Mooring of a Floating Container Terminal
 
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Mooring of the terminal
 

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MCA

Dolphin types

Mooring forces

Arrangement

Installation

A number of possible concepts for mooring the terminal has been identified. The task now is to determine which concept is most suited for the floating container terminal. To determine this, a multicriteria analysis (MCA) has been carried out. In this analysis the concepts have been evaluated using a set of criteria. As can be seen in the MCA, the concepts with the internal turret and the single buoy mooring have not been evaluated. Since the floating terminal will have a bridge connection to shore, it is not allowed to change heading (or weathervane). The internal turret and single buoy concepts are both used for weathervaning constructions and are therefore not suited for mooring the terminal.

 

MCA (Multi Criteria Analysis)

The concepts have been compared using a number of criteria. Since not every criterium is equally important in the final decision, weighing factors have been assigned to every criterium. This finally leads to an overall score of the concept. The dolphin concept turns out te be most favourable for mooring the floating container terminal.

(click on the criteria in the legenda for further explanation)

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Dolphin types

There are four types of dolphins, each with its own advantages and disadvantages. In previous studies, the four types have been compared on four different criteria. The four types and their scores on aspects as reliability, construction, maintenance and usage are mentioned here.

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Mooring forces

The forces acting on the floating terminal are transferred to the mooring dolphins by fenders. The maximum fender reaction is 2300 kN. The number of fenders needed to support the FCT can now be calculated from the environmental conditions and forces. The maximum force acting on the FCT in transverse direction is 15,500 kN indicating a minimal number of 7 fenders. For redundancy a safety factor of 1.4 is applied. Thus 10 fenders are needed in transverse direction. The maximum force acting on the FCT in longitudinal direction is 6000 kN, demanding 4 fenders when including the safety factor.

The number of fenders per mooring dolphin is determined by minimizing the total steel weight of the dolphins. Previous studies indicate the two-fender dolphin minimizes the total weight of the steel structure. With a two fenders per dolphin the number of dolphins in the transverse direction becomes 5. For the longitudinal direction the number of dolphins is 2.

 

Ship mooring alongside

As mentioned, the terminal will have to withstand a "rough" mooring of a containership. The model described in the Terminal -> Forces section results in a speed of both terminal and vessel of 0.21 m/s. The kinetic energy of these masses will have to be absorbed by the dolphin's fenders. The fenders installed on the dolphin are assumed to be one of the largest available, with a diameter of 2 meters. With a design deflection of the fenders of 50%, this results in a design deflection of 1 meter. Within this distance, the fenders will have to absorb the total kinetic energy of both the terminal and the moored vessel. A simple energy conservation calculation results in a required stiffness of the fenders of 1585 kN/m. The total force on the dolphins in this worst case scenario turns out to be 15,850 kN; approximately the same force acting on the terminal during a typhoon. Thus the maximum force on the fenders is marginally higher than the before assumed 15,500 kN. But it must be stated that the method used does not take into account the row of fenders between ship and terminal. Furthermore, a safety factor is included in the fender reaction forces and in the dolphin strenght. Therefore, there is no need to adjust the number of fenders determined before.

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Arrangement

The general arrangement is made with two dolphin types to get the best results. In longtitudinal direction, five dolphins are needed which are placed over the length of the FCT. For these dolphins Type A is chosen because the entire construction is installed below maindeck and will not interfere with terminal cranes and others. In transverse direction on the far end of the terminal, two type B dolphins will be installed. These are easy to install and, because they are located at the end of the terminal, will not interfere with terminal traffic. The picture shows a 3D-model of the type B dolphins located at the end of the terminal.

A cross section of the floating terminal at a dolphin location is shown below

The pictures below show a topview and a side view of the terminal's mooring dolphins arrangement

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Installation

The installation can be done with a crane vessel which can place the dolphins on the harbour (sea) bottom. When all the dolphins are installed the floating terminal structure will be sailed in, at high water, and placed on his designated position. After placing the container terminal, the fenders will be placed and the terminal will be well secured.

 

 

 

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