The Kikeh field, owned by Murphy and Petronas Carigali was the first time to use a Spar platform outside of the Gulf of Mexico and also the first time to use a semi-submersible Tender Assist Drilling Unit (TADU) for drilling along a Spar. This paper presents the design and installation aspects of the lashing system of the TADU and the Dry Tree Unit (DTU) Spar for the Kikeh project. The utilization of the TADU in the Kikeh field significantly reduces the weight and cost of the topsides of the Spar and increases the drilling efficiency. In the mean time it has posed a challenging job for the engineers to design the lashing system for the two floaters. This paper will discuss the TADU/DTU concept and benefits along with TADU lashing system design philosophy, design criteria and environment. Different phases of the design process will be discussed in detail, including concept selection, numerical analysis and model test. Several design concepts including the selected design and other alternatives will be explored with pros and cons of each concept explained. Characteristics of the two body motions and lashing tensions will be demonstrated. The selection of the nylon rope and hardware for the lashing system will be discussed. Analysis methodology and modeling of the TADU/DTU lashing system will be discussed. Model test results will be compared with the analytical predictions. Due to the complex nature of the systems and limitation of the analytical tools, model test served as an important tool in the design process. We will show how the results influenced the design of the gangway between the TADU and the DTU. The installation procedures of the TADU mooring and lashing systems will also be presented.

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