Marine Passage Planning

A passage plan is not a route on a screen. It is the set of decisions you have already made, so that the person on watch at 0300 in worsening conditions does not have to make them from scratch.

Modern equipment has made the drawing of a route trivial and the thinking easier to skip. The four-stage method below is the professional structure, scaled sensibly for a recreational boat.

#Stage 1: appraisal

Gather everything before drawing anything.

The vessel. Draft, air draft, fuel range under power, water, realistic speed in the expected conditions, autopilot power consumption, crew number and experience.

The charts. Current electronic charts for the whole route, plus an independent offline set. Check the Australian Hydrographic Office for relevant Notices to Mariners, and read the Zone of Confidence for any area you will approach closely. See marine charts Australia for why this matters more than GNSS accuracy.

The tide and current. Heights and times at the relevant standard and secondary ports, tidal streams through any constriction, and the vertical datum the chart uses. The tides and currents guide covers the arithmetic.

The weather. Forecast, warnings, and the synoptic pattern behind them rather than a single app's summary. See weather routing.

The destination and the alternatives. Entry constraints, bar crossings, marina depths, after-hours access, and — critically — which alternatives are tenable in which wind directions.

The regulatory picture. Safety equipment required for the waters you will enter, which differs by state and territory and by distance from shore. Confirm against AMSA and your state or territory maritime authority rather than memory.

#Stage 2: planning

Now draw the route, and then interrogate it.

For each leg, check:

• Depth. Charted depth, expected tide at the time you will be there, your draft, your margin
• Survey quality. Is this leg crossing a low-confidence area? If so, widen the margins and consider a detour
• Hazards. Reefs, wrecks, obstructions, isolated dangers, fish-farm and mooring areas
• Restricted and regulated areas. Traffic schemes, port limits, exclusion zones, marine parks
• Air draft under bridges and cables, against the tide state on arrival
• Lights and marks that will be available at night
• Radar conspicuousness of the coastline, for a night or poor-visibility approach
• Escape. If conditions deteriorate on this leg, where do you go?

Then set the monitoring parameters the electronics will actually use:

Cross track error alarm:   0.2 NM coastal / 0.5 NM offshore
Depth alarm:               draft + margin
Arrival radius:            sensible for the waypoint's purpose
CPA / TCPA profile:        coastal or offshore
Anchor watch:              set on arrival, not at 0200

A waypoint should exist for a reason — a course change, a hazard clearance, a decision point. A route of forty waypoints placed to trace a coastline precisely is harder to monitor than a route of eight placed to answer questions.

Also decide, in advance:

• the go / no-go criteria for departure
• the abort criteria for each leg
• the point of no return where continuing becomes the safer option
• who ashore holds the plan, and when they should raise the alarm

Write these down. Under pressure, an agreed threshold is much easier to act on than a judgement call.

#Stage 3: execution

Execution is the decision to go, and the adjustments made to the plan on the day.

Departure timing is usually a tide, light or weather-window problem:

• leaving on the ebb to carry favourable stream
• arriving at a bar or entrance on a rising tide in daylight
• timing a tidal gate
• crossing a shipping lane at right angles, in good visibility, well clear of traffic concentration

Before slipping lines, run the departure checklist — and be willing to use the go / no-go criteria you wrote yesterday, including when the crew wants to leave and the criteria say no.

#Stage 4: monitoring

This is the stage electronics have made deceptively easy. A vessel symbol tracking a magenta line looks like successful navigation.

Monitoring means continuously answering: is the boat where the plan expects, and does the plan still make sense?

Cross-check position independently. Radar range and bearing to a charted feature. Depth against the expected contour. A transit or leading line. Sea-state and visual observation matching expectation. If GNSS and the world disagree, find out why before continuing.

Watch the depth, not only the chart. Depth is a live measurement of reality; the chart is a historical model of it. A depth that reads consistently shallower than charted is a warning worth acting on.

Re-forecast. Fetch weather at planned intervals and compare against what you were given at departure. A forecast that has shifted is a reason to revisit the plan, not a curiosity.

Log. Position, course, speed, wind, barometer, engine hours and anything notable, at a regular interval. A written log is the fallback when the electronics fail, and it makes drift in the situation visible.

Confirm the GNSS source. Particularly after a firmware update or refit, the network may be using a weaker position source than you think. The GNSS guide covers source selection.

#A worked coastal example

A 40 ft yacht, 1.9 m draft, planning an overnight coastal passage of about 110 NM.

Nothing in that table is exotic. All of it is easier to decide at anchor than at 0300.

#Departure checklist

• weather and warnings reviewed, forecast source noted
• tide and stream computed for the whole passage
• charts current; Notices to Mariners checked
• route reviewed leg by leg for depth, hazards and survey quality
• alarms set: depth, XTE, CPA/TCPA, arrival
• primary GNSS source confirmed
• backup navigation charged, offline charts downloaded and opened
• distress beacon registration and expiry checked; safety equipment verified against the requirements for the waters concerned
• handheld VHF charged; DSC MMSI confirmed programmed
• fuel, water, oil, filters, bilge and rig checked
• crew briefed: plan, watch system, night orders, safety equipment locations
• shore contact holds the plan and knows when to escalate

#Bottom line

The electronics will happily take you along a line. Passage planning is the work of deciding, in advance and in daylight, whether that line is the right one — and what you will do when it stops being the right one.