Cold continental air builds up behind the coastal ranges, and when the difference between it and the milder air over the sea grows large enough, it spills over the ridge and accelerates downhill. Gravity does most of the work, which is why the bora is at its most violent where the mountains stand closest to the water.

Sailors here distinguish two kinds. A light bora comes out of a clear sky, frequently with no visible warning at all, which is exactly what makes it worth respecting. A dark bora announces itself: cloud caps the mountain tops, the light goes flat, and rain usually follows. Neither is the easy one. The clear sky version simply hides its intentions better.

Because the bora blows off the land rather than onto it, water tucked close under the shore can look deceptively flat while conditions a mile or two out are anything but. That gap between what you see from a berth and what you find once clear of the lee is the most common way crews underestimate it.

The honest answer is that a medium bora is not, on its own, alarming. Twelve to sixteen knots is comfortable sailing on most charter yachts. The difficulty is that those knots do not arrive from a settled direction. The wind swings, the gusts land well above the average, and you spend the day trimming for a breeze that has already moved on.

The sea state compounds it. With a short fetch and a hard wind, the bora raises steep, closely spaced waves rather than long swell, and short high waves are harder work to navigate than bigger ones with more room between them. Progress upwind slows and the crew tires faster than the log suggests it should.

The recorded extremes belong to winter and to the exposed Velebit stretch, not to a summer charter week. Gusts of around 220 kilometres per hour, roughly 136 miles per hour, have been measured there, and the strongest on record reached 304 kilometres per hour, or 189 miles per hour. You will meet nothing of that order on a July afternoon off Split. It is context for the reputation, not a forecast.

The simplest way to reduce your exposure is to sail in summer. The bora is at its strongest and most frequent in winter, so a week between late spring and early autumn is far less likely to run into a serious one. Our Croatia yacht charter guide covers how the season shapes the rest of the week.

The second is to put a professional aboard. Adding a skipper is not a different or lesser boat, it is the same yacht with someone who has sailed these waters in every kind of weather, and that counts for a lot when the wind starts doing something you have not seen before. Our note on what a skippered yacht charter involves sets out how it works day to day.

Whichever way you go, ask for the all in number before you compare anything: base rate, skipper if you want one, mooring fees, fuel and provisioning. Headline weekly rates in Croatia rarely include all of it, and that gap is where a charter gets expensive after the fact.