They say that boats are getting bigger – and the ranks of gleaming fibreglass leviathans on display at the London Boat Show this year certainly support that view.

But tucked away in the North Hall of London’s ExCeL centre this week is a cockleshell cruiser that single-handedly brings down the average boat length at the show: Tom McNally’s Big C, with a LOA of just 3 feet, in which he hopes to cross the Atlantic.

McNally, a veritable veteran of miniature ocean crossings, aims to ship his tiny craft to Newfoundland later in the year and sail her home to Liverpool to raise money for the cancer charity Sail4Cancer. He had originally planned to sail the boat from Cadiz, following the trade winds – but a death in the family and logistical problems forced him to change his plans. He told PBO, ‘The trade-wind route wasn’t enough of a challenge anyway! The sailing’s much more varied further north.’

The boat is open to the public – one at a time – at ExCeL this week. Curiosity getting the better of me, I tentatively clambered aboard. The interior (pictured below) is little more than a bare shell, with minimal legroom – let alone much space for stores. At 6’2″, my legs were bent and cramped, and my shoulders barely fitted below the deck. But McNally, who stands at a more suitable 5’10, is unconcerned. After all, this boat is only a few inches smaller than the craft in which he made the same journey in 1993. Even so, he will sleep semi-prone in a sling and can only stretch out by standing, somewhat precariously, on the deck.

His food will be stored in the cylindrical floats, seen in the picture above, and his drinking water will come from a hand-operated desalinator – which, he says, he can only use at night, otherwise he would lose more water through sweat than he would gain from pumping.

McNally has moved a step closer to realising his goal this week after the donation of a main hatch from one of a growing list of supporters, the latest of which is marine directory company Bluesheets. The final piece of equipment he requires is a perspex bubble so that he can see out of the tiny cabin.

Tom is Sailing for Sail4Cancer