Proceedings of the Twenty-seventh (2017) International Ocean and Polar Engineering Conference www.isope.org San Francisco, CA, USA, June 25-30, 2017 Copyright © 2017 by the International Society of Offshore and Polar Engineers (ISOPE) ISBN 978-1-880653-97-5; ISSN 1098-6189

Full-scale Measurements and Observations of Icebreaking Notch Towing Operations

Teemu Juhani Heinonen Design and engineering, Technology Inc. ,

Veikko Eljas Immonen Design and engineering, Aker Arctic Technology Inc. Helsinki, Finland

ABSTRACT regarding the forces to the structures of the stern due to contact between two vessels especially when the vessels are rapidly In difficult ice conditions it is sometimes necessary for the icebreaker decelerating. to tow the merchant vessel which can be somewhat risky as high forces act in the towing line. However, relatively little is known about the Soininen (1989) investigated the effects of the icebreaker and merchant forces acting during the notch towing operations. The purpose of this vessel beams to the towing force of the icebreaker during assistance in study is to investigate the notch towing operations by measuring the model-scale. However, the situation in full-scale is somewhat different towing cable forces. Measurements were performed onboard Finnish as the operation of the two vessels affect the forces and also in the icebreaker Kontio during winter 2016. The results indicate that in model tests the merchant vessel did not use any propulsion. Published general the towing line forces are linearly dependent on the mass of the full-scale data of the towing forces during icebreaker assistance is not towed vessel. High force peaks are usually related to slack & rapid easily found. Perhaps this is due to the fact that measuring the towing tightening of the towing cable. It is easier to generate slack with large forces in full-scale during icebreaker assistance is somewhat difficult as vessels as a gap has to be left between the icebreaker and the towed robust equipment is needed for the task. Typically the dimensioning of vessel in order to maintain maneuverability of the icebreaker. In the icebreaker towing winches and cables is related to the bollard pull addition, skills of the helmsman of the towed vessel are crucial factor of the icebreaker while the dimensioning of the bollards of the for towing line forces. If the towed vessel is not able to follow the merchant vessel is based on the strength of the towing cable (Trafi et. icebreaker in straight path, the risk of breaking loose from the towing al., 2011). fork and high forces increase. The purpose of this study is to investigate the notch towing operations KEY WORDS: Icebreaker; merchant vessel; assistance; channel; in full-scale: gather full-scale data of the forces acting in the towing winch; force; cable. line and find contributing factors for high/low loads and investigate how different merchant vessels apply for notch towing. INTRODUCTION The findings can be used for ship design/rule development and also for recommendations & guidelines for towing operations. In difficult ice conditions, especially with ice compression, the merchant ships are occasionally unable to follow the icebreaker with Measurements were performed onboard Finnish icebreaker Kontio their own propulsion power. Therefore it is necessary for the icebreaker during winter 2016 at the Bay of Bothnia. to tow the merchant vessel. It is believed that notch-towing operations The measurement equipment were installed to IB Kontio on 9.3.2016. will increase in the future as the merchant vessels’ engine powers tend Authors were onboard the vessel during 9.-19.3.2016 performing to decrease due to emission regulations. At least the need for icebreaker measurements. After this, the measurement equipment was left onboard assistance is foreseen to increase in the Baltic Sea (Westerberg, 2014). to log autonomously. Totally 21 towing events were recorded during the measurement period. Towing operations require skilled crews and can be somewhat risky as high forces act in the towing line and there is also a risk of collision. NOTCH TOWING However, relatively little measured data is available about the forces acting during the notch towing operations. Previously Starshinov et. al. In notch towing operations the icebreaker tows the assisted vessel. (1990) have measured the forces acting on the stern during Towing is performed in situations when the assisted vessel gets stuck in different type of towing operations. Their study gave information ice or otherwise cannot keep a reasonable speed during the assistance.

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