Calculation of maneuvering performances for pushed convoys with different steering devices

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE, BALATONURED, JUNE 9-11. 1999.

CALCULATION OF MANEUVERING PERFORMANCES

FOR PUSHED

CONVOYS WITH DIFFERENT STEERING DEVICES

Branislav BILEN and Zoran LAJIC

Institute of Technical Sciences of the Serbian Academy of Sciences and Arts

Belgrade, Yugoslavia

Received: June 9, 1999.

ABSTRACT

In the first part of the paper a short description and propulsive comparison of the pushboat project with hybrid steering-propulsion system, i.e. system consisting of central conventional and two side azimuthing thrusters, is given. This project is developed in order to eliminate or minimize all observed propulsive and maneuvering shortcomings of the existing Danube pushboat Second part of the paper is devoted to the comparative analyze of the maneuvering characteristics of the pushboat with: conventional, rudder propellers and hybrid steering-propulsive system. On the end of this paper it is given prognosis of application of the hybrid steering propulsion system on the

seagoing vessels.

PART I SHORT DESCRIPTION AND PROPULSIVE COMPARISON OF THE

HYBRID PUSHBOAT 1.1 SHORT DESCRIPTION

The hybrid pushboat is mainly characterized by its innovative steering-propulsion

complex designed as a triple screw system. The centerline propeller, absorbing about 70% of the installed power, is used for thrust production only. Side propellers-azimuth thrusters, absorbing about 30% of the installed power, are used for maneuvering and production of part of the total thrust force. This way, these two side azimuth thrusters

take over the functions of the numerous existing pushboat rudders. It has to be mentioned

that precise distribution of the installed power between central and side propellers is a

matter of developed numerical procedure that, taking into account given or prescribed

limitations, gives an optimal propulsive and maneuvering efficiency.

This hybrid pushboat differs from existing pushboats ( named as conventional

pushboats) in the following: Main dimensions

The length on the water line is shorter and only amounts to 19.5m; the molded

breadth at 11.33 m is identical with the breadth of the barge E lib; the draught is slightly increased to 1.85m, while the side depth is left unchanged.

Ship's lines

The ship's lines are similar to single screw vessels in design. Transverse sections, including the bilge strakes, are formed as the straight lines. In the centerline on the stem

I.

FIRST EUROPEAN INLAND WATERWAYNAVIGATION CONFERENCE, BALATON CRED, JUNE 9-11. 1999.

is situated a trapezoid "skeg. A similar skeg, with sharp waterline ends, is situated on the

stern with an incorporated stern tube. Standard propeller tunnels are avoided. In the

centerline, the hull

is formed in such a way as to enable

location of the almost

undeformed nozzle. Azimuth trusters are situated in the undeformed nozzle as well. Steel hull construction

The hull construction is made using the usual transversal system of building, with

the exception of the

fore peak region, where the longitudinal system is

applied.

Dimensions of steel plates and angle bars are slightly higher

than the Classification society requirements. The significance of this construction

is the design of the main

engines foundation, which is situated in the boat's centerline along the entire engine

room, which is additionally reinforced with a strong trapezoidal shaped "skeg".

In addition, the hull is provided with only two watertight bulkheads, i.e. fore and after peak bulkheads. Stresses and strains of each element of this construction were checked using the "Maestro" numerical program for a ship's hull strength calculation.

Crew accommodation

The crew is reduced to six crew members. Comfortable accommodations, made in

compliance with relevant regulations, are arranged in the deck superstructure. This

superstructure is executed using the module system of building described in 0 0 E. Each accommodation module is elastically mounted.

Main engine and power transmission

Differing from the present practice, two identical main diesel engines (1800RPM,

abt. 600kW) are installed in line, one behind the other. The rear diesel engine is

connected directly to the propeller shaft via the reverse reduction gear (reduction ratio

abt.

1:7). This propeller shaft is supported by two oil lubricated stern tube sliding

bearings.

The front diesel engine on the flywheel side drives two identical axial piston

variable displacement hydraulic pumps (Rexroth A4VSG 500). Those two hydraulic

pumps energize

two rudder

propeller-hydraulic propulsors - azimuth thrusters

(Hydromarine Rexroth YM-HMA 0500), with I Am diameter nozzle propellers. It is

foreseen that each side azimuth thruster will nominally absorb 150kW, and that the

remaining diesel engine power (abt. 300kW) will serve as the emergency spare. This

emergency spare power may serve either for increasing advance speed, or for executing sharp and crash maneuvers. During nominal operation, pressure in the hydraulic system

will be approx. 140bars, and 280 bars during emergency operation. In order to enable

navigation, when the front engine

is

out of order, a spare axial piston variable

displacement hydraulic pump is provided and driven by the PTO of the front engine reduction gear. One AC shaft generator of 60+80 KVA is directly mounted on the rear

diesel engine aft side.

An alternative solution is also defined. This alternative solution consists of two

mechanical rudder propellers driven by two independent diesel engines. We feel obliged to explain why we, at this moment, prefer hydraulic steering propellers, in spite of their

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE, BALA TON URED, JUNE 9-11. 1999.

very low transmission efficiency, wich amount to only 0.75 and 0.80, respectively.

Hydraulic (indirect) transmission can offer the following advantages:

excellent possibility of propeller RPM regulation in both directions functioning of the driving diesel engine during constant RPM

possibility of absorbing all engine power or reserve power, in any speed range possibility of energizing more consumers from one diesel engine

possibility of installing a shaft generator lower purchasing and maintenance costs, etc.

These numerous advantages of the hydrostatic transmission, in our opinion, can

compensate for its lower transmission efficiency. 6. Electrical installation

The basic difference in relation to conventional pushboats consists in the design of the energy-generating plant. This energy generating plant contains:

one three-phase AC shaft generator as the main power source of 60 to 80KVA

directly mounted on the aft side of the rear diesel engine. The power of this generator should be sufficient to supply all electrical consumers installed on

board including two electric windlasses on the barges.

one diesel-driven, three-phase AC generator as auxiliary power source of

approx. 40KVA sufficient to supply all electrical consumers installed on board. This generator, when necessary, also serves as a harbor generator.

7. Miscellaneous

All other systems on board, such as piping, mooring, anchoring, barge-coupling,

life-saving, firefighting, wheelhouse lifting and lowering etc. have been left unchanged.

We intend to replace the hand operated barge coupling winches with mechanically

(hydraulically) driven ones, with remote control from the wheelhouse. General arrangement of this hybrid pushboat is given in Fig 1

1.2 PROPULSION COMPARISON OF THE HYBRID SYSTEM

Design of the hybrid steering propulsion system is already described in few _published papers and monograph [12], [20], [21], but just for easier reading of this _{paper, we will}

shortly repeat main features of this system. This propulsion-steering system consist of one

central conventional propeller and two side azimuthing thrusters replacing _conventional

rudders. In addition the ships lines in the stern is formed similar

_{to the single screw}

vessels i.e. with sharp skeg carrying central propeller stern tube.

Above all, such a hybrid propulsion and maneuvering complex for the river

pushboat should enable two main goals to be achieved:

Most of elements making a conventional pushboat propulsion arrangement inferior are

removed giving no reason for drastic (20%) reduction of propeller performance in comparison to open water conditions;[4], [5], [6], [7], [8]

3 -c

hr

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE. BALATON ORED, JUNE 9-11. 1.999. a The propeller optimizationbased on open water results can be successfully applied in

design process again (or at least in preliminary design) as the hull influence factors are

going to be less important. Propeller design can be refined using some of existing

numerical propeller models and modem propeller design and analysis techniques.

Fig. 1 G. A. Plan

By an extensive survey of existing literature, it was noticed that a ducted

propeller operating in the close vicinity of hull bottom do not need to experience such a

bad hull influence as determined with conventional pushboat propulsion arrangement. For example, the results of a model propeller propulsion testing in depressurized towing tank

in Wageningen, [9], [10], showed the relative rotative efficiency values can be close to one, even with zero hull-duct clearance configuration. However, in such a case model stem configuration was free from stem tunnel and also free from any other appendages except necessary measuring equipment. So, at zero hull-duct clearance (offering the greatest propeller diameter to be installed) in the absence of cavitation, the values of

relative rotative efficiency r1r(1.022

- 1)063) were determined in the whole range of

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FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE, BALA TON URED, JUNE 9-1 I . 1999. advance coefficients. In bollard-pull condition, at cavitation number equals 0-N=2, the

propeller performance was just 4% decreased i.e. ra.(1-t)'=0.96 in comparison to open

water performance of the same propeller without cavitation.

All these data encourage us to reconfigure the stern part of a pushboat free of

rudders, flanking rudders, propeller struts, stem tunnels and nozzle free of deformation. That way, the stem configuration in front of the main central propeller is as much similar

to an usual single screw ship arrangement as

possible. Naturally, two side mounted steering propellers have to compensate the absence of rudders and even to improve the low speed maneuverability.

A dominant role in propulsion have the central propeller, so the optimum central

propeller and stern configuration were determined by correlation with mentioned

depressurized towing tank measurements [9], [JO]. Due to still present problem of small propeller immersion and air suction danger, a compromise optimum final solution for the

central propeller configuration was found that way, involving a small stem tunnel, no rudders nor flanking rudders, non-deformed nozzle and zero hull-duct clearance with

increased maximum central propeller diameter. A corresponding relative

rotative efficiency value for the central propeller operation was estimated to ra=095

Two side steering propellers are of smaller diameter enabling greater propeller

immersion, they experience no any inflow disturbances and their operating conditions are

quite close to the open water test conditions. Therefore, the value of relative rotative

efficiency fl R=1 .0 can be taken for the side propellers calculations.

In comparison with the previously described conventional pushboat propulsion

system. this hybrid solution introduces the following changes:

The propeller load is decreased by decreasing the total installed power (smaller

pushed convoys S1+1 or S2+2 envisaged) and by distributing the power between three

instead of two propellers. That way the propeller load is kept in a moderate load

region giving higher values of open water efficiency and reduced level of general

cavitation danger.

The stem part configuration is changed by excluding the emphasized stem tunnel and the central propeller strut. The central propeller stem tube with two shaft bearings is located in a stern skeg making the central part of the stern very similar to the stern of

conventional single screw ships. That action should give reduced deviation of

axisymetric central propeller inflow and therefore the higher value of relative rotative

efficiency.

The reconfiguration of stem form also enables the central propeller shaftline to be

reduced to a short propeller shaft with no more than two shaft bearings in the stem tube. The consequence is reduced mechanical transmission losses and also reduced shaftline bearings cost and maintenance expenses.

a The propellers operate in non-deformed nozzles giving higher nozzle generated thrust, uniform propeller inflow, larger propeller blade - hull clearance, no fluctuating blade tip

(over)load and finally a further increment in relative rotative efficiency. A larger

-5-propeller blade - hull clearance means also uniform central -5-propeller inflow, reduced

fluctuating local cavitation and reduced propeller generated vibrations.

The flanking rudders and main rudders are excluded from the propulsion and

maneuvering arrangement giving an uniform propeller inflow, reduced appendages resistance, reduced propeller wake and inflow disturbance and a higher expected relative rotative efficiency again.

o A comparison of the propulsive advantages achieved by the 1200 kW hybrid pushboat

is given in the diagram Fig 1 and technical data of the compared conventional and

hybrid pushboat is given in the table 1 [1], [2], [3] .

140 120 100 80 6 20

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE. BALATONURED. JUNE 9-11. 1999.

1I 0.13

P. = 600kW*2x300kW (hybrid design)(*)

P11= 2x300 kW (hybnd design - side propellers only)

(*) Upper deducted thrust curve calculated with constant side propellers power (variable RPM) Performance prediction

d = 2.5 m

= 7.5rn, P = 2x750 kW (conventional design)

L 0.12

The data used in calculating predictions in Fig. 2 are given in Tab. 1.

Hybrid pushboat Conventional pushboat Central propeller Side propellers Installed power PB-600kW /1800RPM PB=600kW /1800RPM 2 x PB-750kW /1800RPM Transmission efficiency + service reserve 12 % 26 % 14 (Yo Reduction ratio

., i=7.617:1 i=(5.6÷5.1):1 i=7.617:1

Propellers delivered power

PD=530kW 2 x PD7=-,220kW PD=640kW

13 14 15 16 17 us 19

V [km/h]

Fig. 2 Performance prediction

a

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE, BALATON ORED, JUNE 9-11. 1999.

Tab. 1

PART II MANEUVERING

2.1 THEORETICAL BASE

A ship's navigability and maneuverability represent her capability to realize a

determined motion while going ahead or astern and to control change or retention of the direction of motion according to operator's instructions.

The CRN, Danube commission and UN Economic and Social Council Economic

Commission for Europe Inland transport committee [14], have given proposal for the

minimum maneuverability standards. Essence of this proposals gives turning circle

manoeuvre, Zig-Zag test, crash stop test etc.

standards which inland vessel should

comply with.

The compliance with the standards have to be demonstrate based on the results of

the full-scale

trials conducted in accordance with the prescribed procedure. IMO

Resolution A.751 allow, for seagoing ship. that the compliance with manoeuvrability standards can be performed also by the scale model test and/or computer predictions -using mathematical models at the design stage. In this case full-scale trial should be conducted to validate these results. Mathematical model describing vessel's curvelinear motion in the horizontal plane consists of three well known differential equations [15],

(authors Basin, Gofman etc.):

dV, m11 cif tmVyr=T X H -dV dr m

+ V,r=Y,-YR

m+m

"

dt ₍₁₎ dr dVy m66 m" dt =N" ±YRxR mit =MI-211; "122 - 1?1 "22; m26=2,6; M66 "66

fri - mass of pushed convoy;

,222,2A, - added masses in longitudinal (x) and lateral (y) direction, rotational and

inertial added masses;

7

-Propeller RPM 236 319 ''36

Propeller type Ka-5.75 +

No.19A Ka-4.70 + No.19A Ka-4.70 + No.19A Propeller diameter Dc=1850mm Ds=1400mm D=1850mm

Wake factor

we0.20

_wSzO w=-:0.20

Thrust deduction factor tc-,0.20

t4.15

t,-.0.20

Relative rotative efficiency

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE, BALATON()RED, JUNE 9-11. 1999. If derivatives

in the equations (1) are omitted, then a system of

equations

describing a ship's steady turn motion is obtained: X=TX11X X , + mt-V, =0

EY =YH YR - mrV x = 0 (2)

IN =NH +YRx8= 0

Most of the relevant forces, velocities and angles appearing in (1) and (2) are given

in Fig 3.

.5a

100

Fig 3 steering devices generated forces versus angle of deflection

Solution of equations (1) gives numerical values of angular velocity, yaw angle,

overshoot angle etc. versus time for any of the prescribed manoeuvers. Instead of solving ,equitation (1) in this paper a shortcut is proposed i.e. solving equitation (2), giving results for the steady turn manoeuvers only. This results enable correct comparative analysis of

the different steering systems and can gives also possibility to approximately predict

compliance with a.m. manoeuvrability standards.

2.2 NUMERICAL SOLUTION OF EQUATIONS (2)

Every term of last two equation of (2) has the dimensions of force and _moment respectively. By dividing the force equation by EfroffILT and the moment equation by

2

113-;0/0Fr L2T, two more convenient dimensionless equations are obtained:

EY:4,fr,fi,P2)-YR+i.cos/3= 0

INa'N =0 (3)

40 SD

Angle of steering device deflection a(*)

XJ:(8)

0OiiW

Xr T Xr Xr

FIRST EUROPEAN INLAND WATERWAY NAVIGATIONCONFERENCE, BALA TON CRED, JUNE 9-11. 1999.

Equations (3) are two simultaneous nonlinear equations in three unknowns: angular velocity r, drift angle p and non-dimensional transversal steering force V, . It can be only

solved, for a given pushing train, by taking V a parameter. Numerical solution of the

equations (3) for S1+1; S 2+2; and S 2+2+2 pushed convoy configuration is obtained by

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Nondimensionalsteering devicelongitudinal force YRH = YR

Pi2V2LT

0.10

Fig. 7 Diagram randp vs. YR

The dimensionless transversal force

7,

may be generated by any type of

maneuvering device i.e. conventional rudder, azimuth thruster etc. The formulas for the

hydrodynamic force and moment, based on the systematic model tests, are taken from

[16].

The value XR =

represents the relative distance between the ship's center of

gravity and the maneuvering device transversal force [15].

Solution of the first equation of (2) gives speed reduction in a steady turn

maneuver. This equation is solved for pushing convoy S 1+1, and pushboat 800 kW

installed net power, equipped with three type of steering devices as follows:

conventional main rudders (see Fig 1) type A

two azimuth thrusters

hybrid propulsion-steering system type IC

By means of model experiments [16], [17] and literature [15], [13] is possible to

express the first equation in a form which is suitable for numerical calculation: for steering device in case A:

EX a T(J,A(5) (1 -0-{Rx(V)--222 Vy XR r Vy =0 (6)

iterating

0.8

in a necessary range and shown in the Fig 4. 1 1 , I 1 1 1 , 1 I , I S 1+1 - -1-7 - - -i-, - - -- - t - - - -4,- - -;- --r - -;-. i -.--I 0.7 --t-T1

E Ilb E lib

-i

.Li ,, Li L

I.-I t ,

j

--: .i.. L : 1 h=7.5m,d=2.5m , 1 1 r ',_ F , 1 ,--- -4-1 H -1 -T--T -T -T -r

r- I-- r

I 1

II

7 I I 0.6 1 -i-1 I 1 1 1 I

IiIIII

j I ,

,

_._ -4 -L -f- 4-- I-1

II

111111

I 1 I -1-I I CT) al 0.5 -.11 I 7 1 7

t

' L L t-/ 7 1 I 1 I I H -1--H---L---=1_ a) 15 ) Co 0.4 : ,---,...1---,---1

Ii______4_

, 1 .1_ , , I j. _.1.. I L L -1 -7---t. , r r

,-,--i

,i,

!I'll

,--I _T t T

F-T-T-1,--7-7-7---..., J. ---7,---7--:---rr---71--T---C nj Fn. c g 0.3 --: ..., 1 , I 1 1. r I r- ---r--',---1---:---',---I 4 , . 7 t , t

-t. -;

1--- t-- 1---;-- --t--1---0.2 - -, --4- -4 -4 -I- --:- f ' L

II,, ..1

L I J

r,r,i,-1,-1,

IiIIIIIIII

---,--1--1--1---t- ; , T r r- r-7---F -1 --1---0.1

-t

0.0 as I I I I type

0.9 . 0.8 . 0.7 .

0.6

0.5

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE,BALATON (RED, JUNE 9-11. 1999.

for steering device in case B:

EX X Ar(B) t') A2, V,. 1-1-1- m. r = 0 (7)

for steering device in case C:

Ex .[x:(c)

,13)]. (1-

t)-Voi)-

A22.. d+m. r- Vy =0 (8)

Tc - nominal thrust of the central propeller for case "C" The results of those calculations are presented in Fig 5.

2.3 COMPARATIVE ANALYSIS

A calculation of zigzag and turning circle maneuver, which is not given in this

paper, shows that all three considered steering device types

comply with proposed

maneuverability requirements, but obviously, using different angle of deflection.

Differences in the effectiveness of the considered steering devices during steady

turn maneuvers consists of the relative speed i.e. speed reduction shown in Fig 5.

Readings of the diagrams on Fig 5 for dimensionless angular velocity r =0.47, [3=0.290 and Vo=15.7km/h are given in Tab 2.

0.4. 0.3 02 0.1 0 D- steady turning 400kW ti)7rnC 500kW 150kW 400kW Xr T = Xr = Xr Yr Vat, Vat

Angle of deflection [deg]

Tab 5 Efficiency of different steering devices in steady turn maneuver

Steering device type 0 [deg]

V NO V [km/h]

A 26.7 0.633 9.72921 B 32 0.789 12.1269 C 64 0.752 11.558 0 10 20 30 50 00 -40 a

FIRST EUROPEAN INLAND'WATERWAY NAVIGATIONCONFERENCE, BALA TON ORED, JUNE 9-11. 1999.

Tab 2 Efficiency of different steering devices in steady turn maneuver

From Tab 2 it is visible that the hybrid

steering - propulsion complex at equal

dimensionless angular velocity r=0.47: has 20% smaller speed reduction and about 20% higher angular velocity at the corresponding steering device deflection.

2.4. CONCLUSIONS

In the Chapter 4, mentioned powers represent

net-delivered powers to the

propellers and the azimuth thrusters. It means that neither particular type of transmission

system was taken into consideration for the hybrid system side propellers. Considering

the type of the azimuth thrusters transmission systems there are three possibilities such as:

mechanical drive (Z-drive), hydrostatic transmission and electric podded propulsors.

Hybrid steering propulsion system can be realized using any of mentionedtransmission

systems. For medium and low power pushboats, the hydrostatic transmission system is considered as the most suitable. Hybrid steering propulsion system is designed to fully

exploit all the advantages of hydraulic propulsion power transmission (flexible operation,

continuous independent propeller RPM and absorbed power control, one prime mover

drives independently two propellers, superior low speed maneuverability, greater system reliability etc.) while the one, but dominant disadvantage of hydraulic power transmission

(low transmission efficiency) remains in the biggest amount recovered. That feature is achieved thanks to the presence of the third, central, mechanically driven propeller and the optimized distribution of total propulsive power between the central and two side

propellers.

Previously calculated results of propulsion and maneuvering benefit of a pushboat equipped with hybrid steering-propulsion system can be summarized as follows:

It offers 9-10% increase of the overall propulsive efficiency in the straight course

navigation than a corresponding conventional pushboat.

La It may perform 20% better steady turn maneuver with 20% lower speed reduction in

comparison with a corresponding conventional pushboat.

A comparative analysis showed that the hybrid pushboat can be built at a lower price due to reduction of many components (struts, rudders, shaft lines etc.).

Appearance of podded propulsors has increased

interest in diesel -electric propulsion over the last years. Podded propulsor represents azimuthing thruster with

electric sinhronous propulsion motor placed directly on the propeller shaft in a

streamlined body. The available power range lies roughly between 0.5 and 23 MW with

promising transmission efficiency which is

higher then

hydrostatic transmission

efficiency and even a bit higher then the efficiency of a mechanical transmission Z -drive. Benefits offered by azimuthing thrusters and technical benefits which might be

gained by diesel electrical propulsion would certainly expand the area of applications of the hybrid system to the much higher power range (bigger see going vessels).

FIRST EUROPEAN INLAND WATERWAY NAVIGATION CONFERENCE, BALA TON GRED, JUNE 9-1 I. 1999. REFERENCES

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8t.

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