The Study of the Application of Hybrid Propulsion System onOPV withControllable Pitch Propellers

as a patrol ship, the offshore patrol vessel (OPV) 80 m has an operational profile consist of several conditions: loitering (10 knots), patrol (18 knots), and interception (22 knots). Applying diesel mechanic propulsion system, load factor of each OPV 80 m’s main engine during loitering (10 knots) and patrol (18 knots) conditions in sequence have the value of 7% and 49.54%. The load factor permitted by the engine maker ranges between (60% ~ 90%) MCR, However, By applying hybrid propulsion system, the load factor of the OPV 80 m’s shaft motor during loitering condition has the value of 87.26% while the load factor of its main engine during patrol and interception conditions becomes 62.10% and 89.949%.In terms of economic aspects, for 30 years of operation period of OPV 80 m, total of present values of hybrid application is significantly much lower than the diesel mechanical application, with the difference between them is IDR579.205.295.632,-. Keywordsoperational profile, shaft motor,load factor, diesel mechanical propulsion.


I. INTRODUCTION 1
he offshore patrol vessel(OPV) 80 m is one of the patrol ship with the duty to watch over the exclusive economic zone (EEZ) over illegal activities, such as infiltration of foreign troops, smuggling, illegal fishing, piracy, and other similar activities [1].A diesel mechanical propulsion (DMP) system applied to the OPV 80 m [2] operates during all conditions: including loitering (10 knots), patrol (18 knots), and interception (22 knots).
Based on the results of preliminary analysis, load factor (LF) of each main engine during loitering, patrol, and interception conditions in sequence is just about 6%, 45%, and 75%.Such very low LF during loitering and patrol causes the operation of the main engines beyond range of permitted operation condition set by the engine maker all the time.This results in increase ofspecific fuel oil consumption (SFOC) and in a long term decrease of the lifetime of engines' parts due to excessive vibration [3].To overcome this situation, the propulsion system of the OPV 80 m needs to be re-engineered.The reengineering process is carried out by changing the existing DMP system to hybrid propulsion system.The hybrid propulsion system is a dynamic combination of DMP and diesel electric propulsion (DEP) systems (Figure 1).This system has four propulsion modes: shaft motor, shaft generator, mechanical, and booster modes [4].These various propulsion modes could adapt to meet the requirement of the various OPV 80 m's operation condition.Such propulsion system is worth considering to be applied to the OPV 80 m due the operational flexibility it offers.
This paper presents a configuration layout and specification of the hybrid propulsion system applied as well as the comparison between the DMP and hybrid systems in terms of both technical and economic aspects.

A. Shaft Motor/ Power Take Home (PTH)Mode
Shaft motors are used as the only propulsion engineduring loitering condition, while the main enginesare not activated at all [5].The Advantages gained by this mode are: 1. preventing low main engine's LF and lower its usage load for it is inactive at all, and 2. noise and vibration generated will be much lower so that the chances of a successful loitering condition are increasing [6].
Electrical power supply to shaft motors come from diesel generator sets (D/Gs) through main switchboards(MSB) and frequency converters(FC) (Figure 2).On the existing DMP system configuration, 4 x 450 kWe of D/Gsare installed [7].On hybrid propulsion system configuration, compensating for additional electrical load due to the operation of 2 x shaft motors, the capacity of D/Gs is to be increased as much as 2 x the shaft motor rating plus starting load of each shaft motor.Each shaft motor will be started by thefrequency converter (F/C).By using the F/C starter, required starting current can be lowered to 1 ~ 1.5 full load current only [8].

B. Shaft Generator / Power Take Off (PTO) Mode
In this shaft generator mode,the main engines take role as the only propulsion engines [5].To prevent low LF condition on the main engines, some amount of their brake power is used to rotate the rotors of the shaft motors at their rated speed x (1 + slip) (Figure 3) so that the shafts motor are converted to be shaft generators  Operating 2 x shafts generator to supply electrical power requirements will likely reduce usage load of D/Gs.Thisallows at least one unit of D/Gs to be inactive during patrol or interception condition [16].

C. Mechanical Mode
Same as in the shaft generator mode, in mechanical mode, the main engines take role as the only propulsion engines [5].The difference between the shaft generator mode and the mechanical mode lies in the LF of each main engine.In mechanical mode, the LF of each main engine is considered as being within the permitted range, that is (60% ~ 90%) MCR [10].Therefore, shaft generators need not to be activated (Figure 4)during patrol or interception condition [18].

D. Booster / Power Take In (PTI) Mode
In this mode, both the shafts motor and the main engines become the propulsion engines simultaneously [5].This allows decrease in LF of each main engine (Figure 5).Synchronization between RPM of the shaft motors and the main engines is absolutely necessary in order to prevent braking condition on either the shaft motor or the main engines.This means the RPM of both the propulsion engines have to be same each other so that power losses during transmission process in gearbox should not be excessive [17].
Same as in the shaft motor mode, the electrical power suppy to shaft motors comes from D/Gs through MSB and FC.Thus more D/Gs need to activated during interception condition.

B. Prediction of Total Resistance
The initial step of these studies is the calculation of total resistance of each OPV 80 m's operation condition or each speed (Vs) by using Holtrop method [11].The total resistance during services is called R T service acquired by multiplying sea margin (SM) factor with the previously acquired R T with the Holtrop method.
The SM factor varies among sailing routes.For seas around Indonesia e.g.Indian and Pacific Oceans, the SM factor would vary in range of 1.15 ~ 1.20 [12].In case of the OPV 80 m, the greatest SM factor is considered to be 1.20.

C. Prediction of Required PropulsivePower
After acquiring the SM factor for everyVs, the prediction of required power for propulsion on each Vs can now be carried out.The required engine power for propulsion (P B ) is a function of the R T service and Vs like this following formula [13]: where: η  /  = power transmission efficiency through the PTO/PTI gearbox, as much as 0.967 [13] η  = power transmission efficiency through the shafting system, as much as 0.98 [13] η propulsive = propulsive efficiency resulted from the interaction of ship hull and the propeller, initially taken as 0.60

D. Propeller Selection
Steps of the propeller selection for hybrid propulsion system taken as follows.1. Determination of number of propeller's blades 2. Calculation of maximum propeller's revolution speed 3. Calculation of allowed propeller's diameter upper limit 4. Calculation of propeller's diameter, initial ηo, and P/D ratio

E. Ship Hull -Propeller Interaction
Thrust produced by propellers (T Prop ) is to be same as thrust needed by the hull (T Hull ) so that the OPV 80 m could sail at determined Vs with the propulsion engines' LF and speed within permitted operation range.T Prop would be same as T Hull only if T Prop coefficient (Kt Prop ) is same as T Hull coefficient(Kt Hull ).The Kt Hull is determined by the following formula [13]: where: where: Ct =R T service coefficient as function of Vs The Kt Hull vs J curve could be drawn by giving various J numbersin range between 0 to 0.9 into Formula International Journal of Marine Engineering Innovation and Research, Vol. 1 (4) From the intersection point between the Kt Hull vs J curve and the Kt Prop vs J curve on the open water diagram, hull propeller interaction satisfying J number, propeller torque coefficient (Kq), and propeller's efficiency for a given P/D ratioof a given Vs can be acquired.For the type of the propellers used is of Wageningen B series, the J number and Kq are figured out for all P/D ratios in range between 0.5 to 1.4 Vsfor eachVsvarying between 5 knots to 22 knots (maximum) [14].

F. Analysis of Economical Aspects of the Hybrid Propulsion Application
The method used for this analysis is present value (PV).Annual PV of each propulsion system can be determined by using Formula 9 [15].Annual PV for OPV 80 m's operation period of 30 years of each propulsion system application is then accumulated to acquire total PV of each propulsion system application and the difference between them will be amount of savingsas benefit gained from the hybrid propulsion system application.

IV. RESULTSAND DISCUSSION
A. Data Umum OPV 80 M Principal dimensionsof the OPV 80 m are as follows [18]

C. Propulsion Engine Loading Analysis during Loitering Condition
The results of shaft motorpropeller matching MPM) analysis presented by Figure 6.In Figure 6 it can be seen that match P/D ratio for Vs = 10 knots is 0.55 with LF of each shaft motor = 87.26%with each shaft motor produces torque = 273.30%its rated torque and speed = 78.30%its rated speed.

D. Propulsion Engine Loading Analysis during Patrol Condition
The results of diesel engine propeller matching(DEPM) analysis for patrol condition presented by Figure 7.In Figure 7 can be seen that after being loaded by 355 kWe shaft generator, LF of each main engine increases from 51.55% to 62.10% at 1513 rpm with match P/D ratio for Vs = 18 knots is 0.9 .

E. Configuration of the Hybrid Propulsion System
Based on the previous results of the propulsion engine loading analysis, propulsion modes meeting the OPV 80

F. Propulsion Engine Loading Analysis during Interception Condition
The results of diesel enginepropeller matching(DEPM) analysis for interception condition presented by Figure 8.Figure 8can be seen that after being syncedwith 355 kW shaft motor, LF of each main engine decreases from 99.81% to 89.949% at 1988.5 rpm with match P/D ratio for Vs = 22 knots is 0.79.m's required propulsion and electrical power as well as D/Gs loading condition during each operation condition can now be determined as presented by Table 4.

G. Analysis of Economical Aspects of Hybrid
Propulsion Application In this analysis, there are 2 types of cost to be considered: constant and variable costs.The constant cost includes investment cost (IC).IC itself includes purchasing and installation costs of components of both the propulsion systems.Variable cost (VC) includes fuel consumption costs and all maintenance related costs for these costs are time dependent.
Results of calculation and the comparison of IC, VC, ƩCO, ƩPV, and ƩPV difference of both the propulsion systems up to the 30 th year are presented by Table 5.

Figure 1 .Figure 2 .
Figure 1.Configuration layout of the hybrid propulsion system with twin screwCPP (concept on OPV 80 m)

Figure 5 .
Figure 5.Energy flow in booster / power take in(PTI) mode [5] III.Method A. Data Collection Primary data required for these studies are acquired directly from the OPV 80 m's designer, engine makers, and shipyard company.The primary data that needed are as follows.a) Principal dimensions ofthe OPV 80 m b) Maintenance schedule of each component of both DMP and hybrid propulsion systems c) Maintenance costs including spare parts'prices of each component of both DMP and hybrid propulsion systems Secondary data required for these studies are acquired from reviewing existing literature.The primary data are as follows.a) General OPVs'operational profile data b) The configuration of the existing DMP system on the OPV 80 m c) Electrical power required during each operation condition of the OPV 80 m including the number of installed and required runningD/Gsduring each operation condition d) Components and propulsion modes of general hybrid propulsion system d) Investment cost of each component of both DMP and hybrid propulsion systems e) Performance diagram of the main engines, D/Gs, and chosen shaft generator motors (SGM).

Figure 8 .
Figure 8.The results of DEPM analysis for interception condition with 355 kW shaft motor synchronization , Sept. 2017.346-354 (pISSN: 2541-5972, eISSN:2548-1479) 349 7.Kt Prop vs J curve is acquired from open water diagram of the previously chosen propeller.The Kt Hull vs J curve is then plotted onto the propeller's open water diagram. (9)
350 Figure 6.The results of SMPM analysis for various P/D ratios of each Vs varying between 5 knots to 10 knots

TABLE 4 .
SELECTION OF THE HYBRID PROPULSION CONFIGURATION WITH LOAD CALCULATION AND ELECTRICAL SYSTEM

TABLE 5 .
COMPARISON OF IC, VC, Ʃ CO, Ʃ PV, AND Ʃ PV DIFFERENCE OF BOTH PROPULSION SYSTEMS UP TO THE 30 TH YEAR International Journal of Marine Engineering Innovation and Research, Vol.1(4), Sept. 2017.346-354 (pISSN: 2541-5972, eISSN:2548-1479) 354 5. Investment cost of the application of DMP system is IDR 106,639,410,143,-while of hybrid propulsion system is IDR 107,302,399,186,-.Therefore, the difference between them is IDR 662,989,042,-.6.The application of the hybrid propulsion system on OPV 80 m decreases amount of HSD consumedsignificantly, that is from 6817.339 ton/year to 6308.976 ton/year.Such significant decrease means a more economical and environmentally friendly operation condition.7. Up to 30 th operational year of OPV 80 m, total fuel consumption cost for the application of DMP system is IDR 44,428,640,001,434,-while forofthehybrid propulsion system is IDR 41,115,632,805,620,-so that the difference between them isIDR3,313,007,195,813,-.8. Up to 30 th operational year of OPV 80 m, total maintenance costs for the application of DMP system is IDR 326,177,757,012,-while for of the hybrid propulsion system is IDR 817,804,656,701,-The total PV of the application of the hybrid propulsion system is significantly lower than of the DMP system, with the difference between themisIDR579,205,295,632,-.