I have crossed the Bouches de Bonifacio four times, and the first one was the only one I would not repeat. I went on a forecast that read fine for the wider zone and ignored what the strait does to it. By the time I was abeam the Lavezzi the sea was a mess of short breaking water and I was concentrating far harder than the day deserved. The other three crossings were dull, which is exactly what you want. The difference was not seamanship. It was reading the chart of this place properly before I left the berth.
So this is the detail. Not the reputation, which I covered in the broader piece on the bonifacio strait, but the actual lines you draw on the plotter and why.
The numbers that set the rules
The strait is narrow. It varies between roughly 7 and 11 nautical miles wide depending on where you measure, with the pinch around 11 km, under 7 miles, at the tightest. That is the open water. The water you can actually use is far less, because the northern half is choked with the Lavezzi archipelago and its outliers, and the clear shipping corridor between those hazards and the Sardinian shore is only about three nautical miles wide. The recommended route inside that is tighter still, just over a mile.
Depth is the second number that matters. Maximum depth is around 100 metres, but that figure flatters the place. South of the line, towards Sardinia, depths sit around 70 metres. North of it, towards the Lavezzi, the bottom shoals fast and in places dries to three metres or less. Shallow water steepens any sea, and the strait is shallow exactly where the wind funnels hardest.
The current runs up to 4 knots. It is not a clean tidal stream like the Channel. It is driven more by the wind and by the pressure difference between the two basins, which makes the timing harder to call. The point you carry away is simple: when the current opposes the wind, the surface turns vicious, and a 20 knot wind over a 3 knot foul current builds a far worse sea than the same wind running with it.
Drawing the track
There are two passages people use. The southern one keeps you well clear of the Corsican reefs and runs across towards the Sardinian side, between the Lavezzi group and the islands of the Maddalena. This is the route I prefer in any breeze, because it gives the most sea room from the granite.
The northern thread, closer in past the Lavezzi and Cavallo, is shorter and prettier on a flat day but unforgiving. Several of the heads here barely break the surface and the buoyage assumes you are following the marked line, not eyeballing a shortcut. Plot real waypoints between the marks, then cross-check the plotter against the paper chart and against the actual buoys as you raise them. SHOM charts are the authoritative reference for this corner and I do not treat them as optional.
My discipline is to navigate as if the visibility might shut down at any moment, because here it can. A sea fog or a quick squall will hide the Lavezzi in minutes, and the rocks do not move to accommodate you. If I am threading the northern passage at all, it is only on a settled morning with the marks in clear sight and an escape line already drawn.
The reporting system
This is a regulated seaway, not just a hazardous one. After a 1993 tanker grounding the strait was closed to French and Italian flagged ships carrying dangerous cargoes, and a Franco-Italian agreement in 1999 set up the Bonifacio Trafic vessel traffic service and a mandatory reporting system. The whole area was designated a Particularly Sensitive Sea Area by the IMO in 2011.
For a small yacht the reporting obligations largely sit with the commercial traffic, but the lesson for you is the layout. There is a two-way recommended route with precautionary areas around it, and the big ships are funnelled along it. Treat that corridor the way you treat the reefs: stay out of the way of it where you can, monitor AIS, and never assume a coaster or a fast ferry will alter for you in a channel where it has no room to. The cross-strait passenger boats between Corsica and the Maddalena move fast and often in season.
Timing the day
I want under 15 knots forecast in the strait itself, not in the larger sea area, and I add five knots to whatever the model says because the venturi effect is real and the forecasts smooth it. If the bulletin reads 20, I plan for 25 with worse gusts, and that usually means I wait. If a BMS (bulletin meteorologique special) from Meteo France is in force, the decision is already made.
Time of day is the other lever. The thermal sea breeze fills in through the afternoon and stacks on top of any gradient wind, so a crossing at first light in the morning calm is almost always kinder than a midday one. I aim to be through and clear before the breeze builds. From the marina at Bonifacio you are into the strait within the hour and across to the Maddalena or the Sardinian shore in a few more, so an early start leaves the whole afternoon spare.
If you are only day-sailing
Plenty of visitors never cross at all. They sail out from Bonifacio to the Lavezzi, anchor over the white sand for the day and come home. If that is you, the rules change, because the Lavezzi are a strict nature reserve with buoyed zones, mooring restrictions and patrols. I have set the whole thing out in the lavezzi islands mooring guide, and you should read it before you drop the hook, not after a warden has come alongside.
The natural base for all of this is Bonifacio harbour itself, the cleft in the white cliffs that is one of the most extraordinary arrivals in the Mediterranean. I have described getting in and berthing there in the bonifacio harbour arrival guide. It is also the place you wait. There are far worse fates than being weatherbound in Bonifacio for a day with the citadel above you.
What to have ready before you go
A few things I always have sorted before I leave the berth for the strait, beyond the forecast. The track is plotted and the waypoints are in the plotter, with the paper chart open at the right page so I am not hunting for it underway. The escape options are noted: if the sea turns nastier than expected on the southern route, where do I bear away to, and is Bonifacio still a clean retreat if I am early in the passage. The VHF is on and I have noted the Bonifacio Trafic working channel so I can listen to the commercial traffic picture even though my own reporting duties are minimal. And the boat is properly stowed below, because a square breaking sea in the strait will throw anything loose around the cabin in a way the flat Mediterranean rarely does.
Fuel is the last one. The good crossings here are calms, and a calm means motoring, so I want tanks full and a clear idea of my range under power. The distance is short, but the discipline of treating it as a real passage rather than a hop is what keeps it boring, and boring is the goal.
Where the strait sits in the cruise
For most people the strait is the southern pinch point of a full lap of the island, one chapter rather than the whole book. I have built it into the wider route in the corsica circumnavigation itinerary, and the single most useful piece of planning is to arrive at Bonifacio with days in hand. That way you cross on the day the strait gives you, not the day your schedule demands.
Get the timing right and the reefs become scenery. On a still morning the water over the Lavezzi banks is so clear the boat looks like it is floating on light, the Sardinian mountains sit purple on the far side, and the whole crossing is over before the breeze has woken up. The fear this place earns is useful, because it keeps you patient. The patience is what makes it easy.
