Numerical analysis of an over-boarding operation for a subsea template

Abstract

Subsea templates are normally transported to the installation site on the deck of a crane vessel. After being lifted off from the deck, the template is 1) over-boarded from the initial location to the target position by the side of the vessel; 2) lowered through the splash zone; 3) further lowered down to the seabed and 4) finally positioned and landed. All the mentioned phases should be evaluated. Usually, the splash zone crossing phase is taken as the critical phase and analyzed to define the installation weather criterion. The over-boarding phase has not been the focus of analysis due to a large involvement of human actions and little involvement of hydrodynamic effects. During offshore operations, the offshore manager may decide to decrease the defined installation weather criterion if the risk of the personnel safety on deck during over-boarding phase is considered high. Thus, it is of great need to quantify the operational criterion for such operation. The objective of this paper is to perform numerical analyses and define the allowable sea states for a safe over-boarding operation. The numerical analyses using time-domain simulations have been performed in various sea states. Tugger lines have been modelled to control the motions of the template during the operation. The pendulum motions of the subsea template are considered as the critical responses for the assessment of the allowable sea states.

Keywords

• Over-boarding
• Subsea template installation
• Tugger lines
• Allowable sea states
• Pendulum motion