

54 



ULS Marine Ltd. has also developed a program for determining UTM coordinates 

 of the ROV based around a PDP II computer. The company states that i2m (7 ft) 

 geodetic position accuracy can be obtained. 



One area of vehicle navigation that has not been addressed is navigation within 

 a steel structure. The only present means of determining a vehicle's position 

 inside a structure is by a combination of vehicle depth readings, directional 

 gyro, and visual sightings. Since the steel members of the structure reflect 

 and scatter acoustic energy, none of the above systems can be accurately used 

 inside a structure. Magnetic compasses are also of marginal value inside a 

 steel structure since they are affected by the steel itself. 



Several ROV operators have expressed an interest in employing inertial guidance 

 navigation systems. Although no operator has acknowledged using such a system, 

 it is appropriate to describe one such system which has been used by a manned 

 submersible and could possibly be configured for ROV application. Ferranti 

 Offshore Systems Ltd, Edinburgh, Scotland has developed a system specifically 

 for submersible use called HASINS (High Accuracy Submersible Navigation System) . 



The essential elements of the system are Inertial Navigator, a General Electronic 

 Navigation Interface Equipment (GENIE) , Display and Control Unit. The Inertial 

 Navigation is a standard aircraft system containing an inertial platform and 

 Digital Inertial System Computer (DISC) . The platform comprises three acceler- 

 ometers stabilized in all directions by three high precision gyroscopes. The 

 accelerations of the platform are measured very accurately by the accelerometer 

 and the DISC calculates the velocity and the distance moved. This is in the 

 form of standard aircraft measurement units, and electronic processing of this 

 data is then undertaken in the GENIE. The circuitry of this unit reduces 

 the increment into measurements of 1/lOOOth of an inch. Although it is only 

 relative displacement that is derived, the computer adds these algebraically 

 to produce the new positions in latitude and longitude on a grid. The display 

 and control unit allows an operator to insert and read the data, and is also 

 used to switch the inertial navigator into its various operational roles. 



Before a survey commences HASINS must be aligned to true north and a position 

 of an initial, known reference point must be inserted into the control unit. 

 To maintain accuracy the system must undergo periodic updates. In a si±>mersible 

 this is done at intervals of 1 to 10 minutes for several seconds. Updating 

 is automatic, a push button activates the computer. Experiments conducted 

 by Intersub's PC-1204 (a manned svibmersible) consisted of taking seven 

 measurements over a total distance of 259m (850 ft) which demonstrated a total 

 error of 20cm (7.9 in.). (See Section 5.7 for a detailed account of this system.) 



2.1.14 Personnel 



The number of personnel (crew) required to operate, maintain and repair the 

 various ROV systems is shown in Table 2.1, and they range from one to as many 

 as seven. Obviously, the complexity of the vehicle, the work task, and 

 the length of time required for continuous operation are the factors governing 

 crew size. 



There is no standard watch bill or personnel allocations between operators. 

 Some stand a watch of two hours on and two hours off, others for 3 hours and 



