Single-Point Mooring System for Open Sea Operation
Authors: Ninomiya Katsuya , Katayama Masatoshi , Ueda Sueki , Uchida Akira 
Published: October 2008

ABSTRACT
Recently, the SPM system for open sea operation is in a trend of being installed in open seas under severer sea and weather conditions from the viewpoints of the use of larger tankers and their installation site. At the same time, for environmental protection of the ocean and security of safety, severer requirements for controlling discharge of contaminated ballast water from tankers into the ocean and for securing safety in the unloading system are being proposed.
Therefore, a series of tank tests and theoretical analyses were performed on a new type of SPM system for open sea operation incorporated with a "hose-pipe system" that was an improved under buoy hose of the conventional SPM system for sheltered areas.
This paper first presents the outline of the above new type of SPM system for open sea operation. Next, for the dynamic response characteristics of the SPM system, the results of the theoretical analyses and tank tests performed on its response characteristics in waves without tanker are reported as well as the results of a systematic computer simulation of the single point slewing motion characteristics with tanker. Finally, described are the results of the tank tests performed on the response characteristics in waves of the under buoy hose (hose-pipe system).

INTRODUCTION
A great number of SPM systems have been constructed and installed in various places all over the world in the past. In particular, with the expanding demand for oil since 1960, a rapid increase in its number is being observed. An approximate yearly average of 20 SPM systems have been constructed in various countries and approximately 300 SPM systems are now in operation. Of those, approximately 80% are installed in shallow sheltered areas less than 40 m water depth in relatively calm sea and weather conditions. In Japan, 23 SPM systems have been so far constructed and installed in shallow sheltered areas of approximately 20-30 m water depth in inland seas and bays.
The SPM system has been developed along with such a rapid increase in oil consumption that required larger tankers as a means of transportation of oil. Consequently, the installation site has been determined from the viewpoint of favorable sea and weather conditions. However, the recent demand for SPM system installation is replacing that in such a great urgency as in 1960's-1970's. Instead, the following new requirements are being proposed :Installation in deeper and open seas in severer sea and weather conditions.From the viewpoints of prevention of ocean pollution and improvement of safety of the SPM system, replacement of oil with sea water in the loading/unloading line while being without tanker (after completion of oil loading/unloading).Treatment of the sea water in the loading/ unloading line.
Under such circumstances, problems have occurred to the conventional type of SPM system that would not be able to deal with them, as it is. Thus, it has become necessary to develop a new SPM system meeting the above requirements and suitable for open seas of medium water depths (approximately 40-90 m) in severe sea and weather conditions.