Deliberations between the Dutch and the Indonesian governments led to the organization of the Snellius-II Expedition, which took place in 1984 and 1985 in Indonesian territories. The Netherlands Council Oceanic Research (NRZ) is the Dutch coordinating agency. Cooperation between the Free University of Amsterdam and Furgo BV personnel led to the development of a Geotechnical Project, as part of the NRZ's scientific programme, to be included on one of the geological cruises in the eastern Banda Sea. This region is the location of three active plate boundaries and offered a unique opportunity for geotechnical investigations. Previous studies in other active margin areas had showed the influence of tectonic forces on the consolidation (dewatering) of the sediments (Carson, 1977). Excess pore-water pressures were through to play an important role in these processes (von Huene and Lee, 1982). To derive in situ information on pore pressures, and to provide in situ shear strength data for comparison with laboratory data obtained from piston cores, and automated piezocone probe system, called the Sealion, was conceived. This was part of the spin-off from the feasibility study for the Deep Ocean Research Apparatus (DORA) (Richards, 1985) and partly from other corporate research and development. The development and testing of the Sealion (Table 1) in late 1984 and early 1985 for the NRZ is the subject of this chapter.
The initial design of the Sealion was influenced by three principal factors:
the environmental conditions,
the ship's handling capabilities, and
the engineering requirements. The maximum water depth in which the Sealion would be deployed was fixed at 6000 m. at this depth, the experience of the Netherlands Institute for Sea Research was that it was impractical to use an electromechanical Kevlar (aramid fibre) cable because the wires broke prematurely when the cable was tensioned. Only a purely mechanical Kevlar would be available on the NRZ ship, the Tyro This restraint required the design of a fully automated machine without direct control from the surface.
The Sealion would be designed having the capability
of establishing its degree of inclination on the seabed,
of automatically penetrating and retracting, and
of storing data in a solid-state recorder attached to the frame. The Sealion would so be capable of acoustically notifying the ship in which mode it was operating. Using these design criteria, the following list of basic elements was formulated.
Mechanical elements: frame, drive unit and powerpack (power supply and pump unit).
Electronic elements: control and data storage unit, acoustic transmitter, piezocone, inclinometers and penetration sensor.
Those elements having less common usage in geotechnical ocean engineering are emphasized in this chapter.
This ship's hoisting capabilities and deck space confined the base dimensions of the Sealion to 2.4 X 2.4 m and the maximum weight to about 1000 kg when submerged in seawater. A desire for a penetration depth of 5 m necessitated a frame height of about 6m for the intended configuration.