Page 48 - Theory and Design of Air Cushion Craft

32 Introduction to hovercraft

The craft structure was made of GRP following the methods of Karlskronavarvet AB
of Sweden, while a set of mine sweeping gear, and retractable crane with lift capabil-
ity of 2.It were to be mounted on the upper deck stern. Two diesels with rated power
1600 kW for each were to be mounted as main propulsion engines, driving 5 blade
fixed pitch water propellers with diameter of 1.02m, giving low noise level, via a gear-
box with reduction ratio of 2:1. The wet deck of this craft was above the water when
floating. A variable depth sonar (YDS) was to be mounted on the main hull, and
could be extended into the water inside the cushion. In addition, a retractable swivel-
ling thruster and two fixed pitch propellers driven by hydraulic motors were mounted
on the craft to propel it during the mine sweeping operation. Since all mine sweeping
operations were carried out on craft in on-cushion mode, the acoustic signature under
water would be weaker. This application lends itself to SES with high cushion length
beam ratio, and thick sidewalls. The total power of the air cushion catamaran would
be slightly larger than that on conventional mine sweeper craft.
The craft were planned to be completed in the 90s, although a construction order
was never placed. The Royal Norwegian Navy have since further developed this tech-
nology and commissioned 9 SES MCM vessels between 1994 and the summer of 1997.

Medium sized patrol SES

The medium sized SES was seen as a replacement or supplement to the hydrofoil
patrol boat (PHM). The seakeeping quality of a 500t SES would be the same as that
of a PHM, but the SES would possess greater range, deck area and cabin space. For
this reason, some naval strategy experts considered that a combination of 1-2 SES
and 6 PHM would be a good fleet to perform anti-aircraft and anti-submarine mis-
sions, because of its capacity for accommodating various electronic and other equip-
ment as well as more fuel to support the PHM.
Some experts considered that the weapon system on the Spruance class destroyers,
the DD-963 series, was suitable for providing a weapon system for SES. In this way an
SES could be an ideal frigate, destroyer, even aircraft carrier. Its shallow draft, low
underwater noise emission, high speed and large upper deck for carrying helicopters,
guided missiles and STOL/VTOL aircraft to implement various Air-to-Air and Air-
to-Surface missions would all add to the usefulness of the SES.
Enthusiasm to develop military SES/ACV has slowly improved once again in the
USA since the mid 1970s, but based on a steady, step by step approach. The LCAC
programme has become an important cornerstone for ACV technology application.
Design displacement of SES has been extended gradually from lOOt to 200t. Vessels
with 500t, and 1000-2000t displacements are quite practical, but the US technology
lead has been lost, now being taken over by Norway on the military application side,
and China/Japan/Korea for commercial vessels.

1.5 ACV and SES development in China

The Harbin Shipbuilding Engineering Institute (HSEI) started to develop a new kind
of water transport concept - the hovercraft with plenum chamber type air cushion -
in 1957, and completed the first model craft in China with a length of 1.8 metres. The