Allseas’ mechanical trenching machine Digging Donald is a fully remote-controlled and diverless trencher that never touches the pipeline. The machine is operated from Allseas’ dynamically positioned trenching support vessels. Digging Donald creates a V-shaped trench underneath the pipeline using mechanical digging arms and multi-pass jetting. The pipeline gradually sinks into the trench behind the machine.
Digging Donald can operate in water depths up to 450 m and is capable of trenching all types of sedimentary soils from loose to dense sand and very soft to hard clay, as well as specific rock types. The machine has been deployed to trench more than 4000 km of pipeline worldwide. Mechanical trenching, up to 42” diameter, and jetting, up to 48” diameter, can be performed individually or simultaneously. Other trenching operations are possible, such as second pass jetting, backfilling, free span correction or exposing buried objects.
Remotely operated vehicles (ROVs)
Allseas has a comprehensive range of deepwater remotely operated vehicles (ROVs) with the latest high-specification sensors and equipment. ROVs are deployed from Allseas’ vessels to assist with various underwater tasks such as surveys, inspections and maintenance of pipelines and subsea structures. Prior to pipelay, a survey is conducted by an ROV which is operated from a survey vessel and equipped with sensors, cameras and sonar equipment. The ROV transmits information to the survey vessel via an umbilical cable. Results are used to immediately identify possible pipeline hazards such as wrecks, obstacles and seabed unevenness.
ROVs also provide seabed touch down point monitoring and subsea construction support. As soon as the pipeline has been laid, it will be subjected to a ROV inspection. This post-lay survey defines the accurate position of the pipeline, the pipe-seabed configuration and the external status of the pipe. The as-laid results are used determine the need for post-lay intervention works, such as span correction or rock dumping. In case all post-lay intervention works are complete, an as-built survey is performed. The as-built survey defines the final status of the pipeline and the post-lay intervention works.
Mattress installation frame
Where two pipelines have to cross over each other, the pipeline crossing has to be protected. Protection is provided by mattresses, which consist of concrete blocks connected by steel or synthetic rope material. Allseas’ support vessels are able to install concrete mattresses using her remotely controlled subsea installation frame and her ROV-operated mattress installation frame.