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The analysis and redesign of a ship cradle

Leede, M de (2016) The analysis and redesign of a ship cradle.

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Abstract:The goal of this research was to see if the existing cradles could be improved on storage space, floor space and cost. After a cost analysis the goal seemed not to be economically viable, so the goal had to be redefined in order for the research to be useful for DAMEN. The new research goal became; to find a better solution for the cradle for all DAMEN's future vessels. In order to do this the research was divided in three phases; a preliminary phase where the old methods and the basics of a cradle were researched, a conceptual phase where solutions were generated and formed into concepts and finally a final concept was chosen and the detailed phase were final concept was optimized and sketched as a first impression. In the preliminary phase the functions of the cradle were researched first. The most important functions of a cradle were; Fixation of the vessel in x- and y- direction, fixation of the vessel in z-rotation and creating extra room for the multi wheeler and workers. After that the methods DAMEN uses to move the cradles were researched. Together three different types of methods were found caused by the ship type dependency. The same dependency was true for the cradles which result in a huge stock of cradles at DSSi. And finally an analytical analysis was introduced to get an understanding of how loads on the structure work. This was a simplified model that views the cradle as v-shape with supporting beams on the side standing on a cradle bed. The analysis showed that the critical failure mode was bending in the cradle bed and side beams. In the conceptual phase the function defined in the preliminary phase were used to generate solutions. These solutions were then mixed together to form five different concepts. The first concept was a LEGO solution that uses basic modules to assemble a cradle for a random ship type. The second concept was a cradle bed with on top two adjustable modules. This concept was tested on two different types of supports; the keel support and the bulk head support. In all cases the keel support was worse than the bulkhead support, so the keel support was not researched any further. The third concept started with an unmodified modified cradle and had elongations on each side. Two different options have been researched and in the end the framework was the best option. The fourth concept was a sling concept where the ship lays in a sling that was supported by two pinned adjustable beams. The cradle bed was the same as concept II. The last concept was the use of the old cradles on the new ship types. This seemed even after minor adjustments not very feasible. Finally a mix between concept I and concept IV has been chosen as the final concept due to the best combined properties. In the last phase the front and rear cradle was further tweaked for a FF 3808 vessel. These analyses showed that both the front cradle as the rear cradle could improve if the modules were moved more to the stool support, but have an optimum before it reaches the stool support. The profiles have also been researched in this phase and according to the analysis the I-beam is the best to use in this situation. The rectangular beam is the best option for the adjustable beams because the I-beam is not possible over there. In overall this report showed that there are solutions that are lighter, interchangeable and less spacial than the solution used at the moment. Though the model that is used is very limited and can only show which solution is better and can not be used to deliver an end result. For that further research is needed in the form of a FEM analysis. This analysis can also be used to further optimize the weight of the cradle. Another solution that came up during the end presentation was to connect the adjustable beam to the lifting hooks instead of using a sling. This will not only positively effect the stability but will also remove any change of slicing of the sling, which could happen when a ship drops to hard in the sling. So far the feasibility of the concept has not been researched yet, but the advantages of this possible outcome makes it worthwhile for future research.
Item Type:Essay (Master)
Damen Schipyards, Singapore
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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