Wars cmd W@zring
193
particularly for what might be termed ‘high performance’ vessels.
The Royal Navy, for example, had a gas turbine—powered patrol boat
as early as 1947. The use of gas turbines in major warships.followed.
The prevailing policy, however, was to limit them to the role of
auxiliary boosters for conventional power units. Only in February
1968 was the decision taken to abandon diesel or conventional
steam propulsion units in favour of gas turbines in future surface
Vessels.
_
Uncanventional cm
‘
A tremendous boost for the marine gas turbine will come with the
progress of hydrofoils and hovercraft. These ‘surface effect’ craft are
one of the most exciting innovations in marine transport. The idea
for the hovercraft was only put forward in 1956 and, in spite of
experiments on hydrofoils some seventy years ago, large hydrofoil
craft have become feasible only in recent years when large engines
with high power—to—weight ratios and high—load carrying, high—
eiciency foils have become available. Both types of vehicle have
as their aim a reduction in hydrodynamic drag—the hovercraft by
-
moving on a cushion of air and the hydrofoil by ‘ying’ on foils
which act like wings in the water to provide the necessary lift.
Hydrofoils can be divided into three categories according to the
types of foil that they use. There are depth—effect foils, surface—
piercing foils and fully—submerged foils (see gure 23). The depth—
eifect depends on the breadth of the foil which determines how deep
the foil may be below the surface before the ‘lift gradient’ goes and
the hydrofoil craft loses its stability. In practice, the depth range is
sufciently small to rule out the use of depth—effect hydrofoils in
water with high waves. In fact, craft based on this principle can
almost be regarded as being built specially for the extensive inland
waterways of the Soviet Union where they are said to carry more
inter—city passenger traîc than do the roads. More general purpose
vessels, typied by the Swiss—designed Supramar craft, use surface—
piercing foils. They have large vec—section foils fare and aft and ride
much higher above the water than depth—effect hydrofoils.
The foils
are shaped in such a way that waves from any direction tend to
increase the area of lifting surface under the water, providing greater
stability than depth—effect systems. Unfortunately, when the boat
catches up with high waves, the upward and downward motion of
the water causes violent pitching. This potential hazard limits
7
193
particularly for what might be termed ‘high performance’ vessels.
The Royal Navy, for example, had a gas turbine—powered patrol boat
as early as 1947. The use of gas turbines in major warships.followed.
The prevailing policy, however, was to limit them to the role of
auxiliary boosters for conventional power units. Only in February
1968 was the decision taken to abandon diesel or conventional
steam propulsion units in favour of gas turbines in future surface
Vessels.
_
Uncanventional cm
‘
A tremendous boost for the marine gas turbine will come with the
progress of hydrofoils and hovercraft. These ‘surface effect’ craft are
one of the most exciting innovations in marine transport. The idea
for the hovercraft was only put forward in 1956 and, in spite of
experiments on hydrofoils some seventy years ago, large hydrofoil
craft have become feasible only in recent years when large engines
with high power—to—weight ratios and high—load carrying, high—
eiciency foils have become available. Both types of vehicle have
as their aim a reduction in hydrodynamic drag—the hovercraft by
-
moving on a cushion of air and the hydrofoil by ‘ying’ on foils
which act like wings in the water to provide the necessary lift.
Hydrofoils can be divided into three categories according to the
types of foil that they use. There are depth—effect foils, surface—
piercing foils and fully—submerged foils (see gure 23). The depth—
eifect depends on the breadth of the foil which determines how deep
the foil may be below the surface before the ‘lift gradient’ goes and
the hydrofoil craft loses its stability. In practice, the depth range is
sufciently small to rule out the use of depth—effect hydrofoils in
water with high waves. In fact, craft based on this principle can
almost be regarded as being built specially for the extensive inland
waterways of the Soviet Union where they are said to carry more
inter—city passenger traîc than do the roads. More general purpose
vessels, typied by the Swiss—designed Supramar craft, use surface—
piercing foils. They have large vec—section foils fare and aft and ride
much higher above the water than depth—effect hydrofoils.
The foils
are shaped in such a way that waves from any direction tend to
increase the area of lifting surface under the water, providing greater
stability than depth—effect systems. Unfortunately, when the boat
catches up with high waves, the upward and downward motion of
the water causes violent pitching. This potential hazard limits
7