On a former fishing trawler turned boutique cruiser, Rhiannon Batten enjoys the relaxing charms of Argyll's sea lochs and islands – and learns to love a life afloat

'I love Scotland," said Ann, as we lay on wooden loungers in the sunshine, gazing out at glossy headed seals and craggy mountains. Ann was from Dunfermline, so she may have been a bit biased, but it would take a steely soul to argue with her on a day like this.

We were part way through a three-night trip around the sea lochs and islands of Argyll aboard the Glen Massan and, so far, it felt like we had been drifting through the pages of a Visit Scotland brochure. From ruined castles and piles of lobster pots to the kilted man we saw as we pulled up at one coastal village, the scenery had been so tartan-and-shortbread Scottish that, had Rob Roy himself come round handing out pre-dinner canapés, I wouldn't have blinked.

But if that makes the trip sound contrived, it wasn't. The Glen Massan is one of two former fishing trawlers that owners Ken Grant and Andy Thoms have recycled to form luxurious "boutique" cruise ships. Inspired by holidays on Turkish gulets – and stories of British trawlers being scrapped because of the decline in the fishing industry – Grant and Thoms decided to try the Mediterranean formula in the UK. In 2004, they set up the Majestic Line, named after a fictional shipping company in Neil Munro's Para Handy tales.

Four years on, the effort is paying off. That a large proportion of guests are returnees is probably down to the boat's high-end styling, though this is luxury with a small "l". There are no swaying chandeliers, no menus drawn up by Michelin-starred executive chefs, no space in the en-suite cabins for much more than a bed – and there's definitely no dressing up for dinner at the captain's table. What there is, however, is some serious pampering.

From the Glen Massan's tiny galley kitchen, Mary, the boat's chef and chief organiser, produces the kind of no-nonsense gourmet home cooking you always hope to find at local restaurants but rarely do. From a glorious, fennel-laced cullen skink (potato and haddock soup) to "best ever" crab cakes and fresh-from-the-oven cherry biscuits, the food was so good that we all pleaded for a Glen Massan cookbook.

More cosseting came, each night, in the shape of tartan hot water bottles tucked under our duvets before bed. And, for those of us who were fighting off colds, supplies of home-made ginger tea.

Setting off in late afternoon on the first day, we sailed steadily north from Dunoon to Loch Goil, laying anchor overnight just north of the picturesque ruins of 15th-century Castle Carrick. As the sun dipped, a house-party atmosphere developed on board. Fellow guests included Moira and David, celebrating their golden wedding anniversary, and Ann, Johnny, Brenda and Jim, there to unwind after a big family wedding the weekend before. Fortunately we all got on well, because the other thing about a "boutique" cruise is that there's no escape if you don't.

The following morning, after a vain attempt to walk off Mary's full Scottish breakfast with a stroll around Carrick Castle, consensus dictated that we should get back on the boat and head south, to explore the old seaside resort of Millport on Great Cumbrae. It is home to retro cafés, bike shops, a house that prides itself on being only as wide as a front door and the smallest cathedral in Britain. And the best thing about arriving in Millport by boat was that we could leave it again an hour or so later when we agreed that we'd seen enough.

As we set a gentle course from Millport to Loch Riddon, north of Bute, Ann and I settled down on the top deck loungers to bask in the afternoon sunshine and take great gulps of the sharp, briny air. With the light glinting off the water and elegant white yachts criss-crossing behind us, this felt more like being on some glamorous 1920s sailing holiday in the south of France than a short break in Scotland. Deeply relaxed, I peered out, lazily, over the side of the boat as the immaculate reflection of russet hills and pretty waterside cottages drifted past.

Until this point I had never really understood cruising. Like bungee jumping and Club 18-30 holidays, it had never made it on to my to-do list. But the Glen Massan changed my mind.

On a small boat, you have almost as much say when it comes to your itinerary as the skipper and can detour into quieter channels and bays that larger boats can't get into. More importantly, a small vessel is much less intrusive than an ocean liner. Though the Glen Massan wasn't silent, it was quiet enough for us to be able to get close to oystercatchers gathering on the shore, or to seals lounging out on rocky islands, in a way that you rarely can on land. So, instead of just observing the landscape – as you would from a car or on foot – from the boat it felt as though we were part of it.

Before I joined the trip I thought I knew Argyll pretty well, but this was like seeing a new territory. Especially where its human inhabitants were concerned. When it finally got too chilly to stay out on deck, I moved into the wheelhouse and prised a running commentary on the passing landscape from the boat's skipper, Scott, a softly spoken Kiwi. From the water you could see all those castles, baronial piles and great country houses that are always tantalisingly hidden from the road – and Scott was able to tell me who owned them, where they were from and fill in all the interesting background detail.

Some of it was local myth. South of Colintraive, for example, we passed seven look-a-like houses, all right by the shore except one. "The story goes that a rich man had them built for his seven daughters but that one of the daughters got pregnant outside of wedlock so he built her a house that was set back from the others to hide her shame," said Scott. Elsewhere, the facts were more tangible: "That whole estate is owned by Richard Attenborough," he said, pointing out a vast area of farmland as we sailed down the coast of Bute after a walk at Tighnabruaich the next morning.

The snooping also works the other way round when you're in such a good-looking boat. "There's a man in Loch Ridden who always looks out for the Glen Massan," said Scott. "We weren't stopping there for a while last year and he called the company's office because he hadn't seen us for a month and wondered if something was wrong."

The most lavish property in the area is Mount Stuart house. A vast Gothic revival mansion on Bute that's now open to the public, Stella McCartney got married in its white marble chapel in 2003.

When we called, it hadn't opened officially for the season and the current Marquess of Bute, ex-Formula One racing driver Johnny Dumfries, had had his 50th birthday party in the house the night before we arrived. Yet Mary and Scott still managed to set up a private tour for us on our final afternoon. Head guide, Jean, ushered us through the door. Bright, blonde and with a knack for making 10 centuries of family history sound exciting, she whizzed us through the house in just over an hour.

The Third Marquess was a "genius" according to Jean, though "eccentric" might also apply. As well as being home to the world's first domestic heated indoor swimming pool and the first house in Scotland to be lit by electricity, Mount Stuart boasts some extraordinary astrological and astronomical decoration, including the ceiling of the Horoscope Room, which depicts the alignment of the planets at the time of the Marquess's birth. The central ballroom is the building's star attraction. Three floors high and decorated in coloured marble, gilt and bronze, its vaulted ceiling sparkles with silver stars set against deep blue, gold and white paintwork. Stained-glass windows show the signs of the zodiac and, when the sun shines through the crystal stars embedded in them, an extraordinary burst of rainbow prisms lights the room.

Heading out on deck after dinner that evening, I thought back to Mount Stuart's zodiac ceiling. It was a clear night, with the boat hardly swaying in the water and a perfect sprinkling of light dusted across a black sky. If the Third Marquess had been around today, he wouldn't have had to build his ceiling; he'd have been just as dazzled by the view from the Glen Massan.

Traveller's Guide

Getting there

Dunoon (for Holy Loch) and Oban can be reached from Glasgow by train (National Rail Enquiries: 08457 484950; www.nationalrail.co.uk).

Cruising there

Majestic Line cruises (0131 623 5012; www.themajesticline.co.uk) start from either Holy Loch or Oban and cost from £750 per person for three nights or from £1,430 per person for six nights. Prices include full board accommodation with wine at dinner and most on-shore activities. You can also charter a whole boat on the same basis from £7,900 for three nights and £14,900 for six nights, for up to 12 people. Six-night cruises depart on Saturdays and three-night cruises on Tuesdays. There is still some availability for October and reasonable availability for 2009.

Visiting there

Mount Stuart, Bute is open from 1 May to 30 September 11am-5pm Sunday to Friday and 10am-2.30pm Saturday (01700 503877; www.mountstuart.com). Admission £8 per person.

More information

Visit Scotland: 0845 22 55 121; www.visitscotland.com