Ocean Passage Planning - Great Circles, Rhumb Lines & Trade Winds

Prerequisites

This lesson covers ocean passage planning and world climate/seasonal routing for the RYA/MCA Yachtmaster Ocean. Before starting you should:

• Hold, or be working towards, Yachtmaster Offshore (or MCA OOW Yachts), the prerequisite certificate. Offshore-level passage planning (up to about 150 miles from a safe haven), tidal planning, GRIB and synoptic chart use, and watch-keeping are assumed knowledge.
• Have studied, or study alongside, the Global Meteorology (including tropical revolving storms) and Ocean Currents lessons, because ocean routing is mostly about wind, weather and current climate.
• Know the qualifying passage requirements for the Ocean exam: a passage of at least 600 miles (planned and logged), at least 200 miles of it more than 50 miles from land, lasting at least 96 consecutive hours, completed within the last 10 years, with you as skipper or mate of a watch throughout.

The exam requires a written narrative of how you planned and executed that passage (rationale, weather, crew selection, navigation strategy, victualling and bunkering, with log copies), submitted at least 48 hours before the oral. This lesson gives you the framework for that narrative.

Learning Objectives

This lesson covers the passage planning and world climate parts of the RYA Yachtmaster Ocean syllabus (ocean passage planning, worldwide meteorology and the written narrative required for the oral). By the end you will be able to:

• Follow a structured appraisal, planning, execution and monitoring process for an ocean passage (RYA Ocean syllabus: passage planning).
• Use Ocean Passages for the World, routeing (pilot) charts, sailing directions and cruising route guides (RYA Ocean syllabus: sources of climatic and routeing information).
• Explain world climate zones and the seasonal windows that govern the main ocean routes, including tropical cyclone seasons, monsoons, ENSO and ice limits (RYA Ocean syllabus: worldwide weather and climate).
• Compare great circle, rhumb line and composite routes, and calculate distance and initial course (RYA Ocean syllabus: great circle sailing).
• Plan the classic routes: the Atlantic trade wind crossing, the return via Bermuda and the Azores, the South Pacific "Coconut Milk Run", and Southern Ocean and Indian Ocean passages.
• Plan an ITCZ crossing and an atoll pass.
• Calculate fuel, water and food with safety margins, and set contingency plans and decision points (RYA Ocean syllabus: victualling, bunkering and self-sufficiency).
• Plan communications, shore contact and clearance formalities for an ocean passage.
• Write the passage plan narrative required for the exam, and answer the examiner's likely questions about it.

The Planning Process

Ocean planning follows the same four stages you used at Offshore level, on a much larger scale of time and distance:

1. Appraisal: gather information. Climate (winds, currents, storms, ice) for the season; the vessel's condition and capabilities; crew experience; ports and formalities; communications; medical cover.
2. Planning: choose the season, the route and its waypoints, departure window, fuel/water/food quantities, watch system, communications schedule, contingencies and ports of refuge.
3. Execution: choose the actual departure day on the forecast; sail the plan.
4. Monitoring: daily positions and noon-to-noon runs against the plan; weather updates; consumption of water, fuel and food; crew health; and re-planning when reality differs.

The single biggest decision in ocean planning is when. Get the season right and most routes are pleasant; get it wrong and no amount of seamanship will make a hurricane-season crossing safe.

Planning sources

World Climate Zones and Seasons

The diagram below shows the broad climate bands. The pattern is controlled by the global circulation (covered in Global Meteorology): the ITCZ near the equator, trade winds to about 25 to 30 degrees, the subtropical highs (horse latitudes) around 30 to 35 degrees, westerlies in the temperate zone, and polar conditions above about 60 degrees.

Click to zoom

Click to zoom

For detail, the map below shows the Koeppen-Geiger climate classification of the whole world. Tropical climates (the blue and green bands near the equator) mark the trade wind and ITCZ regions. The dry (orange and red) belts around 20 to 30 degrees on either side are the subtropical high-pressure zones, with light winds and clear skies. The temperate zones (green and olive) hold the westerlies, and the cold polar climates mark ice limits. Compare the map with the routeing charts to see why passage seasons follow the climate.

Click to zoom

Image: Beck, H.E., Zimmermann, N.E., McVicar, T.R., Vergopolan, N., Berg, A. and Wood, E.F., CC BY-SA 4.0, via Wikimedia Commons_no_borders.png)

Click to zoom

Everything moves north and south with the sun, lagging it by a month or two. In the northern summer the ITCZ, the trade wind belts and the subtropical highs shift north; in the northern winter they shift south. This seasonal migration is why routes have "windows".

Tropical cyclone seasons

The first rule of ocean planning is to be out of the tropical cyclone areas in their season, or in a recognised safe harbour (ideally a hurricane hole with a proven record, or out of the water).

Click to zoom

The official National Hurricane Center tracking chart for the 2020 season (a very active year, with 30 named storms) shows how much of the Atlantic basin and Caribbean can be affected in one season. Note the swathe of tracks across the main development region at 10 to 20 degrees N, the recurving tracks off the US east coast, and the late-season storms in the western Caribbean. A single year is not a forecast, but it shows why insurers and skippers treat the whole season as dangerous.

Click to zoom

Image: National Hurricane Center and National Weather Service (NOAA), public domain, via Wikimedia Commons

Click to zoom

Click to zoom

Insurers usually define "named storm" exclusion zones and dates, which often dictate where a yacht must be. Out-of-season storms do occur (for example an early June Atlantic storm, or a May cyclone in the South Pacific), so always keep watching the forecasts.

The Indian Ocean monsoons

North of the equator the Indian Ocean is governed by the monsoon. The north-east monsoon (November to March) is the season for westbound passages from South-East Asia and India towards the Red Sea or East Africa. The south-west monsoon (June to September) is strong, wet and rough in the Arabian Sea; it suits eastbound passages but is often too boisterous for comfort. The transition months bring variable winds and the two peaks of North Indian Ocean cyclone activity.

Click to zoom

El Niño, La Niña and a changing climate

The El Niño Southern Oscillation shifts weather across the Pacific and beyond. In El Niño years the Pacific trades weaken and the cyclone risk spreads further east across the South Pacific (French Polynesia is more exposed); Atlantic hurricane activity tends to be suppressed by increased wind shear. La Niña generally does the opposite: stronger trades, more active Atlantic seasons, more cyclones in the western South Pacific and Australian region. Check the current ENSO outlook (published by national met services) when planning.

Click to zoom

Routeing charts are based on decades of historical data. A warming climate is changing some of that: longer and more intense cyclone seasons, poleward expansion of storm activity, shifts in the trade winds and more Arctic sea ice retreat. Use the climatology as your starting point but check recent seasons, keep departure dates flexible, and do not assume the old "safe" dates are guaranteed.

Click to zoom

Sources of Routeing Information

The RYA expects you to name the publications and know what each contains. Carry paper copies as well as electronic versions.

When using a routeing chart, read the month you intend to sail, then the months either side, because your passage will straddle them. Look at the percentage of gales in the zone you will cross, the frequency of calms, the resultant wind direction and the mean current. A route that gives 5 percent gale frequency is acceptable; 15 percent or more is not for a small yacht.

The Passage Timeline and Average Speed

A rational passage time estimate uses the average daily run, not the best speed. A rule of thumb for a cruising yacht of 10 to 15m with a waterline length of 9 to 12m:

• Maximum hull speed in knots is about 1.34 times the square root of the waterline length in feet. A 36 ft waterline gives 8 knots.
• A realistic ocean passage average is about 60 to 70 percent of hull speed over many days, allowing for calms, reefing, headwinds and rough nights.
• For the 36 ft waterline yacht, 70 percent of 8 knots is 5.6 knots, or about 134 miles per day. Trade wind passages often give 120 to 150 miles per day.

Use the slow passage time when planning stores: take the best realistic daily average, then use 20 to 25 percent less. For Las Palmas to Barbados (about 2,700 miles by the usual route), an average of 130 miles per day gives 21 days; plan stores for 26 days.

Add the delay between planned and actual departure. Never let a departure date become a deadline: the weather and the vessel's readiness decide.

Communications and Shore Contact Plan

Part of planning is deciding how you will talk to the world, and who will worry if you stop.

• Satellite phone or Iridium GO: voice, text and data. Test it before departure. Keep a laminated card with the phone numbers of the MRCC for each area, TMAS (Telemedical Maritime Assistance Service) and your shore contact.
• HF/SSB radio (optionally with Pactor modem): no subscription; used for cruising nets and weather. Needs a good ground plane and a licence (the Long Range Certificate or GMDSS General Operator Certificate for the operator).
• AIS, EPIRB and PLBs: AIS for collision avoidance, a 406 MHz EPIRB registered in the vessel's name, and PLBs for each crew member on deck.
• Shore contact: a named person who knows the plan, the vessel description, the crew list, the liferaft and EPIRB details, and who has a clear instruction (for example, "if you have not heard from me by 24 hours after the overdue date, call the Coastguard"). Agree a position-report schedule (once daily at a set time) and a procedure for the shore contact if a report is missed.
• Float plan: lodge with the Coastguard (a UK Coastguard "Voluntary Safety Identification Scheme" form, form CG66) if sailing from UK waters.

Formalities, Clearance and Insurance

Ocean passages cross national boundaries. Plan for:

• Passports, visas and crew list: many countries require advance clearance or a visa for stays beyond 90 days. Check each country's rules and the cost of cruising permits.
• Customs, immigration and health clearance at the first port of entry; fly the yellow Q flag until cleared in countries that require it.
• Vessel documents: registration (Part I British Registry or Small Ships Register), insurance certificate, radio licence, and proof of ownership.
• Insurance: most policies exclude named storm zones in season, and cover a specific cruising area. Confirm that the passage and the dates are covered, and that the crew are insured as crew.
• Cash, communications and spare parts shipping: remote ports may have no bank and long customs delays on imported parts.

Pre-Departure Preparation of the Yacht

Examiners will ask what you checked before leaving. Use a written checklist, signed off, and keep it in the passage file:

• Rig: inspect standing rigging, swages, chainplates and the mast step. Carry spare halyards and rigging wire, bolt croppers and a jury rig plan.
• Sails and sail repair: storm jib and trysail set up and tested. Spare sail cloth, sail repair tape, needle and palm.
• Engine and systems: service done, spare filters, belts, impellers, oil and a fuel polishing plan. Test bilge pumps and carry a second manual pump.
• Steering: emergency tiller tested, and a plan for jury steering. Spares for the autopilot or wind vane.
• Safety equipment: liferaft recently serviced, grab bag packed, lifejackets and harnesses, jackstays, flares in date, fire extinguishers, first aid and medical kit to the appropriate scale for the area.
• Ground tackle and drogue or sea anchor: ready for heavy weather and for anchoring in remote anchorages.
• Electronics and navigation: paper charts and electronic charts, sextant checked, almanac and tables, spare GPS, handheld VHF, two ways of receiving weather.

Route Geometry

Great circle and rhumb line

A rhumb line crosses every meridian at the same angle: a constant course, drawn as a straight line on a Mercator chart. A great circle is the shortest distance between two points on the sphere; on a Mercator chart it appears as a curve bowed towards the nearer pole, and its course changes continuously (except along the equator or a meridian). On a gnomonic chart a great circle is a straight line.

Click to zoom

The saving from a great circle is greatest on long east-west passages in high latitudes and negligible near the equator or for north-south passages.

For a sailing yacht, the wind usually matters far more than a few miles' saving. In the trade winds you go where the wind serves; the great circle matters more on long high-latitude passages such as the Southern Ocean or the North Pacific.

Calculating the great circle

With a calculator (latitudes positive North, longitudes positive East, d.long = destination minus departure):

• cos D = sin Lat1 x sin Lat2 + cos Lat1 x cos Lat2 x cos d.long; D in degrees x 60 = distance in miles.
• Initial course: tan C = sin d.long / (cos Lat1 x tan Lat2 minus sin Lat1 x cos d.long), resolved into the correct quadrant.
• Vertex (highest latitude reached): cos Lat vertex = cos Lat1 x sin C.

You will notice that this is the same spherical triangle as a sight reduction: the departure takes the place of the observer and the destination the place of the GP. Alternatively, draw the straight line on a gnomonic chart and transfer points every 5 or 10 degrees of longitude to the Mercator chart, or let the GPS or plotter calculate it. In practice the great circle is sailed as a series of rhumb line legs between waypoints every 5 to 10 degrees of longitude, recalculated from the current position each day.

Composite routes

On a high-latitude passage the great circle may take you into ice, or into far worse weather. A composite route follows a great circle from the departure up to a chosen limiting latitude, runs along that parallel (a rhumb line), then follows a second great circle to the destination. It is the shortest route that does not go beyond the limit.

Click to zoom

For example, the Cape Town to Fremantle great circle reaches 44.5 S, well into the Roaring Forties. A yacht might choose a composite route limited to 40 S: a little longer, but with less exposure to the worst seas and the risk of ice.

The Classic Routes

The Atlantic circuit

Europe to the Caribbean (westbound). The traditional route leaves the Canary Islands (or Cape Verdes) after the hurricane season, usually late November to January. The old advice is "head south until the butter melts, then turn right": sail south-west towards about 20 N, 25 to 30 W to pick up the steady north-east trades, then run west to Barbados, Antigua or St Lucia. Las Palmas to Barbados is about 2,700 miles by the trade wind route; at 5 to 6 knots average that is about 18 to 22 days. The great circle is barely shorter, but the rhumb line or great circle from the Canaries can leave you in the light, fickle winds under the Azores High. In December the ITCZ lies well south (around 5 N) and is not crossed on this route; the main hazards are squalls in the trades, a rolly downwind passage, gear chafe and occasional light-wind spells when the trades are weak. Carry enough fuel to motor through a calm patch of a day or two and to charge batteries.

Caribbean to Europe (eastbound). Leave in April to early June, before the hurricane season builds. Go north to Bermuda (about 900 to 1,000 miles from the Virgin Islands or Antigua), then east to the Azores (about 1,800 miles), then on to Europe. The challenge is to find wind: too far south and you sit in the Azores High's calms; too far north and you meet the westerly depressions and gales. Many yachts follow the "38 to 40 N" corridor, adjusting daily to the position of the Azores High.

Click to zoom

The Pacific: the "Coconut Milk Run"

From Panama (or the Galapagos) westward across the South Pacific to Tahiti, Tonga, Fiji and New Zealand or Australia. Typical timing is to leave Panama in February or March and the Galapagos in March to April, reaching the Marquesas as the South Pacific cyclone season ends, then cruising the islands from May to October in the south-east trades before heading south to New Zealand (or north of the equator) by November. Galapagos to the Marquesas is about 3,000 miles, often the longest leg a cruising yacht ever makes, usually taking three weeks or more.

From Panama the first problem is the Gulf of Panama calms and the doldrums; boats often motor-sail south-west to find the south-east trades south of the Galapagos.

Atoll passes: the Tuamotus

The Tuamotu archipelago is a chain of low coral atolls, many only a couple of metres high with palms on top, so they are visible only at about 8 to 10 miles. Charts may be based on old surveys with offsets of up to a mile from modern GPS positions. Lagoons are entered through narrow passes where the outflow can exceed 6 knots, with standing waves when wind opposes the ebb.

Click to zoom

Plan:

1. Never approach atolls at night; time your arrival for daylight, heaving-to offshore if needed.
2. Calculate slack water (local tide and pass guides; outflow is also driven by swell filling the lagoon, so slack can be shifted by hours).
3. Enter with good light from behind you, a lookout aloft or on the bow, and ready to abort.
4. Inside the lagoon, navigate by eye between coral heads with the sun high (roughly 1000 to 1400).
5. Treat chart plotter positions with suspicion: check them against radar and eye; use satellite imagery overlays where available.

The ITCZ (doldrums)

Passages between the hemispheres cross the ITCZ: a belt of calms, squalls, thunderstorms and torrential rain, variable in width from a few miles to a few hundred, and moving north and south with the seasons. In the Atlantic it is generally narrower in the west and further north in the northern summer.

Click to zoom

Strategy:

• Use the latest satellite images and GRIB/weatherfax to find where the ITCZ is currently narrowest, and cross there, generally at right angles.
• Carry enough fuel to motor through it (allow 24 to 72 hours).
• Reef before squalls: a dark, defined cloud base often brings gusts of 30 to 40 knots, followed by calm and rain. Use radar to track squalls at night.
• Collect rainwater; keep electronics clear of lightning risk (disconnect antennas, keep handheld GPS and VHF in the oven or a metal box as a precaution).

The Southern Ocean

South of about 40 S the westerlies blow almost unobstructed round the globe. The resulting seas are among the largest on earth, and icebergs drift north into the 40s and 50s in some seasons.

Click to zoom

Eastbound passages benefit from the westerlies and the Antarctic Circumpolar Current (generally 0.5 to 1 knot east); westbound passages in these latitudes are extremely hard. Plan for the austral summer (roughly November to March), set a limiting latitude based on current ice reports and the yacht's capability, and prepare the yacht and crew for sustained gales: storm sails, a drogue or series drogue, heating, robust washboards and hatches, and conservative watch systems.

Click to zoom

Southern Ocean waters (and much of the open ocean between about 70 N and 70 S) are within GMDSS Sea Area A3; only beyond the coverage of geostationary satellites (the polar regions, Sea Area A4) do you need HF DSC or polar-orbiting satellite systems for distress communications.

Safety Margins, Bunkering and Victualling

Water

Allow a basic minimum for drinking and cooking of about 3 litres per person per day in temperate conditions and more in the tropics (4 to 5 litres), plus washing allowances. Plan on the slow passage time plus a margin, and keep a separate emergency reserve that does not depend on the watermaker.

Click to zoom

Worked example. Four crew, Las Palmas to Barbados, planned 20 days. Plan for 25 days (slow passage) x 4 persons x 4 litres = 400 litres. Add 25 percent: 500 litres. The yacht carries 400 litres in tanks: make up the rest with 100 litres in jerry cans spread around the boat (so a single contaminated tank or a split jerry can does not lose everything), plus bottled water in the grab bag. A watermaker producing 30 litres per hour can make the daily need in about half an hour of running, but must not be relied on alone: if it fails, the tanks and cans must get you there.

Fuel

A sailing yacht carries fuel for motoring through calms, battery charging, refrigeration and the watermaker, and an emergency reserve for entering harbour or clawing off a lee shore.

Worked example. Engine consumption 2.5 litres per hour at 5.5 knots cruising revs. Planned motoring: 48 hours through calms = 120 litres; battery charging 1.5 hours per day for 25 days = 38 hours at 1.5 litres per hour (lighter load) = 57 litres. Total 177 litres; add 25 percent: 221 litres. The yacht has a 200 litre tank: carry 40 litres in cans. If the yacht is fuel-limited, decide in advance how much may be used before the reserve is reached (for example, no motoring for speed once tank contents fall below 100 litres).

Mid-ocean bunkering is rarely possible. Identify where fuel is available on the route (and of what quality; carry a filter funnel and spare filters) and plan for each leg to be self-sufficient.

Food

Provision for about 150 percent of the expected passage time: a 20-day crossing gets 30 days' food, with the extra in long-life staples (rice, pasta, tins, dried food). Plan menus by day, use fresh food first, and stow by week so you know what remains. Account for crew dietary needs and for the fact that refrigeration can fail.

Contingency Planning

There are often no ports of refuge for thousands of miles. Mid-Atlantic in the trades, once past the Cape Verdes, turning back against the trade wind is usually not practical; you go on. The plan must therefore rely on the yacht being self-sufficient: able to repair, jury-rig, treat injuries and cope without outside help for days.

Click to zoom

For each major contingency write down what you will do:

Also set decision points: for example "if the watermaker fails before 30 W, divert to Mindelo; after that, ration and continue", or "if the forecast at 48 hours before departure shows a depression track south of 30 N, delay". Writing these down beforehand avoids tired decision-making at sea.

Crew and Watch Planning

Choose crew for competence, temperament and health; a three-week passage tests relationships. Brief the plan, roles, safety equipment and emergency drills before departure. Design a watch system that gives each person enough sleep over many days (fixed or rotating watches; two on, four off for a crew of six; three hours on, six off for three) and a skipper who is not on the rota or is lightly loaded. Address medical history, seasickness management and any regular medication, with reserves.

The Passage Plan Narrative (Exam)

For the Yachtmaster Ocean oral you submit a narrative of your qualifying passage. Structure it as follows:

1. The passage: yacht, crew, dates, distance (planned and logged at least 600 miles), time underway (at least 96 hours), and the 200 miles more than 50 miles from land.
2. Rationale: why this route, this season and this departure window; the climatology consulted.
3. Weather: forecast sources before and during the passage, how you used them, and what you actually experienced.
4. Crew selection and organisation: experience, briefing, watch system.
5. Navigation strategy: route, waypoints, great circle or rhumb line, current allowances; astro work undertaken (sun-run-meridian and compass check).
6. Victualling and bunkering: quantities, calculations, margins and what was actually used.
7. Preparation of the yacht: material condition, spares, safety equipment.
8. Contingencies and any incidents.
9. Log extracts and sight forms: authentic, made at the time.

Click to zoom

Worked Example: Planning a Passage from Bermuda to the Azores

Appraisal. 12 m sloop, crew of four, two with ocean experience. Departure from Bermuda late May. Routeing chart for May/June: winds mainly south-west to west at Force 3 to 5 north of about 36 N, lighter and variable under the Azores High further south; gale frequency 5 to 10 percent north of 40 N; Gulf Stream meanders well to the north; hurricane risk low but non-zero from June.

Route. Great circle distance 1,789 miles, initial course 068 T, rising to about 38 N. The great circle is close to the ideal latitude band for wind, so plan to follow it roughly, dropping south if a depression threatens, or north if the Azores High expands. Waypoints every 10 degrees of longitude for reference only.

Time. At 130 miles per day, 14 days; plan for 18.

Water. 4 x 3.5 litres x 18 days = 252 litres, plus 25 percent = 315 litres. Fuel. Allow 3 days' motoring for the High, plus charging: compute as above.

Weather. Daily GRIBs and text forecasts via satellite; leave on the back of a cold front for a fair westerly; avoid departing with a low forecast to cross the route in the first 4 days.

Contingencies. No refuge for 1,800 miles; Flores (western Azores) as first landfall alternative to Horta. TMAS via MRCC Ponta Delgada.

Worked Example: Las Palmas to Barbados With Numbers

Appraisal. 13m sloop, waterline length 11m (36 ft), crew of five including the skipper. Departure from Las Palmas in the last week of November, after the end of the Atlantic hurricane season (1 June to 30 November). Route: south-west to about 20 N, 20 W (Cape Verde area), then west along the trade wind belt.

Distance and time. Rhumb line about 2,630nm. Hull speed is 1.34 x square root of 36 = about 8 knots. Seventy percent gives 5.6 knots, or 134 miles per day. Passage time is 2,630 / 134 = about 20 days. Plan stores for 26 days.

Water. 5 crew x 4 litres x 26 days = 520 litres. Add 25 percent: 650 litres. The tanks hold 450 litres; carry 200 litres in 20-litre containers spread around the boat. A watermaker making 40 litres per hour is a bonus, not a basis for the plan. Plus bottled water in the grab bag.

Fuel. Engine 2.8 litres per hour. Motoring for the calm patch near the Cape Verdes (about 36 hours): 101 litres. Battery charging 2 hours per day for 26 days: 52 hours x 1.8 litres per hour = 94 litres. Total 195 litres; add 25 percent: 244 litres. The tank holds 180 litres; carry 70 litres in cans. Decision point: no motoring for speed once total fuel is below 100 litres.

Food. 150 percent of 20 days is 30 days of food for 5 crew: 150 person-days.

Weather and route. Use the November routeing chart: north-east trades Force 4 to 5, gale frequency under 2 percent, mean current 0.5 knots west. Leave on a day when the GRIB shows trades established south of 25 N. Pass between the Canaries and Cape Verdes to pick up the trade as soon as possible, then gybe down the wind to Barbados.

Contingencies. Mindelo (Cape Verde) as the one port of refuge on the early part of the route, after which the nearest land is the Caribbean. Decision point: if the autopilot or steering has an unrepairable fault before 25 W, divert to Mindelo.

Communications. A satellite phone for daily GRIB downloads and text forecasts. A fixed daily position report at 1200 UTC to the shore contact. EPIRB registered; PLBs for the night watch.

Examiner Expectations

• The oral takes about 1.5 to 2 hours and starts with your narrative. Know every line of it. If you cannot explain a decision, it will be marked down.
• Be ready to justify every number: why that quantity of water, why that margin, what the slow passage assumption was.
• Be ready to say what happened that was not planned and what you did about it. Examiners prefer honest accounts of a problem well managed to an account of a flawless passage.
• Expect questions about the climatology: why that season, what the hazards were, where the ITCZ was, where tropical storms form and what the cyclone season is.
• Expect a "what if" on a different route: say the Pacific or the Indian Ocean. Know the seasons and the main hazards for each.
• Know your great circle and composite route methods in principle, even if you rely on a GPS or plotter in practice.

Common Mistakes

• Choosing the route first and the season second. Always start with the season.
• Assuming the great circle is best for a sailing yacht: in the trades, wind and comfort matter more than a few miles.
• Relying on the watermaker with no independent reserve.
• Planning water and food on the average passage time rather than a slow one.
• No written contingency plan or decision points, leading to poor decisions when tired.
• Ignoring the ENSO state or recent changes in storm seasons.
• Approaching low islands or atolls at night, or trusting chart plotter positions near reefs.
• Underestimating crew fatigue on long passages.
• Not documenting the passage properly for the exam (missing log copies, unclear qualifying distances).
• Treating a departure date as a deadline instead of waiting for a weather window.
• Not testing communications equipment before leaving, or not telling the shore contact what to do if you go quiet.
• Forgetting insurance exclusions, clearance paperwork and visas until the last week.

Summary

• Plan in four stages: appraisal, planning, execution, monitoring. The season is the first decision.
• Use Ocean Passages for the World, routeing/pilot charts, sailing directions and route guides.
• Climate zones and storm seasons shift with the sun. Stay out of cyclone areas in season (Atlantic 1 June to 30 November; South Pacific and South Indian November to April; North Indian two seasons around the monsoon changes).
• Great circles save most on long high-latitude east-west passages; composite routes add a limiting latitude.
• Atlantic: west in the trades from late November; east via Bermuda and the Azores in May/June. Pacific: Coconut Milk Run from February to November. Southern Ocean: eastbound in the austral summer.
• Carry 125 percent of planned fuel and water, 150 percent of food, and an independent water reserve.
• Write down contingencies and decision points; be self-sufficient.
• Submit a clear narrative of the qualifying passage for the exam.

Check Your Understanding

1. What are the minimum requirements for a Yachtmaster Ocean qualifying passage?

Answer: At least 600 miles (planned and logged), at least 200 miles of which more than 50 miles from land, a minimum of 96 consecutive hours underway, completed within 10 years of the exam, as skipper or mate of a watch throughout.

1. Why do yachts sailing from the Canaries to the Caribbean usually go south before turning west?

Answer: To get out of the light, variable winds under the Azores High and into the steady north-east trade winds, which are more reliable further south (around 20 N). The traditional advice is to sail south until the butter melts, then turn west.

1. When is the North Atlantic hurricane season, and when does it peak?

Answer: Officially 1 June to 30 November, peaking from August to October.

1. On what kind of chart does a great circle appear as a straight line, and how is it sailed in practice?

Answer: On a gnomonic chart. In practice it is sailed as a series of rhumb line legs between waypoints, often every 5 to 10 degrees of longitude, transferred to the Mercator chart and recalculated as the passage progresses.

1. What is a composite route and why would you use one?

Answer: A great circle to a limiting latitude, a rhumb line along that parallel, then a second great circle to the destination. It gives the shortest route without going beyond a latitude chosen to avoid ice or severe weather.

1. Four crew plan a 22-day passage. Using 4 litres per person per day for a slow passage of 26 days and a 25 percent margin, how much water should be carried?

Answer: 4 x 4 x 26 = 416 litres; plus 25 percent = 520 litres, with part of it independent of the tanks (cans or bottles) and not relying on the watermaker.

1. What is the South Pacific cyclone season and how does it shape the Coconut Milk Run?

Answer: November to April. Yachts leave Panama in February or March to reach French Polynesia as the season ends, cruise the islands from May to October, then move south to New Zealand or Australia (or out of the area) before November.

1. Give four precautions for entering a Tuamotu atoll pass.

Answer: Arrive in daylight only; time the entry for slack water (allowing for swell-driven outflow); have good light from behind and a lookout aloft or on the bow; be ready to abort; treat chart plotter positions with suspicion and navigate visually.

1. How might an El Niño year affect a planned South Pacific crossing?

Answer: The trade winds tend to be weaker and less reliable, and the tropical cyclone risk extends further east, so French Polynesia is more exposed than usual. The skipper should check the ENSO forecast and allow more margin on timing.

1. What topics must your narrative account for the Ocean oral include?

Answer: The rationale behind the passage plan, consideration of the weather, crew selection, navigation strategy, victualling and bunkering, with copies of relevant log pages, plus the astro evidence (sun-run-meridian and compass check) and evidence of the vessel's preparation.

1. What publications would you consult to select a route and a season for a passage from the Cape Verdes to Brazil?

Answer: Ocean Passages for the World (NP136) for the recommended route and distances; the UKHO routeing charts for the relevant months for wind roses, gale frequency, current and tropical storm limits; Admiralty Sailing Directions for the coast and ports; a cruising guide such as World Cruising Routes for seasonal advice.

1. A yacht has a 10m waterline length (about 33 ft). Estimate the daily run and the time for a 2,000 mile ocean passage, and say what time you would plan stores for.

Answer: Hull speed is 1.34 x square root of 33 = about 7.7 knots. A 60 to 70 percent average gives roughly 4.6 to 5.4 knots, or 110 to 130 miles per day. At 120 miles per day the passage takes about 17 days. Plan stores for at least 20 to 21 days (20 to 25 percent more), and food for 150 percent of the expected time.