Coastal Passage Planning

Pilotage Plans

A pilotage plan is the detailed, step-by-step guide for navigating the final approach to a harbour, anchorage, or narrow waterway. While the passage plan covers the open-water route, the pilotage plan covers the last few miles — where hazards are closest and margins are thinnest.

What it includes: Approach bearing and distance from the last offshore waypoint. Leading marks or transits for the channel. Depths at the planned state of tide. Buoy sequences and light characteristics. Speed limits and no-wake zones. VHF channel for the harbour or port authority. Berth or anchorage assignment. Tide height at arrival time and its effect on available depth.

Why it matters: The final approach to a harbour is where most groundings happen. The crew is tired from the passage, it may be getting dark, and the chart transitions from open water to dense detail. Having the pilotage plan prepared in advance — with the approach sketched, the buoy sequence listed, and the depths checked against tide — means the navigator can guide the boat in without interpreting the chart under pressure.

Night approaches: If there's any possibility of arriving after dark, the pilotage plan must include light characteristics — which lights you'll see in sequence, their colours, flash patterns, and sectors. An unfamiliar harbour at night is disorienting. A pilotage plan turns it into a sequence of identified lights that confirm you're on track.

Tidal Gates and Timing

A tidal gate is a point on the route where the tide must be at a specific state for safe passage — either because the depth is insufficient at low water, the current is too strong to transit against, or the conditions are dangerous at certain states.

Depth-limited gates: A bar at a harbour entrance may have 2 meters at chart datum but 4 meters at high water. If your draft is 1.8 meters, you can cross the bar only near high water. Miss the tide and you wait 12 hours or divert to another harbour. The passage plan must be built backward from these gates — departure time is determined by the required arrival time at the gate.

Current-limited gates: Some passages are only feasible with a fair tide. The Swinge (Alderney, Channel Islands) runs at 6 knots on spring tides. Motoring against it at 6 knots means zero progress. Sailing against it is impossible. The passage plan must deliver the boat to the Swinge with the current running in the right direction — which determines departure timing from the previous port.

Planning around gates: Work backward. Determine the time window at the tidal gate (e.g., 'must arrive between HW-1 and HW+2'). Calculate the passage time to the gate from the previous waypoint. Subtract to find the required departure time. If the departure time is unreasonable (0300, or before the weather window opens), adjust the plan — leave earlier and slow down, wait for the next tidal cycle, or choose a different route that avoids the gate.

Chaining gates: On a coastal passage with multiple tidal gates, the timing can cascade. Missing the first gate delays arrival at the second, which may mean waiting a full tide cycle. A passage with three gates may have only one departure time per day that threads all of them correctly.

Bolt-Holes and Contingency Planning

A bolt-hole is a harbour or anchorage along the route that you can reach if conditions deteriorate, the crew is struggling, or equipment fails. Identifying bolt-holes before departure is one of the most important elements of coastal passage planning.

Selection criteria: A bolt-hole must be accessible in the conditions you're planning for. A harbour with a bar that's only crossable at high water is not a bolt-hole if you might need it at low water. A marina that requires a VHF call for the lock bridge is not a bolt-hole if you might arrive with a dead radio. The best bolt-holes are all-tide, all-weather harbours with straightforward approaches.

Pre-planning the approach: For each bolt-hole, prepare a basic pilotage plan before departure — approach bearing, channel depth, key buoys, and VHF channel. Store the approach waypoint in the chartplotter. If conditions deteriorate, you want to press one button to navigate to the nearest bolt-hole, not search the chart while the boat is pitching in 30 knots.

Decision points: Along the route, mark the points where you must decide whether to continue or divert. These are typically the points beyond which a bolt-hole is no longer reachable — once past that point, you're committed to the remaining passage. Making the diversion decision early is always better than making it late.

Traffic Separation and Inshore vs Offshore Routing

Coastal passages often cross or parallel Traffic Separation Schemes (TSS) — designated shipping lanes that organize commercial traffic flow. How you handle TSS crossings and whether you route inshore or offshore of them is a significant planning decision.

Crossing a TSS: Under COLREGS Rule 10, vessels crossing a TSS must do so at right angles to the traffic flow — as close to 90 degrees as practicable. This minimizes time in the lane and presents a clear aspect to approaching ships. Plan the crossing at a specific point, note the traffic density (AIS data from previous passages or pilot books), and cross in good visibility if possible.

Inshore traffic zones: Many TSS have inshore traffic zones between the scheme and the coast. Small vessels can use these zones to avoid the main shipping lanes. The trade-off: the inshore zone may have less traffic but more hazards (rocks, lobster pots, fishing boats) and potentially less sea room.

Offshore routing: Routing offshore of the TSS gives maximum sea room and avoids crossing the lanes entirely, but adds distance and may put you in rougher conditions. For coastal passages along a busy shipping coast, the decision between inshore (shorter, more hazards, some traffic) and offshore (longer, more sea room, must cross lanes at some point) is a key planning choice.

AIS and radar: Commercial ships in a TSS are moving at 15–20 knots and may not see a sailing yacht on radar, especially in rough seas. Having AIS (receive at minimum, transmit ideally) makes you visible in the TSS and allows you to identify approaching ships early. Cross when you have a clear gap — not when you think a ship will alter course for you.