Guy Martin wants to beat the 25-year-old speed record for a human-powered boat. It means pedalling a specially-built boat along a 100-metre course at an average speed of 21mph: a speed normally reserved for expensive speedboats or racing yachts. It's Guy's most physically and technically challenging record attempt yet, so he employs the services of two Olympic legends: Sir Chris Hoy trains Guy like an Olympic cyclist, and Sir Ben Ainslie hands over the helm of one of his multi-million-pound America's Cup yachts to demonstrate the cutting-edge technology of hydrofoils: underwater wings that help a boat fly across water. Guy then builds two different machines that use hydrofoils: a carbon-fibre catamaran made with help from the University of Lincoln, and a canoe fitted with a giant aeroplane propeller, assembled in his own back garden.