The DOLPHIN (Deep Ocean Logging Platform Instrumented for Navigation) has been produced by the Bedford Institute of Oceanography — with five Dolphins now available for mapping the ocean floor.
The DOLPHIN is a semi-submersible (see illustration) capable o~ making 15 knots in order to maintain a 12-knot bottom survey speed ~or at least ~our hours. However, its endurance has proved to be about 20 hours. It is powered by a 120 hp marine diesel, and can stably operate continuously in 10-foot breaking seas — which have a minimum period o~ six seconds. Control of the DOLPHIN is by a UHF radio link within a line o~ sight range o~ up to about 10 km. Its diameter of 39 inches, length o~ 19.5 feet and displacement o~ about 2.5 tons are adequate for carrying remotely controlled echo sounders, positioning systems and control systems for this semi-submersible.
As shown in the illustration, the radio antenna receives command data and telemeters data back to a control console on the mother ship conducting the bottom survey.
The snorkel head of fiberglass contains a float valve which prevents the ingress of water if a wave washes over the top of the snorkel mast at any time.
The snorkel mast or “strut” is about 3 hull-diameters in length, making the running depth at least 3 meters and causing the wave-making resistance o~ the submersible to become negligible.
The vertical distance between the center o~ buoyancy and the center of gravity o~ this submersible is .45 o~ the diameter — creating adequate static stability. This equates to 17.5 inches for the 39-inch diameter hull and is achieved through the use of a lead keel of 550 Kg weight.
There are five compartments: forward ballast; fuel tank; sealed engine-room; rear ballast; and engine exhaust and tailshaft.
The strut is fitted with rotating faired segments which are necessary in order to maintain hydrodynamic stability during turns at high speeds. The bow planes operate independently of each other and are used for roll and pitch control. The DOLPHIN is designed for a maximum depth or 60 meters.
Commands from the operator on the mother ship to the semi-submersible are received by the onboard radio-receiver which reeds directions into the DOLPHIN’s control systems. Command signals include operational depth. heading, and vehicle attitude, both in terms of pitch and roll.
Sensors shown at the upper left or the diagram measure the position and beading or the vehicle. and signals from the sensors are compared in the central microcomputer with the commands from the radio. Error signals are generated as a result and actuate the electro-hydraulic valves which control the hydraulically operated planes and rudder which control the vehicle. In order to ensure stability, rate or change signals. derived from sensors and from error signals. are mixed with the error signals so as to provide damping. Finally. the positions or the hydroplanes are measured and fed back so as to give proportional control.
The depth or the vehicle is measured by a pressure sensor which is mounted in the nose or the vehicle and fed from ports located at points on the nose such that venturi effects have no impact on the pressure measurement. A vertical velocity signal is generated from a vertical accelerometer, the signal from which is integrated. The depth error signal. controls the forward hydroplanes acting in unison; these hydroplanes are located at approximately the centre or mass and centre or pressure of the vehicle.
Roll of the vehicle is measured by a pendulum inclinometer mounted in the vehicle, and the output is used to control the forward planes differentially. The pitch of the vehicle is measured by a second pendulum inclinometer, the output of which controls the rear hydroplanes. The rudder is controlled by the output from a directional gyroscope which measures the heading of the vehicle.
Other functions on the vehicle are operated by direct command. The operator can send a signal which directly operates a small motor driving a lead screw which slowly opens or closes the throttle of the engine thereby giving a direct control of speed. The ballast tanks are controlled by valves which allow air to vent from the tanks and other valves which blow air from the high pressure air supply into the tank. All of these operations are directly operated vis the radio link.
A number of safety features are incorporated into the vehicle. They range from relatively simple devices such as automatic engine shut-off (in case of overheating or lubricating oil failure) to sophisticated routines to stop the engine, set the hydroplanes to climb, and blow the main ballast tanks (in case of malfunction of radio control link, excessive water level in the engine room, etc.}. If, because of some malfunction, the vehicle descends accidentally to a 10 metre depth the automatic stop-routine is triggered; as a further safety precaution, if the vehicle reaches a depth of 20 metres, an emergency valve is opened which blows high-pressure air directly from the air supply into the ballast tanks.
The operator controls the vehicle and is kept informed of its performance by a command console. The console is based on an IBM personal computer and a series of controls are provided for he various functions listed above. A joystick control operates the heading by moving it laterally. When the joystick is left in its central position, the vehicle continues on a constant course. The depth of the vehicle, the engine speed, and the static angles of pitch and roll have continuously variable controls whilst functions such as venting air from the ballast tanks are controlled by on/off switches.
All the data are converted to an appropriate digital form for transmission to the display console.
First tests took place in Indian Arm, a fjord near the ISE factory at Port Moody. When initial diving trials, controlled by the operator, were carried out, a technique for automatic control was developed in which the required depth was set on the control console, the ballast tank flooded and the engine speeded up, whereupon the vehicle dived automatically to the correct depth . At the end of the dive, throttling back resulted in DOLPHIN surfacing gently as speed diminished to zero .
During sea trials it was round that when DOLPHIN was running into seas, it ran on a horizontal line and the waves had no effect on its vertical position but when running with the seas it tended to follow the water surface. This is not serious as adjustments are built in to accommodate the effects of vertical movement.
Initially, just over 14.5 knots was achieved but the design speed of 15 knots was achieved by means of a redesigned propellor. Radio interference caused by equipment on the mother ship CSS BAFFIN interfered with the control transmission but this was cured with an antenna filter.
Once all DOLPHINs have been delivered to the Bedford Institute of Oceanography, a continuous programme of mapping all year round willbe possible. Conditions can be extremely difficult and the stable platform provided by DOLPHIN will give increased accuracy and greater endurance together with reduced manning requirements.
DOLPHINs fitted with 220hp British Sabre engines are under test at sea. These will provide a further dimension to the use of high speed asymmetric, dynamically stabilised vehicles to be used as instrument platforms.[This article was digested from one prepared by the Bedford Institute of Oceanography tor Underwater Systems Design– March/April, 1986.]