The development of a new roller track gravity gate for self-unloader bulk carriers

Abstract

This study is fundamentally relevant to the development of a new enhanced Roller Track Gate (RTG) for the gravity type Self-unloading Bulk Carriers (SULS), called the Multi-functional Roller Track Gate (MRG). Self-unloading Bulk Carriers (SULS) are specialized types of dry bulk carrier vessels, principally because these ships discharge their cargoes without the assistance of external sources. In 1908, the first commercial vessel of these types started trading in the Great Lakes region of North America. Subsequent to the inception of SULS, the technology has developed mainly in the hull structure and onboard unloading systems. Due to the 1980s GL shipping recession, SULS migrated internationally and are now trading worldwide. Eight gravity gates for SULS were investigated in detail prior to designing the MRG. These examinations of previous gates were primarily to address the inherent issues and develop a new gate that would correct the current problems, when discharging dry bulk cargo with the existing gravity gates. The newly designed gate is accompanied with special control system that improves the discharging operations of these type vessels. This gate resulted in being heavier when compared to the existing RTG. However, this study also addresses and mitigates the associated improvements in this new type gate that increases the ship’s lightweight with the possibility of increasing payload / deadweight. High tensile steel was introduced for the hull to compensate for the added gate weight. The steel weight reduction investigation resulted in greater weight than what was required for offsetting the gate weight. The additional weight savings allowed for greater cargo lift for the vessels examined. The economic case study confirmed that by replacing the present Roller Track Gate with the Multi-functional Roller Track Gate, the shipowners’ would benefit from improve discharging performance, less port turn around time and reduced manning cost.