Analysis method and the related computer program to predict the towing condition of a towed vessel using multiple tugboats and pushers

Abstract

When towing a disabled vessel using one or multiple tugboats and/or pushers, it is important to estimate the direction and speed of the towed vessel, and the towing forces of tugboats and/or pushers each. This paper studies the prediction methods of hull resistance in calm water and added resistance due to external forces, that is, wave, wind, drifting, hull roughness, propeller locking and shallow water effect for the towed vessel. Although it is good to use the value of a model test results for hull resistance in calm water, as it takes a lot of cost and time, statistical analysis method was used. Various empirical methods including KRISO regression formulae were adopted to predict the hull resistance in calm water. For added resistance due to external forces, ISO 15016:2002 method was adopted for the added resistance due to waves, JTTC and Blendermann Chart were done for the added resistance due to wind, SR208 and KRISO method were done for the added resistance due to drifting, ITTC-78 method was done for the added resistance due to hull surface roughness, USCG Towing Manual method was done for the added resistance due to propeller locking, and Lackenby method was done for the speed loss due to shallow water effect. Also, in this paper, the towing position, direction and force of tugboats and/or pushers were defined, whereby how to calculate the towing force and yawing moment on the towed vessel was established. And then, by finding out the state where the sum of towing force of the forward direction of tugboats and/or pushers and the whole resistance of the towed vessel become the same, and the stable state where the sum of the yawing moment of tugboats and/or pushers becomes 0, the method of estimating the forward direction and velocity of the towed vessel was established. All of these analysis methods were made into a computer program, and especially by providing GUI environments, they were made easy for users to use. If the program developed through this paper is used, it is considered that the situation of towing the disabled vessel could be quickly and exactly simulated in advance in the real salvage site.