Abstract
An investigation has been conducted to quantify the influence of breakwater length on the wave induced motions and associated mooring line and fender loads of a ship at an offshore LNG carrier berth. The motions and mooring loads were assessed against standard limiting criteria to establish the breakwater length that provides safe operational conditions. The study was conducted in two phases. The first phase involved conducting physical model scale experiments in the Australian Maritime College’s Model Test Basin to measure wave forces and moments on the constrained ship for an irregular wave environment with breakwaters of 0, 1.4, 1.9, 2.3 and 2.5 times the ship length. In the second phase the wave forces and moments, berthed ship particulars and mooring arrangement particulars were used as input to numerical simulations to predict the motions of the berthed ship and associated mooring line loads and fender loads. Results are presented for a selected mooring arrangement and an irregular wave environment that represent design conditions at the site. With the exception of sway motion, for intermediate breakwater lengths the berthed ship motions were greater than without a breakwater. However, when the breakwater was extended to 2.5 ship lengths all ship motions were less than those experienced without a breakwater. The fender loads exhibited a similar trend to the berthed ship motions; however a breakwater length of 1.9 ship lengths was sufficient to produce maximum fender loads less than those experienced without a breakwater. With the exception of the spring mooring lines, when the breakwater was extended to 1.9 ship lengths and beyond all maximum mooring line loads were less than those experienced without a breakwater. The study provided important information that can be used to design a breakwater of sufficient length to reduce the likelihood of damage to equipment and/or disruptions to loading operations.