Publish and Present
More and larger Post Panamax container ships have visited PortMiami after the deepening of the entrance channel and the addition of the new locks in the Panama Canal. This trend is expected to continue. These wider and deeper draft ships squat more. This is particularly relevant in Miami as ships need to enter the channel on arrival with a speed of approximately 12 knots to maneuver in strong and varying cross-currents due to the Gulf Stream that are prevalent near the channel entrance. This speed is maintained in the outer end of the channel, where bank effects cause it to squat deeper in the water.
PortMiami tasked consultant Atkins North America, Inc., to retain the services of W.F. Baird & Associates, Ltd., to study the projected squats of container ships currently operating at the port. As part of the study, squat was measured during arrival channel transits of 17 Post Panamax container ships. Gulf Stream and tidal currents were measured simultaneously during nine transits. The squat and current measurements were used to calibrate and validate the numerical model for squat and wave response, Wavescat. The model was calibrated to include counter-currents and to represent increased squat at the stern due to propeller wash effects.
The simulated squat corresponds well to the measurements. Squat is generally larger for wider ships. However, hull shape is critical and particularly affects the dynamic trim angle. Container ships with fine bow shapes squat bow down, while fuller shaped ships squat stern down.
The calibrated model was subsequently used to develop an underkeel clearance forecasting application. The application includes computation of all underkeel clearance components, squat, heel (due to turning and wind) and wave response. Five Post Panamax container ships are included in the application with capacities ranging from 5,700 TEU to 13,800 TEU.