A Hydrofoil is a specially designed hydrodynamic surface that creates
lift significantly exceeding drag. The main function of the hydrofoil is to
lift the ships hull out side the water. At low speeds the ships hull sits on
the water and the hydrofoils are
totally submerged in water, but as the speed increases the hydrofoils
create lift, bringing the hull outside the water surface.
The basic principle of the hydrofoil concept is simply to lift a ship's
hull out of the water and support it dynamically on wing-like lifting surfaces,
i.e. hydrofoils, to reduce the effect of waves on the ship and to reduce the
power required to attain modestly high speeds. Engineers and naval architects
have been intrigued with the possibilities of this concept for many years. A
United States patent for a hydrofoil was defined in the late 1880s, about the
same time as the early airplane and airfoil patents. The earliest record of a
successful hydrofoil flight is 1894 when the Meacham brothers demonstrated
their 14 foot test craft at Chicago, Illinois. This compares with the Wright
brothers' first airplane flight in 1903. The early attempts to exploit the
hydrofoil concept were frustrated by lack of suitable structural materials and
power plants. However, advancement in these areas, much of it stemming from
aircraft developments, has permitted development over the past 30 to 40 years
of the technology necessary to achieve and demonstrate reliable and effective
hydrofoil ships for both military and commercial below.
HYDROFOIL BASICS
Many people are familiar with airfoils. Foil is simply another word for
the wing (such as the wing on an airplane). A hydrofoil is a wing that 'flies'
in water. Hydrofoil is also used to refer to the boat to which the water wings
are attached. A hydrofoil boat has two modes of operation:
(1) as a normal boat with a hull that displaces water and
(2) with the hull completely out of the water and only the foils
submerged.
Hydrofoils let
a boat go faster by getting the hull out of the water. When a normal boat moves
forward, most of the energy expended goes into moving the water in front of the
boat out of the way (by pushing the hull through it). Hydrofoils lift the hull out
of the water so that you only have to overcome the drag on the foils instead of
all of the drag on the hull.
The foils on a
hydrofoil boat are much smaller than the wings (foils) on an airplane. This is
because water is about 1000 times as dense as air. The higher density also
means that the foils do not have to move anywhere near as fast as a plane
before they generate enough lift to push the boat out of the water.
The hydrofoils
generate lift only when they are in the water; if they leave the water, the
boat will crash down onto the surface of the water (and thus submerge the
foils) until the foils generate enough lift to lift it back out. Like an
airplane, a hydrofoil must be controllable in terms of pitch, roll, and yaw.
Unlike an airplane, a hydrofoil must also maintain a consistent depth. Whereas
an airplane has a range of about 40,000 feet in which to maintain its altitude,
a hydrofoil is limited to the length of the struts, which support the boat
above the foils.
Although the basic concept of hydrofoils has been around for 85 years, it
has only been in the last 35 years through advances in materials, light weight
propulsion plants, and control theory, they have become a viable open ocean
concept. Involved. The design of a hydrofoil demonstrates the very essence of
engineering that is the trade-off and compromise among often-conflicting
requirements of many disciplines to arrive at a good balanced design.
CONCLUSION
Although the
basic concept of hydrofoils has been around for 85 years, it has only been in
the last 35 years through advances in materials, light weight propulsion
plants, and control theory, they have become a viable open ocean concept.
Involved. The design of a hydrofoil demonstrates the very essence of
engineering that is the trade-off and compromise among often-conflicting
requirements of many disciplines to arrive at a good balanced design.
