Your route crosses a shallow bar that only has enough depth 3 hours either side of high water, and high water is at 1400. Everything else about the passage is flexible. What does this single fact most directly determine?

The window in which you must depart so you reach the bar in time

The course to steer for the leg approaching the bar

The window in which you must depart so you reach the bar in time

🗺️ Building a Complete Passage Plan

By now you can plot a course, read tides, and take fixes. A passage plan stitches all of that into one document you can actually skipper from. It answers four questions in advance: where you'll go (the route), what could hurt you (hazards), when you must arrive (timing), and what if it goes wrong (contingencies). In the UK the RYA teaches this, and SOLAS Chapter V legally requires every vessel — even a small yacht — to plan a passage before departure.

Start by breaking the route into legs: straight-line segments between waypoints (specific lat/long positions). For each leg you note the course to steer (already corrected for variation, deviation, and tidal set from earlier cards), the distance, and an estimated time at your planned speed. A 30 nm passage might become five legs of 4–8 nm each, turning at a headland, a buoy, or a safe-water mark.

Now overlay hazards and timing. Mark drying banks, rocks, traffic lanes, and overfalls, and defend each with a technique from earlier cards — a clearing bearing or a safe contour. Bake in tidal gates: points like a shallow bar or a race that are only safe within a time window, which fix your departure time. Finally, plan contingencies: identify ports of refuge ('bolt-holes') along the way, a plan for reduced visibility or a failing engine, and clear abort points where you'll turn back rather than commit. A good plan is one you can still follow when the GPS dies and the fog rolls in.