Planning a coastal passage: legs, timing and a bail-out bay
A plan that gets you into a strange bay with light to spare is mostly arithmetic, plus some honesty about how fast the boat really goes. How we put one together.
In this piece
- What passage planning means on a small boat
- How to plan a sailing route: start with a realistic speed
- A worked example: 32 miles at 5 knots
- Work the departure time back from daylight
- Hazards, headlands and clearing distances
- A bail-out bay for every leg
- Go or no-go, and where you turn back
- Using a sailing route planner
- Fuel, water and a tired crew
Passage planning for a day along the coast means answering a few plain questions before you let go the lines: how far it really is, how fast this boat will cover it with this crew, what time you have to leave to arrive in daylight, what the wind does on each leg, and where you go if any of it turns out wrong. Most of the answers are arithmetic. The part people get wrong is the speed.
Here is how we plan a coastal hop of about 30 miles, sums included, for tidal waters and the mostly tideless Mediterranean alike.
What passage planning means on a small boat
The IMO’s guidelines for voyage planning on ships split the job into four stages: appraisal, planning, execution and monitoring. On a 12 metre cruiser the words are grander than the work, but the order holds. Appraisal is gathering what you need: the chart, the pilot book, the forecast, the state of the boat and crew. Planning is drawing the legs and doing the sums. Execution is leaving when you said you would and following the line you drew. Monitoring is checking at every waypoint that reality still matches the plan, and changing the plan the moment it does not.
How to plan a sailing route: start with a realistic speed
The polar diagram, the brochure or your memory of one glorious afternoon says 7 knots on a beam reach in 15 knots of wind. That is speed through the water, on flat water, with a clean bottom and someone steering for it. A real passage also contains the slow part leaving harbour, the lull in the lee of an island, the half hour spent reefing, and the short sea that knocks a knot off every time the bow drops into it.
For a cruising monohull of 11 or 12 metres (36 to 40 ft) on a mixed day, we plan on an average of 5 knots over the ground and adjust from there. Your own log beats any rule: divide distance by time for your last ten passages and you have your number.
Upwind is slower than it looks
If the destination is dead upwind, you cannot point at it. Once leeway is counted, a typical cruising boat tacks through 90 to 100 degrees, so she sails 45 to 50 degrees off the true wind on each board. What counts is velocity made good (VMG), the part of your speed that goes toward the mark. At 45 degrees off the wind that is boat speed times cos 45°, about 0.71; at 50 degrees, about 0.64. Six knots through the water becomes roughly 4 knots toward where you want to go, and the distance you actually sail grows by 40 per cent or more. Add the sea that builds against you, and a 20 mile beat takes about as long as a 30 mile reach.
A worked example: 32 miles at 5 knots
Say the passage is 32 nm from harbour to anchorage, and you have settled on 5 knots. Time is distance divided by speed:
32 ÷ 5 = 6.4 hours. The 0.4 is a fraction of an hour, not 40 minutes: 0.4 × 60 = 24 minutes. So the passage takes 6 hours 24 minutes.
Now split it into legs, because every change of course changes the wind angle, and the wind angle sets the speed. With a northwesterly of 15 knots forecast, the example looks like this:
| Leg | Distance | Course | Wind angle | Plan speed | Time |
|---|---|---|---|---|---|
| 1. Harbour to the cape | 12 nm | 200° | 115°, broad reach | 6 kn | 2 h 00 min |
| 2. Cape to the channel | 12 nm | 250° | 65°, close reach | 5 kn | 2 h 24 min |
| 3. Channel to the anchorage | 8 nm | 300° | 15°, on the nose | 4 kn made good | 2 h 00 min |
| Whole passage | 32 nm | 5 kn average | 6 h 24 min |
The average is still 5 knots, but the table shows what the single number hides: the last two hours are a beat, at the end of the day, when the crew is tired and the afternoon breeze is often at its strongest. In the Aegean in summer, where the wind usually builds through the afternoon, that is close to a rule. If the forecast gives 15 knots at noon and 22 at 16:00, the plan speed for leg 3 drops, and so does the appeal of that anchorage.
Work the departure time back from daylight
We like the anchor down with at least two hours of daylight left. That leaves time to look the bay over, try a second spot if the first will not hold, or give up and go to the bail-out with light to see by. Rocks, weed patches and floating lines all show far better at 17:00 than at 21:00.
So the sum runs backwards. If sunset is at 19:00, you want to be anchored by 17:00. Take off 6 hours 24 minutes and you get 10:36. Then add a margin, because something always takes longer: a reef, a lull that lasts an hour, a net to motor round. On a passage this length we add about an hour, which makes the departure 09:36. Call it 09:30. For a longer passage, or an arrival you do not know, add more.
Tides, streams and tidal gates
In tidal waters the stream can fix the departure time more firmly than daylight does. A 2 knot stream against you turns 5 knots through the water into 3 over the ground; with you, into 7. Where the stream runs hard round a headland or through a sound, that place becomes a tidal gate, to be passed within a window around slack water or as the stream turns fair. Plan the gate first and work the rest of the passage out from it. The tidal stream atlas gives rate and direction hour by hour. Mark any stretch of wind against tide, too: 15 knots against a 2 knot stream raises a short, steep sea out of all proportion to the wind.
Most of the Mediterranean is close to tideless, with a range of a few tens of centimetres, so there the tide usually drops out of the sum. Not everywhere: the Strait of Messina and the Evripos channel at Chalkida run hard enough to plan around, and a few days of strong wind sets up currents along some coasts. The pilot book will say.
Hazards, headlands and clearing distances
With the legs drawn, go along each one looking for whatever can hurt you within a mile or two either side: rocks, shoals, wrecks, fish farms, traffic separation schemes, and the shallow patch off the point that every local skipper knows about.
Headlands deserve the most attention. Wind accelerates and bends round them, the sea steepens where it meets the shallower water off the point, and any current runs fastest there. The Kafireas strait, between Evia and Andros, is the Aegean’s textbook case: a fresh northerly on either side and a good deal more in the gap.
We give most headlands half a mile in settled weather and a mile or more with a sea running, further where the chart marks overfalls or a race. Where the route has to pass close to a danger, add a clearing bearing: a bearing to a charted object, say a lighthouse, that keeps you in safe water as long as it stays “not less than” or “not more than” a given figure. A check with the hand-bearing compass takes seconds and needs no battery.
Check every waypoint on the largest-scale chart
A route drawn on a small-scale chart, or on a phone zoomed out to fit the whole day, will cut cheerfully across a rock that only appears two zoom levels in. Step along each leg at the largest scale you have, look either side of the line, and read each waypoint’s latitude and longitude back against the chart. A typo in the minutes will steer the boat with total confidence onto the wrong side of something.
A bail-out bay for every leg
For each leg, name the place you will go if the wind comes in harder than forecast, the engine stops, someone is hurt or seasick, or you are simply behind time. It has to be reachable from that leg in the weather that would send you there.
| Leg | Bail-out | Good in | The catch |
|---|---|---|---|
| 1 | Back to the harbour you left, a close reach | Any wind | A lost day |
| 2 | The bay tucked in behind the cape | Northwest through north | Open to the south, and swell wraps in when it blows from the west |
| 3 | The fishing harbour on the island, 2 nm off the route | Most directions | Small, and often full by late afternoon in summer |
The “good in” column is the one that matters. A bay that is flat calm in the northwesterly becomes a lee shore if the wind backs into the southwest overnight. Look at which way the mouth faces and at the forecast for the hours you would spend there; our guide to choosing an anchorage covers the rest.
Go or no-go, and where you turn back
Decide the night before what would keep you in harbour, and write it down, because at 08:00 with the crew keen and the coffee made, every forecast looks fine. Our list is usually short: forecast gusts on the exposed leg above a figure we set for this boat and this crew, models that disagree by more than a Beaufort force, swell running into the arrival bay, a crew member unwell. The forecast itself deserves care; we wrote a separate piece on how to read a marine forecast.
Then put decision points on the route, by time and by place. “If we are not past the cape by 12:30, we go into the bay behind it.” “If it is blowing more than 20 knots true at the channel, we do not start the beat.” With a 09:30 start the cape should come up around 11:30, so 12:30 allows an hour of slippage. A decision made in advance needs only a glance at the clock. One made on the spot, cold and wet, tends to be “let’s push on”.
Using a sailing route planner
We draw the first rough version on a phone and the real one on a chart. SafeBoat’s route planner takes the start and the end by search, by your current position or by pressing and holding on the map, with up to 8 stops in between. Tell it sailboat or motorboat and a speed in knots, which is where your honest 5 knots goes, then either just create the route or ask for AI help.
The AI advice is advice. It has never seen the bay, the new fish farm or the rock that is not on the map, so the skipper checks each leg and each suggested bay against the chart and the pilot book before relying on any of it. If a phone is one of your plotting tools, read our notes on offline charts on a phone before you lose signal.
Fuel, water and a tired crew
Plan fuel as if you will motor the whole way, because on a windless day you will, at the revs you are happy to run for hours. If you do not know the burn at those revs, fill the tank, motor a measured number of hours, fill it again and divide; few fuel gauges on boats are good enough to replace that figure. Keep a reserve on top: we like to arrive with at least a third of the tank left. Carry more drinking water than seems sensible in summer, some of it in bottles in case the tank or the pump lets you down.
Fatigue is the reserve people forget to plan. A six hour passage after a late night, with one competent sailor aboard, is a different trip from the same passage with three rested ones. Make the food before you leave, expect someone to be seasick on the first day out, and put the hardest leg where people will be freshest if the route allows. In our example it does not, which is one more reason the bail-out for leg 3 is on the list.
Then tell someone ashore where you are going and when you expect to arrive. A float plan takes five minutes and gives them a time at which to start asking questions.
Put the whole plan on one sheet the evening before and tick the waypoints off as you pass them. On a day that goes to plan you will hardly look at it. On a day that does not, it has already made the hardest decisions for you.