The afternoon heat is so intense that we can see smoke starting to rise above the distant hills. My phone suddenly issues a strange sound that I’ve not heard before – a Greek civic alert to every mobile phone in the region warning that a forest fire has broken out.We are not alarmed. For a start, our holiday home is not in peril, as we are on a boat.But nor is the 38C heat an issue. That’s because this is a yacht which has – joy of joys – a fabulous new gizmo: air conditioning.We are not on a cruise ship or some swanky oligarch’s plaything. We are in the Greek islands for a week’s holiday, renting a conventional family sailing boat. Except this one does not entail going to bed in a sauna.For years now, the world has expected air conditioning as standard in a Mediterranean hotel or villa, especially with temperatures rising year on year. However, it is not yet commonplace in boats.That is changing, with air con now available in quite a few. And what a relief it is. After an oven-like voyage the year before, my wife, Diana, declared that she would not board another boat unless it had air con.Oh, and she wanted a catamaran. These are less wobbly, have a large galley (kitchen) and you do not have to go below to reach it.I simply typed my demands into Borrowaboat – which has more than 20,000 craft in over 70 countries on its books. We wanted a boat that could sleep eight in four cabins (the two of us plus another couple plus our two younger teenage children, each of whom wanted to bring a friend). Our idea was to cruise around either the Cyclades or the Saronic islands. You can get to both from the marina at Lavrio, south of Athens, so we would start from there. Robert Hardman used Borrowaboat to arrange a family holiday sailing around the Greek islesBorrowaboat found us a Lagoon 42 – a well-regarded model. This one was five years old with the latest kit, including – crucially – air con in every cabin. What’s more, at just under £6,000 for a week (about £100 per person per night), it is not very different from a mid-range hotel or villa. It also had a more rudimentary cabin at the very front for a skipper, should we need one.I have the basic Royal Yachting Association qualification to charter a yacht, but I opt to hire a pro on this occasion – since we have other people’s children on board.It might be an extra £170 a day but it means peace of mind – and someone else can worry about dropping anchor.Lavrio is a 40-minute cab ride from Athens airport and has plenty of shops for stocking the boat with food and drink.We arrive at lunchtime, fill several supermarket trolleys, meet our skipper, Manolis, and tell him we are itching to get under way as quickly as possible. Robert and his family enjoyed sailing between different Greek islands, including Kea – where they stopped for daytime swims – and Aegina, where some of his clan take scooters up to the Temple of AphaiaBy dusk, we are miles down the coast, anchored beneath the majestic Temple of Poseidon at Sounion. We swim then dine on roast chicken as the sun goes down.The weather apps show that the wind will get stronger as the week goes on. Manolis gives us our options, so we decide to head for the more exposed Cyclades to start and then cross to the more sheltered Saronics midweek.We start with the island Kea – plenty of bays for daytime swims and a lively little port for the night. The next evening, we are quietly at anchor off Kythnos with its famous spit of sand at Kolona, where two bays lap the same beach on either side.The air con does its job beautifully each night. It can run off the engine so you give that a burst to cool the interior before bedtime and then switch it off. Small cabins chill quickly.Over in the Saronic Gulf, we tie up on the quayside at historic Poros, which has plenty going on. We also want to see the famously pretty isle of Hydra but Manolis explains that the harbour there is chaotic and full (I suspect he just can’t face the aggro of all the other boats). So we just hop over there on a hydrofoil from Poros.The next day we enjoy a bracing sail to the island of Aegina, where some take scooters up to see the mighty Temple of Aphaia. I opt for a swim and a book. The joy of a boat is a different view and a different swimming pool every day.Back at Lavrio for our last night, it’s as hot as Hades with another forest fire on the horizon. Having re-connected our power supply to the mains system on the jetty, we crank up the air con to maximum. That night, for the first summer’s night on any boat in southern Europe, it’s so cold that I go to bed under a blanket. TRAVEL FACTS Borrowaboat has yachts of all sizes in more than 70 countries. Greek-based catamarans with air conditioning start at £3,700 for 6-8 people per week. (borrowaboat.com; 020 3318 3641).