30 SECOND BRIEFING:

HYDROFOILS

Hydrofoils on boats are nothing new. They’ve been around since 1898 when Italian inventor Enrico Forlanini started working on them. ● His ideas were adopted and developed by commercial boatbuilders and navies during the 20th century but began to fall out of fashion in the 1990s due to high building and running costs. ● Foils have come back into focus in recent years due to the excitement surrounding the new generation of foiling America’s Cup yachts, which are capable of speeds of over 40 knots. ● Foils work like an aeroplane wing. The shape and angle of the foil is designed to deflect water downwards and encourage water to flow faster over the top surface than the bottom one. ● This creates high pressure on the underside of the foil and low pressure on the top, which ‘sucks’ the foil upwards until it lifts the main hull clear of the water. ● At a certain speed, the lifting force is balanced by the weight of the boat, allowing the craft to ‘fly’ at a fixed height above the water. ● Because the surface area of the foil is much smaller than that of the main hull, the types of drag and wave resistance which act on the boat are reduced, allowing it to cruise faster using less power. ● There are two main types of foil: surface-piercing foils like the U-shaped structures fitted to Seabubbles ,and fully submerged T-foils like the ones fitted to International Moth sailing dinghies. ● Although fully submerged foils are more efficient and less prone to wave action, they are trickier to control and less stable during turns.