INGENIEUR
SPECIAL REPORT
Subsea Trenching ROV
Offshore Electrical and Telecommunication Cable Installation Part 2
By Ir . Roslian Efendy bin Syafrial Engineering Manager WS Offshore Pte Ltd , Singapore
Part I of this article appeared in Vol 91 of The Ingenieur ( July-September 2022 ).
3.1 Design Standards
As explained in Table 3 of the Underwater technology DNV-RU-UWT-Part 1 General regulations Chapter 2 Class notations , Edition August 2021 , the underwater type notations for a trenching unit , or sled , are described as underwater working machines and the design is based on Underwater technology DNV-RU-UWT- Pt . 5 Chapter 9 , Underwater working machines and systems Edition August 2021 . Important considerations on the design aspect as required in the document are stated below : a . static test of the lifting points at the working machine with 2.2 times the safe working load SWL ( weight + payload NL of the working machine ), b .
c .
d . static test of the connecting points for the umbilical at the working machine with 2.2 times the maximum permissible tensioning load of the umbilical , components of working machines which are subjected to external pressure should be designed for at least 1.0 × collapse diving pressure CDP , and the lifting points at the working machine should be designed against rupture at eight times the safe working load SWL and shall be clearly signed and marked with their safe working load SWL .
Any sub-component that requires housing , probably formed in a cylindrical or cubical shape , must adhere to following requirements : a . the collapse diving depth CDD [ bar ] is the diving depth decisive for the design of the pressure hull . The collapse diving pressure CDP is the pressure for which the pressure hull will collapse under load
Table 3.1.1 : Safety factors for TDP and CDP related to NDP of unmanned UWT systems [ 14 ].
64 VOL 92 OCTOBER-DECEMBER 2022