DP Pipe-Laying and Crane Barge: Procedure for Defining Operational Window and Capability Plots Using Dynamic Simulations Available to Purchase

Special station-keeping requirements must be defined for a safe operation of a DP pipe-laying and crane barge. When a pipe is being laid in shallow waters, small displacements of the launching ramp may induce large forces on the pipe or even to deviate it from the defined route. Offshore crane operations are performed in close proximity with other vessel or platform, and large loads are transported in a pendulum configuration. Again, a precise positioning of the barge is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. Due to these special DP requirements, it has been shown in the present work that a simple static analysis of the DP System is not adequate in this case. Dynamic effects related to wind gusts, slow drift forces, propellers response, DP filtering and time-delay must be considered since the initial stages of DP specification. The common approach of considering an amount of 20% extra power to compensate for dynamic effects may underestimate the necessary power. A fully non-linear dynamic simulator was then used to carry out a complete analysis of the barge. Thrust utilization capability plots were obtained for the DP design environmental condition, considering the occurrence of a single failure. After that, an analysis of the environmental conditions in the Brazilian waters was carried out, and a comprehensive set of more than 1700 conditions were obtained. Dynamic simulations were then used to define the operational window of the barge as well as the estimated downtime for each operation. The barge is also able to operate in a DP-mooring assisted mode. The simulations were used to define under which operational and environmental conditions that such mode must be used.