Coastal Passage Planning - Tidal Gates & Ports of Refuge

Prerequisites

You should already hold, or be working at the level of, RYA Day Skipper, and be comfortable with:

• Chartwork to the standard of the Advanced Chartwork lesson: EPs, multi-hour courses to steer, secondary port tides and stream interpolation.
• Basic pilotage plans for a familiar harbour in daylight.
• IALA Region A buoyage, light characteristics and the sectors shown on charts.
• Reading shipping forecasts and inshore waters forecasts.

The Yachtmaster Coastal candidate is expected to plan and skipper passages of up to around 150 nm, including at night and in unfamiliar waters, so this lesson pulls together navigation, meteorology and crew management into a single process. SOLAS Chapter V, regulation 34, also makes passage planning a legal requirement for all vessels going to sea, including pleasure craft.

Learning Objectives

By the end of this lesson you will be able to:

• Apply the Appraisal, Planning, Execution and Monitoring (APEM) cycle to a coastal passage (syllabus: passage planning).
• Gather and weigh information from charts, almanacs, pilot books, notices and forecasts.
• Identify hazards and plan contingency anchorages, diversion ports and escape routes.
• Plan tidal gateways, slack water windows and multi-leg sequences, including the point of no return.
• Recognise wind-against-tide hazards.
• Plan a night passage, including light identification and watch arrangements.
• Produce a one-page pilotage plan for an unfamiliar harbour by day and night (syllabus: pilotage).
• Execute visual and blind pilotage using transits, clearing lines, depth contours and radar parallel indexing.
• Set quantitative abort criteria and make sound decisions under uncertainty.
• Calculate departure times, courses to steer and arrival times across tidal streams hour by hour, and work out a tidal window over a bar (syllabus: tidal streams, tidal heights and passage timing).
• Assess a weather forecast against defined go/no-go limits for the boat and crew (syllabus: meteorology and passage making).
• Plan a crossing of a traffic separation scheme and a night approach, including the range at which each light should first be seen (syllabus: COLREGs, lights and night passage).
• Design a watch system and fatigue plan, and brief the crew and a shore contact (syllabus: crew management and skippering).

RYA syllabus mapping (Coastal Skipper / Yachtmaster Coastal, G158): this lesson covers the Navigation items "passage planning" and "pilotage" and the Seamanship and Skippering items on crew management, watchkeeping and decision making. Specifically: appraisal using almanac, pilot books, Notices to Mariners and forecasts; planning of tidal gateways, contingency ports, night passages and the written pilotage plan; execution and monitoring including visual and blind pilotage; and the abort and diversion decisions an examiner expects a skipper to justify. The syllabus expects you to demonstrate these practically and to be questioned on any topic up to Yachtmaster Coastal level.

The APEM Cycle

Professional mariners use a four-stage cycle. It is not a one-off form to fill in; it repeats throughout the passage as conditions change.

1. Appraisal: gather every relevant piece of information.
2. Planning: turn that information into a route, timings, contingencies and a crew plan.
3. Execution: carry out the plan, adapting it sensibly.
4. Monitoring: continuously check progress against the plan and feed new information back into appraisal.

Appraisal

Information sources

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Check the dates: a ten-year-old pilot book or uncorrected chart can be dangerously wrong about buoyage or depths in a shifting estuary.

Hazard identification

Go along the whole route on the chart and mark every hazard, then pair each with a contingency.

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Typical hazards: shoals and banks (with the tidal height you need to cross them), overfalls and tidal races (Portland Bill, St Alban's Head, the Alderney Race), shipping lanes and TSS crossings, firing ranges, lee shores, and harbours that cannot be entered in onshore gales. For each hazard ask: how will I avoid it, how will I know I am close to it, and where do I go if I cannot get past it?

Weather appraisal and go/no-go limits

A forecast is only useful if you have decided in advance what you will accept. Gather at least three sources (for example the Met Office inshore waters and shipping forecasts, a GRIB file or weather routing site, and the forecast given on VHF or NAVTEX by the Coastguard), compare them, and look at the trend as well as the headline. Then compare them with limits set for this boat and this crew.

Use the pattern of pressure change too: a fall of 4 hPa or more in three hours ("falling rapidly" in forecast language) signals strong winds close behind, and a sharp veer with a clearing sky after a cold front usually means gusty weather for several hours. Write the forecast and your decision in the log. Remember that the forecast is for a sea area, and local effects (sea breezes, headland acceleration, katabatic winds) can add several knots.

Vessel, crew and shore-side appraisal

Check the boat as well as the passage: engine hours, fuel and water, gas, charged batteries, the state of sails and reefing gear, bilge pumps, navigation lights, VHF with DSC, handheld VHF and a charged phone, radar reflector, the position of the liferaft, flares in date, lifejackets and tethers, the first-aid kit, and the contents of the grab bag. Check the crew too: experience, qualifications, medical conditions and allergies, seasickness tablets taken in good time (at least an hour before sailing). Finally, leave a passage plan ashore with a reliable contact, stating the boat's description, the crew number, the route, the ETA and the time when the contact should alert HM Coastguard if you are overdue and cannot be reached (dial 999 and ask for the Coastguard, or call on VHF Channel 16). Consider registering with the Coastguard's voluntary identification scheme (CG66) and update your shore contact when the plan changes. This reflects the intent of SOLAS V regulation 34 and the RYA and MCA guidance for yachts.

Planning

Contingency anchorages and diversion ports

Every passage needs bolt holes. A good contingency list states the shelter offered by wind direction, the holding, depths, and whether it is usable at night or at any state of tide.

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An anchorage sheltered from northerly winds is useless when a front veers the wind into the south-west. List more than one, covering different wind directions, and include an all-weather, all-tide port if one exists.

Route, waypoints and clearing the dangers

Draw the track on the largest-scale chart that covers each leg. Place waypoints where you want to alter course, and at places you can positively identify (a buoy, a lighthouse abeam, a clear transit). Check every leg for dangers within a safe margin: as a rule of thumb stay at least 1 nm off a headland with overfalls or an unlit danger, 0.5 nm off a charted rock if there is no tidal set across it, and more if the tide sets towards it. Waypoints should not lie on top of a hazard: put them to the side of a buoy, not on it, so a sailing yacht does not run into it or into another yacht doing the same. Measure each leg's True course and distance, convert the courses to Magnetic, and put them in a table.

Course to steer with tidal stream: a worked example

Leg of 12 nm on a track of 090T. Boat speed 5 knots through the water. The tidal stream sets 180T at 2 knots for the whole leg, so it is at right angles to the track.

1. At the start of the track, plot the stream for one hour: 2 nm along 180T.
2. From the end of that stream vector, swing the dividers set to 5 nm (the distance the boat goes in one hour through the water) until the point touches the track. That line is the heading to steer.
3. By calculation: the angle to correct is asin(2/5), which is about 24 degrees. The stream is setting you south, so steer north of the track: 090 minus 24 = 066T.
4. Ground speed along the track = the square root of (5 squared minus 2 squared) = the square root of 21, about 4.6 knots.
5. Time for the leg = 12 / 4.6 = 2.6 hours, or about 2 hours 37 minutes.
6. Convert to a compass course: with variation 3 degrees West, 066T becomes 069M. Deviation is then applied if the compass has any.

If the stream changes during the leg, split the leg into one-hour segments and work each one in turn, using the average of the hourly rates from the stream atlas.

Passage timing, hour by hour

Do not average a stream blindly over a long leg. Step through it hour by hour.

Example: a 20 nm leg along a track with a favourable stream, boat speed 5 knots. The stream rates along the track from the atlas are 0.5, 1.5, 2.0 and 1.0 knots in successive hours.

The last nautical mile takes 1.0 / 6.0 hours, about 10 minutes, so the total time is 3 hours 10 minutes. Without the stream the leg would take 4 hours. Reverse the stream and it is slower than 4 hours, and in a strong foul stream you may make nearly no progress, so you wait in port.

Remember to plan the stream at each part of the passage from the correct hour of the atlas, using the time of high water at the reference port (for example HW Dover) and converting to the time zone you are using.

Tidal gateways

A tidal gateway is a place where the stream is so strong, or the sea state so dangerous with the wrong tide, that you must pass it at a particular time: headlands, races, narrow sounds and river bars.

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Planning a gateway:

1. From the stream atlas, find when the stream turns in your favour at the gateway (relative to the reference port HW).
2. Convert to clock time for the day, in the right time zone.
3. Work backwards: distance from departure divided by realistic speed (be pessimistic) gives departure time.
4. Add a margin: aim to arrive near the start of the favourable stream, not halfway through it.
5. Identify the point of no return: the point after which, if late, you would be committed against a building foul stream with insufficient sea room or engine power to retreat.

Rule of thumb: a 6-knot yacht punching a 3-knot stream makes 3 knots over the ground and doubles its passage time. A 2-knot stream with you and 2 against for the same six hours is not a wash: you spend more hours in the foul tide because you are moving more slowly through it.

Wind against tide

When wind blows against the stream, waves are shortened and steepened. A Force 5 against a 3-knot spring stream off a headland can produce breaking seas that would be unremarkable in open water.

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Plan to pass headlands and races with the wind and tide together where possible, keep well off (several miles) or very close inshore inside the race where pilot books recommend, and consider neaps rather than springs for marginal passages.

Multi-leg sequencing

Longer passages may involve several gateways in sequence. Missing the first by half an hour can cascade into missing all of them.

Build in buffer time and identify an intermediate haven before each gate. Decide in advance: "if we are more than 30 minutes late at gate A, we go into haven 1 and wait for the next tide." Making that decision at the planning table, not at 0300 when tired, is the point.

Crossing a traffic separation scheme

Crossing a TSS is a common coastal challenge (the Dover Strait, off the Casquets, the Channel Islands approaches). Under Rule 10 you must cross on a heading as nearly as practicable at right angles to the general direction of traffic flow. A vessel under 20 m or a sailing vessel must not impede the safe passage of power-driven vessels following the lane. Rule 10 also says to avoid crossing the lanes so far as practicable, so ask whether you need to cross at all (inshore routes may avoid it). If you must cross, do so away from the points where lanes converge and note any advice on the chart. Your heading is at 90 degrees to the lane but your track may not be.

Example: the lanes run 045T/225T, so you head 135T or 315T. Your boat speed is 5 knots and the tidal stream runs along the lane at 3 knots. You are crossing a scheme 6 nm wide (two lanes and the zone between). At 5 knots across the lanes it takes 6 / 5 = 1.2 hours, 72 minutes. In that time the stream carries you 3 x 1.2 = 3.6 nm along the lane, so your track over the ground is a long diagonal. Plan where you will emerge and check the sea room and other hazards at that point. Rule 10 refers to the heading, so you steer at 90 degrees to the lanes even though your track is diagonal: ships watching you see a vessel apparently crossing at right angles and can predict your movement. Do not offset the heading into the stream to make good a track at right angles.

During the crossing keep a sharp lookout, use the radar and AIS if fitted to find the CPA of ships, and be prepared to alter course for a ship, but remember to alter by a large amount and then return to the heading when clear. Vessels generally should not use an inshore traffic zone when they can safely use the adjacent lane, but vessels under 20 m, sailing vessels and vessels fishing are allowed to use it. Rule 10 also says a vessel other than one crossing, joining or leaving a lane should not normally enter the separation zone or cross a separation line, except in an emergency or to fish within the zone.

Night passages

Night changes everything: crew alertness, light identification, depth perception and the speed with which you can deal with problems.

• Lights: list every light you expect to see, with characteristic, range and sector colour, and the time you expect to raise and dip it. Sector boundaries make excellent position lines.
• Night vision: red lighting only on deck and at the chart table; full adaptation takes 20 to 30 minutes and is destroyed by a single white torch.
• Fatigue: human alertness is lowest between about 0200 and 0500. Avoid scheduling difficult pilotage then, and consider doubling up watches.
• Safety: harnesses clipped on at night as standard, lifejacket lights checked, danbuoy and throwing line ready, MOB procedure briefed.
• Arrival: entering an unfamiliar harbour at night is a skill the examiner will test, but if you have the choice, plan to arrive in daylight or wait offshore until dawn.

Seeing the lights: worked range example

At night the first sight of a light is a position check. The geographical range (the limit set by the curve of the earth) in nautical miles is about 2.08 x (the square root of the light's height in metres + the square root of your eye height in metres). The light is also limited by its nominal (luminous) range, and it appears at the shorter of the two, though poor visibility cuts both.

Example: a lighthouse is charted Fl(2) 10s 30 m 20M. Your eye is 2 m above water.

1. Geographical range = 2.08 x (5.48 + 1.41) = 2.08 x 6.89 = 14.3 nm.
2. Nominal range = 20 nm, but the light cannot be seen beyond 14.3 nm because it is below the horizon.
3. So in clear weather you will first see it at about 14 nm. In haze or rain it may not show until you are well inside that distance. Write the expected time of first sighting in the plan: at 6 knots, 14 nm takes 2 hours 20 minutes, and treat a later sighting as a reason to check your position.
4. The light will "dip" below the horizon when you are leaving it at about the same distance. Taking the moment it dips gives you a position line that is a circle of that radius around the light.

Include, for the passage plan, a table of lights: name, characteristic, height, nominal range, geographical range from your eye height, time and bearing expected. Mark the sector limits, because stepping from white into red is an unmissable warning at night.

Watch systems and fatigue

A well-planned watch system is part of the plan. With a crew of four on a 24-hour passage, one suitable pattern is two watches of two people, running three hours on and three hours off at night, which keeps people fresher than four hours, and rotating the pairs so that the same people do not always take the deepest night hours. Whoever is the skipper may be off the watch rota and available for pilotage, but should not be sleep-deprived at arrival. Examples:

Provide hot food and drink at each handover, a handover brief (position, course, traffic, weather, any concerns) and a requirement that anyone who is unsure, tired or worried calls the skipper at once. Sleep before the passage and eat regularly; seasick crew should be encouraged to drink and to stay in the cockpit looking at the horizon.

Documentation

A complete plan can be executed by another skipper if you are incapacitated.

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The essentials: waypoints with courses and distances; tidal heights and gateways with times; pilotage plans for departure and arrival; a watch schedule; contingencies with decision rules; and a crew brief. Summarise the critical numbers on a single laminated card for the cockpit.

Pilotage in Unfamiliar Waters

Pilotage is navigation by eye (or radar) in close proximity to dangers, where there is no time to plot on a chart. The work is done in advance so that, on the day, you only need to compare what you see against your plan.

Preparation

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Allow at least 30 minutes of focused study before arrival, preferably at anchor or offshore with a settled crew. Study the overview chart, then the large-scale harbour chart, the almanac and the pilot book. Then build a mental picture: shut your eyes and run through the approach mark by mark. Identify the three most serious hazards, decide your abort criteria and brief the crew on their roles.

The pilotage plan

Condense everything onto one page that can be read in a moving cockpit at night.

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A practical format is a sketch with legs drawn as a series of arrows, each labelled with bearing (Magnetic, because that is what you read off the steering compass), distance, and what you should see at the end of the leg. Write the clearing bearings and the depths you expect beside each leg. Include VHF channels, tidal constraints, decision points, and the "if... then" contingencies.

Practise writing plans from the chart and almanac alone within 30 minutes; swap plans with another crew member and try to follow theirs. If they cannot, it is not clear enough.

A one-page pilotage plan: example layout

Below is an example of the table from a pilotage plan for an unfamiliar harbour, written with Magnetic bearings (variation 3 degrees West applied) and a height of tide for the planned time of arrival of 3.0 m.

Write the plan so that anyone can follow it: a drawn sketch next to the table, a clearing bearing such as "keep the lighthouse bearing more than 250M to stay north of the rocks", the VHF channel for the harbour office, the abort rule ("depth less than 3 m or visibility under 0.5 nm: stop and turn back on the reciprocal 218M"), and the latest safe time to enter.

A tidal window over a bar: worked example

The bar is charted as drying 1.1 m. The yacht draws 1.9 m and the skipper wants 0.6 m of clearance, so the required depth over the bar is 2.5 m, and therefore the height of tide must be at least 1.1 + 2.5 = 3.6 m. The tide table says LW 0800 height 1.0 m and HW 1400 height 5.6 m (range 4.6 m, so a twelfth is 0.38 m).

1. At 1100, three hours after LW, the tide has risen 6/12 of the range, 2.3 m, so the height is 3.3 m. At 1200, four hours after LW, it has risen 9/12, 3.45 m, so the height is 4.45 m.
2. The height 3.6 m is reached 0.3 of 1.15 m of the way through that hour: about 16 minutes after 1100, so 1115.
3. On the falling tide, three hours after HW (1700) the height is again 3.3 m, and two hours after HW (1600) it is 4.45 m. The height drops to 3.6 m about 44 minutes after 1600, so about 1645.
4. The window is 1115 to 1645. The best time to cross is near the middle, 1330 to 1400, with most water and the smallest stream. Add a margin of at least 30 minutes each side for lateness and a swell, so aim for an arrival between 1145 and 1615.
5. State the point of no return in the plan: if you will not reach the outer buoy by 1545 you divert to the all-tide port or stay out.

Leading lines, transits and clearing bearings

A leading line (two marks in line, charted with a bold line giving the true bearing) keeps you in the channel: if the rear mark moves to the left of the front, you are to the right of the line and should steer left, and vice versa. Practise saying it: "rear mark is open to the right, so steer to starboard". A transit also checks the steering compass: if the transit bears 038T and the compass reads 042 when the marks are in line, with variation 3 degrees West (038T is 041M), the deviation on that heading is 1 degree West (compass 042 is greater than magnetic 041 by 1 degree). Use it as a check, not to adjust the compass.

Choosing landmarks

Not every object is equally trustworthy.

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Prefer permanent, charted structures (lighthouses, church spires, towers). Lit marks and distinctive buoys are next. Be wary of anything temporary or generic: cranes appear and disappear, anchored ships swing, and "a white house on the hill" may be one of twenty. Remember buoys can drag off station.

Visual pilotage execution

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1. The navigator stands where they can see, with the plan, binoculars and a hand-bearing compass.
2. Give a running commentary: "Red can number 4 ahead fine on the port bow; depth 8.2 m, which is what we expect; next alteration onto 060° when the church comes into transit with the light."
3. Use transits and clearing bearings rather than buoy-hopping.
4. Before each turn, identify the next mark positively from at least two characteristics: shape, colour, topmark, light, and expected bearing and distance.
5. Tick off legs on the plan as they are completed.

The greatest danger is confirmation bias: having decided that a buoy is the one you expect, the mind keeps finding reasons to confirm it. Never accept an identification on partial evidence. Counting the buoys and noting their numbers prevents the classic error of turning one mark early.

Depth as a pilotage tool

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At each waypoint, know what depth to expect (charted depth plus height of tide). A gradual change consistent with the chart confirms you are on track; sudden shoaling means you are out of the channel or have found an uncharted bank. Stop, or turn back onto your reciprocal, and re-establish position.

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You can follow a chosen contour as a "virtual handrail" along a steep-to coast in poor visibility. Remember charted depths are referred to chart datum (approximately LAT), so add the height of tide: a 5 m contour with 3 m of tide should read 8 m below the surface.

GNSS in pilotage

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GNSS is a useful aid but not a primary pilotage tool in confined waters. Small-scale or older charts may be offset from the WGS84 position by tens or even hundreds of metres; signals can be masked or reflected by cliffs and buildings; and the plotter knows nothing about a buoy that has moved. Use GNSS to establish an approximate position, then refine with visual references, radar and depth.

Blind pilotage with radar

When visibility closes in, radar becomes the primary sensor.

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Set the range scale short (0.75 to 1.5 nm), tune gain and clutter for the conditions, then use the Variable Range Marker (VRM) for distance off a charted, radar-conspicuous feature (a breakwater head, a steep cliff) and the Electronic Bearing Line (EBL) for its bearing. Range is more accurate on small-boat radar than bearing, so two ranges make a better fix than two bearings.

Parallel indexing

Parallel indexing lets you keep to a track with no plotting at all.

On the chart, draw your intended track and measure the perpendicular distance from it to a conspicuous radar target (a headland, a pier end). On the radar, set an index line (or the offset EBL) parallel to your track at that distance. If the target echo slides along the index line, you are on track. If it drifts inside the line, you are being set towards the hazard. Prepare index lines for each leg before you lose visibility; they are much harder to set up in a hurry.

Cognitive load and the sterile cockpit

Pilotage overloads the brain: steering, traffic, marks, depth, radio calls and crew questions all at once.

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Prepare everything that can be prepared before entering the critical zone: fenders and lines out, sails stowed, engine running and checked, VHF on the right channel, berth confirmed. Delegate: helm steers the course given, one crew watches for traffic and reports, one reads the sounder aloud. Prioritise navigation and collision avoidance; paperwork and conversations wait.

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Borrowed from aviation, the sterile cockpit rule means no non-essential conversation, no phones and no distractions during harbour entry, restricted visibility, heavy traffic and close-quarters manoeuvring. Tell the crew when it starts and when it ends.

Execution and Monitoring

Adapting the plan

No plan survives unchanged. The skill is to adapt sensibly and transparently.

When you change the plan, write it in the log with time and reason, tell the crew and recalculate the knock-on effects (tidal gateways, ETA, fuel). Ask continuously whether the assumptions in the plan are still valid: is the wind as forecast, is boat speed as planned, is the crew coping?

Monitoring

Fix at regular intervals (hourly offshore, much more often near hazards) using more than one method. Compare progress with the gateway timings; compare actual weather with the forecast; watch crew fatigue and fuel. The earlier you detect a problem, the more options remain.

Abort Criteria and Decision Making

Setting abort criteria

Abort criteria are decided coolly at the chart table, in numbers, before departure or entry. When a limit is reached, you execute the abort without debate.

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Examples:

• Visibility under 0.5 nm at the outer mark: do not attempt the entry; hold offshore or divert.
• Cross-track error over 50 m in the buoyed channel: stop, re-identify marks.
• Not past the outer mark by HW-1 (bar harbour): divert.
• Sustained wind over Force 6 or 7 from the exposed quadrant: harbour unusable; go elsewhere.
• Depth less than planned minimum: stop and back out on the reciprocal.
• Engine failure in a narrow channel: anchor immediately, then call for assistance (PAN PAN, or MAYDAY if in grave and imminent danger).

The enemy of good aborting is sunk-cost thinking: "we have come so far, it would be a shame to turn back now." Discipline beats hope.

A decision-making framework

1. Identify the options (including doing nothing, heaving to and waiting).
2. Assess risks and benefits of each.
3. Consult the crew where time allows; they may have noticed something you have not.
4. Decide clearly.
5. Communicate the decision and what it means for each person.
6. Record the decision and reasons in the log.

Examiners value the quality of your reasoning more than the outcome: a well-reasoned diversion is a pass; a lucky arrival after ignoring your own criteria is not.

Worked Example: Poole to Yarmouth (Isle of Wight)

A 30 nm passage eastward in a 32 ft yacht making 5.5 kn, crew of four, forecast SW 4 to 5, occasionally 6 later, visibility good, becoming moderate in showers.

Appraisal. Hazards: Poole Bar and the chain ferry at the harbour entrance; the overfalls south of Hengistbury Head and off the Needles; the Shingles bank on the north side of the Needles Channel; wind against tide in the Needles Channel when the stream is ebbing west. Contingencies: return to Poole; anchor in Studland Bay (good in westerlies); Lymington as an alternative to Yarmouth.

Gateway. The key constraint is the Needles Channel. With a south-westerly wind you want the east-going (flood) stream, which in this area runs roughly from about HW Portsmouth -0500 to HW Portsmouth +0100 (check the atlas for the day). Wind and tide will be together. Arriving at the Needles at the start of the favourable stream gives you the most of it and the smallest seas.

Timings. Poole Bar to Needles Fairway about 15 nm. At 5.5 kn plus about 1 kn of favourable tide on average, around 2.5 hours. If HW Portsmouth is 1300 UT (1400 BST), the stream turns east around 0800 UT; aim to be at the Needles around 0830 UT, leaving Poole by 0600 UT.

Point of no return. Once inside the Needles Channel with the flood running east at 3 to 4 kn, turning back west is impractical; your commitment point is Needles Fairway. Decision rule: if the wind is over Force 6 at the Fairway or visibility is under 1 nm, divert to Studland or go back to Poole.

Pilotage plan for Yarmouth. Leading line, berthing instructions from the harbour office on VHF, ferry movements, and the depth on approach. Abort: if the harbour is full or the ferry is manoeuvring, hold off or go to Lymington.

Execution. Departure is 40 minutes late because of a slow breakfast. At 0710 UT the EP shows you will reach the Fairway at 0910, still well within the favourable stream. Logged, crew told, continue. Showers reduce visibility to 2 nm briefly; you take fixes every 20 minutes and use the radar to confirm distance off the cliffs. Arrival in Yarmouth at about 1130 UT, after a total passage of just under five hours.

Further Worked Examples

Fuel, water and endurance

A 32 ft yacht motors at 5.0 knots and burns 2.5 litres an hour; the tank holds 80 litres. The passage is 60 nm and the forecast has a light-wind period of 6 hours. If the wind dies you would motor for 6 hours, using 6 x 2.5 = 15 litres. Add a reserve: the usual rule of thumb is to plan to use no more than two thirds of the tank, here about 53 litres, leaving a third for the unexpected. Motoring flat out for the whole passage would take 60 / 5 = 12 hours and 30 litres, so the plan is safe. Now compute water: four crew drinking 3 litres a day each plus cooking gives about 15 litres a day, so a 36 hour passage needs about 22 litres plus a reserve of at least 2 litres per person per day for emergencies. Record these figures in the plan so that the crew can see the margins.

A tidal gateway calculation

Your yacht makes 5.5 knots. The gateway is a headland 12 nm from the start, where the stream runs at 3.5 knots at springs, east-going from HW Dover -0100 to HW Dover +0500 and west-going the rest of the time. HW Dover is 1130. You want to round the headland with the stream, so the east-going stream runs from 1030 to 1630, so with a margin of one hour each side you aim to arrive between 1130 and 1530. The 12 nm will take about 2 hours 10 minutes through the water, but the first part of the passage has the stream against you. Work this out hour by hour from the atlas, take the average stream, and add the figure to your boat speed: if the average stream over the leg is 1.0 knot against you, your speed over the ground is 4.5 knots and the leg takes 12 / 4.5 = 2 hours 40 minutes. Leave the start at 0850 to arrive at 1130, the earliest time inside your margin. A later departure is acceptable, but one after 1250 would put you at the headland after 1530 and outside the margin.

Choosing between two plans

Compare plan A (leave at 0600, stay inshore, arrive at the harbour at low water with 1.0 m under the keel on the bar) and plan B (leave at 0900, take the stream, arrive one hour before high water with ample depth). Plan B uses the stream, gives a safer entry and a daylight arrival. Plan A gets in earlier but its margin on the bar is too small for the forecast swell. Write down your reasoning in the log. Examiners will usually accept either plan if you justify the choice with numbers and have contingencies.

Briefing the crew

A short, structured brief makes the plan real. Cover the route and timings, the weather and the reefing points, the watch system, the places that need all hands (the gateway, the harbour entrance), the abort criteria, the emergency actions (man overboard, fire, VHF distress), and the role each person has. Ask a question at the end, for example "Where is the nearest port of refuge if we turn back at the Fairway?", to check that the plan has been understood.

What the examiner expects

• A complete plan on paper before departure, with tidal heights, streams, waypoints, ETAs and alternatives.
• Evidence that you used several sources of weather information and that you have a margin for error.
• A skipper who monitors, logs and updates the plan rather than treating it as fixed.
• Clear reasoning when you divert, delay or abort; do not apologise for making a cautious decision.

Common Mistakes

• Optimistic speed estimates. Plan on realistic speed for the conditions; a slow boat misses gates.
• One forecast source. Use at least three and plan for the worst plausible.
• Contingencies that ignore wind direction. An anchorage only works if it is sheltered from the wind you will have.
• No point of no return. Decide where commitment begins before you get there.
• Pilotage plans in True. Use Magnetic for anything read off the steering or hand-bearing compass.
• Buoy-hopping. Use transits, clearing lines and depth; buoys move and are easily misidentified.
• Vague abort criteria. "If it gets bad" is not a criterion; "visibility under 0.5 nm" is.
• Sunk-cost persistence. Being late is not a reason to accept higher risk.
• No time-zone check. Tide tables in UT, watches in BST.

Summary

• Passage planning is a legal requirement and follows the APEM cycle continuously.
• Appraise all sources, identify every hazard and pair it with a contingency that works in the forecast wind.
• Tidal gateways and slack windows drive departure times; plan the point of no return and buffers for multi-leg passages.
• Avoid wind against tide at headlands and races.
• Night passages need light lists, red-light discipline and watches planned around the 0200-0500 low.
• A one-page pilotage plan in Magnetic, with clearing bearings, depths and decisions, lets you navigate by eye without plotting.
• Use reliable landmarks, running commentary, depth checks, radar ranges and parallel indexing; treat GNSS as a check.
• Manage cognitive load with preparation, delegation and a sterile cockpit.
• Set numeric abort criteria in advance and act on them without hesitation.

Check Your Understanding

1. What are the four stages of the APEM cycle and why is it described as a cycle?

Answer: Appraisal, Planning, Execution and Monitoring. Monitoring feeds new information back into appraisal, so the plan is continuously revised throughout the passage.

1. What is a point of no return at a tidal gateway?

Answer: The point after which you cannot safely turn back because the stream will be against you with insufficient sea room or power to retreat. You must decide to commit or divert before reaching it.

1. Why is wind against tide dangerous at a headland, even in moderate winds?

Answer: The opposing stream shortens and steepens the waves, producing breaking seas out of proportion to the wind strength, especially in races and overfalls at springs.

1. Your plan has three gates in sequence. You are 45 minutes late at the first. What should your plan already say?

Answer: It should have a pre-decided rule, such as diverting to an intermediate haven if more than 30 minutes late, then waiting for the next favourable tide rather than pushing on and missing later gates.

1. Why should pilotage plans normally show Magnetic bearings?

Answer: Because the helmsman and navigator read bearings from the steering compass and hand-bearing compass, which show Magnetic (after deviation). Converting from True in a busy cockpit invites errors.

1. How does parallel indexing work?

Answer: You measure, on the chart, the perpendicular distance from your intended track to a radar-conspicuous object, then set a radar index line parallel to your heading at that offset. If the object's echo stays on the line you are on track; if it moves off, you are being set off track.

1. A buoy has the right colour and is roughly where you expect, but you cannot see its number. What do you do?

Answer: Do not accept the identification on partial evidence. Check its shape, topmark, light, bearing and distance against the plan, count the marks passed, and check depth. Guard against confirmation bias.

1. Give three examples of quantitative abort criteria for a harbour entry.

Answer: For example: visibility less than 0.5 nm at the outer mark; cross-track error greater than 50 m in the channel; not past the outer mark by HW-1; wind over Force 6 from the exposed sector; depth below the planned minimum.

1. What is the sterile cockpit rule and when does it apply?

Answer: No non-essential conversation, phones or distractions during critical phases: harbour entry and exit, restricted visibility, heavy traffic and close-quarters manoeuvring.

1. Why is "we have come this far" a dangerous reason to continue?

Answer: It is sunk-cost thinking. The time already spent does not change the risk ahead; decisions should be based only on current conditions and the abort criteria.

1. A passage uses 2.5 litres of fuel an hour under engine and the tank holds 80 litres. What is the maximum engine endurance if you keep a one third reserve, and what does it mean in practice?

Answer: Two thirds of 80 litres is about 53 litres, giving about 21 hours of motoring. In practice you should plan to use the engine for much less, because the reserve must also cover the entry to an unfamiliar harbour and a diversion.

1. You have planned to arrive at a headland gateway between 1130 and 1530, and you are running 90 minutes late at the half-way point. What should you do?

Answer: Recalculate the ETA from the current EP, compare it with the window and the abort criteria, and decide. If the new ETA is still inside the window, continue and log the decision; if not, divert to the contingency port or anchorage while you still have the option, and tell the crew.