INGENIEUR
Figure 3.3.1 : Control panel of URI-T ROV Trencher . ( Source : Korea Institute of Robot and Convergence ) [ 15 ].
This overall control signal communication ( up and down between trencher and control station ) is called telemetry . For a system with an umbilical cable length of less than 1500 meters , hard wire telemetry communication is possible . For the system with more than 1500 meters umbilical , a fibre optical line is more suitable because of its stability and fast response . The fibre optical system can carry RS232 , RS422 , RS485 or even ethernet signal . Figure 3.3.4 shows an example of a fibre card system .
The console module is located inside the control cabin and all data is transferred to the trencher ROV PC for central processing with a user interface as in Figure 3.3.1 . The remote module is located inside the trencher main control pod . All signals from the surface or going to the tools and sensors are interfaced here .
3.4 Jetting Unit
A jetting unit is the most important aspect of a trenching ROV . It determines how good the performance of the vehicle is . If a trenching system can ditch a trench efficiently in a specified time and consistently with same depth of trench , it is considered a successful operation in any project . On average , the pressure provided by the jetting unit is around 10 bar , but the jetting flow differs depending on the type of vehicle . For example , the higher performance vehicles require a higher flow of water . This indicates how fast the jetting is or how deep the trench can be dug .
Figure 3.3.2 : Specific UI for ST216 Trencher system ( jetting activity window ) belong to OMS Group Sdn Bhd made by Perry Slingsby UK . ( Source : Now Forum Energy Technologies UK )
Several aspects to be properly considered while designing a jetting unit , such as depth of trench , width of trench , soil strength to be removed by water jet , and the speed of removal based on the jetting flow .
The designer has to carefully consider the material and strength of the mechanical jetting unit ’ s sword , the hydraulic cylinder for the sword to move up , down , port and starboard , the size of the cavity of the jetting sword , the material and internal shape of the jet nozzles , pump size , etc .
Emphasis on the vehicle ’ s stability is crucial to ensure that the vehicle can travel horizontally while trenching without tilting up at the rear side . Other than providing a few rear facing nozzles aligned at certain angles , some operators put counterbalance weights at the back of the vehicle to counter the tilting moment . This could just be a few blocks of metal or any other heavy material as long as the vehicle can move forward efficiently by the power of the horizontal thrusters . It is also good to have vertical thrusters that can balance the tilting moment in the design .
In most conditions , the jetting sword / arm , will share both water pumps so that should one water pump fail , both jetting swords can still function but with lower performance due to the lower flow . Some vehicles have the ability to control the water flow , and some have a fixed flow . The signal for up , down , port and starboard movement of the sword are provided by linear transducers . A linear
68 VOL 92 OCTOBER-DECEMBER 2022