The presented paper covers essential aspects and requirements for offshore loading systems. Response characteristics of typical concepts and associated design forces for the mooring and anchoring systems will be discussed. The need for model tests compared to anchoring and mooring systems in respect to strength and durability. The governing factors for the lifting efficiency including operational limitations with respect to weather conditions are considered. The paper concludes with some considerations from the certification point of view. Introduction Offshore loading systems for the initial temporary or permanent solution to the transportation of production to the shore is receiving increasing attention from operators in the North Sea. Offshore loading of oil as such is well known to the Industry, however, sufficient experience from hostile environments like the North Sea hardly exists. The few systems operating in the North Sea must be regarded as prototype and the next generation of offshore loading units now being developed will be able to incorporate a number of the valuable lessons learned. Reliability and efficiency are key words in selection of the most suitable system and this paper will focus on a number of engineering aspects of importance in this context. Figures and tables are purposely made in a schematic and general format to indicate the tendency rather than actual measured or calculated values. Articulated buoyant towers without storage capacity and large volume floating anchored storage vessels will be the main types of offshore loading systems discussed in this paper as there appears to be a tendency in the industry towards these types of concepts. A number of refined concepts utilizing one shuttle and one storage tanker whereby the latter is remotely connected to the buoy in different ways, articulated towers with two universal joints, one semisubmersible, etc., are proposed or even in use, but will not be subject to detailed comments here, as this is regarded as being outside the scope of this paper. Concepts The general concept which has proven successful for offshore loading is the single point mooring (SPM) idea. The tanker is moored with bowlines to a single point only, allowing the vessel to rotate freely (weathervane) around the buoy. The different developments may be divided into two main groups on the basis of the type of fixation used; CALM and SALM (see fig. 1). The catenary anchor leg mooring buoys (CALM) are the most commonly used offshore loading system. The simplest and most widely used being the single buoy mooring buoy (SBM).
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