Semi-submersible pipelaying craft equipped for laying pipes on sea beds, including deep beds, and the method of operation

A semi-submersible pipelaying craft equipped with the following means for launching and laying pipes, including at great depth and under hostile environment conditions, comprising:

• (a) an articulated or composite launching ramp including an inner fixed inclined ramp, an intermediate internal inclinable ramp hinged to the fixed ramp, and an outer inclinable external ramp hinged to the internal ramp;
• (b) means operatively connected to the craft and the internal ramp for connecting the internal ramp to the craft and for moving and locking the internal ramp for navigation of the craft and launching and laying pipe, and in hostile environmental conditions;
• (c) means operatively connected to the craft and the external ramp for connecting the external ramp to the craft and for moving and locking the external ramp for navigation of the craft and launching and laying pipe, and in hostile environmental conditions;
• (d) a horizontal swivel assembly on the craft and adjacent the fixed inclined ramp for aligning, with the pipe being laid, the pipe portions to be welded thereto, and for bringing said pipe portions up to the pipe being laid;
• (e) an assembly of rocker cradles and tensioning devices on the fixed ramp for supporting and conveying pipe to be laid from the swivel assembly to the internal ramp;
• (f) an assembly of rocker cradles on the internal ramp for supporting and conveying pipe to be laid from the fixed ramp to the external ramp;
• (g) an assembly of rocker cradles on the external ramp for supporting and conveying pipe to be laid from the internal ramp to the sea side of the external ramp;
• (h) a system on the craft for unloading the pipes from the supply craft and for storing them and bringing them up to the swivel assembly;
• (i) an electronic control system on the craft which processes the data received from the various sensors and compares it with the programmed data for the laying operations, in order to impose on the pipelaying craft an optimum automatic dynamic positioning so that even under hostile environmental conditions, the pipe lays on the sea bed along the required trajectory, even at great depth;
• and
• (j) means operatively connected to the craft for controlling the peak loads on the pipe laying system which can occur during the pipe laying operation.