• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.184-198
• /
• 2020

Decisions of the design speed, MCR, and engine capacity have been empirically made by assuming the value termed the sea margin. Due to ambiguity regarding the effect of some factors on the sea margin, the value has been commonly decided based on experience. To evaluate the value from a new viewpoint, it is necessary to construct an approach to estimate the sea margin through an objective procedure based on a physical and mathematical model. In this paper, a framework to estimate the actual sea margin of an LNGC based on the maneuvering equations of motion is suggested by considering the hull, propeller, rudder, and given sea route under wind and waves. The fouling effect is additionally quantified as the increase of total resistance by considering the re-docking period. The operation data is reviewed to amend the increase of the total resistance considering the speed loss of a ship. Finally, the factor of how much the resistance increases due to fouling is newly obtained for the vessel. Based on the comparison of the estimated sea margin with the empirical range of the sea margin, the constructed framework is regarded as feasible.

• Journal of Korea Port Economic Association
• /
• v.25 no.3
• /
• pp.67-92
• /
• 2009

A tugboat (tug) is a boat that maneuvers vessels by pushing or towing them. Tugs move vessels that should not move themselves alone, such as ships in a crowded harbor or a narrow canal, or those that cannot move themselves, such as barges, disabled ships, or oil platforms. Tugboats are powerful for their size and strongly built, some are ocean-going. Historically tugboats were the first seagoing vessels to receive steam propulsion, freedom from the restraint of the wind, and capability of going in any direction. As such, they were employed in harbors to assist ships in docking and departure. Towage is in essence a service by one vessel to another vessel for a fixed remuneration. The most common reason for requiring this service is the lack of its own motive power. Conventionally, towage is defined as "the employment of one vessel to expedite the voyage of another, when nothing more is required than the accelerating of her progress". Apart from accelerating vessels, acquiring towage service is a common practice for towing barges, platform of drilling oil, floating ship yards, etc.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.7
• /
• pp.1267-1273
• /
• 2022

Although the Korea shipbuilding industry has recently been receiving most of the orders for ships in the world, production processes are being disrupted due to a shortage of manpower at the production site. This is because the workers quit the shipyard as both work and wages were reduced due to the long slump in the shipbuilding industry. The main reason for the increase in orders was the large-scale orders for Qatar LNG carriers, and the situation in which the technical specifications required for ships are becoming more complex is also working to an advantage. Because the contract delivery time is of utmost importance for ships, the dock launch plan is the most important management item among the shipyard's major processes. The structure to be built in the dock may be a hull that has left the design work or a finished vessel, and in some cases, it is often at the level of some blocks of the hull. When launching, the hull is affected by the hogging or sagging moment due to the fluid force, and securing the safety of the structural strength of the block connection is of utmost importance. In a normal process, the connecting member launches after welding has been completed, but in actual shipbuilders, quick decision-making is needed on the conditions for securing structural safety to comply with the docking schedule. In this study, a detailed analysis method and applicability using a bending stress evaluation method and finite element analysis modelling were analyzed to rationally judge the above-mentioned problems from an engineering point of view. The main contents mentioned in the thesis can be used as good examples when conducting similar structural strength evaluations in the future.