Captain Henk Hensen is a Master Mariner FG. After his career at sea he became a Port of Rotterdam pilot for 23 years, during which time he started the first combined simulator training courses for harbour pilots and tug captains, and participated in many port studies, including simulator research. Following his piloting career he continued to work as a marine consultant on the nautical aspects of port studies, harbour tug advice and simulator training and research, and as an expert witness. As an author, his publications include Ship Bridge Simulators (1999), Tug Use in Port (2003), Tug Stability (2016), co-authored with Dr Markus van der Laan, and numerous articles in nautical magazines. Captain Hensen is a Fellow of The Nautical Institute and of the International Tugmasters Association, and a member of the International Federation of Shipmasters. He was elected Tug Personality of the Year 2010 by the British Tugowners Association.
Markus van der Laan graduated at Delft University of Technology in 1991 as Naval Architect. In 1997 he finished a Ph.D. thesis on Environmental Tanker Design in cooperation with Shell. Since 1997, he has been director of IMC, a consultancy firm active in the development and engineering of various ship designs and associated ship equipment, including 360 degree towing systems for tugs (the Carrousel with Multraship, the DOT system with Mampaey Offshore Industries), the SafeWinch with Kraaijeveld winches (received the IMO 2008 Seatrade Award), the V-POD electric propulsion with Verhaar Omega and recently the development of the All-Rounder tug in Malaysia. In addition to various developments, he is also involved as a technical expert in the investigation of tug accidents and damage cases.
Henk Hensen, Markus van der Laan
Over the years numerous harbour tugs have capsized, often with tragic consequences. Stability is a complex subject and mainly a specialism of naval architects. Tug masters seldom have this detailed knowledge – yet they experience the effects of a tug’s stability every day when manoeuvring their tug, either free sailing or when assisting ships.
Tugs will often be working with towline forces, hydrodynamic forces, steering and propulsion forces at or near their maximum with respect to the vessel’s stability.
It is, therefore, not just desirable but necessary for tug masters to have at least a basic idea of the elements of stability. They need to know where the limits are, and what the consequences could be, if tug handling practices don’t conform to the rules of stability in normal circumstances and also when extreme conditions such as dense fog and storms occur. Furthermore, a tug’s stability is not a static condition but can change with every moment. Alterations in the amount of bunkers or stores, water on deck, slack tanks and ice accretion, all complicate the stability situation. These various factors could combine to affect stability in a negative way and may even culminate in a very dangerous situation for the tug.
In writing this handbook, master mariner and pilot Captain Henk Hensen and naval architect Dr Markus van der Laan have focussed on the practical aspects of stability, tug design and equipment and also on the consequences of unsafe procedures. Their emphasis is on harbour tugs, although several of the topics covered apply equally to seagoing tugs.