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Summary
The thesis presented here aims to contribute to the knowledge and understanding of the application of separation of functions of the Trailing Suction Hopper Dredger (abbr.: TSHD). Separation of functions is defined as the separation of the storage and transportation functions from the other functions of the dredging cycle of the TSHD. Normally the dredging cycle of the TSHD consists of sailing to the dredge site, dredging, sailing to the unload site and unloading. When separation of functions is applied, a barge can perform the storage and transportation functions. This can be achieved by the offshore transfer of the material that the TSHD pumps up from the seabed and loading it into the barge; subsequently the barge can sail back and forth to the unloading area and deliver the dredged material.
Separation of functions can be applied for two main reasons: either to increase production or to decrease production cost. Production is increased because when separation of function is applied, the utilization of the dredging installation is increased, because no time has to be “wasted” on transportation of the material by the TSHD. Production costs are decreased because when separation of functions is applied, the same production can be achieved with smaller, cheaper, equipment or more production can be achieved by the same equipment with relatively less costs.
In order to successfully research the dredging process of the trailing suction hopper dredger, when separation of functions is applied and when it is not, a computer model is built. This model is defined using the dredging cycle of the TSHD and barges. This is done for the case that the functions are separated and not, as well as the case called “intermediate separation of functions” in which both the TSHD and barges sail between dredging and unloading location. The aim of the computer model is to create an experimental environment that can be used to investigate this logistic system. In the computer model, several different scenarios can be run to appraise the applicability of separation of functions on these scenarios. Using the model, several scenarios are researched. For each run of the model, besides the time each piece of equipment spends in each state, i.e. sail, wait, transfer, dredge (TSHD only) and unload, also the total volume of produced dredged material was measured. After the model is run, the costs per cubic meter of dredged material is calculated, which is one of the most important benchmarks in the dredging industry. It can be concluded that separation of functions as it is applied to dredging projects in the Persian Gulf can also be successfully applied to other projects in other regions of the world, namely for the land reclamation of the Maasvlakte 2 in the North Sea and for dredging marine phosphates off the coast of Namibia. Considering costs, and when sailing distances are small, the results shown a slight increase in cost. But when sailing distances are large, the results show a dramatic decrease in costs. When production
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is considered, separation of functions or intermediate separation of functions is in almost all cases of positive influence to the amount of produced material.
It is recommended to research what the effect on the value of the dredger would be, and therefore effects on costs for depreciation and interest as well as maintenance and repairs, when an entire new dredging vessel would be designed which would also be able to perform the dredging functions of the TSHD when separation of function is applied, but none or smaller installations are provided for propulsion and storage of the dredged material.
Another important recommendation is to take another look at the design of the installation used for offshore transfer of the dredged material between dredger and barge in order to improve the capability the dredger for transferring dredged material in offshore conditions. This could dramatically improve performance of the separation of functions concept.
Finally, it is recommended to investigate and measure all the critical decision factors which influence the decision of the dredging contractor to apply (intermediate) separation of functions to its dredging operations and prepare its dredging fleet to this task.
