Fifth International Symposium on Marine Propulsion SMP’17, Espoo, Finland, June 2017 Multi-pod icebreakers. Influence of bow thruster units on icebreaker performance in open water and ice conditions.* Leonid G. Shchemelinin1, Aleksander I. Malikov1, Ilkka Saisto2, Artur Nerman2 1Krylov State Research Center (KSRC), St. Petersburg, Russia 2Aker Arctic Technology Inc., Helsinki, Finland ABSTRACT 1 INTRODUCTION The development of infrastructure for transportation of Aker Arctic Technology Inc. proposed the designs of crude hydrocarbons from continental shelf of the Arctic icebreakers that can be operated in restricted shallow seas required the designing of special-purpose icebreakers water areas with specific ice conditions in order to that can be operated in restricted shallow water areas with support the operation of Novoportovskiy terminal and specific ice conditions. provide year-round export of Liquefied Nature Gas For these purposes, Aker Arctic Technology Inc. proposed (LNG) from port Sabetta. The distinctive feature of these the designs of icebreakers equipped with several icebreakers is that they have one or two thruster units at azimuthing thruster units. These designs are featured by the bow in addition to two stern units. installation of one or two thruster units at the bow in Previously, the installation of additional propellers at the addition to two stern units. bow of icebreakers was practiced many times, in Aker Arctic Technology Inc. ordered and KSRC particular, on icebreakers of “Kapitan Belousov” type and performed in its towing tank the model investigations of some others. The installation of these propellers resulted propulsion and pulling performance of such kind of in the reduction of ice resistance due to washing of the vessels in open water conditions. Within the scope of hull by propellers’ slipstream. Moreover, they were used these investigations, KSRC analyzed the effect of one or for washing of broken ice features. two thruster units on propulsion and pulling performance The installation of azimuth thruster unit at the bow of of vessels at various power distribution between bow and icebreaker suggests a high maneuverability in open water stern units. and ice conditions, which is very important in restricted In particular, these investigations showed: water areas. Also propeller flushing effect reduces ice resistance and improves ridge penetration capability significant difference in operation conditions of PS and SB stern thruster units for the vessel with one On the other hand, it is evident that the installation of the thruster unit at the bow; additional thruster unit at the bow of a vessel can affect influence of bow thruster units’ toe-out angle on the operation of the main stern thruster units and reduce vessel’s propulsion performance at various speeds; the efficiency of propulsion plant. significant difference in the efficiency of power Open water model tests were performed in KSRC towing consumption by bow thruster units between bollard tank in order to determine the propulsion and pulling pull and full speed modes. performance of such vessels. Moreover, it was Moreover, the paper presents separate results of ice model investigated how bow thruster units effect the interaction tests of such icebreakers performed in Aker Arctic ice between stern units and vessel’s hull. basin. Self-propelled models were used in the tests performed in bollard-pull and similar modes as well as in full speed Keywords modes at various power ratio of bow and stern thruster Icebreakers, bow thruster units, propulsors’ interaction. units. The tests were performed according the procedure of self-propulsion tests for multi-shaft vessels referred to in the paper (Kanevsky et al 2011a). Ice model tests were performed in ice basin of Aker The following meanings of subscripts are assumed Arctic Technology Inc. hereinafter: Some results of mentioned investigations are included in A – values related to stern thruster units; this paper. F – values related to bow thruster units; – values related to SB thruster units; 2 CONFIGURATION WITH ONE THRUSTER UNIT AT SB – values related to PS thruster units. THE BOW AND TWO THRUSTER UNITS AT THE PS PS Unit SB Unit STERN 0,2 0,2 W W The model of icebreaker (project Aker ARC 130A) was A PS A SB used in the investigation of interaction between stern 0,1 0,1 0,0 0,0 thruster units and the hull of icebreaker equipped with one additional bow thruster unit. -0,1 -0,1 The photos given in figure 1 show the layout of bow and -0,2 -0,2 stern thruster units installed in “ahead running” position. 0 1 2 3 4 K 5 0 1 2 3 4 K 5 DE DE P /P = 0 P /P = 0,25 P /P = 0,43 DF DA DF DA DF DA Figure 2. The relationships of wake coefficients w for SB and PS stern thruster units at various power ratios of bow (PDF) and stern (PDA) thruster units. Figure 1. Thruster units installed on the model of Aker P /P = 0 0,6 DF DA ARC 130A icebreaker. P /P = 0,25 t DF DA P /P = 0,43 Basic parameters of Aker ARC 130A icebreaker thruster DF DA units are given in Table 1. 0,4 Table 1. Basic parameters of Aker ARC 130A icebreaker thruster units Type Pulling 0,2 AZIPOD Stern units Number 2 Power at unit’s propeller MW 7.5 0,0 0 1 2 3 4 K 5 Propeller diameter m 4.2 DE Type Pulling AZIPOD Figure 3. The relationships of thrust deduction factor t at Bow unit Number 1 various power ratios of bow (PDF) and stern (PDA) thruster Power at unit’s propeller MW 6.5 units. Propeller diameter m 4.0 Such configuration of thruster units features a significant Design speed of the vessel kn. 16 difference in operation conditions of PS and SB stern units due to the influence of bow unit slipstream. It can be The investigations were performed at right-handed illustrated by the relationships for wake coefficient in rotation of bow unit’s propeller and at various power Figure 2 as well as by performance curves of PS and SB distribution ratio of bow and stern units in bollard pull models of unit behind hull given in Figure 4. mode as well as in running modes. PS Unit SB Unit 0,5 0,5 10K 10K Test results are given as relationships between wake Q Q K T 0,4 K 0,4 10K T 10K coefficient w (Figure 2) and thrust deduction factor t Q Q 0,3 K 0,3 K (Figure 3) and effective thrust load coefficient KDE T T (Voytkunsky 1985) at various ratios of units’ power. 0,2 0,2 0,1 0,1 KDE coefficient is determined as for the vessel with 3 0,0 0,0 propellers: 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 J J P /P = 0 P /P = 0,25 P /P = 0,43 T DF DA DF DA DF DA K V 2 D2 D2 : E (1) DE PA PF Figure 4. Thrust coefficient KT and torque coefficient KQ for SB and PS stern units versus advance JV at various power where: DPA and DPF = diameters of propellers of stern and bow thruster units respectively; V = model speed; ratios of bow and stern units. TE = total effective thrust of the thruster units; water density. 3 CONFIGURATION WITH TWO THRUSTER UNITS AT 0,26 P /P = 0,25 K DF DA THE BOW AND TWO THRUSTER UNITS AT THE E P /P = 0,5 0,24 DF DA STERN P /P = 1 DF DA The model of port icebreaker (project Aker ARC 124) 0,22 was used in the investigation of interaction between stern thruster units and the hull of icebreaker equipped with 0,20 two additional bow thruster units. 0,18 The photos given in figure 5 show the layout of bow and 0,16 stern thruster units installed in “ahead running” position. 0,14 0 5 10 15 20 Figure 6. Total effective thrust coefficient KE versus toe-out angle of bow units φ for various power distributions between bow and stern units in bollard pull mode. Figure 5. Thruster units installed on the model of icebreaker Based on results of these investigations it was decided to Aker ARC 124. proceed self-propulsion model tests with bow units turned Basic parameters of Aker ARC 124 icebreaker’s thruster at toe-out angle of φ=10º. As it was expected, the greatest units are given in Table 2. effect of toe-out angle is observed at the equal power at Table 2. Thruster units of icebreaker Aker ARC 124 the bow and stern thruster units. Type AZIPOD Subsequent model tests in running modes were also ICE1400 performed at various ratios of power delivered to bow and Stern units Number 2 stern thruster units. The results of these tests are given as Power at unit’s propeller MW 3.0 relationships between wake coefficient of stern units wА Propeller diameter m 3.0 (Figure 7) and thrust deduction factor t (Figure 8) and Type AZIPOD load coefficient KDE. ICE1400 KDE coefficient is determined as for the vessel with 4 Bow units Number 2 propellers of the same diameter: Power at unit’s propeller MW 3.0 TE (3) Propeller diameter m 3.0 KDE V DP : Design speed of the vessel kn. 15 4 and thrust deduction factor t is determined as: The tests of this model included the studies of the effect T of the toe-out angle of propeller shafts’ axes of the bow t 1 E (4) T units on the effective thrust of icebreaker in bollard pull i mode.