Unmanned Underwater Surface Vehicle is broken down into four major components:
The wingsail assembly is a hard surface, all composite airfoil similarly shaped to airplane wings standing vertically erect on the boat. The assembly is fabricated entirely from composite materials and engineered to withstand the harsh conditions of waves breaking over the top of it. Composites, impervious to salt water and corrosion, strong, lightweight and engineered to have low electromagnetic and visual cross sections. The wingsail assembly has a symmetrical main leading wing that creates thrust from the wind. Trailing behind the main wing, mounted on control arms is a symmetrical flap airfoil. The flap can be cambered either left or right of the main wing creating a higher lift coefficient depending upon port of starboard point of sail. A round mast section supports the wingsail assembly from top to bottom. At the wingsail’s base control belts link to a hydraulically operated motor, which precisely controls the direction of the main wing, therefore regulating the amount of thrust the wingsail assembly produces directly from the wind. The wingsail assembly is balanced about the rotational axis of the mast, so it spins easily even in light winds.
The entire wingsail is fully cantilevered and rotates 360 degrees independently of the vessels hull. The wingsail is mounted on composite bearings and the mast is affixed to the folding mechanism, which can lower the entire wingsail assembly backward 90 degrees into a slot on the vessels deck. This unique feature effectively hides the wingsail from overpowering winds and assures that the vessel has low hydrodynamic drag during underwater operations. The wingsail stands six feet high when erect with a VHF communication antenna, anemometer, LED navigation light and a 360-degree Electro Optical and Infrared camera mounted on top.
The composite hull of the UUSV is eight feet long with an overall platform width of 19 inches, drafting only 32 inches and having a designed total displacement weight of 160 lbs. Buoyancy changing water ballast systems are located at the bow and stern of the hull. Precise distribution of the UUSV’s center of buoyancy by shuttling water back and forth between fore and aft tanks will enable underwater propulsion termed “gliding.” A horizontal glider style airfoil is mounted to the vessels deck amid ship to provide the thrust necessary during underwater operations. Both the deck and the upper portion of the glider wing will be covered with one square meter of solar cells. Located inside the hull are twin redundant hydraulic control rams that simultaneously lower the sailing bulb keel and raise the wingsail assembly. The bulb keel will provide vessel fore and aft stability, supply a counterforce to the wingsail’s side thrust component and provide vessel self-righting capability during rough sea sailing conditions; twin redundant steering rudders are located at the stern of the vessel that control directional heading during surface and subsurface operations.
A hydraulic motor, located inside the hull, is positioned next to the wingsail assembly. The angle of attack of the flap airfoil is also controlled with the hydraulic motor coupled to a slave servo mounted inside the wingsail at its base. The UUSV’s processor controls the wingsail by input from a solid-state sonic anemometer mounted at the top of the wing as well as from data supplied by Global Positioning System and Inertial Navigation Sensor (INS).
The INS units mounted inside the hull near the vessel’s center of gravity monitors the vessel’s roll, pitch, yaw and acceleration/deceleration. The masthead anemometer supplies the processor with data concerning wind speed and direction combined with a sonic sensor that measures boat speed through the water. This control architecture assures that the wingsail will never over or under power the vessel based on commanded speeds and preset vessel safety parameters.
The platform is steered by twin rudders working in unison but driven independently by hydraulic servos located inside hull. This rudder arrangement provides redundancy for a critical vessel control function. Twin redundant electrically driven jet drive systems, with vectoring thrust for auxiliary surface and underwater propulsion, are located inside the hull at the stern. The hull also contains the following: wingsail/keel mechanical folding mechanism, water ballast systems, energy storage and power management, low pressure hydro/electric pump, hydro/electric distribution valve body processors, VHF radio, Iridium phone, INS/GPS, passive hydrophones and payload sensor bays. A VHF antenna is located at the top of the wingsail’s mast and an Iridium satellite antenna is mounted on deck. A Controller Area Network (CAN) wiring bus is used for the electronics system architecture because of its standardized, robust simplicity.
With no on board fossil fuels, the key to the UUSV’s high degree of mission persistence is its ability to collect and scavenge energy from the surrounding environment and use it for propulsion or store it in its batteries. The UUSV’s wingsail will efficiently convert wind energy directly into thrust allowing the vessel to sail up to one half of the true wind speed – with an engineered maximum speed of 6 knots.
The vessels platform provides 1 square meter of mounting area for solar cells of which more than half can be exposed to the sun all the time. Assuming an average solar incidence angle for the un-occluded panels of 45 degrees, the effective normal area is approximately over one third meter squared. During a five hour day of insolation, high-quality gallium indium phosphide (GaInP) solar cells will be able to add a 440 Watt hr/day charge to the batteries on the surface decreasing with depth to about 15 Watt hr/day in 29 ft. of clear water. State of the art Lithium Ion batteries in the hulls will total at least 5 Kw / hr at an energy density of 700 W/hr/Liter. Increased battery capacity is easily accommodated since battery mass helps provide ballast for subsurface operations.
UUSV Modes of Operation
The vessels modes of operation are:
When the vehicle is in surface mode it can sail prolonged periods of time from energy supplied by the wind alone. The UUSV will travel at approximately one half of the speed of the wind up to a top speed of 6 knots. Higher speeds, although attainable, will be governed to create a safety margin. If no wind is present, the vessel can hold station or maneuver using its auxiliary electric water jet drives. As previously discussed, the vessels roll, pitch, yaw, acceleration/deceleration are monitored by the INS/GPS and course can be adjusted to increase stability or take advantage of wave energy. The ballast system can be used to increase the stability of the vessel while sailing. The anemometer on top of the wingsail continuously analyzes the wind speed and direction and allows the processor to adjust and optimize the wingsail’s thrust; precisely maintaining set commanded courses and speeds. The INS/GPS unit supplies exact location and speed allowing for the UUSV’s to have a cross track error of less than three meters while in surface sailing mode.
In semi-submerged mode, the vessel’s hull is partially flooded by the water ballast systems so that the UUSV can sink to a controlled depth of 1 to 3.5 feet. In this state, the vessel becomes substantially more stable when encountering rough surface conditions and has low visibility if required. As the ballast systems take on water and the UUSV starts to submerge, the wingsail is held in position down the centerline of the vessel presenting as low a drag profile to the water as possible. Only the mast top 360-degree view camera, environmental sensors and antennas project above the surface in semi-submerged mode. The solar cells, being tuned to the blue-green light spectrum, will remain fully functional in semi-submerged mode as well.
As the UUSV continues to take on water ballast and submerge below 4 feet, the wingsail is folded down towards the stern and locked in this position by its lowering and lifting control ram. As the control ram is lowering the wingsail, the keel is simultaneously pivoted in a scissoring motion upward. The lowering of the wingsail and pivoting of the keel reduces the hydrodynamic drag of the vessel while in fully submerged mode, enhancing maneuverability and conserving energy. The rudders act as elevons and in conjunction with the ballast system, and the underwater glider wing control the boats underwater pitch, roll and yaw attitudes. The rudders also regulate the vessel’s underwater heading and by supplying vectored thrust from the jet drives underwater maneuvering can be enhanced. The vessel will have a top speed fully submerged of two knots in glider mode and four knots using the auxiliary jet drive. The UUSV’s initial designed operational depth will be 75 feet (generation 1) with a subsequent version’s capable of 650 feet (200 meters). In fully submerged mode the boat will be able to completely avoid harsh storm conditions and be virtually undetectable from the surface.
The UUSV’s ability to go from surface to fully submerge in less than one minute will provide a self-defense mechanism from attack, piracy or being overrun by larger vessels. With the technological evolution of solar panels that are able to collect energy down to 29 feet and by employing glider UUV buoyancy changing technology, the vessel’s subsurface operations time will be exceptionally long. Persistent underwater station keeping coupled to passive sonar will provide highly effective subsurface and surface vessel detection capability while the UUSV remains completely hidden .