a separate Tidal Atlas.Watch The table is keyed to high water time at a named standard port (in this example, Victoria) and lists hours from −6 to +6 relative to that high water.1:29 Each row gives two pieces of data: the tidal stream direction in degrees true and two speed figures — spring rate and neap rate in knots.3:01 At tidal diamond A, three hours before high water at Victoria, the direction reads 297°, the spring rate 1.4 knots, and the neap rate 0.7 knots.2:40 The tutorial compares tidal diamonds directly against the Tidal Atlas method: diamonds require only the chart itself and suit precise numerical lookup, while the Tidal Atlas is pictorial and better suited to passage planning because successive hourly pages show tidal flow across a whole route at a glance.3:38 Both methods produce the same output — a direction and a speed.3:24
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