Z. Radisic: Principal 'Types and Characteristics of Harbour Tugs ZORAN RADISIC, M. Se. Visoka pomorska skola Zrinsko-Frankopanska 38, 21000 Split, Republika Hrvatska Integrated Transport Review U. D. C.: 656.618 1\ccepted:Jan. 7, 2002 l\pproved:Sep.30,2003 PRINCIPAL TYPES AND CHARACTERISTICS OF HARBOUR TUGS ABSTRACT Tug today represents irreplaceable part of port infrastruc- ture in all the world harbours and it is almost unthinkable to run a business of some port in international relations without using them. All the world ports intend to get equipped with better equipment in order to be more competitive for cargo han- dling. Modernization of port includes harbour tugs as well. Their purchase depends on the financial power of the investor in infrastructure, whether the state or a private company which is the common owner of the tugs fleet in the port with which it most often has a "Concession contract" for undertaking the mentioned activities besides the rest of the known contracted ways of cooperation. KEYWORDS conventional tug, azimuth stern drive tug, tractor tug, pivot, gob rope, girting, bollard pull, shaft power, admiralty coefficient, displacement 1. INTRODUCTION In the seamanship a very seldom mentioned and elaborated category of small ships, very useful for the manoeuvring within the ports and on all seas is repre- sented here as the fleet of tugs. In literature, the effect of these ships on the whole maritime economy is often neglected but in fact their value is of paramount importance in manoeuvring during bad weather conditions in limited areas of a world port in particular. Each port has its own particular features which de- termine the way of use of the tugs. Generally, the fol- lowing conditions are crucial in choosing and using the tugs: - volume of traffic in the port, - types of ships serving the port, - navigational obstacles in the port, - conditions of environmental protection, - local laws and habits, - available sizes and types of tugs, - experience of crew serving them. Promet- Traffic- Traffico, Vol. 15, 2003, No. 6, 381-386 2. PRINCIPAL TYPES OF HARBOUR TUGS There are three basic types of harbour tugs: 2.1 Conventional tug; 2.2 Azimuth stern drive tug; 2.3 Tractor tug. 2.1. Conventional tug The oldest types of tugs are the conventional ones. They are still present in almost all the world ports, al- though they are pushed away more and more by con- temporary tugs with better manoeuvring capabilities. In the beginning they had steam propulsion, which has been abandoned. Nowadays, they are equipped with diesel engines having one or two propellers respec- tively. With single propeller, depending on the type, the most common is the right-handed (although left- -handed are also quite often met), and are equipped with a classic rudder. The power plant complex is placed at the stern with the towing hook in the middle of the tug. Figure 1 - Conventional tug The main characteristic of these tugs is high reli- ability and efficiency of power expressed in the force of "bollard pull". 381