Research on the Identifying Parameters of Tugs Performance: A Review

Abstract

[Abstract] In the history of maritime navigation, the first civilizations used the auxiliary boats of the ships to perform tasks of assistance in port manoeuvres that can be called towing, but nowadays the towing has become a lucrative commercial activity and a relevant key of the safety in the shipping industry. However, after several centuries and the huge evolutions of the design, the operation and the performance that the tugs have been subjected, there are still no internationally accepted standards to define their characteristics in an objective way. This lack of tools to quantify the capabilities of the tugs became even more apparent after the genesis of the escort towing. Therefore, this paper provides a general review of the historical evolution of identifying parameters used to assessing the tugs performance. It shows the first rudimentary methods as the installed horsepower; the bollard pull (BP), still widely employed, although sometimes wrongly; polar diagram of thrust vectors and “butterfly” diagram, which do not take into account the particulars of an assisted vessel; the tons of steering pull, mainly for escort tugs and finally, the computer programs. However, despite all computer tools currently available to assess a tug performance, most of the classifications societies require the traditional sea trials in order to classify an escort tug with the corresponding notation.