The first thing the Mediterranean does to a sailor used to the Channel is fool them. The wind is gentle, the sea is flat, the sun is glorious, and within three days half the crew has a thumping headache, is snapping at each other and cannot work out why. The answer is almost always the same: the heat got to them before they noticed it was a problem. On a Riviera cruise, the weather that hurts you is not a gale. It is a cloudless afternoon and a water bottle nobody refilled.
I have made every mistake on this list. Here is what I learned to do instead.
Why a boat is a heat trap
You feel safe on the water because there is always a breeze and the sea looks cool. Both are lies your body believes. The breeze dries the sweat off your skin so fast you do not realise how much you are losing, and the sea reflects the sun straight back up at you, so you are cooked from above and below at once. Add a dark deck, a sail that funnels hot air, and the reflective glare off the water, and a moored boat in a Cote d'Azur August can be brutally hot even when the air temperature reads a civilised 30 degrees.
The body has two failure modes here, and they sit on a spectrum. Heat exhaustion comes first: heavy sweating, weakness, dizziness, headache, nausea, a fast pulse, and a core temperature that climbs into the 37 to 40 degree range. Catch it here and rest, shade and fluids fix it. Let it run, and you reach heatstroke, defined by a core temperature above 40 degrees with confusion, agitation or collapse, and the telling sign is that the sweating may stop and the skin go dry. Heatstroke is a genuine medical emergency that can kill, and it is the point at which you stop treating and start calling for help.
Reading the early signs in your crew, and yourself
The cruel thing about heat is that judgement goes before you notice it has gone. The person becoming irritable, clumsy or confused is often the one in trouble, and they are the last to know. So I watch the crew, not myself, and I ask them to watch me.
The simplest field test is urine. Pale and plentiful means you are hydrated; dark, scant and infrequent means you are behind and need to catch up now. Headache, fatigue and a dry mouth are the early flags. Stop bothering to make conversation, going quiet, losing the thread: those are later and more serious. If anyone is confused, has stopped sweating, or is staggering, treat it as heatstroke, get them in shade, cool them aggressively with wet towels and water, and call 15 or use VHF channel 16 offshore.
How much to drink, in real numbers
Forget the gentle "eight glasses a day" advice; that is for an office. A sedentary person in the heat needs around 2.5 to 3 litres a day. Someone moderately active climbs to 3 to 3.5, and a person sweating hard in hot, humid conditions, which is exactly a sailor handling lines and sails in a Riviera August, can need 4 to 5 litres in a day. That is a serious volume, and you will not drink it by accident.
The trick is to drink before you are thirsty, because thirst lags behind the deficit. I keep a marked bottle each and we agree to empty it by midday and again by sundown. Plain water is fine for most of it, but if you are sweating buckets you also lose salt, and water alone can leave you feeling worse. Add an electrolyte tablet or sachet once or twice a day on the hottest days, and eat salty snacks. Skip the trap of trying to hydrate on beer and rose at the lunch anchorage; alcohol and strong coffee are diuretics and make you lose more than you take in. Save the drink for the evening, once you are tied up and the day's water target is hit.
Shading the boat, the thing that changes everything
The single biggest comfort upgrade on a Med boat is shade. A bimini over the cockpit is the minimum. A boom tent or a large awning rigged at anchor turns the deck from a frying pan into somewhere you can actually sit, and drops the cabin temperature below by several degrees. Wet a sarong or a towel and hang it in the companionway and the breeze through it cools the cabin like a poor man's air conditioning.
Time your day around the sun, the way the locals do. The hours from roughly noon to four are when the UV peaks and the heat is worst. That is the time to be at anchor in a shaded cockpit, swimming, or ashore in the cool of a stone building, not beating up the coast in full sun. Sail early and late. A dawn departure from Saint-Tropez beats a midday slog every time, and it is when the wind is often best too.
Sun, the slower damage
Heat is the urgent risk; the sun is the chronic one, and the reflection off the water roughly doubles your exposure. Use a high-factor, water-resistant sunscreen, factor 30 as a floor and 50 on faces and the backs of hands, and reapply it far more often than feels necessary, certainly after every swim and every couple of hours. The places people miss are the tops of the ears, the back of the neck, the part in the hair and the tops of the feet. A wide-brimmed hat, a long-sleeved UV shirt and proper sunglasses do more than any cream, because they simply block the sun.
Sunburn is also a heat problem, not just a cosmetic one: badly burned skin cannot sweat or cool properly, so a bad burn makes heatstroke more likely the next day.
Children and older crew need extra watching, because both regulate temperature less well than a fit adult and both are slower to complain. A child absorbed in swimming or fishing off the stern will not notice they are overheating until they are unwell, so I make the water and shade rules non-negotiable for them rather than optional. The same goes for anyone on certain common medications: some blood pressure tablets, antihistamines and diuretics blunt the body's ability to cope with heat, which catches people out who have cruised the south for years and then wonder why this season feels harder. If a crew member is on regular medication, a quick word with a pharmacie about heat is worth having before the hottest weeks.
When it tips into an emergency
Most heat trouble never gets past tired and grumpy if you act early. But know the line. If someone is confused, stops sweating in the heat, has a temperature you can feel is dangerously high, vomits repeatedly or collapses, that is heatstroke and it is an emergency. Move them to shade, lie them down, cool them with water and wet cloths and fanning, and call for help: 15 for the SAMU or 112 ashore, channel 16 to the CROSS offshore. The full procedure for raising medical help on the water, and the telemedicine service behind it, is in a medical emergency at sea in France, and the kit that should be aboard for exactly this is in the medical kit for French coastal cruising.
It is also worth thinking about cover before you go, because a heat collapse offshore can mean a lift-off and a hospital stay; the costs and the offshore insurance traps are in repatriation and medical evacuation cover for France.
The Mediterranean rewards the cruiser who respects the sun and punishes the one who treats it like a stronger version of home. Shade the boat, drink before you are thirsty, sail at the cool ends of the day, and the Cote d'Azur in summer is everything the brochure promised. Ignore all three and you will spend a beautiful week with a headache, wondering why paradise made you feel so rough.
