Newcastle's fender forces
Newcastle invested in research to pinpoint pressures on moored ships
Last month's Port Strategy highlighted the importance of fender research, something that Australia's Newcastle port heartily supports. Dave MacIntyre reports
The Port of Newcastle is one of the world's leading coal export ports, and when a new berth was proposed at Walsh Point as well as channel widening and deepening, it collaborated with the Australian Maritime College (AMC), to investigate the forces and motions produced by a passing ship on a vessel already berthed.
The port was conscious that a moving ship generates interactive forces causing the berthed ship to move on its moorings. These motions should be minimised to prevent interruptions to loading/unloading procedures and damage to mooring equipment.Previous studies had identified surge as the most prominent form of ship motion, and the port's response was to stop coal loading and remove the loader heads from the ship while other ships passed. This practice was implemented to eliminate the risk of damage to loader heads due to ship motion.
Seeking more specific conclusions, port chief executive Gary Webb and Jonathan Duffy from the Tasmania-based AMC produced an academic paper "Berthed ship - passing ship interaction: a case study for the Port of Newcastle" which sets out the detail of how the evaluation was conducted.
Specifically the effect of widening and deepening the existing channel and the effect of developing further shipping berths was studied in order to determine whether the proposed changes would exacerbate motions experienced by a capesize ship berthed at Dyke 5 in the Steelworks Channel.
Forces and moments induced on the berthed ship by a passing ship were determined using physical scale model tests in the Model Test Basin at the AMC. Ship models approximately 4m in length were employed, and models of the channel geometry were constructed to a scale ratio of 1:72.5. The water depth within the basin was adjusted to represent that required within the channel.
Stationary ship models, representing berthed ships at Dyke 4 and 5, were constrained in various degrees of freedom.
Readings of the forces and moments produced were used as input to a mathematical model, which accounts for the dynamics of the ship and the mooring line and fender forces, to predict the surge, sway and yaw motions as the moving ship passes the berthed ship.
One outcome from preliminary tests was to confirm that, in general, the forces and moments experienced by the model at Dyke 5 were marginally greater when another capesize ship was located at Dyke 4.
A total of 16 different test conditions were conducted. For each experimental test run the surge, sway force and yaw moment were measured. Once the force for each mooring line was obtained this was resolved into surge force, sway force and yaw moment in a body-fixed axis. These were then summed to give the total forces and moments due to the mooring lines.
The fender reaction was also calculated and the forces measured were used as input to the mathematical model
Conclusions drawn from the study demonstrate the motions of the berthed vessel at Dyke 5 were reduced when the existing Steelworks channel was widened and the lateral separation between berthed and passing vessels was increased.
Deepening the existing Steelworks Channel and increasing both berthed and passing vessel draughts was found to have detrimental impacts on the berthed vessel motion, particularly at a speed of 4 knots.
The widened and deepened channel configuration with increased vessel separation and draughts produced marginally greater yaw motion than the existing configuration at a passing vessel speed of 3 knots and a more significant increase in surge motion at a speed of 4 knots.
These findings have subsequently become an integral part of the ongoing planning and development process for the Port of Newcastle.
Since then the port has also been modelled on the Ship Handling Simulator at the AMC, which has been used to assist in the evaluation of dredging requirements, channel/basin design and to establish safe environmental operating conditions. The marine pilots from the port have contributed to this study and are also using it as a useful training exercise.
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