S201
S201 is an 8.9 tonne vehicle intended for 48hr operation at depths up to 300m. This project is an example of our rapid prototyping capabilities. From outline specification to launch took just 14 months. Dived performance is maximised by attention to streamlining of the outer hull and by the use of advanced motor technology to directly drive the main propeller. Surface running is possible with one crewmember on deck and hatch closed, at speeds up to 6kn in modest sea state, but the vessel's primary mode of deployment is by crane-in.
The vehicle utilises an advanced suite of navigation equipment. This consists of an PHINS 3 axis fibre-optic gyro navigation unit coupled to a Doppler velocity log (DVL). These are processed by onboard PC to continually provide track information. An ultra short base line unit (USBL) communicates with the surface boat to provide position information also. A GPS sensor provides absolute position whilst on the surface. In addition to the navigation and battery management PCs, two more PCs are fitted for side-scan sonar, forward scanning sonar and video. A combination of new generation Phosphate-based Lithium-Ion batteries and rare-earth magnet technology main propulsion motor provide performance and endurance remarkable for a vessel of this size and type.
The submarine comprises a steel inner pressure hull, containing the majority of the machinery, and an outer streamlined fairing. The outer fairing also incorporates the four lateral main ballast tanks and bow tank which are blown dry using high pressure compressed air for surface running. Fairing panels are removable for access to the hull penetrations and the high pressure air and life support oxygen storage cylinders, and for removal of the pressure hull aft hemisphere to access internal equipment.
The outer fairing has a circular cross-section and comprises GRP nose and tail mouldings and steel midships sections, these forming the lateral main ballast tank covers. The pressure hull is offset downwards in the fairing, improving surface stability and external equipment accommodation. The lower surface of the fairing comprises a galvanized steel belly pan continuing the cylindrical hull form. The upper surface comprises a GRP moulding incorporating a low profile sail with streamlined hatch fairing.
The pressure hull forward hemisphere is equipped with a small circular viewport downward looking at 45 o to horizontal. The removable forward hemisphere allows the future option of an alternative forward section with large viewport and modified bow main ballast tank. Surrounding the forward part of the hull is the bow moulding, the upper half of which forms the bow main ballast tank by means of a GRP inner skin hugging the pressure hull forward hemisphere. This bow buoyancy counteracts the tendency to dive when running at speed on the surface. The lower bow fairing section features a bonded-in acrylic transparent section to allow observation from the viewport whilst maintaining the streamlined hull form.
To allow manoeuvring of the submarine close to the sea bed, bow lateral and stern lateral 1kW electric thrusters are fitted, together with a midships mounted 2kW vertical down- thruster. Depth control is also effected by the dive-planes and/or trimweight in combination with forward motion.
Neutral buoyancy whilst dived is maintained by two internal 1 atmosphere variable ballast tanks with a total capacity of 140 litres, located in the forward pressure hull section. The variable ballast allows some compensation for varying crew and equipment loads. Water ballast is pumped out using a positive displacement pump driven by an electric motor and taken in using external pressure, with impeller pump assistance for surface or shallow depth use.
