We have already studied about conventional ship design and hull strength of ships. Now we will study about a type of boat which uses a totally different hull design. Hydrofoil boats are the boats that use the technique of hydrodynamics using hydrofoils (wing like structures under the boats) for locomotion. This technique is used for the efficient use of engines that power the boat. We have already learnt about the generic aspects of hydrofoil sailboats in another article here, so in this article we will focus on their working principle and design.
Hydrofoils are wing-like structures which are mounted on struts below the hull of the sailing structures, which can vary from small boats to big passenger boats. The unique geometry of the hydrofoils allow the sailing structures (small boats or passenger boats that use hydrofoils) to use the power supplied by the engine efficiently. There are many variations of the hydrofoil that has been developed over the years.
In normal boats, the water in front of the hull is pushed out of the way. The surface area of the boat in contact with water is more and this requires more energy to push the boat forward. In hydrofoils, this is not the case. When the boat is in rest, the hydrofoils are fully submerged in water and the entire hull is in contact with the water. When the boat starts moving and the speed gradually increases, there is a lift experienced by the boat which is due to the use of hydrofoils. Thus there is a reduce in drag as the hull of the boat is lifted and the energy required to power the boat reduces. This results in increase of the speed of the boat.
Why the Lift is Experienced?
In a practical perspective, water is never still. It has waves, so there are crests and troughs. The hydrofoils are lifted in crests. When there are troughs, the hydrofoils leave water, so they land with a crash. This might be dangerous as it might topple or the hydrofoils might crash.
Problems like ventilation is a major problem faced when designing hydrofoils. Ventilation occursat the air-water interface. This happens when the hydrofoil keeps lifting and it meets the air-water interface and at that point, the air is sucked down the lifting surface of the foil and this results in crashing of the boat, as air is much less denser than water and the lifting process stops once the air-water interface is met.
Also the angle of attack should be kept in mind while designing hydrofoils. The angle of attack is adjusted by sensors and other electronic components in modern day hydrofoils.
Some of the configurations used are the V shape and the inverted T-shape. Each configuration has its own advantages and disadvantages. In some configurations ladder foils are also used which are relatively more stable in high seas.