The Countess of Arran

The Countess of Arran, who has died aged 94 in Devon, was one of the most adventurous women in power-boat racing and set many records – notably the first woman to travel on water at over 100mph. With reason, she was considered the fastest granny on water. In 1980, she drove her rocket-like craft called Skean-Dhu on Lake Windermere and won the highest accolade in power-boating, the Segrave Trophy.

Lady Arran once emerged black and blue after been tossed around in rough water, admitting, "I only drive at two speeds — flat out, and stop." When asked why she did it, she replied: "For Scotland".

Her love of speed began in her youth when she was brought up on an island on Loch Lomond where her parents owned a wooden bungalow on the Isle of Inchconnachan. The island is situated in a popular beauty spot known as The Narrows and the name is gaelic for The Colquhoun's Island.

Fiona Bryde Colquhoun was the daughter of Sir Iain Colquhoun, 7th Bt of Luss, Chief of the Clan Colquhoun and a distinguished soldier in the First World War. She was brought up mostly on the island – swimming every day before breakfast in summer and winter – and educated by a governess. While still a teenager Lady Arran was introduced to the thrills of power-boating when she was driven across Loch Lomond in Miss England III, a hydroplane powered by Rolls-Royce aero-engines.

Just before war was declared in 1939, Lady Arran was in her husband's supercharged Mercedes car when it clocked up 100mph on Oxford Street in central London. She exclaimed on emerging from the car: "That was rather fun." During the war she was a driver with the Wrens and worked for the Ministry of Information.

Throughout her life Lady Arran kept a wide selection of animals on the island – notably badgers and wallabies. She introduced the latter in the 1940s and some locals considered they threatened the capercaillies in the surrounding area. The badgers roamed around Inchconnachan undisturbed – the family had to wear Wellington boots inside the house to prevent being bitten.

Lady Arran loved a challenge and in 1966 was the only woman competitor in the Paris Six Hour Race and finished in her Badger 14th out of 90. She began competing in offshore races in 1970, racing very successfully her beloved Highland Fling. It was notoriously difficult to handle – a fact that made it all the more exciting for Lady Arran. She sailed it in the World Championships on Lake Windermere in 1972 and took the Class setting a record for travelling at 82 mph.

In her fifties Lady Arran took part in the Round Britain offshore race and on her technically advanced last power-boat, Skean Dhu, in 1979, won the Class 2 World Record from the Italians again on Lake Windermere: aged 71. She was the World Offshore powerboat speed record holder in Highland Fling.

Lady Arran, in the 1980s, decided to take up horse driving and Prince Philip, a keen competitor in the sport, was amazed at her challenging driving.

Lady Arran, who was buried at Luss, preserved a strong Scottish identity at sporting events – invariably wearing some item of clothing of the Colquhoun tartan. She was a much loved figure in the sport for her drive, enthusiasm and energy. As one friend commented, "Fiona was a wonderful woman on and off the water."

Her husband died in 1983. The elder of their two sons, the 9th Earl of Arran, survives her.