A radical solution by Stolt Comex Seaway led to the creation of the surf zone coring and construction system - Surf Rider.
Drilling the seabed in search of geotechnical information in the volatile surf zone is a daunting and difficult task. Faced with the necessity of obtaining surf zone geotechnical data in the Oakajee Deepwater Port project in Western Australia, Stolt Comex Seaway (SCS) developed a surf zone core sampling system that can withstand the rough conditions.
In late 1997, SCS conducted geotechnical coring operations using a subsea coring rig and air divers, but was unable to reach critical areas of the bay due to shallow water and large surf. SCS's ultimate system is self contained, mobile over variable terrain, and able to withstand breaking waves in water depths up to four meters. The system is known as the Surf Zone Mobile Drill Rig (MDR).
The MDR is a 63-ton marinized Liebherr excavator, upon which is mounted a column and work platform for the performance of a wide variety of shallow water tasks. The power pack for the vehicle is mounted on the platform to deliver power to the tracks and excavator bucket. The operator can maneuver the vehicle from the drivers' station or from an elevated location on the work platform.
During operations in November 1998 to January 1999, the MDR was used to drill nine core holes to a depth of 25 meters below the seabed. The MDR performed this work in up to 3.5 meters water depth and reached distances of 200 meters offshore, enduring days of harsh treatment in the surf zone. During this time, drilling operations progressed from high above the surf.
Vehicle stability was naturally the most critical issue in design and was compounded by lack of visibility in white water and liquefaction of the seabed by the washing-machine action of the waves at shorebreak. Application of operational limits on vehicle inclination and judicial use of in-water diving support provided the operator with feedback during repositioning of the MDR. In addition to this, the presence of the excavator's arm and bucket was a significant tool in maintaining vehicle stability.
The vehicle is currently stationed on Varanus Island in the Northwest of Australia waiting to commence a pipeline stabilization task in the tidal and surf zone. With other uses, such as a shallow water crane, trenching machine, piling tool, as well as a drilling and grouting platform, the "Surf Rider" vehicle is proving to be a useful tool for shallow water construction.
