Eco-warrior turns green on his voyage across the Pacific

Banking heir hit by seasickness nine days into 8,000-mile trip

David de Rothschild is young, enviably good-looking and heir to one of the world's great blue-blooded banking fortunes. However, Neptune is a great leveller who cares little for your wealth or indeed whether you are on a highly publicised mission to clean up his polluted oceans.

Since setting off from San Francisco nine days ago aboard a 12-tonne catamaran made from recycled bottles, the billionaire, self-styled eco-warrior has been forced to contend with a condition known only too well among sailors since man first ventured on to the waves: chronic sea sickness. Video footage from the boat shows the green-faced environmentalist slumped on the deck of the raft "struggling to hold on to his lunch" as the craft pitches and rolls in the elements.

The poster boy for the modern environmental movement, who at 31 is the youngest Briton to have reached both geographical poles, has tried to make light of his stomach-churning predicament, brought on by high winds and 20ft waves. "I actually think today was the first full day where I have kinda felt normal, I had a smile on my face that wasn't induced by gag reflexes," he joked. "My lack of nausea has also opened up a whole new world of boat activities, I tried some fishing. No luck yet."

De Rothschild's Plastiki mission (named in honour of Thor Heyerdahl's 1947 Kon-Tiki project) aims to highlight the huge quantity of non-biodegradable plastic rubbish in the world's oceans by sailing 8,000 miles across the Pacific. The son of the banking billionaire Sir Evelyn de Rothschild, he runs an organisation, Adventure Ecology, which seeks to highlight the plight of the planet with a series of high-profile expeditions.

The six-strong crew plans to track close but not through the infamous Pacific Trash Vortex, a vast patch of sea off Hawaii containing millions of tonnes of discarded plastic bottles, bags and packaging – an area said to be six times the size of the UK.

Mr de Rothschild came to the environment movement by way of show jumping, music merchandising, naturopathy and organic farming. Despite his pedigree, he prides himself on never seeking money from his family to fund his adventures and likes to remind interviewers that he worked in a bar to pay for his first car – a Ford Fiesta. In a recent interview he said: "Stuff does not equal happiness. The more shit you have the more you've got to worry about."

Expedition director Matthew Grey, a former Army captain, who is overseeing the voyage from San Francisco, said the sea sickness was "part and parcel" of the challenge. "They are in high spirits. They are enjoying a bit of sunshine and the elation of being out on the open sea," he said. The raft has been proceeding at a stately three to six knots since setting off but is still on schedule to reach Sydney in two-and-a-half months.

Retch and famous: Seasickness sufferers

*Admiral Lord Nelson The hero of Trafalgar was no stranger to a strategic vomit at the ship's rail. He suffered all his life, despite going to sea at 12. He used to tell his men the best cure was "sitting under a tree".

*T E Lawrence The Arabian adventurer suffered from profound motion sickness when riding a camel.

*Neil Armstrong First man to walk on the Moon, but like a third of US and Soviet astronauts he suffered from motion sickness in space. The US federal government invested millions attempting to solve the problem.