The International Maritime Organisation (IMO) is a specialized agency responsible for the safety and security of shipping and the prevention of marine and atmospheric pollution by ships. Air pollution is one of the contributors, CO2 emission is recognised as the biggest contributor to the increasing temperature of the Earth. Global warming is a controversial topic and actions are taken to reduce further rising of the temperature on Earth. The IMO has set limits for vessels on the emission of NOx and SOx. Currently, the IMO is negotiating on how to limit the emissions of CO2 to reach a reduction of 50% in comparison to 2008. The purpose of this research is to provide an emission model for TSHDs showing an emission profile (CO2, SOx and NOx) per cycle of operations, and present emission reduction methods. Within the emission model there are eight main parts that are connected and create the results. The results are shown per cycle of operation and are calculated per phase. The six main phases of a cycle of operation are: Loading, transit loaded, connecting, discharge, disconnecting and transit empty. The first part of the emission model determines the hull resistance. The second part consist of the trailing resistance. This part is split up into three more detailed segments: the calculations for the cutting force, cutting depth and trailing force. The trailing and hull resistance together form the total resistance within the loading phase. For the transit phases, only the hull resistance is used for the total resistance. With the total resistance known, the propeller is matched to the main engine in the third part. The fuel consumption and emitted emissions are calculated in the fourth and fifth part. The power requirement for the other engines, pumps and auxiliary equipment are calculated in part 6th through 8th. For each job, specific input is required for the calculations. Combining this input and the calculation parts, the emissions, fuel consumption and fuel cost are given per dredged m3.
Five methods to reduce the emissions for TSHDs are researched. First, the type of power arrangement is researched. A mechanical power arrangement with a combined drive and a direct drive, an electrical power arrangement and a hybrid power arrangement are investigated. The variations of power arrangements are implemented on the Dodge Island. Second, the difference between a fixed (FPP) and controllable pitch propeller (CPP) is researched. Most modern day TSHDs use a CPP, as the efficiency during the wide variation of operating conditions is greater than a FPP. The third method to reduce the emissions is to find the optimal loading speed. The optimal speed is researched for a floating visor and a fixed visor. The most common solutions to comply to the limit of the SOx emission is using ultra low sulfur diesel or installing a scrubber. The fourth reduction method is focussed on the use of scrubbers. The most used types of scrubber are the dry, open loop, closed loop and hybrid scrubber. The last method to reduce the emissions is shutting off the engines when not in use. The trade-off is the wear of the engine. To verify the results of the emission model, the fuel consumption of multiple completed jobs is compared with the predictions of the emission model.

Great Lakes Dredge & Dock (GLDD) is one of the biggest dredging companies in the USA which provides engineering services in dredging and land reclamation. GLDD came up with an idea to develop a working model that can estimate spillage when using a cutter suction dredger (CSD) for cutting soft material like sand. The main reason for this is because not every material that is cut from the seabed contributes to production. A part of the material is lost since it doesn’t enter the suction mouth and contributes to spillage. Spillage can be defined in a number of ways. GLDD defines spillage as “the difference in elevation between the maximum depth at which the dredge cuts (cutting depth) and the depth obtained after dredging (after dredging depth)”. Theoretically, spillage is defined as “the material that is displaced from the seabed which does not enter the suction pipe and thus does not contribute to production”. The aim of this thesis is to identify and describe the types of spillage that occur while dredging soft material like sand and to use this information to create a numerical model that estimates spillage. Four types of spillage are found, namely; soil that disintegrates and is directed away from the cutter head (Type-1), soil that enters the cutter head but not the suction mouth (Type-2), soil that does not enter the cutter head when cutting large bank heights (Type-3) and breaching of the bank after the cutter head has passed (Type-4). The numerical model focuses only on Type-2 spillage. The foundation of the model is based on the theory that the cutter head of a CSD behaves like a combination of an axial and centrifugal pump with an inflow present near the nose and an outflow present near the cutter ring. For simplicity, the cutter head is divided into two slices with the top slice (2) having an inflow and the bottom slice (1) having an outflow. It is assumed that the outflow from the bottom slice circulates back to the top slice and re-enters the cutter head. Equations for pressure and flow are derived from the pump affinity laws for each slice. A constant, β, is a parameter that influences the flow and an initial value is assumed which is later calibrated. Using the concept of the continuity equation, an implicit equation for the height of the bottom slice (w1) is found. In the model, spillage percentage is defined as the ratio of the circulating flow to the total outgoing flow. Real life data from The Texas (GLDD) is used in the model. The constant β is calibrated using spillage values obtained from hydrographic surveys. Sensitivity analyses are performed on the various operational parameters of the dredge as well as on β. To study the influence of β on the relationship between the operational parameters and spillage, a number of β-values are used to plot data. For the validation of the model, the spillage value obtained from the model is compared with the spillage values obtained from the hydrographic surveys. As the spillage is in close proximation with values observed in the industry, the model is said to be working as intended. In order to further validate the model, the results obtained from the model are compared with the results obtained from experiments performed by Marco den Burger and the results are almost similar. Thus, it can be concluded that although the model is simple, it is able to provide realistic values of spillage.