Passage planning step by step: from first idea to casting off
as of 07/10/2026 · 6 min read
In short: Good passage planning follows a fixed order: boat and limits, route and daily legs, weather window, tides and bridges, ports of refuge, formalities, fuel and, last of all, a float plan left with someone ashore.
Passage planning runs in ten steps: set your boat data, lay out route and waypoints, split the distance into daily legs, choose the weather window, allow for tides, streams, bridges and locks, note ports of refuge, check formalities, plan fuel, file a float plan and go through the checklist before casting off. Each step builds on the last.
Which boat data do I need for passage planning?
Draught, mast height above the waterline, a realistic speed and your limits for gusts and waves. These decide which harbours, bridges and weather situations are an option for you at all.
Draught decides harbours, anchorages and bars; mast height decides fixed bridges. The speed that counts is not hull speed but what the boat actually averages. More accurate than a fixed speed is a polar diagram: it gives boat speed for each wind angle and wind strength. In Sailseer you pick a boat profile and adjust the values:
| Profile | Speed | Draught | Mast | Gusts up to | Waves up to |
|---|---|---|---|---|---|
| Dinghy or pocket cruiser up to 25 ft | 4.5 kn | 1.2 m | 10 m | 22 kn | 1.0 m |
| Cruising yacht 30 to 36 ft | 5.5 kn | 1.8 m | 16 m | 30 kn | 2.0 m |
| Cruising yacht 40 ft and over | 6.5 kn | 2.2 m | 20 m | 34 kn | 2.5 m |
On top of that come the boat type (sailing boat with or without engine, motorboat), pointing angle, leeway and the time lost per tack. Boat speed comes from a polar diagram scaled to your speed; a GPX track from your last trip gives a suggestion for your own planning speed.
How do I set the route and waypoints?
Start and destination first, then the stopovers. After that, check every straight leg on the official chart for shallows, restricted areas and traffic separation schemes.
Sailseer lays the route through a network of tracks around land and shallow water. You add stopovers as search fields, much like in Google Maps, or drag the line on the map to a harbour. If you want to set the line yourself, “Manual” turns the route into waypoints that you move around just as on a chart plotter. Every straight leg is checked against land and depth from EMODnet and marked red if it crosses land or water that is too shallow. Alternative routes show whether another way is barely longer, and traffic separation schemes appear along the route with a note on COLREGs Rule 10.
How far can I get in a day's sailing?
Divide the distance by your average speed and, on holiday, plan no more than six to eight hours a day. The day's run is the distance covered in 24 hours; it matters mainly on long passages through the night.
| Average speed | in 6 hours | in 8 hours | Day's run (24 h) |
|---|---|---|---|
| 4 kn | 24 nm | 32 nm | 96 nm |
| 5 kn | 30 nm | 40 nm | 120 nm |
| 6 kn | 36 nm | 48 nm | 144 nm |
| 7 kn | 42 nm | 56 nm | 168 nm |
Upwind the distance grows: with a tacking angle of 90 degrees you sail about 1.4 times the direct distance. Keep a reserve for harbour manoeuvres, tidal streams and calms. The multi-day trip in Sailseer splits the route into daily legs according to your daily budget (default: 30 nm a day, leaving from 08:00, arriving by 16:00, seven days including one reserve day) and picks each day's destination by draught, facilities and berths. Without a destination it becomes a round trip.
When is the weather right for departure?
When wind relative to your course, gusts, waves, tidal stream and daylight suit boat and crew over the whole route. You can only commit to that two to three days ahead.
“Check weather” works through every full hour of the next 120 hours as a departure, using the consensus of nine weather models for each place and hour, plus waves, tidal streams and waiting times. Each departure gets up to 100 points, and the weakest leg counts: green from 70, yellow from 45. A gale warning, a thunderstorm situation or waves above the boat's limit set it to zero. How to read a window is explained in the guide Weather window.
What do I need to consider with tides, streams, bridges and locks?
They often decide your timing more than the wind does: a tidal inlet can only be crossed with enough water, you will hardly make headway against a strong stream, and a bascule bridge only opens at set times.
Sailseer factors the tidal stream into speed over ground and, if the boat cannot make headway against the stream, the plan waits for the turn of the tide. On request, the multi-day trip checks a tidal window over the shallowest bar in the last 10 nm before each day's destination. Bridges and locks appear on the route with their opening times, for example the Lindaunis bridge on the Schlei or the Kiel-Holtenau lock on the Kiel Canal. Waiting time goes into the schedule, and the route avoids any fixed bridge your mast will not fit under. More in Tides and tidal streams and Bridges and locks.
Where do I go if things do not work out on the way?
To a port of refuge you picked before casting off: easy to reach, with enough depth and an entrance that still works in an onshore wind.
Sailseer spreads ports of refuge along the whole route instead of bunching them at the destination, and in a multi-day trip lists them for each day. Every harbour info page gives depth and services from diesel to chandlery, and Range shows which harbours you can reach from a given harbour within a set distance.
Which formalities and how much diesel should I plan for?
Crossing a border can mean clearance, customs, papers and fees, depending on the country. For diesel, what counts is engine hours in calms, harbour manoeuvres and a reserve in the tank.
Sailseer lists the formalities for each country on the route, such as the vignette and tourist tax in Croatia; more in the guide Clearing in. The route calculates fuel from engine hours, consumption, tank reserve and range, and fuel stations come from the harbour info pages.
What belongs on the checklist before casting off?
- Read the official marine forecast and warnings and compare them with your plan (Reading a marine forecast).
- Check the route on the official chart and confirm tides and bridge times.
- Check the engine (oil, coolant, V-belt), diesel, water and gas.
- Have life jackets, harnesses and tethers, life-saving equipment, bilge pump, VHF radio and first aid kit ready.
- Brief the crew: man overboard, distress call, watch schedule.
- Pack the paperwork: boat papers, radio licence, passports, insurance.
- Load the route onto the chart plotter as GPX.
- File a float plan with someone ashore.
How does Sailseer help with passage planning?
Sailseer is free, works without an account and brings these steps together on one map: route with stopovers, weather check comparing departures over 120 hours, multi-day trip with ports of refuge, GPX for Garmin, Raymarine and B&G (one route per day in a multi-day trip) and the float plan, which alerts your shore contacts if you are overdue. If you are chartering a boat, the guide Planning a charter trip covers the particulars.
Sailseer is a planning aid and not for navigation: check the route on the official chart before casting off. Official charts, marine forecasts and warnings take precedence.
Frequently asked questions
How many nautical miles can you sail in a day?
With a cruising yacht averaging 5 kn, about 30 nm in six hours and 40 nm in eight; much less upwind, against the tidal stream or in a calm. Sailseer's multi-day trip plans with no more than 30 nm a day by default.
What is a day's run?
The distance a vessel covers in 24 hours, traditionally measured from noon to noon. At an average of 5 kn that is 120 nm.
How early should I start planning a sailing trip?
Route, harbours, formalities and bridge times weeks ahead, the weather only in the last week: roughly from five to seven days out, firmly two to three days before departure. Sailseer compares the departures over the next 120 hours.
How many reserve days do I need?
Plan at least one reserve day per week, more in areas where strong winds can last several days, for example with the Meltemi. In Sailseer's multi-day trip, reserve days shorten the sailing days instead of sitting in the schedule.
How do I get the planned route onto my chart plotter?
As a GPX file: Sailseer writes GPX 1.1 for Garmin, Raymarine and B&G, with one route per day in a multi-day trip. The other way round, you can load routes from OpenCPN, Navionics or your plotter as a route; more under GRIB and plotter.
Do I need a float plan?
It is not compulsory, but it is a good safety net: someone ashore knows your route and ETA and is alerted if you do not check in. In Sailseer, the overdue email goes to up to three shore contacts after a grace period of 1, 2 or 4 hours.