Port-to-port distances in the Mediterranean: the nautical mile calculator

How many miles between Marseille and Ajaccio? How long to reach Porquerolles from Cassis, Naples from Sardinia or the Balearics from Sète? Our port-to-port distance calculator answers in an instant, along a real sea route that rounds the coasts, headlands and islands as a boat would, and always stays in depths of more than 10 metres.

Choose a departure port and an arrival port from 127 ports and anchorages: the sea distance in nautical miles and kilometres is displayed, with the passage time at four speeds, the price of a delivery with skipper included and the route drawn on the map. We use it every day to prepare our cruises and deliveries from Marseille. It is free and open to all sailors.

A sea distance calculator is only worth something if it gives the route a boat can really follow. Drawing a line between two ports is not enough, and hugging the coast is not either: in many areas, the seabed rises well before the shore, and a sailboat that gets too close risks running aground. We therefore rebuilt each sea route from the bathymetry, that is, the relief of the seabed.

A navigation grid built on the seabed

The western Mediterranean and the Atlantic seaboard, from the Canaries to Brittany, were divided into a grid of cells about 0.3 mile, or 550 metres, across. For each cell, we keep the shallowest depth measured by the best available source: the SHOM digital models on the French coasts and Corsica, the EMODnet model for the rest of Europe, and the global GEBCO grid offshore. Keeping the shallowest point of each cell is a cautious choice: a single isolated rock is enough to close a passage.

Four rules applied to every safety route

The headlands treated with a 3 mile margin are: Cap de Creus, Cap Sicié, Cap Camarat, Cap Corse, Capo Caccia, Capo Spartivento (Sardinia), Cabo de la Nao, Cabo de Palos, Cabo de Gata, Cabo de São Vicente, Cabo Espichel, Cabo Finisterre, Cabo Ortegal, Pointe de Penmarc’h, Capo Palinuro. The recognised passages, where the route may run 0.2 mile from the coast as long as the depth stays above 10 metres, are the following:

• Marseille harbour, between the Frioul and the coast
• South Marseille harbour, from Pointe Rouge to La Croisette
• Riou and Calanques passage
• Bay of Cassis and Cap Canaille
• Bay of La Ciotat and Île Verte
• Grande Passe of Porquerolles
• Passage between Porquerolles and Port-Cros (Bagaud)
• Passage between Port-Cros and Le Levant
• Lérins islands passage
• Strait of Bonifacio, Lavezzi and Cavallo
• La Maddalena archipelago

The shortest path, then a measurement on the sphere

On this grid, a shortest-path algorithm looks for the shortest route from one port to another, crossing only navigable cells. The route is then smoothed by line of sight to remove the small zigzags of the grid, and measured segment by segment on the Earth’s sphere, to a tenth of a mile. The first and last segments link the quay to open water by the shortest approach channel. The 8,001 possible port-to-port distances between the 127 ports were calculated in this way, one by one.

We compared the results with the distances published by nautical guides and routing tools. On coastal trips, our sea distance is sometimes slightly longer: that is the price of the safety margin, and it is intentional. On crossings, the difference is around one mile.

The port-to-port distance is also the basis for the price of our deliveries. The rule is simple and shown clearly under each calculator result:

• Route distance: the exact sea distance from the calculator, along the safety route.
• + 2 % for approaches and harbour manoeuvres: leaving port, getting under way, approach and berthing on arrival, which do not appear in a quay-to-quay route.
• × €4 per billed mile, professional skipper holding the Capitaine 200 licence included, with a minimum of €350 for short trips.

For example, from Port Corbières to Ajaccio: route distance 186.4 miles + 2 % approaches and harbour manoeuvres = 190 billed miles, i.e. €760. The 15 % weather margin only applies to the estimated duration of the delivery, never to the price.

The skipper’s return travel, harbour fees, fuel and provisioning are added at cost, with no mark-up. Our boat delivery simulator uses exactly the same distances and details all the options; you can reach it in one click from the calculator result. For the most requested destinations, see also our Marseille Corsica delivery and Marseille Balearics delivery pages.

At sea, distances are measured in nautical miles. One mile equals 1,852 metres: it is the length of one minute of arc of latitude on the Earth’s surface. This definition has a huge practical advantage: on a nautical chart, the latitude scale on the vertical edge serves directly as a ruler. One degree of latitude is 60 miles, one minute is one mile. The navigator takes the length of the route with dividers and transfers it to the edge of the chart, at the level of the sailing area.

Speed is measured in knots, that is, miles per hour. A sailboat making 6 knots covers 6 miles in an hour, about 11 km/h. To quickly convert a sea distance into kilometres, multiply the miles by 1.852, or more simply by 2 and subtract 7 %.

Not to be confused with the statute mile, which measures only 1,609 metres. All the port-to-port distances on this page are in nautical miles, rounded to the tenth; the calculator also gives the sea distance in kilometres.

Passage time is simple to calculate: the sea distance in nautical miles divided by the average speed in knots. The calculator shows it for four typical speeds: a sailboat at 6 knots, a motor cruiser at 8 knots, a fast boat at 15 knots and a speedboat at 25 knots. Each duration includes a 15 % weather margin, as is customary among professional skippers.

Why a 15 % margin

An average speed is never held continuously. A sailboat sailing upwind has to tack, a rough sea slows motor boats down, and entering and leaving port takes time. The 15 % margin covers these usual contingencies. In a sustained headwind it may not be enough: tacking sometimes lengthens the route by 40 % or more. For a crossing, also plan a fuel reserve of at least a third.

Wind, sea and timing

Check the marine weather for the whole duration of the passage, not just at departure. Our Beaufort scale explains what each wind force means. Over a long distance, leave so as to arrive in daylight at a port you do not know, and always keep a fallback port within reach.

The data were resampled and combined by LOCVOILIER to calculate the routes; they are not reproduced as such. In accordance with the conditions of these producers, we point out that these seabed models must not be used for navigation. The port-to-port distances on this page are planning estimates and do not replace official nautical charts, sailing directions or notices to mariners.

To find out more: SHOM’s data.shom.fr portal, the EMODnet Bathymetry portal and the GEBCO grid.