Leonid I., VISHNEVSKY, D.Sc., Krylov Shipbuilding Research Institute, Moskovskoye shosse 44, St.Petersburg, Russia,

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1 Leonid I., VISHNEVSKY, D.Sc., Krylov Shipbuilding Research Institute, Moskovskoye shosse 44, St.Petersburg, Russia, Anatolij-Branko R., TOGUNJAC, Ph.D.,Malaya Morskaya 18-20, Institute Giprorybflot, St.Petersburg, Russia, SHIP BLADE PROPULSORS: NEW TECHNICAL SOLUTIONS, RESULTS OF INVESTIGATIONS Summary: The paper describes new technical solutions for ship blade propulsors and related results of hydrodynamic investigations. The new developments are aimed at solving the following traditional marine and shipbuilding tasks related to propulsors: improvement of propulsive performance and energy saving, vibration decrease, increase of reliability, and provision of multifunctionality. The authors describe the design of propulsors in the development of which they directly participated. The description is accompanied by the analysis and review of analogues and prototypes. Key words: propulsor, propulsive performance, energy saving. BRODSKI KRILNI PROPULZORI: NOVA TEHNIČKA RJEŠENJA, REZULTATI ISTRAŽIVANJA Sažetak: Rad opisuje nova tehnička rješenja brodskih krilnih propulzora i rezultate hidrodinamičkih ispitivanja ovih propulzora. Istraživanja su usmjerena ka traženju rješenja tradicionalnih brodskih i brodograñevnih pitanja, vezanih za propulzore: povećanje propulzivne učinkovitosti i ušteda energije, smanjenje vibracija, povećanje pouzdanosti djelovanja, osiguravanje mnogofunkcionalnosti. Dan je opis propulzora, u čijem razvoju su autori izravno sudjelovali. Opis propulzora prati analiza i pregled sličnih projekta i prototipova. Ključne riječi: propulzor, propulzivna učinkovitost, ušteda energije.

2 Introduction The last years in the more then centennial history of developing screw propellers as ship s propulsors have been marked by new technical solutions aimed at the improvement of hydrodynamic properties and by new design of multipurpose propulsors. Multipurpose propulsors ensure different modes of ship s movement within the complete speed range. This paper contains review some new ship blade propulsors (including so called variable pitch propeller) patented in Russia offered by authors and main theoretical background related to this propulsors. The monograph [1] contains more information about this new propulsors and includes description of nine patents. 1. Variable pitch propeller 1.1. Comparison of variable pitch propellers and controllable pitch propellers Today exist several designs of variable pitch propellers (VPP) resulted from research development and full-scale tests. It is worth noting that interest to such propellers in the world is no steady growth. The constructional feature of this propeller is a movable clamping between the propeller and the hub. The most detailed works are related to VPP with "free" moving blades within the disk plane near the operating position. The main principle of such propellers operation is defined by hydrodynamic and centrifugal forces. The interest to VPP can be explained by its ability to fulfill the function of a controllable pitch propeller (CPP), ensuring, first of all, required power within the wide range of changing mode of propeller operation. Such modes are usually met in operating conditions. In this case fixed pitch propeller (FPP) to be designed as optimal one with the condition of reaching maximum ship speed on the calm water does not allow to realize the having reserves in improving running qualities in wide range of service conditions. Fig. 1 The operating principle of VPP At the same time properly designed VPP has no such drawback. The same is concerned with CPP. However, for the rotating its blades it is necessary to have forced (hydraulic) driven being very expensive and complex device and requiring special service about it during operating. Besides, the changing of FPP by CPP in the vessels is connected with huge additional expenditure and with hard working with shaft line. Being with hydraulic driven of blades there is ecology's danger of environment due to oil leak.

3 1.2. The operating principle of VPP To illustrate the principle of the VPP operating a diagram is given in fig.1 showing the forces which act on one of the blades. The blade motion is provided within the disk plane in relation to point A at the hub. The research results have demonstrated that the relative displacement of the blade in direction opposite to that of the propeller rotation is accompanied by increasing in the moment M 1 caused by centrifugal force and decreasing in the moment M 2 caused by hydrodynamic forces. When the blade is deflected in the opposite direction the picture is reversed. This blade position on the hub is determined by equality of action of the mutually opposed moments. In depending on the propeller operation mode (advance ratio) the blade position will be different. As this take place the propeller hydrodynamic characteristics as compared with those of the propeller with fixed blades will change (see fig. 2) as the above motions (in relation to the pivoting point A located off the propeller axis) cause the changing of the propeller geometry (see fig 2). This very important quality of VPP opens the prospect in some cases to use it instead of FPP self-providing the optimal main engine load at the intervening modes of operation and correlation engine operation with the propeller at the service conditions without force driven only at the expense of action of hydrodynamic, inertia and, in general case of elastic forces. Fig. 2 Hydrodynamic characteristics of VPP Notations are related to: fixed blades; "free" blades. The typical feature of VPP is the fact that hydrodynamics characteristics of the propeller due to movable blades relative to hub have less of slope against the horizontal axe. Moreover the geometrical characteristics of VPP may be chosen in such a way that in all range of modes of its operations it is able to process full power of main engine without overloading at any conditions of ship going. This is important quality VPP as at the designing of FPP, as rule, it is tended to hydrodynamic decreasing of load in ship services due to acting of waves, getting hull roughness and so on. Here it is not need to take such care off. Excluding of this reserve in applying of VPP it is allowed to get maximum ship speed on calm water and in doing so to increased her propulsion qualities Results of design The fulfillment of design researches of VPP in applying to "Ladoga" of sea-river going ship shown that year economical effect is more than 10000$ in year. This result has been gotten in service conditions, which was out of the calm deep water and was connected with the decreasing of service consumption with the equality of freight turn-over. This result may be considerably

4 increased if operating economy is connected with freight of vessel. However, in this case the quantity will be considerably depended on market interest to be taken place in the region. Another way to use VPP may be connected with improvement of pulling characteristics of ship. The matter is that FPP being design for processing full power with aim for reaching maximum speed does not allow to use available power reserve in the conditions of towing of any object due to restriction power consumption in depending of shaft rotation. In fig. 3 it is shown calculation data relating to trawler with the results of full scale tests. They are confirming that to be said. From this results it is seen that propulsion ship qualities in the case of VPP with fixed and "free" blades on the hub are practically the same (curves 1,3). At the same time at the mode of pulling (curves 2,4) due to restriction characteristics of main engine (curve 5) VPP allows to process more power. It gives the trawler more high pulling characteristics. In this example the speed of trawling increase by 0,4 knots and pulling of towing hook by 350 kg. The general view of VPP arranged on trawler is shown in fig 4. This result is explained by moveable of blades on the hub. With the increasing of propeller load the blades move to decreased pitch (negative angle ψ, see fig. 2) what resulted in to decreasing hydrodynamics moment on the VPP and in the case of keeping the taking up the power to need for increasing rotation that is to change operation mode of engine in high rotation domain (see fig. 3), where its restriction curves allows to take off more power what result in to increasing pull characteristics of trawler. Fig. 3 The passport diagram of the trawler with VPP Notations are related to: VPP; FPP;,Ο full scale data.

5 Fig. 4 The general view of VPP arranged on trawler 2.1.Podded propulsors with two-stage blade system Let us write an expression defining the efficiency of the contra-rotating propellers (CRP) components that are located on the radius r using the theory of an ideal screw propeller [1], [2]: 2 1 ( U T1 U T 2 ) ωr ( dti 1 + dti 2VA ) VA 2 U T1 + U t 2 ηir = =,(1) ( dq ) U 1 U i1 + dqi2 A A2 ωr VA where V A - ring component translation velocity; dq i - ring component moment; dt i - ring component thrust; U A1, U A2 - axial induced velocities from the forward and aft screw propellers. U T1, U T2 -tangential induced velocities from the forward and aft screw propellers. ω - angular rotational speed( assuming that ω 1 = ω 2 = ω). It follows from (1) that the maximum efficiency of the CRP is attained when U T1 = U Т2, i.е. in case of elimination of the residual swirling of the propulsion device wake along each radius. This condition ensures equality of the distributed moment characteristics and, thereby, of the moments Q i1, Q i2 [1],[2].This principle puts on base of design procedure for CRP [1],[3]. Let us consider the podded propulsor (PP) described in the patent [4], Fig.5. Its twostage blade system consists of two co-axial contrarotating screw propellers. The distinctive feature of this PP is that the drive electric motor built as birotative with a contrarotating stator coupled with the screw

6 propeller shaft and a rotor coupled with another shaft with a contrapropeller being coaxially installed aft of the screw propeller. Fig.5 The principle of the PP with the contrarotating screw propeller Basing upon theoretical grounds a CRP should be designed taking into account that in operating conditions the screw propellers must be balanced according to distributed moment characteristics, i.e. the condition U T1 - U T2 = U = 0 is met at all the radii. Due to the inaccuracy of calculating methods and in case of a CRP non-standard operation screws often prove to show a disbalance what concerns not only the distributed moment characteristics but the summarized as well. It is reasonable in design process to control the balance of the moment characteristics using to U T. The fig.6 shows the different variants of residual swirling after the CRP U T. The most unfavorable distribution is represented by the type 3, which is characterized by the maximum values of the residual swirling of the wake. Such distribution is observed in case of serious mistakes made in the process of designing or during non-standard modes of a CRP operation at severe loads, for instance, when a mechanical transmission is used to rotate screw propellers. In case of mechanical transmission the speed ratio of a forward and aft screw propellers is constant (usually n 1 = n 2 ) and the CRP performance curves can be represented in a traditional form, i.e. as a function from one advance, fig.7. Fig.6 Radial distribution of the residual swirling U T behind CRP, types: 1- U T =0, Q 1 =Q 2 ; 2 - U T 0, Q 1 =Q 2 ; 3- U T 0, Q 1 =0.6Q 2 [3]

7 Fig.7 Typical view K T - J and K Q J curves of CRP (n 1 =n 2 ), J 1 -advance coefficient on design mode of operation, Q 1 =Q 2 ; J 2 -advance coefficient on mode of operation with large load (trailing),q 1 Q 2 The disbalance of a CRP with mechanical transmission as to the moments in certain operational conditions being different to the design mode of operation takes place due to the changing of the ratio between the tangential and axial induced velocities as the load changes. Consequently, it is inevitable for propulsors with mechanical transmissions operating within a wide load range to get disbalanced when a residual swirling of the wake follow the type 3 pattern. The inductive losses induced by the U T even in case of a serious disbalance are not so great [3], however inductive tangential components coincide with the tangential components of velocities of a viscous wake which finally results in the increasing of the swirling, and, consequently leads to losses [5]. According to a rough estimation, losses only on the stern propeller cap can attain up to 50% of the values being characteristic for single screws (see fig.8). Fig.8 Hydrodynamic force on propeller cap of single screw ( K DT =J/ K T ) [6] The use of a birotative electric drive ensures the equality of moments at any possible loads on the screw propeller (n 1 n 2 = var). By this means, for the PP from the patent [4] the only possible type of disbalance is the type 2 (fig.6), which, naturally, improves the propulsor hydrodynamic efficiency. While applying a rigorous approach towards the designing of a PP aimed at the maximum hydrodynamic efficiency it is necessary to strive for the proper balance between the CRPs as to distributive moment characteristics by placing the control over the U T into the algorithm of a design calculation and by foreseeing the measurement of the U T parameter during model tests.

8 Among existing two-stage multipurpose propulsors Podded CRP [7] ( the Podded CRP concept features a contra-rotating propeller on an electric pod located directly behind the main propeller in the centerline skeg) has the residual swirling similar to proposed [4] ( tipe 1 or 2, see fig.6). The negative characteristic Podded CRP is long length of propulsor and large distance between forward and aft screw propellers (this feature decrease hydrodynamic efficiency of CRP). Azimuth thruster Ulstein Aquamaster 1 [8] in theory has the zero residual swirling ( type 1, fig.6) only on design mode. At all another mode this propulsor has the residual swirling according to type Contra-rotating propellers with shifted blade connection on the hub CRP are subjected to action of periodical hydrodynamic forces even in uniform flow. It takes place due to mutual hydrodynamic influence of forward and aft propellers. In this case with the most influence it is naturally subjected the aft propeller located in hydrodynamics steam of forward propeller. Periodical hydrodynamics forces cause of vibration of CRP and its sound radiation. So a ship designer has the interest to minimize these forces in any case. The patent [9] offers the technical way to decrease periodical hydrodynamics forces acting on CRP by using the shifting blades on the hub [1]. In the formula for the patent of CRP has been described in the following way: ship propeller having the forward propeller and coaxial located aft contra-rotating propeller differing by the fact that at least the blades of aft propeller are connected with the hub by mobile unit as this takes place every blade is mounted with possibility to rotate around axe passing through the root part of blade and located parallel to the axe of propeller shaft in so doing every blade of the propeller is arranged with possibility to rotate around horizontal axe with the angle ±10 0, fig.9. Fig.9 The principle of the contra-rotating propellers with shifted blade connection on the hub 1- forward propeller; 2- aft propeller; 3 and 4 axes of rotation of free blades The design of single propeller with shifting blade connection are known [10],[11] and they are used to correlate propeller and engine in wide range of operation as well as to decrease vibration s activity of propeller[11]. The blade of CRP with shifting blade operates similar to single screw propeller. Very important quality of propeller with shifting blade connection opens prospect in some cases to use it instead of control pitch propeller (CPP) self-providing the optimal main engine load at the intervening mode of operation and correlation engine operation with the propeller at the service condition without force driven only by the expense of action of hydrodynamic, inertia 1

9 and in general case elastic forces. This propulsor should have U T according to type 1 and 2 in wide range of operation (fig.6) because of shifting blades Two-stage multipurpose propulsor Another important step in the further technical development of a two-stage multipurpose screw propulsor design was achieved by using a contrapropeller not only in passive mode (i.e. without rotation and, consequently, without any energy supply) but in reactive mode of operation as well. The offer was patented in Russia under the number [12], [13]. The patent describes a two-stage propulsive system having the following performance: - energy saving full speed mode being achieved by means of hydrodynamics; - slow speed and dead slow speed; - emergency speed; - maneuvering in combination with traditional rudder for all speed range and at the stopping mode as well. Fig.10 General view of the propulsor: patent No (with dual-mode contrapropeller) The propulsor (fig.10) consists of a two-stage blade system and two self-contained drives. The front step functions as a screw propeller and the back step can operate both as screw propeller (reactive mode) and as stationary contrapropeller (passive mode). The back step blade position of the propulsor (further named as contrapropeller) is regulated by the pitch control mechanism. The length of contrapropeller blades is restricted and does not exceed a half of the screw propeller blades length, and the contrapropeller is mounted in such way that permits its hub to turn in horizontal plane and equipped due to turning device. Consequently, the propulsor, when used in combination with a traditional rudder, guarantees the backing up of propulsion and steering unit main functions: back step of the propulsor provides both slow speed and maneuvering of vessel even in the case of a screw propeller and steering rudder are damaged. The above mentioned statement is very important. While analyzing technical risks that may arise in the course of operating a vessel such factors as loss of speed and loss of manoeuvrability among the most dangerous events. Loss of speed and manoeuvrability can be provoked by storm weather conditions, grounding, ice damages, onboard equipment failure etc. The ability of the described propulsor to back up a screw propeller and its drive eliminates to a great extent the possible cases of total speed and manoeuvrability loss. It helps to increase ship s or vessel s survivability and can be used as a basis for risk tarification and, consequently, may result in the decrease of insurance premium paid by a ship-owner in connection with a contract of marine insurance being concluded.

10 From a hydrodynamical point of view the most complicated design task is represented by a contrapropeller blade system. Depending on the mode of operation a contrapropeller can be used as follows: energy-saving unit (blades operate in passive mode), back screw propeller in the pair of contra-rotating propellers, puller or pusher propeller of a steering thruster. Hydrodynamic calculation of this multi-functional propulsor demonstrated with a fishing vessel (trawler) as an example, proved that the use of its rear step (contrapropeller) both in passive and reactive modes is rather efficient however having certain deficiencies [14]. During full speed and trawling modes the propulsor ensures 5-7% efficiency increase in compared to a traditional nozzled screw propeller. At the same time, losses subject to nonoptimal contrapropeller blades geometry during its reactive mode of operation made 8-12%. The blade being designed for contrapropeller mode of operation in the reactive mode operation demonstrated non-optimal behaviour in regard to the radial distribution of hydrodynamic load [14]. These are the consequences of the contrapropeller dual mode of operation. Velocity fields in the propulsor disk in passive and reactive modes of operation differ principally from each other and while choosing the geometry of a blade intended to be used in both modes of operation it is necessary to find a compromise solution. Such decision was offered by the authors and patented in the Russian Federation [15]. The definition of the invention is as follows: 1. A blade propulsion device comprising: a screw propeller and a contrapropeller of less diameter being coaxially mounted behind the propeller and having controllable pitch blades and a pitch adjusting mechanism; a mechanism used to turn said contrapropeller around the vertical axis and a mechanism used to lock the hub of said contrapropeller, and being different from known solution in that the each blade of said contrapropeller has a curve stacking line and is curved in such a way that its suction or pressure sides at the blade edge faces the hub surface of said contrapropeller. 2. A device according to claim 1 differs in that the curve stacking line for the blade is located tangentially towards the cylinder surface having radius equal to said contrapropeller radius and an axis that coincides with the contrapropeller axis. 3. A device according to claim 1 differs in that the mechanism of pitch adjustment provides for the possibility to bring the contrapropeller blades into position where they being movably fixed in the hub have the possibility to move relative to the contrapropeller disk plane. A curve stacking line, fig.11, helps to eliminate the deficiency in contrapropeller blade geometry (pitch increase at the end of blade) during reactive mode of operation and resulting from its multi-functional nature. The curve stacking line of the blade unloads the end of blade within the range of existing angles of attack. In case of a contrapropeller it means that notwithstanding the fact that the blade pitch increases towards the periphery (fig.12, [14]), there are no conditions for the development of intensive cavitation at the blade tip (no pressure peaks along the suction side at end of the blade will occur as the resulting velocity vector V i will be located in the plane of the screw propeller blade excluding angle of attack depended on the pitch). Minimizing the occurrence of cavitation brings vibration down and eliminates the conditions for blade erosion. The unloading the ending part of contrapropeller blades improves its hydrodynamic efficiency by optimizing the radial distribution of load.

11 Fig. 11 Lateral and normal view of contrapropeller blade with curve stacking line, R=0.81 m [16] Conclusions Fig.12 The radial distribution of pitch ration: 1-contrapropeller; 2- optimal screw propeller [16] The use of the new ship blade propulsor described in this paper will allow to: - increase the propulsive characteristics of ships up to 5-15%; - decrease vibration of the propulsive complex; - increase reliability of the propulsive complex. For successful implementation of the new propulsors, the authors have developed methods to calculate the blade systems geometry. However the proposed measures are not sufficient implement all the proposed types of propulsors. It is necessary to solve the most important non-hydrodynamic technical tasks: - develop a bi-rotative electric motor for sea conditions; - develop steerable thruster with dual-mode contrapropeller and locking device to the contrapropeller shaft. REFERENCES [1] ВИШНЕВСКИЙ Л.И., ТОГУНЯЦ А.Р.: Корабельные лопастные движители: Новые технические решения, результаты исследований,судостроение, Санкт-Петербург,2011.

12 [2] TOGUNJAC, A.R.: Hydrodynamic Reasons of Choosing the Two Stage Blade System for New Multipurpose Propulsors. Proceedings of 14 th International Scientific and Professional Congress Theory and Practice of Shipbuilding, SORTA-2000, Rijeka, Croatia, 2000, p [3] TOGUNJAC, A.R.: Utjecaj hidrodinamičkih faktora na geometrijske značajke, koeficijent korisnosti kontrarotirajućih vijaka, Brodogradnja 37 (1989) 1-4, p [4] БЕДЕКЕР В.Ф., ТОГУНЯЦ А.Р.:Судовая движительно-двигательная установка типа «поворотная колонка». Патент Официальный бюллетень "Изобретения" 28, [5] ПАШИН В.М., ТУРБАЛ В.К.: Пути повышения пропульсивных качеств судов, Судостроение, 1986, 10, стр.3-8. [6] ТУРБАЛ B.K., ШПАКОВ B.C., ШТУМПФ В.М.: Проектирование обводов и движителей морских транспортных судов, Судостроение, Л, [7] LEVANDER O.: New Concepts in Ferry Propulsion, Scandinavian Shipping Gazette, September 28, 2007, p [8] :Aquamaster Rauma News, 1, April [9] ВИШНЕСКИЙ Л.И., ТОГУНЯЦ А.Р.: Судовой движитель. Патент , Официальный бюллетень "Изобретения" 29, [10] Don J. MARSHALL.: Variable Pitch Marine Propeller.United States Patent [11] VISHNEVSKY, L.I., MAVLUDOV, M.A., SADOVNIKOV, D.Y., ZUBAHIN, V.F., YAKOVLEV, Y.K.: Experience of the Creation of the Propeller with Shifted Blade Connection in the Hub as Applied to the High Speed Craft with Underwater Wings.NSN 2001 Proceeding, S.-Petersburg, Russia, [12] ТОГУНЯЦ А.Р.: Способ движения и маневрирования судна и лопастной движительный комплекс. Патент Официальный бюллетень ВНИИПИ «Изобретения, 34, [13] TOGUNJAC A.R.: «Two-Stage Multipurpose Screw Propulsor», Brodogradnja, 44 (1996) l, p [14] TOGUNJAC A.R., KAPRANCEV S.V.: «Estimation of Hydrodynamic Efficiency of Fishing Vessel Two-stage Multipurpose propulsor», XIII Symposium on Theory and Practice of Shipbuilding SORTA-98, Zadar, Croatia 1-3 October, [15] ТОГУНЯЦ А.Р., ВИШНЕВСКИЙ Л.И.: Лопастной движительный комплекс. Патент Официальный бюллетень ВНИИПИ «Изобретения, 21, [16] TOGUNJAC A-B., VISHNEVSKY L.,: Duel-Mode Contrapropeller with Curve Stacking Line for Blade, Proceedings of 19 th International Scientific and Professional Congress "Theory and Practice of Shipbuilding", SORTA-2010,Split, Korcula, Lumbarda municipality, Croatia, 2010.