34 



2 . 1 . 7 . m Cleaning 



Prior to any of the testing techniques described above in sections 2.1.7.j 

 through 2.1.7.1 and for detailed visual inspection, whatever fouling organisms 

 are present on the structure must be removed. For localized cleaning of 

 areas of a few square centimeters virtually any ROV with a manipulative 

 capability can be equipped with a rotary brush or grinder which will satisfy 

 this requirement. For larger area cleaning and in the acute angles of "K" 

 joints, high pressure water jets up to l,054kg/cm2 (15,000 psi) are employed 

 by divers. In 1978 Sonarmarine Ltd. developed and operationally used a water 

 jet from its vehicle SMT 2. The water jet pump is carried on the vehicle 

 (therefore it does not have to overcome the hydrostatic head) and can operate 

 to any depth. The pump feeds a reaction jet and delivers pressure up to 

 351kg/cm2 (5,000 psi) at a flow rate of 38 liters (10 gals) /minute. The 

 jetting can clean away encrusting organisms (barnacles, serpulid worm tubes, 

 bryazoan, etc.) down to bare metal at a rate equal to the diver-held devices 

 of the same pumping capacity. 



2.1.7.n Current Measurements 



Three vehicles have the capability of measuring water currents. The measure- 

 ments are made by a savonius rotor with magnets spaced equally on the perimeter 

 of its base. A magnetic switch counts the pulses per time interval and the 

 speed is registered on a taut bandmeter such that, for example, 83.5 rpm 

 equals one knot. Current direction is sensed by a vane connected magnetically 

 to a compass. There are a variety of commercially available current meters 

 which provide a wide range of data, generally speeds of 0.1 to 6.0 knots 

 -2% and direction of to 360 degrees ±7 degrees are acceptable. Current 

 measurement devices also serve as a rough measure of vehicle speed and course. 



2.1.7.0 Temperature Measurements 



Only those vehicles employed in scientific research are equipped with water 

 temperature measurement instruments (ANGUS 003 and CORD II) . The sensing device 

 is one of a variety of thermistors commercially available which generally 

 span a range of -2 to 35^0 and provide an accuracy of ±0.03C. Display can 

 be either digital or analog. 



2.1.7.P Magnetic Compass 



After visual navigation, the magnetic compass is the primary means of ROV 

 navigation. The variety of compass types is as wide-ranging as is the 

 variety of ROVs , consequently, no one magnetic compass will serve to describe 

 the field at large. Generally, a magnetic fluxgate sensor is used which will 

 provide an accuracy of -1 degree. On many vehicles the compass information 

 is telemetered electronically to the surface and displayed digitally on the 

 control panel. On others the compass is located in a position on the vehicle 

 such that it is read by the CCTV and displayed on its monitor. 



2.1.7.q Gyrocompass 



Most of the gyrocompasses used on ROVs are directional gyros which are 

 referenced to the magnetic compass and used when the vehicle is in the 



