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In the face of developments in maritime transportation due to globalization, ports are tending toward new tugboat investments in order to respond to the increasing demand. Due to the high costs of tugboats, organizations may face high investment costs. It is important to determine the most suitable number of tugboats, considering the variables in a port area where towage services will be provided. In this study, a simulation model was developed to determine sufficient tugboat allocation according to some variables in ports. The simulation model was subjected to various experiments, and statistical analyses of the obtained results were performed. The relationships between the variables affecting the level of towage service were revealed. [ABSTRACT FROM AUTHOR]

In order to study the construction technology applicable to the floating transportation of immersed tubes in the Dalian Bay Subsea Tunnel, combined with the meteorological and hydrological conditions of the Dalian Bay and the channel characteristics of the floating, the towing effect of different tugboat combinations under different conditions was tested through the immersed tube floating drills. Based on the test data and effect analysis of floating drift, base groove steading ship, steering operation and emergency disposal, the optimal towing technology of immersed tube for Dalian Bay Subsea Tunnel was established. This technology has been successfully applied in the floating construction of 18 immersed tubes in the Dalian Bay Subsea Tunnel, effectively controlling the average drift value of immersed tubes’ floating transportation to be less than 5 m, and the maximum drift value to be less than 25 m, which greatly improves the technical and economic benefits of immersed tubes floating transportation and ensures the controllable safety risk. [ABSTRACT FROM AUTHOR]

The common practice in world-wide ports is that they have determined procedures regarding number of required tugs depending usually on most important factors such as weather criteria and size of vessel. This article presents various rules for some ports which is defined in their Safety Management System and criteria in choosing optimum number of tugs and optimum bollard pull. It is also described how various towage requirements can be assessed through the use of maritime simulators and which parameters are important and how the same can be obtained and assessed. General guidelines will also be defined in the article which must be taken into consideration for optimal choosing of tug boats. The science method used in this article is known as comparative analyses between computation and simulation on simulator; results are presented in figure 10. [ABSTRACT FROM AUTHOR]

The synthetic fiber ropes are commonly employed as the main material for the towing line to connect the towed ship and tug boat. The diversity of material e.g. polyester, aramid, and HMPE could impact the behavior of towing system and lead the instability of towed ship. Following the practical method previously proposed for the towing system analysis, authors aim to present a numerical model to properly take into account the characteristics of fiber ropes into the towing system. Specially, the dynamic stiffness of fiber ropes which is determined according to the mean load of the towing line is considered when solving the governing equations in the time domain. A detailed iteration procedure for the calculation of dynamic stiffness is described. The performance of dynamic yaw and lateral offset of towed ship under various wind speeds are discussed. The effect of various types of fiber ropes for the towing line and the initial length is also investigated thoroughly. Results of case study show that diverse material characteristics could influence the ship's directional stability significantly. The shorter towing line and stronger wind can reduce the fishtailing effect of the towed ship while the longer towing line would make the motion period larger. • Three types of synthetic fiber ropes are studied in the towing operation. • The dynamic stiffness considering mean load is employed in the numerical model. • Dynamic towing analyses are performed to study the ship behavior under wind loads. • The impacts of material diversity, towing line length, dynamic stiffness and wind speed are discussed. [ABSTRACT FROM AUTHOR]

Amphibious tractors are capable of towing loads over land and water, which will save time effectively and reduce the cost of transport between water and land. Due to their smaller displacement and more fragile stability, the hydrodynamic characteristics of amphibious tractors are quite different from those of tugboats. The towing position will significantly impact the attitude and resistance characteristics of the vehicle. In this paper, the towing position of a light amphibious tractor is thoroughly investigated, in order to improve hydrodynamic characteristics and reduce energy consumption of vehicles. First of all, the towing force effect is researched based on the force equilibrium model. Secondly, a numerical model is established referring to the Reynolds Averaged Navier-Stokes method, which is validated by towing experiments. Moreover, various towing position forms are evaluated to research the towing effects and working principles. Eventually, a coupled model of pitch and heave motion is established to investigate the dynamic response in the longitudinal plane. Results indicate that towing positions at the rear of the vehicle, combined with low height, are conducive to the hydrodynamic performance of amphibious tractors. • The hydrodynamic characteristic of an amphibious tractor is investigated. • The effects of longitudinal and vertical towing positions are studied. • Towing force position significantly affects the resistance, trim, and stability. • Lowing the towing position can improve the trim and resistance characteristics. • Setting the towing force at the rear can improve the initial stability and seakeeping. [ABSTRACT FROM AUTHOR]

An escort tugboat comes to the aid of a vessel when that vessel is navigating in confined waters and at a speed that is usually higher than six knots. In the escort manoeuvre, two systems come into play. One is the propulsion and steering of the vessel. The other involves the tug winch in terms of the tension it exerts and the length of towline released. In this way, the tug winch becomes a key piece of equipment. Along with the difficulties of carrying out the manoeuvre itself are the risks resulting from the operation of the winch. For this reason, automatic manoeuvring systems have been developed to facilitate this operation. They consist of information technology applications that help the skipper with manoeuvring the tug. At the same time, they make it possible to display and monitor the most important parameters of the towing winch. This study will describe a control system for the towline so that it can help carry out the towing manoeuvre with an escort tug. It indicates the control parameters for the manoeuvre, as well as the operational variables of the winch on which the system runs. [ABSTRACT FROM AUTHOR]

Ship Maneuvering Simulators have proved to be powerful tools for analyzing the feasibility of docking, steering, and braking maneuvers under the assistance of tugboats. To represent tugboats' actuation, the so-called "vector tug" model is normally applied. This model is usually represented as simplified external forces, causing a significant loss of realism concerning the tugboat's towing force and its actuating position. The main objective of this work is to provide an innovative approach for vector tug actuation modeling in such a way that both the towing forces and tugboat positions are correctly predicted during direct Push and Pull operation modes, which are usually performed under low speeds, during docking maneuvers. Besides, the steering and braking maneuvers will be addressed, with the corresponding predictions during the Indirect Pull operation, where the tugboat acts as an aerofoil, with the resultant lift force generated being transmitted across the tow line. In order to perform the predictions, the authors first used CFD methods to obtain the hydrodynamic coefficients for a harbour tugboat hull and an escort tugboat hull. Afterwards, they developed a Static Equilibrium Model combined with optimization techniques. The obtained results were validated against literature data and in the Numerical Offshore Tank Laboratory (TPN-USP) simulator. [ABSTRACT FROM AUTHOR]