Day Passage Planning with APEM Framework - Step by Step

Prerequisites

This lesson sits in the RYA Day Skipper syllabus after chartwork, tidal heights and streams, and weather. Before you start you should be able to:

• Plot a course to steer allowing for tidal stream and leeway, and work out an estimated position (Day Skipper chartwork lesson).
• Read a tidal stream atlas and tidal diamonds, and work out the height of tide at a standard port.
• Interpret a shipping forecast and an inshore waters forecast, and know the Beaufort scale.
• Recognise IALA Region A buoyage and the common chart symbols.
• Have the sea time recommended for the Day Skipper practical course: about 5 days, 100 nautical miles and 4 night hours aboard, ideally after RYA Competent Crew.

Passage planning pulls all of these skills together. If any feel shaky, revisit them first, because a plan is only as good as the calculations inside it.

Learning Objectives

This lesson covers the RYA Day Skipper shorebased syllabus topic "Passage Planning" (appraisal, planning, execution, monitoring, tidal gates, ports of refuge, crew briefing) and the passage planning element of the Day Skipper practical course. By the end of this lesson you will be able to:

• Explain the legal duty to plan a passage (SOLAS Chapter V, Regulation 34) and what it means for a leisure skipper (syllabus: passage planning, legal requirements).
• Use the APEM cycle (Appraisal, Planning, Execution, Monitoring) to structure a day passage in familiar tidal waters (syllabus: planning a coastal passage).
• Identify tidal gates and work backwards from them to a departure time (syllabus: use of tidal streams and tidal heights in planning).
• Choose sensible waypoints, design a route and mark clearing bearings and safety contours (syllabus: waypoints, route, hazards).
• Prepare pilotage notes for departure and arrival, including a night entry plan (syllabus: pilotage planning).
• Identify ports of refuge and set clear abort and go/no-go criteria (syllabus: contingency planning).
• Calculate fuel, water and provisions with a sensible reserve.
• Deliver an effective crew briefing, and leave a shore contact with the Coastguard or a responsible person.
• Monitor progress, adapt the plan and document your decisions (syllabus: monitoring and passage records).

Why Plan at All?

The legal duty

SOLAS Chapter V, Regulation 34 applies to every vessel that goes to sea, including a 9 m family yacht on a day sail. The skipper must plan the passage before departure, taking into account at least:

• The weather forecast, and what you will do if it changes.
• Tidal heights and streams, and how they affect timing and depths.
• The limitations of the vessel and the experience and fitness of the crew.
• Navigational dangers along the route, including traffic separation schemes and restricted areas.
• A contingency plan: where you will go if things go wrong.
• Leaving details of your intended passage with someone ashore.

For a short trip in local waters the plan may be a page in the log and a few notes on the chart. For a longer passage it will be more detailed. The Maritime and Coastguard Agency does not prescribe a form, but if there is an incident, investigators will ask what planning was done. "I've sailed it many times" is not a plan.

The practical reason

A plan moves the thinking to the chart table in harbour, where you have time, light, a stable surface and a cup of tea. At sea, with a wet chart, a seasick crew and the wind rising, you will make worse decisions. The aim is that most of the decisions you need at sea have already been made: "If the wind is above Force 5 at the headland, we turn back."

The APEM Framework

Professional mariners and the RYA use a four-stage cycle called APEM. The diagram below summarises each stage.

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Appraisal: gather everything first

Appraisal means collecting and studying all the information before you commit to a route. Do not start drawing lines until you have done this.

Ask the key appraisal questions:

1. How far is it, and how long will it take at a realistic average speed (not the best speed the boat has ever done)?
2. Is there a tidal gate (a headland, race, bar or channel) that dictates when I must be somewhere?
3. Is there enough daylight, with a margin?
4. What is the weather doing, and is it within the limits of this boat and this crew?
5. Where can I go if it all goes wrong?

If the honest answer to the last question is "nowhere", rethink the passage.

Planning: turn information into a usable plan

Planning converts appraisal into concrete detail:

• Plot the route on the paper chart with tracks, bearings and distances between waypoints.
• Calculate departure time from tidal gates and daylight.
• Work out course to steer for each leg, and ETAs at key points.
• Mark clearing bearings and depth contours that warn you of hazards.
• Write pilotage notes for departure and arrival harbours.
• Identify ports of refuge and decide abort points.
• Set go/no-go criteria for weather.
• Calculate fuel, water and food.
• Prepare the crew briefing.

Execution: carrying out the plan

Execution starts with pre-departure checks (engine, gas, safety kit, weather update) and the crew briefing. It continues through departure, navigation and arrival. Keep the log going, fix your position regularly, and compare where you are with where the plan said you would be.

Monitoring: is the plan still valid?

Monitoring runs alongside execution. Are you on track and on time? Has the forecast changed? Is the crew coping? A good plan includes decision points where you consciously ask "do we carry on?" When reality departs from the plan, you change the plan. The RYA would rather see a well-reasoned diversion than a rigid skipper pressing on.

Tidal Gates

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What a tidal gate is

A tidal gate is a place where the tidal stream makes passage impractical or dangerous unless you time it correctly. Typical examples:

• A headland with a tidal race (Portland Bill, St Alban's Head, the Needles approaches).
• A narrow channel where the stream runs at 3 to 6 knots.
• A harbour bar that breaks or dries at low water.
• A harbour with a sill or lock that is only open around high water.

At a race, the danger is not only slow progress. When wind opposes a strong stream, the sea becomes short, steep and breaking. A small yacht can be knocked down or swamped in overfalls that would be harmless an hour later at slack water.

Working backwards from the gate

The golden rule: plan the gate first, then work backwards to your departure time. The timeline below shows a typical favourable window with a buffer built in.

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The method:

1. From the tidal stream atlas, find when the stream at the gate turns in your favour and when it turns against you. In this example it is favourable from HW+0100 to HW+0400 (HW at the reference port).
2. Choose a target arrival early in the window, here HW+0130. Arriving at the start gives you a buffer if you are late.
3. Measure the distance from your departure point to the gate.
4. Estimate your speed over ground on that leg, allowing for the stream you will meet on the way, not just your boat speed.
5. Divide distance by SOG to get passage time. Subtract this, plus a margin, from the target arrival time. That is your latest departure time.
6. Decide what you will do if you are early (a safe place to wait or slow down) and if you are late (an anchorage or an alternative destination).

Why the margins matter

If your boat does 5 knots through the water and you meet a 3 knot foul stream, your SOG is 2 knots. A 4 mile stretch that would take 30 minutes with the stream (SOG 8 knots) takes two hours against it. If wind is also against the stream, you may face standing waves. Missing the gate by an hour can cost you six hours, or force a dangerous decision. Build in a buffer of at least 30 minutes, and more if the forecast is uncertain or the crew is inexperienced.

Rules of thumb

• Springs roughly double the neap rates; check which you will have.
• Streams turn earlier close inshore than offshore, and often run harder off headlands.
• Slack water is short at springs. Do not rely on "arriving at slack" without a margin.
• Wind against tide over Force 4 near a headland race is a warning sign; over Force 5 it is usually a no-go for a small yacht.

Waypoints and Route Design

Choosing waypoints

A waypoint is a position you navigate to. It must be safe to arrive at, because GPS will take you there very precisely. The chart view below shows good and bad placement.

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Principles:

• Place waypoints in safe water, clear of hazards. Never put a waypoint on a buoy, a rock or a shoal; boats have hit buoys by steering exactly to them. Offset by a cable or two.
• Do not put waypoints in a shipping lane or in the middle of a traffic separation scheme.
• Put waypoints where you change course, and consider the wheel-over point: the boat needs room to turn.
• In confined water, space waypoints closely and set the cross-track error (XTE) alarm so it sounds before you reach danger.
• Check every waypoint against the paper chart. Typing errors and chart datum differences can shift a position by hundreds of metres. Read the latitude and longitude back from the plotter and plot it.
• Name waypoints meaningfully (e.g. "HEAD-S" for 5 cables south of the headland) and write them in the log with bearing and distance from a charted feature.

Designing the route

The shortest line is rarely the best. The diagram compares a direct route that crosses shoals and a shipping lane with a safer dog-leg in deeper water.

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When designing a route:

• Keep in deep water where the extra distance is small; shallow water steepens waves and reduces your margin.
• Cross traffic separation schemes at right angles (heading, not track), as required by COLREGs Rule 10, or avoid them.
• Stand well off headlands with races unless the plan specifically uses an inshore passage at slack water.
• Think about the wind angle. Six hours beating into 25 knots exhausts a crew. A longer route that lets you reach may be faster and safer.
• Keep a lee shore in mind. If the forecast wind is onshore, give the coast a wider berth.

Clearing lines and contours

Mark a clearing bearing or a safety depth contour along any leg that passes close to a hazard. For example: "Keep the church spire bearing more than 045 degrees (M) to stay clear of the Shingles." If the echo sounder reads less than your safety depth, you know immediately you are off track. These checks work even if the GPS fails.

Ports of Refuge and Contingency Planning

Ports of refuge

A port of refuge is a harbour or anchorage you can reach and enter safely if the passage has to be abandoned. The diagram shows refuges identified along a coastal route.

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A real port of refuge must be:

• Enterable at any state of tide, or at least during the period you might need it. A drying harbour is no refuge at low water.
• Safe to enter in the conditions that would make you divert. A harbour with a bar that breaks in onshore winds is not a refuge in an onshore gale.
• Within reach. On an exposed coast, aim to have shelter within 2 to 3 hours sailing, roughly every 10 to 15 nautical miles.

Write the essential pilotage details for each refuge in your notes: the approach, the entry depth, the VHF channel, and any night lights in case you are late.

Abort points and go/no-go criteria

Decide in advance what will make you turn back or divert, and where you will make that decision:

• Go/no-go before leaving: "If the forecast is above Force 5, or visibility below 2 miles, we stay in harbour."
• Decision point at sea: "At the headland waypoint at 1100, if we are more than 45 minutes behind schedule or the wind is above 20 knots, we divert to Port B."
• Hard limits: "We will be alongside by 1900, one hour before sunset."

Pre-decided criteria protect you from the pressure to keep going ("we're nearly there", "the crew have to catch a train"). When you are tired and cold, a written rule is easier to obey than a judgement you have to make from scratch.

Leaving word ashore

Tell a responsible person ashore your route, ETA, number of crew, and when to raise the alarm if they have not heard from you. In the UK you can also register the boat and crew details on the Coastguard's voluntary safety scheme so that information is available in an emergency. Update your contact if you divert.

Fuel, Water and Provisions

Fuel

Work out fuel from engine hours, not hope. The diagram gives typical figures.

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A small cruising diesel burns roughly 2 to 4 litres per hour depending on revs and load. To calculate:

1. Estimate motoring hours: passages in light winds, foul tide, harbour entry and exit, battery charging.
2. Multiply by consumption at your usual cruising revs.
3. Add a reserve of at least 25 per cent, and preferably more on an exposed coast or with a tidal gate, because you might have to motor against a foul tide to reach refuge.
4. Check the actual tank level by dipstick or sight gauge before you leave. Fuel gauges on yachts are notoriously unreliable.

Example: you expect 3 hours motoring at 3 litres per hour = 9 litres. Add a contingency allowance of 2 extra engine hours (6 litres) for a possible diversion: 15 litres. Add 25 per cent reserve: about 19 litres. Carry at least 20 litres usable fuel. Remember that the last few litres in a tank may be unusable if the pick-up is above the bottom, especially in a seaway.

Water

Allow at least 1.5 to 2 litres of drinking water per person per day, more in hot weather, plus water for cooking and washing. For four crew on a day sail, carry at least 8 to 10 litres even if the main tank is full, in case the tank is contaminated or the pump fails.

Food

Prepare food that is easy to eat in a seaway: sandwiches, flasks of soup or hot drinks, cereal bars, fruit. A hungry, dehydrated crew is a tired, cold and error-prone crew. Low blood sugar affects judgement, and that includes the skipper's.

Crew Briefing

What to cover

An unbriefed crew cannot help you when it matters. Use the checklist below before every passage.

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A Day Skipper briefing typically covers:

1. Destination, route, ETA and the main hazards.
2. Tidal gates and the timing pressure they create.
3. Weather forecast and what would make you change the plan.
4. Who does what: helm rota, navigation help, sail handling, cooking.
5. Safety: lifejackets and when to wear them, harnesses and jackstays, location of flares, liferaft, grab bag, fire extinguishers, fire blanket, first aid kit, gas shut-off, seacocks, bilge pumps.
6. Man overboard: who does what, how the MOB button works, where the lifebuoy and dan buoy are.
7. VHF: how to send a DSC alert and a Mayday, which channels you monitor.
8. Seasickness: tell someone early, stay on deck, stay clipped on.

How to brief

Make it a conversation, not a lecture. Ask people to point to the grab bag or explain how to use the VHF. "Sarah, what's our abort criterion for the headland?" Repeat-back checks reveal confusion that silence hides. Match the depth to the crew: a novice needs more than an experienced friend. Post a short written summary at the chart table. If the plan changes, re-brief: never assume everyone noticed the course alteration.

Executing and Monitoring the Plan

Keeping track

• Fix your position at least hourly on an open-water passage, more often near hazards. Use a mix of GPS, visual fixes and depth so that one error does not mislead you.
• Write log entries: time, position, course, speed, log reading, wind, barometer, sail plan, engine hours.
• Compare actual with planned: are you ahead or behind? Is cross-track error growing?
• Get updated forecasts during the passage (Coastguard MSI broadcasts on VHF, or the inshore waters forecast).

Adapting the plan

The cycle below shows how monitoring feeds into diagnosis, adjustment and documentation.

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When you notice a difference between plan and reality, ask why:

• Is the stream stronger than predicted (springs, wind-driven current)?
• Is boat speed lower (foul bottom, poor sail trim, wrong sail plan)?
• Has the wind shifted or strengthened against the forecast?
• Is the crew more tired or seasick than expected?

Then decide early. If you will now reach the tidal gate after it closes, divert or wait now, rather than racing a deadline and arriving exhausted in a rough race. Safety trumps the schedule every time.

Write down what you changed and why, with the time. It helps you think clearly, records your reasoning, and shows an examiner mature judgement.

Time, Speed and Distance: The Numbers Behind the Plan

Every plan rests on three relationships: distance equals speed multiplied by time, speed equals distance divided by time, and time equals distance divided by speed. Distance is in nautical miles, speed in knots (nautical miles per hour) and time in hours. To convert minutes to hours, divide by 60; to convert decimal hours back to minutes, multiply the fraction by 60.

Worked numbers: a leg of 14.5 miles at a planned SOG of 4.5 knots takes 14.5 / 4.5 = 3.22 hours, which is 3 hours and 13 minutes (0.22 x 60 = 13). If you leave at 0915 you expect to arrive at about 1230.

Plan with ground speed, not boat speed

The speed you use must be the speed over ground (SOG). For a yacht making 5 knots through the water with the stream running 2 knots along your track, SOG is 7 knots with the tide and 3 knots against it. Where the stream is across the track, you steer to allow for it and the resulting SOG is a little lower than boat speed (use a tidal vector triangle on the chart). Where the stream changes hour by hour, split the leg into hourly steps using the atlas: the distance covered in each hour is your SOG for that hour, and the sum gives the ETA.

A stepped tidal leg

You sail 5 knots through the water on a track of 090 degrees true. The atlas gives the stream along track as 1.5 knots east for the first hour, 0.5 knot east for the second, then 1.0 knot west for the third hour.

• Hour 1: SOG 6.5 knots, distance 6.5 miles.
• Hour 2: SOG 5.5 knots, distance 5.5 miles, cumulative 12.0 miles.
• Hour 3: SOG 4.0 knots, distance 4.0 miles, cumulative 16.0 miles.

For a 14 mile leg you finish in the third hour: you need 2.0 more miles at 4.0 knots, or 30 minutes, so the ETA is 2 hours 30 minutes after departure. If you had used a simple average boat speed of 5 knots you would have said 2 hours 48 minutes. The stepped method is both more accurate and shows you where the leg goes slow.

Pilotage Notes for Departure and Arrival

The Day Skipper syllabus expects a written plan for entering and leaving harbour, since most groundings happen close to land. For each harbour, write the following on one page, ready to be read in the cockpit:

1. Chart and publication references: large scale chart number, almanac page, pilot book reference.
2. Tidal constraints: the depth over any bar or sill, the height of tide needed (calculate it) and the earliest and latest time of entry.
3. The approach: the landfall mark, the line of the entrance, the leading marks or sector lights, with bearings in degrees magnetic as you will read them from the hand-bearing compass.
4. Hazards: rocks, shoals, moorings, ferry or commercial traffic, speed limits.
5. The marks in order, with light characteristics for a night entry (Fl.G.5s and so on) and their expected bearings.
6. Clearing bearings and depths that tell you at once that you are off the line.
7. VHF: harbour master channel, port control, whom to call and when.
8. Berthing information: visitor berths, pontoons, fuel berth, locks and bridge times.
9. Abort options: where you would turn round or anchor if the entrance became unsafe, such as a breaking bar.

Write your sketch plan with the marks drawn as a simple chart. The skipper who enters a harbour for the first time at night with no notes depends entirely on luck; the one with a clear page reads the plan and confirms each mark as it appears.

Planning for Weather

The weather forecast sets go/no-go criteria, and the criteria should be written into the plan. For a Day Skipper the usual sources are the Shipping Forecast and inshore waters forecast from the Met Office and Coastguard, the Navtex broadcasts, a weather website for synoptic charts, and local knowledge. Three points deserve emphasis.

• Wind against tide. A wind of Force 4 or less over tide is usually comfortable; Force 5 and above against a stream of 2 knots or more produces short, steep seas. Plan to cross races and shallow banks only when wind and tide run the same way, or at slack.
• Wind direction and the coast. An onshore wind makes a lee shore: give headlands a wide berth and avoid harbours with a bar that breaks. An offshore wind makes the water flat near the coast but builds a sea further out, and can carry a drifting yacht away.
• Timing of change. Forecasts give a time window for veers, backs and frontal passages. Plan to be tucked in before a cold front arrives, with its squalls and wind shift of 90 degrees or more.

Set limits for your own boat and crew: for example, "Maximum wind Force 5 for a coastal day passage with novices aboard, and no crossing of Race X in wind over tide." Write them down before you see the forecast, so that you are not tempted to adjust them to suit the day.

Restricted Areas, Traffic and Other Constraints

The route must be checked for features that restrict or regulate passage. Look for them on the chart and in the almanac:

• Traffic separation schemes (TSS): COLREGs Rule 10 applies. Do not use a separation zone, cross lanes at right angles (heading, not track) and in the shortest practicable time, and avoid crossing near the ends of the scheme. A vessel under 20 m or a sailing vessel must not impede a vessel following the lane.
• Firing ranges and exercise areas: the chart shows the limits and the almanac gives the telephone number and VHF channel for range control. Check on the day.
• Wind farms, cables, pipelines and wrecks: keep out of safety zones around offshore structures and note the anchoring prohibitions.
• Harbour limits and fairways: speed limits, permission to enter or cross, and the priority of large ships in a channel (Rule 9).
• Marine protected areas and seasonal restrictions: for example seal haul-outs and eelgrass beds.

Night and Daylight Considerations

A passage that begins in the dark or ends after sunset is a different challenge. Calculate sunrise and sunset from the almanac, and civil twilight if you need it. A Day Skipper passage should normally be planned to finish in daylight, with an hour in hand, but if it will involve darkness:

• Prepare a lights list with each light's characteristic, colour, period, range and bearing.
• Check the nominal range against the visibility: the luminous range of a light falls in poor visibility.
• Plan the watch system and make sure there is enough crew to keep a lookout and steer.
• Add fuel and warm clothing, as crew tire faster and feel colder at night.
• Keep a bright chart table light red or dimmed to protect night vision.

Tools: Paper, Plotter and Almanac

Use paper charts and electronic navigation together. The plotter gives a position and a cross-track error, but you must plan, confirm and back-up on paper, because a plotter can fail, can have an old chart base, and can mislead through a datum or scale error. Record the plan in the log or on a passage plan form with at least these fields: route and waypoints (latitude and longitude, bearing and distance from a fixed feature), course to steer for each leg, distance, ETA and tidal gate times, hazards and clearing marks, ports of refuge, VHF channels and contacts, go/no-go criteria, fuel and water check, and the person ashore who has the plan.

Second Worked Example: Re-timing for a Spring Tide

Your friend asks for the same passage as in the worked example below, but on a day of spring tides. The stream at Point X now runs at 3 knots instead of 1.5, and the race is more severe. HW at the reference port is 1030.

• The favourable stream window is HW+0100 to HW+0500, or 1130 to 1530.
• Slack water lasts only about 30 minutes either side of the turn at springs, and the flow builds rapidly.
• You choose to arrive at 1200, thirty minutes after the stream turns, when it is fair at only 1 knot and the race is still settling.
• Leg A to Point X is 9 miles. With 0.8 knot foul at springs, SOG is about 3.7 knots for the first hours, then improves to 5 knots as the stream turns. A stepped calculation gives about 2 hours 20 minutes.
• Departure: 1200 minus 2h20 minus a 30 minute margin = 0910.

The lesson of this example is that the same route, in the same boat, needs a different plan on a different day. Springs and neaps change the answer.

Exam and Practical Tips

• A Day Skipper candidate is expected to work from a given tidal atlas and set of data to produce a time of departure, a course to steer and an ETA. Show every step; method earns marks even if the arithmetic slips.
• Name the APEM stages in order, and say what you do in each.
• State the SOLAS Chapter V Regulation 34 requirements without being prompted. Examiners like candidates who know why they plan.
• When asked for an abort point, give a place, a time and a reason ("At waypoint 3 by 1100; if not there, divert to Harbour C because the stream will be foul").
• Talk through contingency options before being asked: a port of refuge on each side of the tidal gate, and a reserve of fuel.

Worked Example

The passage

You are planning a day passage from Harbour A to Harbour B, 18 nautical miles to the west along an exposed coast. Halfway, 9 miles from A, is Point X, a headland with a tidal race. Your yacht cruises at 5 knots through the water. Four crew: you, an experienced friend and two novices.

Given:

• HW at the reference port: 1000. Neaps.
• At Point X, the stream runs west (favourable) from HW+0100 to HW+0500, max 1.5 knots at neaps. It runs east (foul) from HW-0100 onwards to HW+0100 and the race is worst at mid-flood.
• Between A and Point X, the stream averages 0.5 knots against you until HW+0100, then turns fair.
• Forecast: West or southwest 3 to 4, occasionally 5 later. Sea slight to moderate. Good visibility.
• Sunset 2030.

Step 1: The gate

The favourable window at Point X is 1100 to 1500. Target arrival 1130, early in the window, giving a 3.5 hour buffer before the stream turns.

Step 2: Back-plan the departure

Leg A to Point X: 9 miles. The forecast wind is west to southwest, so you will be beating or motor-sailing. Allow an average speed through the water of 4.5 knots, minus 0.5 knots foul stream for most of the leg: SOG about 4 knots. Passage time: 9 / 4 = 2 hours 15 minutes. Add a 30 minute margin. Departure: 1130 minus 2h45 = 0845.

Step 3: The second leg

From Point X at 1130 to B, 9 miles, the stream is now fair at about 1 knot average: SOG about 5.5 knots. Time about 1h40. ETA at B about 1310. Even if the wind rises and you are slow, you have six hours of daylight in hand.

Step 4: Contingencies

• Port of refuge before the headland: Harbour A itself (2 hours back downwind).
• Port of refuge after the headland: Harbour C, 4 miles beyond Point X, all-tide access.
• Decision point: the waypoint 2 miles east of Point X, planned for 1100. If you are later than 1230 there, or the wind is above 20 knots true from the west (wind against the east-going stream would be a problem later), you turn back to A.
• Fuel: 3 hours possible motoring at 3 L/h = 9 L, plus 2 hours contingency = 15 L, plus reserve: carry at least 20 L. The tank holds 60 L and is dipped at 45 L. Fine.

Step 5: What actually happened

The diagram below shows how a real day can depart from the plan.

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Suppose at 1030 you are only 5 miles out, because the wind came in at Force 5 on the nose and two crew are seasick. At your current 3 knots you will reach Point X at about 1150, which is still inside the window, but the seasick crew are getting weaker and the forecast "occasionally 5 later" has arrived early. Your decision: you are still on the safe side of your abort criteria, but you are trending towards them. You decide to bear away and motor-sail into Harbour C, which you can reach comfortably, and log: "1030. 5nm E of Pt X. W5, 2 crew seasick, SOG 3kn. Diverted to Hbr C to rest crew and reassess. Will review forecast for afternoon window or tomorrow."

That is exactly the kind of decision the RYA wants a Day Skipper to make: early, reasoned and recorded.

Worked Example: The RYA Course Notes Passage, Porth Dinllaen to Caernarfon

The RYA Day Skipper practical course notes use a real passage on the Lleyn Peninsula in North Wales to show how the pieces fit together. It is worth working through because it has two tidal constraints and shows the "work backwards" method in action.

How far. Porth Dinllaen to Caernarfon is 17 miles overall: 12 miles from the anchorage to the Caernarfon Bar (about 2.5 hours at 5 knots) and 5 miles from the Bar through the Menai Strait to Caernarfon (about 1 hour). At a boat speed of about 5 knots the whole journey takes roughly 3.5 hours.

Constraints. The chart and pilot book show two tidal constraints:

1. The pilot book states that Victoria Dock marina at Caernarfon is entered through gates accessible HW plus or minus 2 hours.
2. A note on the chart states that the Caernarfon Bar, where the depths in the entrance to the Strait change continually and the buoys are moved accordingly, should only be crossed within 3 hours either side of high water.

The times. The tide table gives HW Caernarfon at 1250 in standard time; adding one hour for British Summer Time gives HW 1350. So the gates are accessible from 1150 to 1550, and the Bar is passable from 1050 to 1650.

When will the stream be favourable? Tides in the area are based on HW Caernarfon, and a tidal stream atlas (easier to read than tidal diamonds) shows the new flood starting from Porth Dinllaen at about 0900 and running towards the Strait, and the stream in the Strait turning at HW, 1350. The notes therefore plan to arrive earlier, at 1300, with the last of the incoming tide, rather than fight the ebb through the Strait.

Working backwards from the arrival time:

Pilotage. Three places need a plan: leaving Porth Dinllaen, the Bar, and the arrival at Caernarfon. Leaving Porth Dinllaen, the rocks to the north are marked by an isolated danger mark but the danger is a rock awash; the notes give three ways to clear it: a waypoint on the rock with a proximity alarm set to 400 yards, so that if the alarm sounds you stop or alter course; a clearing line from the flagpole on the Coastguard lookout; and the 10 m depth contour, which once crossed confirms the rock is cleared. The Bar is a narrow buoyed channel through sandbanks: plot the course from buoy to buoy and cross each one off as it is passed, because even a simple buoyed passage is easy to lose in a cross-stream. Draw the expected cross streams on the plan as a reminder, and keep each buoy in transit with the land behind it to hold a good course over the ground.

Navigation. The forecast of south-west 3 with long sunny periods allows an easy sail and a direct course up the peninsula; a course to steer allowing for the tide may need working up. A waypoint for the Bar is plotted on the chart, entered into the GPS and double-checked, and a "waypoint web" (a fan of bearing lines and range rings drawn round the waypoint) is drawn on the chart so that the GPS range and bearing to the waypoint can be plotted as a position in seconds.

Running the passage. Obtain the latest forecast; be prepared to change plans and stay in port; if the forecast is good, leave promptly; hoist sails in the shelter of the land; delegate tasks; log the position every hour; watch for cross tides at the entrance and consult the pilot book about calling the harbour master. In the notes the yacht arrives early because of the fair tide, which is the right way round: early at a gate is a wait, late is a problem.

Common Mistakes

The diagram summarises five classic mistakes and their corrections.

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• Treating the plan as a one-off. A plan is a set of assumptions. Keep testing them and change it when they fail.
• Waypoints on dangers. Offset waypoints into safe water and check every one on the paper chart.
• Racing a tidal gate. If you are going to be late, divert or wait early. Do not fight a foul stream through a race.
• Assuming fuel and water. Dip the tank. Do not trust yesterday's memory or the gauge.
• Lecturing the crew. Ask questions and get repeat-backs. Silence is not understanding.
• Using best-ever speed. Plan on a realistic average including tacking, reefing and slow periods.
• Forgetting daylight. A day skipper plan must finish in daylight with a margin; sunset is a hard limit, not a target.
• No contingency. If you cannot name where you would go if it goes wrong, you have not finished planning.

Summary

• Passage planning is a legal requirement (SOLAS V Reg 34) and the foundation of safe skippering.
• Use APEM: Appraisal (gather everything), Planning (route, timings, contingencies), Execution (brief and go), Monitoring (check and adapt).
• Identify tidal gates first and work backwards to a departure time, with a buffer of at least 30 minutes.
• Put waypoints in safe water, never on dangers, and verify them against the paper chart.
• Prefer routes in deep water, away from races and lee shores, even if slightly longer.
• Identify genuine ports of refuge and set abort criteria in advance.
• Calculate fuel and water with a reserve, and check levels physically.
• Brief the crew interactively and re-brief when plans change.
• Divert early, document why, and remember that safety beats schedule.

Check Your Understanding

1. Which regulation makes passage planning a legal requirement for leisure craft, and name four things it requires you to consider.

Answer: SOLAS Chapter V, Regulation 34. You must consider weather, tides, the limitations of the vessel, the experience of the crew, navigational dangers, and a contingency plan, and leave details ashore.

1. What do the four letters of APEM stand for, and in which stage do you decide your ports of refuge?

Answer: Appraisal, Planning, Execution, Monitoring. Refuges are identified during Appraisal and written into the plan during Planning.

1. A headland's favourable stream runs from HW+0200 to HW+0500. HW is 0930. The headland is 12 miles away and you expect an SOG of 4 knots. What is your latest sensible departure time, with a 30 minute margin and aiming to arrive 30 minutes into the window?

Answer: The window opens at 1130; target arrival 1200. Passage time 12 / 4 = 3 hours, plus 30 minute margin = 3h30. Depart by 0830.

1. Why should you never put a waypoint exactly on a navigation buoy?

Answer: GPS will take you very precisely to it, risking collision with the buoy or the danger it marks. Offset waypoints into safe water.

1. Give two features that make a harbour a genuine port of refuge.

Answer: It must be enterable at the state of tide when you would need it, and safe to enter in the wind and sea conditions that would force you to divert (for example, no bar that breaks in onshore winds).

1. You expect 4 hours motoring at 3 litres per hour. What is the minimum fuel you should carry, using a 25 per cent reserve and allowing 2 extra hours for contingency?

Answer: (4 + 2) x 3 = 18 litres; plus 25 per cent = 22.5 litres. Carry at least 23 litres usable fuel, and check by dipping the tank.

1. You are 1 hour behind schedule and will reach a tidal race just as the stream turns foul, with wind against it. What should you do?

Answer: Divert to a port of refuge or wait somewhere safe for the next favourable window. Do not try to beat the gate; a foul stream against the wind in a race produces steep, breaking seas.

1. Why is a repeat-back better than just asking "Does everyone understand?"

Answer: People rarely admit confusion. Asking someone to explain the abort criterion or show where the grab bag is proves they understood.

1. Name three things to check when monitoring progress against the plan.

Answer: Actual versus planned position and ETA, the updated forecast versus the planned weather, and crew condition (fatigue, seasickness), plus fuel used.

1. A 15 mile leg has a stream along track of 2 knots in your favour for the first 2 hours, then 1 knot against. Your boat speed is 5 knots. When do you arrive?

Answer: Hours 1 and 2: SOG 7 knots, so 14 miles in 2 hours. The final mile is at SOG 4 knots (5 minus 1): 15 minutes. Arrival 2 hours 15 minutes after departure.

1. What do you check before crossing a traffic separation scheme, and how do you cross?

Answer: Check the chart, almanac and any local notices, and the traffic. Cross the lanes at right angles (heading, not track) in the shortest practicable time, avoid the separation zone and the ends of the scheme, and do not impede vessels following the lane (COLREGs Rule 10).

1. Why must a plan for a spring-tide day differ from the same passage at neaps?

Answer: Streams at springs are much stronger (roughly double neap rates), slack water is shorter and races are rougher. Timings, margins and the go/no-go criteria need to change.

1. HW Caernarfon is 1250 standard time on a summer day. The marina gates open HW plus or minus 2 hours and the Bar may be crossed HW plus or minus 3 hours. What are the two windows in local time?

Answer: Add one hour for BST: HW 1350. Gates 1150 to 1550; Bar 1050 to 1650. Plan to be through the Bar and alongside inside both windows, and before the stream in the Strait turns at HW if it will be against you.

1. What is a waypoint web and why draw one?

Answer: A fan of bearing lines and range rings drawn on the chart around a waypoint, so that the range and bearing to the waypoint read from the GPS can be plotted as a position in seconds without a plotter or dividers.