AN INNOVATIVE TRAILING SUCTION HOPPER DREDGER WITH AFT-CENTER DRAG SYSTEM AND A WIDE SPAN DRAG-HEAD

摘要

The new "Seiryu-maru" is a highly advanced multifunctional high-capability trailing suction hopper dredger with an oil recovery system. She is capable of three major functions: dredging of environmentally-friendly leveled dredging by thin layers; oil recovery - capable of handling low- to high-viscosity oil in the open sea, and accident control - prompt response in the event of an disaster such as large-scaled oil spill and earthquake, etc.The vessel was ordered by the Chubu Regional Bureau of the Ministry of Land, Infrastructure and Transport (MLIT) of Japan and completed in March 31, 2005. Since then, she has been engaged in dredging work in Nagoya Port in Japan.She has replaced the first-generation "Seiryu-maru", which was a very conventional trailing suction hopper dredger with drag-arms on both sides. The new "Seiryu-maru", however, has been completely changed from the old one in design but keeping the capacity of the mud hold unchanged. She is an outstanding vessel unparalleled in the world with regard to her basic concept of dredging systems. The dredging system is based on adoption of the world's largest-class wide span drag-head 7.2 m in width which permits high accuracy in leveled dredging without left-over, excessive or stripe dredging; while the old "Seiryu-maru" adopted the conventional drag-heads of 2.0 m width. Adoption of the ultra-wide drag head has resulted in a hull layout that accommodates a drag-ladder at the aft center of the vessel, a so called aft-center draghead system. In actual dredging operations in Nagoya Port, highly accurate dredging with a high mud concentration has been realized.This paper shall present the results of comparison study in dredging efficiency between the old and the new "Seiryu-maru", namely conventional side drag system versus aft-center drag system, based upon the measured data of dredging production, dredging cycle time and dredged bottom surface during the dredging trial. The finding was that the total dredging efficiency of the new dredging system achieved a level abt.35% higher than the old one.