NAVE PROSYSC, Numerical Algorithm for Vessel Propulsion Systems Configuration

Technical University of Delft

National Technical University of Athens

NAVE

PROSYSC

Jr:

trjerin

rio

Numerical Algorithm for VEssel

PROpulsion SYStems Configuration

Diploma Thesis

by Dandolo Pace

Delft, 8 November 1995

Technical University of Delft

National Technical University of Athens

NAVE

PROSYSC

Numerical Algorithm for VEssel

PROpulsion SYStems Configuration

Diploma Thesis

by Dandolo Pace

Foreword

The current report is an account of the work conducted by Dandolo Pace in order to fulfill partially the requirements of the Master of Science degree in

the Faculty of Mechanical Engineering and Marine Technology, Section

Marine Engineering (OEMO) of the Delft University of Technology. Head of

the Marine Engineering Section is Prof. ir J. Klein Woud.

The work has been conducted in the Laboratory of Marine Engineering of the Department of Naval Architecture and Marine Engineering in the National

Technical University of Athens (Greece), under the supervision of Professor,"

P. Ioannidis, in the frame of the European Community student exhange

programme ERASMUS. The project has been completed in twelve months (April, 1994 to March, 1995).

The results of the project (numerical code, databases, selection algorithms)

will be particularly useful to marine engineering students of the departments of both universities and to professional marine engineers. Due to its user

friendly nature (information exhange) and environment (Visual Basic for MS Windows), the entire package, in its eventual form (after the databases have been enriched and the algorithms and code have been tested and validated in

Table of Contents

Summary

Introduction 7

2 Main Engine Selection 13

2.1 Main Engine Selection Criteria & Procedure 13

22 Numerical Code Description 14

2.3 Numerical Application 20

3. Gearbox Selection 23

3.1 Gearbox Selection Criteria ₂₃

32 Numerical Code Description 28

33 Numerical Application 33

4. Economical Aspects 37

4.1 Introduction ₃₇

4.2 Procedure 43

4.3 Numerical Code Description 52

4.4 _{Numerical application 56}

5 Shafting System Dimensioning 59

5.1 Introduction ₅₉

52 Procedure 62

5.3 Numerical Code Description 80

5.4 Numerical Application 90

Bearing Arrangement 97

6.1 Introduction ₉₇

62 Mis-Alignment Theory and Method 99

6.3 Numerical Code and Application 102

Conclusions 123

Contributions 127

Suggestions for Future Work 127

References Appendices

Al IACS Requirements

A.2 Data Files _X

A.3 DataBase Listings _XII

A.4 Engine Manufacturers data 9..

Summary

The main occupation of the marine engineer is to configure the propulsion

system of a specific ship. As soon as the power requirements are known and the propeller(s) is(are) designed the marine engineer must select a suitable

power plant / _{gearbox(es) and design accordingly the shafting system.}

Auxiliary equipment selection and other systems (lubrication, cooling, etc.) design follow.

The present work concerns the first of the aforementioned tasks. _{For the} purpose of this thesis, the propulsion system in consideration consists of a

single engine, a gearbox with one gear quill shaft (input shaft) and _{one final}

gear shaft (output shaft), and a single propeller.

Suitable algorithms are developed that enable the engine selection based on

power requirements and cost considerations out of a database of existing engines. Similarly, a suitable gearbox is selected from another database,

matching the required propeller regime to the chosen engine. The dimensions of the various segments of the shafting system are then calculated according to LACS (International Association of Classification Societies) requirements. A numerical code is constructed, in Visual Basic 3.0 for MS Windows, that implements the previous algorithms. A _{user friendly package of the databases}

and codes enables the user to go through all the steps of the power plant

selection and shafting system design

_{until the final configuration is}

acceptable. A static analysis then helps to determine the

proper bearing

arrangement (number of

bearings, interbearing distance and suitable

(mis)alignment).

The latter is performed using the PC-Frame 3.5 code

developed at the TU Delft.

The work shows that it is easy to iterate the entire procedure of power plant selection and shafting system design as required without having to use time

consuming manual calculations.

_{The code allows the designer}

_marine

engineer to perform easily and with almost

_{no cost of time a sensitivity}

technical considerations but also economical factors play an important role on deciding the final system configuration.

Further enrichment of the databases, inclusion of vibration calculations (for

use in flywheel dimensioning, elastic couplings, torsional dampers, etc.),

cooling and for other auxiliary systems design, electrical power generation, extension of the algorithms to allow for multiple engine, gearbox, shaft, and propeller configurations, a possible employment of a total energy system, will

broaden the applicability of the package and the set of end users. As the

1.

Introduction

One of the most important steps in the ship design process is the selection of the power plant installation and the dimensioning of the shafting system. As

soon as the initial design of the propeller as well as the initial values

concerning the power requirements of the specific vessel (engine power at a

specific propeller speed) are known, the marine engineer must select the

suitable power plant installation engine(s), reduction gear(s)) and accordingly

dimension the shafting system.

This is generally a time consuming task that has to be performedmany times as the builders advancein_ the ship design spiral (Fig. 1.1). Therefore, it helps

the designer a lot if this task is computerized. This way a sensitivity analysis

of different designs can be easily performed even in the initial stages. Hence,

the main concern of this thesis has been to address the following problem:

"Develop a computer code that selects an engine and gearbox installation and

dimensions the shafting system, according to power requirements, economical considerations, and possible designer set criteria."

The goal of this report is to outline the steps taken in order _{to answer this}

question.

_{The importance of the work lies not only in the fact that it}

produces a satisfactory solution, but also in the fact that it constitutes a solid

basis for addressing, in a similar manner, the most general problem of a

-propulsion system design for any ship and any power plant configuration.

For the purpose of this thesis, the vessels considered _{are commercial ships}

with constant service speeds for long operating periods (roll-on roll-off, cargo,

bulk carriers, etc.) with a power plant installation consists of 4-stroke _medium speed Diesel engine(s), reduction gear(s) with _{a single or double input shaft}

and a single output shaft, and a propeller(s) with the corresponding shaft

STRUCTURE PROPLL SION SYSTEm ARRANGEMEN TS LIGHT SHIP WEIGHT CAPACITIES POWERING REOU I RENENT S STABILITY \HLLL FORM NV DIMENSIONS AUXILIARY SYSTEMS DESIGN EVALUATION MULL MACHINERY/ CARGO SYSTEMS COST

Fig. 1.1 Ship design spiral (Marine Engineering)

Therefore, the work here covers the cases where the propulsion

plant configuration is one of the following:

a single engine, a single reduction gear

with one input and one output

shafts, one shaftline and a single propeller

multiple engines, multiple reduction gears with one input and one output

shafts, multiple shaftlines, and multiple propellers (that is separate

shafting systems)

two engines, a single reduction gear with two input shafts and one output

shaft, one shaftline and single propeller

ELECTRONIC AND NA VI GAT ION SYSTEMS INTEGRATED LOGISTIC SUPPORT SHOCK NOISE DESIGN FOR PRODUCTION

Consequently, the engine selection can be performed only on an MCR basis. That is the maximum continuous rated power at the required propeller speed. This information is provided by the naval architect who designs the hull and who also provides the load curve for clean and fouled hull. The input is used

by the algorithm developed to browse through a database of 4-stroke,

medium speed Diesel engines and filter out a small set of alternatives from which the user can select one for further analysis. The selection also depends on an economical analysis for which a separate algorithm has been developed

and incorporated in the main one.

The second step is the reduction gear selection performed in a similar manner.

Based on allowed torque and a calculated required reduction gear ratio, the algorithm browses through the database of existing single input shaft, single output shaft reduction gears. Subsequently, the marine engineer can select one from the set of those meeting the initial requirements.

The next step is the design of the shaft line. _{The analysis is based on the}

LACS requirements (International Association of Classification Societies). The

designer can choose from a solid or hollow shaft, from _{a direct or viscous}

coupling and can separately dimension the propeller, the intermediate, the

thrust, the final wheel, and the gear quill shafts, with all the

_necessary flanges, bolts, fillet radii, and tapering lengths and diameters as well as the

thrust collar. Subsequently, he can construct the entire shaftingsystem.

It is important to underline the fact that standardized_{parts are economically} more convenient than customized parts. The engines and the gearboxes will be selected on the basis of characteristics declared by the manufacturers. _The shafts diameters are also standardized. _{Any modification to the "normal"}

values may result in an unacceptable rise in costs. The whole design procedure is based on this fact.

The above procedure is implemented in _{a numerical code called PROSYSC.}

This is written in Visual Basic 3.0 for MS Windows.

_{The code is a user}

reasonable way and simplifies the selections through graphical presentations of data (load curves, engine diagrams) and pop-up windows. The shafting

design is accompanied by detailed, scaled drawings of the various shafts

(propeller, intermediate, and thrust) as well as of the complete shafting

system.

The final step is to configure the proper bearing arrangement. Then an

analysis is performed using the PC-Frame code developed in TU Delft and the final number and vertical and horizontal positions of bearings are chosen

so as to meet the rules that concern the bearing influence factors. The

PC-Frame code is run through the main PROSYSC, but is supported by individual

Visual Basic 3.0 subroutines for its input data calculation. This concludes the work performed in the frame of this thesis.

Alternative designs, such as cases without a gearbox are easily addressed by this work, while different kind of propulsion plants (such as turbines, etc.) cannot be answered due to lack of data (database enrichment necessary) or due to increased numerical code complexity (extensive code modifications

inevitable). Theoretically, however, the problem is answered easily. Further

considerations, such as torsional vibration calculations (for elastic couplings

dimensioning, etc.), electricity generation, auxiliary system design, total energy systems, are not possible to address given the time limits.

Before we close this section, we will give a brief outline

of the text of the

thesis. Chapter 2 of this report contains the description of the Main Engine selection criteria, method, engine database, and numerical code developed.

Chapter 3 presents the gearbox selection procedurein a similar way as well as

the gearbox database construction. In Chapter 4 the economical aspects of

the engine selection procedure are described. The dimensioning of the

shafting system as well as the corresponding numerical codes are given in Chapter 5. Chapter 6 describes the bearing arrangement and in particular the

Finally, Chapter 7 contains the conclusions of this work, Chapter 8 its

contributions to the academia and the industry, and Chapter 9 our suggestions

for future work. The logical links and the general design procedure is

represented in Fig. 1.2.

V

1

Primary inputs

14

Shafting Global Drawing

V VP 5 Maintenance Costs Calculation V

Fig. 1.2 Flow chart showing the relations between the project's different

items: _{Chapters 2 and 3 will discuss blocks 1, 2 and 3. Chapter 4 describes}

blocks 4. and 5, chapter 5 block 8 to 14. Block6 is the subject of chapter 6.

t:

9 10 11 12 13

Propeller Shaft intermediate Thrust Gear Quill Final Wheel

Shaft Shaft Shaft Gear Shaft

2 Resistance& Power Curves

3 Engine Selection

Gear Box Sel.

.411-111P-4 Total Costs Calculation 6 Bearings Alignement: External Programme 8 First input For Shafting Design

2.

_{Main Engine Selection}

2.1

_{Main Engine Selection Criteria and Procedure}

The choice of a ship propulsion plant depends mainly on the type of vessel

and its operating profile (the ship's speed as a function of the kind of

operations and time), the configuration of the propulsion alternatives and energy generation system, and the general economic situation, ruled by oil

price.

In our case, the economical situation usually dictates the propulsion system

philosophy: when the fuel price is low, the cheapest suitable engine is

selected, because the ship owner is relatively indifferent to the running costs.

When the fuel price is high, the designer selects the engine that has low

running and maintenance costs. This concept is of paramount importance and is based on the total costs over the life of the ship. The economical aspects of the propulsion plant will be discussed in chapter 4.

However, in this preliminary design stage, the following criteria are applied: minimum necessary power at a given propeller speed

three user set criteria: fuel consumption, weight and revolutions _{per minute} of the engine

The engine prime requirement to be met is the power necessary at the given

propeller speed, that has previously been calculated by the naval architect. This power takes into account the transmission mechanical losses, has a margin for hull fouling over the years, considers possible adverse weather

conditions, and is the principal input for the main engine selection.

The three criteria for the set selection are secondary. Nevertheless, they are important, because they filter out unwanted engines and therefore _{define a}

set of engines consisting of valid alternatives.

_{For example, the fuel}

consumption may be considered acceptable only under a certain value, whilst the weight of the engine should not be higher than a specified amount. The

user may know that,

for example, the most standard reduction gears

supporting high torque, have reduction ratios with values lower than 4.

Therefore, he may want to set a maximum value for the engine's MCR speed,

obtaining a better set of valid alternatives.

The first step is to select a set of engines from the four stroke medium speed

engine database. At the moment, the

database' consists of 721 records

(engines), ordered in ascending MCR power. This set contains engines with a

MCR power equal to or greater than the aforementioned necessary power,

from which one engine will be chosen. After the reduction gear selection and matching to the selected engine, an economical analysis is carried out, and its

results stored. Then, a second engine can be selected from the previously

constructed set, and the procedure is carried out in a similar way. This is

repeated, until the designer finally chooses the suitable engine and gearbox

combination.

2.2 Numerical Code Description

When already installed in Windows, PROSYSC is runned by clicking its icon.

If the user starts in the DOS environment, he should then run the prosysc.exe file (Windows still required). The title window then appears, but has to be

clicked twice for the continuation of the program.

For the correct

implementation of the program, the database files and the data files must

also be loaded in the appropriate directories.

The main code is written in Visual Basic 3.0 (for Windows). This allows the use of queries that, when applied to the engine database, select a small subset

Engine Gearbox Selection

V 3

77.-.

Input query upper limit MCR power

input lower E. upper limits of the secondary

Yes

Run engine query

6

Selection* engine from grid

7

Input torque query upper limit ratio query lower and upper limit

number of requested records

V

8 Run Gearbox query

9 no

Are there any records in C query results grid'

C----15

Propulsion plant Economical Evaluation

____,...---Input required MCR power and propeller speed

5

Are there any records in the query results grid')

no

yes yes

11

Select two alternative gearboxes

no

12 Run

power characteristics and resistance curves yes 13 operating point in the acceptable graph area, no yes 10-2

Rerun Query with another selected engine") V

no 10-1

Rerun Query with new boundaries?

yes

V

4

Select one gearbox V

MCR Power and Propeller Speed

Continue Quit

Fig. 2.2 The firstinp.frm form

The entire available assortment of engines is contained in a database file

created in

the environment of Dbase IV (for MS-DOS).

This file

(modce_w2.dbf) is converted for use in the ensel.mdb Access file. The Vbasic code and the Access files are easily linked thanks to the data control

custom buttons.

Fig. 2.1 shows the global engine and gearbox procedure, with blocks #3 to #6 representing the engine selection procedure, and blocks #7 to #14 the gearbox

selection procedure. The input, as well as the output values (block #2, Fig.

2.1), are presented in separate windows, calledforms'. The firstinp.frm form

(Fig. 2.2), the practical implementation of block #2, has two frames, one for the fouled hull condition (the most important one) and the other for the clean

hull situation. Each frame contains two input text boxes: the first is for the

requested MCR power and the second for the requested propeller rpm. By

clicking the "Continue" button, we run the subroutine that attributes these

values to global variables, and activate the "Engine & Gearbox Selection" window.

The engine and gearbox selection procedures are on the same window, in operations) time Clean Hull MCR Power Propeller _!270 Speed

Condition Fouled Hull

MCP Power Propeller Speed Condition"- ''''''''' [kW] [rpm] [kW] Irpml 1760 280 i 1500

their relatively great amount, the various items are coded following a letter and number system (Fig. 2.3a, obtained by clicking B11). The numbering of the text boxes (used for introducing input or reading output) starts with the letter "T", the buttons (used to run subroutines) with a "B", data controls

(scroll button connecting text boxes to databases) with a "D", option frame

with an "0", and grids (database sets listings) with a

The engine query is summarized in blocks 3 and 4 of Fig. 2.1. The input

values are the minimum required propeller power and a maximum user

defined power limit. This maximum value is introduced in order to restrict the set of engines, and thus to avoid the choice of engines that have too much power (the required fouled hull power has already been chosen, in excess, by the naval architect). These two values appear in text boxes T2 and T3, the latter may be modified (Fig. 2.3a). The user may limit the final number of engines contained in the set, typing the desired amount in the requested

records text box 110. Finally, the boundaries of the secondary criteria can be

set: text boxes T4 (lower limit) and T5 (higher limit) are reserved for the

engine's rpm, T6 and T7 delimit the Specific fuel consumption, whilst 18 and

T9 restrict the database in the weight of the engines. Pressing the "Engine

Query" button B 1, activates the query subroutine.

The query amount of found records (appears in T11), can be exactly, or

partially, the requested amount of records. On the other hand, it may also result in too few records, or no records at all. It is then possible to change the query ranges and/or options, and re-run the query. This action is schematized

by the loop from block 5 to block 3 (Fig. 2.1).

The subset of engines thus defined is displayed in a grid (G1) and is then

available to the user. Name, model, MCR at given speed, Fuel consumption,

number of cylinders and price (if available), are displayed in the different columns of the grid. Note that the value 0 appears in the grid cells only if

the data is not available in the database. If the user decides to select a record

containing one or more missing items, he must then contact the engine builder

lacking values become inputs in the following design steps. It is also possible

to enter the missing data in the database by typing them in the textboxes

which are connected with this database (T14, T15, T16 and T17).

The final choice has to be selected by using the data control (D1)._----\

selected (or to be selected) n g ine ame appears T12, and the model in

Its MCR power is in text the weight in T!6, and its price in T17. By

clicking the "OK Engine" bu ton (B2), we confirm the engine choice. This

action will display the resulting torque factor in kW min (T18) and the

required reduction ratio (T20).

These two values are the inputs for the

gearbox query' . It also saves other values (such as power, fuel consumption, price and weight), that serve as input for the eventual economical analysis and

shafting dimensioning. To select another engine from the existing query set,

or to run another query, the user must first click the "New Engine" button

034).

Power Rangeof query: Propels MCR Between NCR Speed Matt Engine Model MCII-Powet MCR-S pried Nan Price and end To 1and 72 T4 iEnd 131 we I I 114 1144lEssion DI III NY

Ti Requested propeller speed( T2 Required, power

T3 Upper power limit T4 Lower rpm limit 'T5 Upper rpm! limit T6 Lower SFOC limit 17 Upper SFOC limit

T8 Lower !engine weight limit T9 Upper engine weight limit

T11 Number of engines found T12 Selected engine name T13 Selected engine model

T14 Selected MCR power T15 Selected MCR speed

T16 Selected engine weight TI7 Selected engine price

f4

712 ₁

01 134 "0 1

B2he

'Torque Range for the Query Between Men Between Ewe& Gere-Bwr Mae Torque sea Red. Ratio Men no I TB Reduction Gear Ratio

Requited Cenfigurenow Price F7T-0

I4 ileducti02,,th

Rat% 131 "i.°2 T321 choice na choice , BOW

cirri° I

and tonnes r22 I 736 T23 729 lksv kw.ran

Fig. 2.3a The Selection form structure T20 Necessary ratio

T21 Red] Ratio lower limit!

T22 Red Ratio upper limit T23 Number of requested gearb. T24 Number of found gearboxes T25 Gearbox name

T26 Gearbox model(

T27 Selected] gearbox max !torque T28 Selected] gearbox red ratio

TIO Number of engines requested T29 Selected gearbox weight

T301 Selected gearbox price T31 Test ratio I

T32 Test ratio 2

T33 Engine and gearbox weight T34 Engine and gearbox price T35 Gearbox max mass limit T36 Config. User-set value (35)

Oflede fled inns ewes& T37 T25 724 I 12T1 Plant Jidda Weight Puce cool BS 17231 I TM

A

4,11' 89 She 13 S. Bias 1-Bacl 121.2-;71

BI Run engine query B2 Accept Selected engine B3 Run gearbox query

B4 Unlock engine selection B5 Configuration setting B6 Accept select gearbox B7 Unlock test ratios

B8 Run economical evaluation B9 Run resis. & power graphs

1310 Run shafting design

BII Print actual form! 812 Go to initial input

GI Selected engines grid! G2 Selected! gearboxes grid

T18 Selected engine torque factor T37 'Config. User-set value (35) _{D1 Engines database control}

T19 Upper lim torque factor

II Ilime OCR illirendl5FMC he/44404141

I =MitrEinnCrM Tom

II SINZER 1765 /OW 113 is II 1 tmuwn_ 3.524 1.77 25 113955

SENT _{MEM moo 180} 13.5 352000 MI EINTJES 3.522 1.78 3.85 0

SENT 1770 1000 183.6 11.7 354000 3 M777113.579 18 05 14C

MAN 1800 10 14.4

as

OHMANN_ 3476 a A 154734

S SKI_ 1000 10 14.5

ra

LOHMANN_ 3.476 : 02 .1 159320

FINCANTIERI/00 4 10 01 i0 I DELOHMANN, 3.383 : .1 166233

YAMMAR 1838 72u tar e fillLOHMANN_ _{1522 Luna -..2 101951} WAERTSILAE1840 1000 196 12.2 1 1:.LOIIMANN_ 3.522 2575 7.8 187226

i NIIGATA 1840 1000 II 0 9 LOHMANN_ 3.45 2.6 2_9 102000

IS FINCANTIERI18441 2100 0 0 10 ICHNAIIN 3.446 3.1 78 1%167

tt7=== Torr-ror:

ENGINE AND GEAR-BOX SELECTION

and 79 requested recants laud

rn

end I 720 I I 734 733 j tanner S 1 73 TS T7 'wanes Inol Till 3 14 7 0 0 0 I s I _kW 1 IT1 I 1 S.F.O.C. r

2.3

Numerical Application

To illustrate the procedure, let us consider an example (Fig. 2.3b) where the

required power is 1760 kW (fouled condition), at a propeller speed of 280 rpm.

The required power is the lower limit of the "power part of the query.

Automatically, the upper limit is set at 1.2 times the lower limit (1760

en

= 2112 kW). The latter is a default calculation, and its value can be changed by

the user. We then set the secondary "filters". We choose for the

"MCR-Speed" boundaries respectively 420 and 1120 rpm (there are fewer gearboxes

with ratio <15 and we want to keep the torque relatively low), and we also

know that a gearbox is necessary.

We want to consider only engines

consuming up to 200 g/kWh (the upper limit). Since this data is not always

known for all the models, we set the lowest SFOC limit equal to 0 g/kWh,

which is the database default value for any missing data.

We consider acceptable all engines weighting up to 15 tonnes (upper limit). Similarly to

the SFOC one, this lower limit is set equal to 0 tonnes. Finally, we define the

amount of records (engines) that the user wishes to be part of the set: 10

records. The resulting query is in other words:

"find the first 10 engines, in ascending MCR-power order, having at least a

MCR power of 1760 kW and a maximum of 2112 kW, at MCR speed between

420 rpm and 1120 rpm.

The engines must have a maximum fuel oil

consumption of 200 g/kWh and must not weight more than 15 tonnes."

Note that the engines are already arranged in ascending order in the database, and will therefore appear in the grid also in ascending

order. The result of

this query appears in the engine's query result

grid. We then choose the

engine. Generally, this first choice depends on user's preferences (political,

strategic or practical, international agreements, land of operations, personal

contacts etc.). Other factors, such as the fuel consumption, also play a role.

first record" button of the engine datacontrol DI, obtaining the displaying of the first engine of grid in the textbox 112. Then, we click (in this case once)

on the "go to the next record" button, until the requested engine name and

model appear respectively in textboxes T12 and T13. We finally confirm the choice by clicking the "OK Engine" button, making the engine's properties

available for further code processing.

Should the designer select an inappropriate engine, he may select another by

clicking the button "New Engine" (B4, Fig. 2.3a), which unlocks the data

control. If the set of engines does not offer him a suitable choice, he may

then run a new query with new boundaries values.

MCR Between MCR Speed Mass Engine Model ass Price 1760 420 0 0 MCR-Power 11760 MC9---9 peedli000 13.5 3520001 requested records found 10 1 SEMT PIELSTICK PA5 255 L8 )(kW] [1/min] tonnes OK Engine New engine Gear-Box Name Torque Red_ Ratio Mass Price

Nil

R 3601 choice Reduction Gears Ratio2 choice Other choice of ratios

1

011 NAME Model Rattof Roan Rmax Er

COOMANI4=1111

Actual Prot, Speed 18_35 OK GearBox ton 279_41 Economics Res Curve Shaft Design] Print Form Back to Start:

Fig. 2.3b The engine and gearbox selection form: numerical application

II Name INCA !S peelS FOCNVeig! Price

1 SULZER 1760 1000 199 15 0 2 SEMT 1760 1000 180 13.5 352000 .11=111W1770 1000 183.E 11.7 354000 4 MAN 'Mill1000 199 14.4 0 5 SKL 1800 1000 185 14.5 0 6 F1NCANTIE 1804 1050 0 0 0 7 VAN MAR 1838 720 197 0 0 8 WAERTSIL 1840 1000 196 12.2 0 9 NIIGATA 1840 1000 0 0 0 10 RUSTON 1865 1000 200 14.210

ENGINE AND GEARBOX SELECTION

-Gearbox Query.

rpm] Default 1 Torque Fact LT.76.---iand 2.64 _[kNolmin] Configuration Between

and 2112 [kw] Mass Max 5 tonnes _requested

5 and

records found

1120 1/ruin e. ductaon Gear Ratio Ii

Between 3.535 and 3.607

and 200 _{g/kwh Exact}

3.571 Gear Box Query

tonnes

Required Configuration: COAXIAL ['Base Code

1.8 _{[kW. min]} 3.579 4850 _kg 141167 280 -Engine Query : Propeller LOHMANN NAVILUS_GWC_4 493167 Plant Totals Mass Price Engine Query and 1

Gearbox Selection

3.1

Gearbox Selection Criteria and procedure

'This procedure is based on two criteria:.

the maximum allowed torque on the gearbox quill i(i e, input) shaft

the necessary reduction ratio, in order to meet propeller speed requirements

The gearbox selection procedure takes its inputs from the engine selection

Once the engine is chosen, _{the coupled gearbox must at least support the}

engine maximum torque. For this, purpose, we introduce a torque factor':,

which is the ratio of the engine power and of the speed this power is

delivered,, expressed in [kW min] It is used as the standard torque measure

from the majority of gearbox manufacturers.. The engine's maximum torque2

factor must be equal to, or less than the maximum allowed torque on the

reduction gear quill. The engine's maximum torque ,corresponds to the torque

factor at MCR conditions. the ratio of MCR power and MCR speed, We will

illustrate this, in the next paragraph..

Fig. 3.1 The engine power curve and the different load curves

Let us consider the engine power curve of Fig. 3.1, and the load curve #I. The intersection of the two curves is A, which is the point of operation at 111%

MCR power and 100% of the corresponding MCR speed (note that in the

figure, the abscissa represents the engine speed, which is proportional to the propeller speed). The relative torque factor is then equal to the ratio 100/100

= 1. Suppose now that the sea situation changes, resulting in a shift of the load curve to the right (curve #2). If we exploit the engine's possibilities

fully, we find a new operating point, B: 100% of the MCR power and more

than 100% of the MCR speed, lets assume 102%. The resulting torque factor is then 0.980.

The more the curve moves to the right, the more the factor

decreases. If we consider a shift to the left the load curve (curve #3), the

operational point

lies on the power line with gradient equal to one

(theoretically, this line starts at (0,0) and ends at (100.100), the MCR operation

j4- point), which is in this case also the torque factor. Note that if we choose any operation point "under" the power curve (Fig. 3.1, blue line), the torque ratio will always be under the value 1, since the rpm values in that region are always greater than the power values. Therefore we can conclude that the

highest torque factor is always the MCR-point point A to be changed

The gearbox selection is performed in a similar manner to the engine

selection. One gearbox is finally chosen from a restricted set. This set

consists of elements answering to restrictions set by the user. The first one concerns the maximum allowed ingoing torque, a

value that must not be

exceeded. The second restriction states that the gearbox reduction ratio must be equal to the required ratio, or to be within an acceptable range. This item

will be discussed in the next paragraph. The configuration type is the third 'filter' applied for the selection and has the following four characteristics:

Number of Input and Output (0/I) shafts (single input-single output, twin

input-single output)

I/O shaft offset (coaxial input and output shafts, diagonal offset, vertical offset, horizontal offset)

Finally, a maximum gearbox mass limit may be set by the user. This 'filter' is particularly useful when specific requirements regarding the transmission's

total mass are in order.

For a given model of gearbox, the manufacturers offer a set of precise ratios

(standard) to choose from, within a given range.

For instance, for the

LOHMMANN NAVILUS GWD 42.45, five precise ratios can be delivered in the range 12:1_4:11 : 1.9737, 2.5484, 2.9286, 3.5833 and 4.000. If the requested

ratio does not belong to the standard values, the gearbox can usually be

delivered with designer's required ratio, provided that the value lies within

the given range. The latter may have the following two consequences.

Firstly, factory's machines may not be able to engineer the exact requested

ratio. Secondly, standard spare parts cannot be used, the cost of the gearbox will increase and the manufacturing of custom-sized parts (be. gearwheels) will inevitably result more expensive. Supplementary costs estimation for the larger' gearboxes selection is 10%. For smaller gearboxes, the request of a

'customized' ratio may raise considerably the expenses (up to 2-3 times).

The latter suggests the introduction of a tool, that enables the gearbox

selector the assessment of a choice. We therefore define an "acceptance

area" (Fig. 3.2) in the engine power and hull load graph: the requested

operating point must lie in this area if the gearbox ratio is to be considered valid. _{First, it is necessary to describe the engine power curve. To limit the} code size and to keep it applicable to all engines included in the database, the engines characteristics are all constructed in the same manner. Each engine

power curve is divided into three parts.

Engine power characteristic

Take for example the blue curve of Fig. 3.2, which is the engine power as a function of the propeller rpm when the gearbox with a ratio i is applied. The first part of this curve is the line starting from (0,0) and ending in point a,

i.e., the MCR point (PMCR _{nMCR,1 ) The propeller speed at engine's MCR}

A "v\'''

Out

Ycurve is "flat" and goes from ai to bi. The abscissa of point bi is of the order

of 5% of the nmcw. (3% in fig. 3.2). When the maximum speed is reached, the

power decreases radically. This explains the vertical line drop from point bi (through ci ), representing the last part of the engine power curve, in terms of

engine rpm reduced by a gearbox reduction ratio of a value equal to fT

speed) vs engine power. (a,, bi, ci and di) delimit the "acceptation -region". In this example, the selected reduction ratio is and engine power are respectively slightly lower and higher than the requested values (less than 1%in both cases)

Load curves

The load curves are based on the following assumption

P

ci 3

f n

where P is power required, n the propeller speed

and a is a constant.

Subscripts f and c stand respectively for fouled and clean hull condition, since

the code will plot both curves. This constant is found by replacing P and n b

1 .0 3 nu",

propeller /pm

Structure of the engine power curve: engine reduced rpm (propeller

Requested operation point and "acceptance "area

On the load curve, we find the required operational point (red disk in Fig. 32).

Its coordinates are the required engine power (which can be equal to or less than the selected engine power) and the propeller required speed. Consider

the example of Fig. 3.1: if the selected engine has exactly the required power,

and the gearbox required ratio is equal to i , then the requested point of

operation is exactly ai. A gearbox ratio can be accepted if this point is in the

rectangular region delimited by the points ai,bi,ci and di (Fig. 3.2). These

points are delimiting a region in which the engine operates between 100% and 103% of the nmaki value and between 97% and 100% of MCR power Pmcx, .

Therefore, the coordinates of these points are

ai: (PMCR,i nMCR,i)

b : (Pmcki , 1,03 12mcki )

C : (0.97 P mcxi , 1,03 rimcR,i)

3.2 Numerical Code Description

This is developed using also Vbasic 3.0 (for Windows) in a similar way as in section 2.2 above. The selection is made out of a previously constructed and now updated gearbox database. This database file is originally meice.dbf and is converted to the access database file, similarly to the previous engine selection, to the Vbasic environment. In the flow diagram of Fig. 2.1, the

gearbox selection procedure is represented by block 7 through block 14.

The procedure starts by defining a query (block 7), that will reduce the choice

to a subset of gearboxes.

The creation of a subset using the required

configuration, the maximum allowed torque criterion and the necessary reduction ratio through suitable queries, will allow the final choice of the

most suitable gearbox.

We are considering the eng&gear.frm form, and the letter-number code still refers to Fig. 2.3a. The input lower limit is the calculated engine database

field engine torque factor (118). The text box is connected to the calculated database field "Torq" by the data control Dl. The input upper limit (T19) is

again user defined (as in Section 2.2), and the default value is equal to 15 times the selected engine torque factor. The gearbox configuration must be

set in the "Gearbox Configuration" window (Fig. 3.3). The latter is activated by clicking the "Configuration" button (B5).

-Input and Output Shaft:

'Positioning ce) Coaxial Diagonal Vertical Horizontal Same side r) Twin input Rotation Direction

0

Opposite Reversible Back to Query G C

0

The calculated selected engine angular speed to required propeller angular speed ratio (T20), i.e. the reduction ratio, is the determining factor for the

final selection. Since it is not always possible to find a gearbox that has the exact required reduction ratio, the query inputs are lower (121) and an upper (T22) reduction ratio limits. By default, these two limits are respectively

equal to 0.9 and LI times the exact ratio. Nevertheless, the user can try to

find immediately the gearboxes having the required reduction ratio by setting both the lower and the upper value equal to the necessary ratio. The user has

also the choice of limiting the amount of records: the amount of requested

records must be entered in text box 123.

Pressing the -GearBox Query" button (B3), the subroutine GearQuery is

executed, followed by the subroutine GboxFamily. The first activates a query that searches the database analogously as described in Section 2.2.

The second one runs a separate programme, based on the Selection Curves

method (Fig. 3.4). _{Each gearbox model can be ordered whithin a given}

minimum and a maximum value of ratio and torque factor. The code first

determines the model', i.e. running through the list of different models, until

the required ratio (iq) and required torque factor (Tq) fits the model's

range. Each model can be delivered in different types, characterized by a

maximum torque factor curve, which is function of the reduction ratio. The required max. torque T

q

is compared to the significant torque values on the curves (i.e. in Fig. 3.4 T3639, T 39.42. . T60.66) for iireq,until Lei,

The model denoted xy.zx is thus a valid alternative.

Once one type is

determined from a model, the code continues the

range test with the

remaining models. Finally, the retrieved the different model

types are annexed to the to the results of the GearQuery subroutine. _{Each gearbox}

model is entered as different record in the database, in a similar way to the gearbox types with exact ratios and max. torques. The fields RRA T_EX (exact ratio) and TORQ_EX (max. torque) of the families (models) contain the _{value '4', as opposed to the exact values for the gearboxes with exact} ratio.

NAVILUS LOHMANN GW:GWL Class LRoS, RV. GL 0-52.59 60.66 49.54 45.49 42.45 39-.41 36.39 2 3 3.7 51 5 5 Rt.ducbon Ratio

Fig. 3.4 Navilus (model GW) Selection Diagram: the selected type is the 42.45

The results of the query will appear in grid G2, and display gearbox

characteristics values, such as ratiO, torque, weight, and price. The extra costs

involved by the choice of a customized gearbox may confirmed or modified in the -Economics" window (see Chapter 4). The unavailable or not entered

values in the database (meice.mdb) are by default set equal to zero CO)'. As in

Section 2.2, the subset may contain the required amount of records, some or none at all. The amount of found records appears in textbox T24.

If the requested ratio is in the list, then the user may select the

chosen gearbox, using the reduction gears datacontrol D2. This step is in block 14 of

Fig. 2.1. The data control is a useful scrolling device that enables user to

browse through the records of the database. This datacontrol connects the

meice.dbf database file fields to the text boxes T25, T26, T27, 129. and T30.

In these text boxes we find the name, model, maximum tolerated torque

factor, reduction ratio, weight and price.

10 7 6 5 2 76 0.9 0 8 0.7 0.6

If the desired value is not available, another acceptable ratio can be selected,

following the procedure sketched in Fig. 2.1 (block 11 through block 14). PROSYSC offers the possibility of graphically evaluating two alternative

gearboxes, and choosing the best one, or rejecting both. The two potentially

valid reduction ratios must be typed in the ratio mo and ratio (P32)

textbooks. Usually, ratiol is the ratio below the requested value, whilst ratio2

is larger.

The latter would mean either a redefinition of some of the query limits (Fig.

2.1 loop from block 9 to block 7), or a change of engine (loop: block#9 to block#6). Button B4 unlocks the engine datacontrol (D1). The chosen ratios are then typed in the reduction ratio lower and upper limit boxes, (T21) and

(T22).

The graphics window (Fig. 3.1) is set active with the "Res Curve" button (B9).

Pressing the "Draw" button on this new form (window), the relevant

subroutine will show

three engine/gearbox characteristics: with ratio!, ratio2 and requested ratio the propeller fouled and clean load characteristics

the fouled and the clean hull requested operation points.

In case that both ratios are valid, the final decision may be made by looking at the clean hull curve. This can give some idea of the hull load _{curve fouling}

'path': one solution may show a more advantageous clean to

fouled

development (both the clean and the fouled requested operation points lie in

one of the acception areas)

The graph scale is based on percentages of the _{selected engine MCR-values} and requested propeller speed: the selected engine _{MCR-Power = 100% and}

the requested propeller spe,ed=100%. _{Therefore, an engine coupled to the}

requested ratio will have a MCR-speed equal to 100% on the graph, i.e. the coordinates of point a., (Fig. 3.2, where i = exact), on the engine curve with

Engine Power & Resistance Curve (% selection values)

=Pi

371P_Li laNTI Data

- Data WAERTStLAE SACII Pew 1775 (101/1 ipo 1500 Ins! Pow clean 1500 9c5Jj Pop cloan rpm 270 /rpm] PON NISI 1100 [kW] Pow geci nm 200 11/390 Engel tab° 9258 Wit T 1.10 r1001n1 10 101, Pes.1 97 93 km& 99.31 Pew2 1011 Run? ten 00 1165 [kW) 293.93 Opol 1775WWI 779 41 Imall Lttgend-5.119 5.303 Meal Fouked asap ideal ratio ratiol curve fouled requested oper. point

//71

scale number/. TOO fouled curve (100,100)

clean hull oper.

clean hull curve

ratio2 curve

Fig. 3.5 Graphical plots of the selected engine coupled to threedifferent gearboxes. the ideal (gray, fictitious), and the two alternatives to be tested

(curve with ratiol plotted in blue, ratio2 in pink).

The code offers the possibility of zooming in and out the graphs (Zoom+ and

Zoom- buttons), setting the desired zoom-step. The graph legend appears when the "legend" button is activated. The engine data, at MCR conditions,

can be made visible by pressing the "Data" button displaying two frames. The first frame from the left, the "intersection points- frame, displays the intersection points of the fouled load curve with the two alternative power

curves in terms of the graph scale (blue and pink) and in absolute terms ([kW]

and [rpm]).

In the second, named "Data", we find

all the technical

information regarding the selected engine at MCR

conditions, the two

considered ratio values and the requested ratio. We also find the engine power at corresponding

propeller speed when the engine is used at its

20010:111

The fouled load curve is plotted in red, whilst the clean load curve is yellow. The same colors are respectively used to represent the requested fouled and

clean hull condition operation points. The selected engine power curves are:

gray for the engine with fictitious gearbox having the requested ratio pink for the engine coupled to the gearbox with the ratiol ratio blue for the engine coupled to the gearbox with the ratio2 ratio.

The acceptance area is not indicated on the graph to avoid overcrowding and thus loss of clarity. This region is easily estimated using the scale numbers, plotted in green on the abscissa and the ordinate. The graph on paper of Fig.

3.5, is obtained by clicking the "Print" button.

3.3 Numerical Application

Let us resume the example considered in Section 2.3. The selected engine is the 8 cylinders SEMT Pielstick PAS 255, with a maximum torque factor of

1.76 kW.min. This value can be found in text box T18 in Fig. 2.3b, and will be

used as lower limit for the torque factor part of the query. The upper limit appears in T19, and is equal to 2.64 kW min (which is the default value: five

times the engine torque factor). We are looking for a coaxial input/output

shafts.

The code sets, in a similar way, the defaults values of the reduction ratio

query part. The lower limit is 3.214 (121) and upper limit is 3.928 (T22). The exact value appears in text box T20 and is equal to 3571. As a result of the

aforementioned constructed query, we would like to obtain

a set of ten

records (gearboxes). We type this input in T23. The final query is in words:

"Find coaxial input-output gearboxes, that tolerate at least a torque factor of

1.76 kW.min and a maximum of 2.64 kW.min, _{that have reduction ratios}

between 3.579 and 3.607 with mass less than 5 tonnes. Display the first 5

The query is executed by pressing the "Gear box query" button (B3). The

result appears in grid G2, where the query-matching records are listed in

ascending torque factor order. The LOHMANN NAVILUS GWC 42.45 3.5

(ratio = 3.579) is the only valid alternative found in the present database. The

relative difference between required and available ratio

is 0.2%, (new propeller speed: 279.4 rpm). This variation in reduction ratio (i.e. propeller

speed) may be considered small enough to accept the proposed model.

In conclusion, a possible configuration of the propulsion plant consists of a 8

cylinders in line SEMT PIELSTICK PA5 255, MCR of 1760 kW at 1000 rpm,

coupled to a LORMANN NAVILUS GWC 42.45 reduction gearbox with a ratio of 3.579. If the engine is operated at MCR power (1760 kW), the new

propeller speed would be 279.4 rpm.

To illustrate the use of the "Load Curve-, we will propose another alternative to the previously discussed choice. The latter can be achieved by redefining the gearbox query. In our example, we set new values for the reduction

ratio's range in the textboxl ("1-21) and ratio2 (T22): 3.50 and 3.70 respectively (required ratio ±3%). All the other variables remain unchanged.

The query provides a set of three alternative gearboxes (Table3.1)

Table 3.1 Result for the new query (3.52 <required ratio <3.7)

We choose to compare the GC 500 and the GWC 42.45. Therefore, we first assign the value 3.52 to ratiol and 3.579 to ratio2, then we enter these values

in the appropriate textboxes: i.e respectively T31 and T32. Pressing the "Load

Curve" button (B9) we activate the load curve and engine power graphics

# MODEL RATIO TORQUE MASS PRICE

1 Navilus GC 500 3.522 1.77 2.50 83 955 $

2 Reintjes WAF 352 3.520 1.78 3.85 (not entered)

values can be displayed by clicking the "Data" button. The legend may be

visualized by pressing the "Legend" button. The curves appears, on full scale,

by clicking the "Draw" button. We are interested in MCR region, and thus need to magnify the drawing around that point. Therefore, we set the zoom step on 90 (this can be done with the spin button' or just by typing the value

in the appropriate text box). The graph of Fig. 3.6 appears when the "zoom+" button is pressed.

sr. M

Co all Dal 011.1111, I-MIE I 21161114 Zeam lawn 190 If

50

upend

- 1622

..

to.49d

Fig. 3.6 The graph produced by the code (selected engine of Chapter 2)

The requested operating point (the red circle) is in the accepted operating

area. More specifically, it lies on the flat part of the engine curve with ratio] equal to 3.579. Even though the operating point is _{not exactly the MCR point}

of the curve describing the engine coupled to the ideal gearbox (ratio = 3.571), the code reports in the "Intersection Points" frame, that the intersection _point

is (100.00,100.00). We know that the _{power required is equal to the selected}

engine power (100 on graph scale). The propeller speed of the intersection

point on graph scale is equal to 1000/3.579x280= 100.002, which is rounded off to 100.00 (the code only shows 2 decimal figures).

-10 Pawl 117.91 1106 IIIW1

III 73 711 /1/15,1 04..1

Pal100 / MOW'

PlatIGO 03 atm i..1

The requested 'operation point is outside the 'acceptance area' of the pink

curve.. Nevertheless, at the intersection of the power curve with the fouled

load curve, the engine delivers 98% of its MCR power at 99.6% of the

requested propeller and thus also MCR speed, corresponding to 1724 kW at

996 rpm (equal to 278.88 rpm of the propeller),

The final choice depends on various factors. For 'example, one could chose

the OW 500, accepting a trade off in required speed and available power (difference between engine power curve and load curve) for a reduction in

gearbox cost (57210$ less, or 60% less).

However, if we adhere to the set

criteria, we will select the is the best technical solution of two alternatives the GWC 42.45., The operation point of the other alternative engine/gearbox

combination results outside the acceptance area and should therefore be

4.

Economical Aspects

4.1

Introduction

Before we proceed with the description of the method used for the

economical analysis of a propulsion system, we will

first give some

information regarding the acquired cost data.

In its general sense, the technical-economical study includes both the

technical analysis and the economical one, that is the determination of the cost of the ship, of the cost of its outfit, and of its operational cost. In the frame of this, we will restrict ourselves to the technical-economical analysis of the propulsion system and, especially, to its specific cost, specific weight,

and specific consumption in combination with the fuel cost. It is important to

note that cost data have mostly relative value since the material and labor

prices rise continuously [Ioannidis, 19851.

Specific cost

The prices for the Main Engines and all the necessary auxiliaries for

a

Propulsion System are variable

and many times depend on

specific circumstances. It is therefore not possible to have absolute cost data. Fig. 41

[Marine Engineering, 1992] gives the total cost of the various Propulsion

alternatives as a function of the maximum continuous shaft power.

A better picture of the situation is given in Fig. 4.2, where the data of the

previous Figure are used to draw the specific cost (that is, cost/installed shaft

3.5 3.0 2.5 2.0 1.5 10 costs A' 10-4 HP 1.5 1.0 0.5 0 installed shalt power HPNI173

1111111111111111111

MI

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UT

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GI's-Tild.'11111-11

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II

WM

9

IIIPArlirdIll

EP'

II

. III

nuclear direct drive diesel gas turbine fregener) steam tort_ geared diesel ---"---.: 14 18 22 26 30 34 35

SNP RATING OF PROPULSION PLANT (THOUSANDS)

Fig. 4.1 Total costs of various propulsion alternatives vs. MCR shaft power.

Specific weight. so 160 X 140 120 100 0 ₈₀ 0 0- 60 40 20

MN

fk;Iiexi

rIbk,titzi

flic) sr% 4f

coif".

111=11111

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14 18 22 26 30 34 38 42

SHP RATING OF PROPULSION PLANT (THOUSANDS]

Fig. 4.3 Specific weight vs shaft power

Fig. 4.3 [Marine Engineering, 1992] gives the specific weight in absolute units

as a function of the installed maximum continuous shaft power. This element

is very important for the ship design, because the weight of the Propulsion

Plant decreases the carrying ability of the vessel. Furthermore, the size and position of the Propulsion System need to be known for the balancing of the ship, especially in the cases of a fully or partly loaded vessel. Many times the

weight of the fuel necessary for a trip of specific length is added

to the

weight of the machinery, because fuel decreases the carrying capability of the

ship. The quantity of the fuel required, for the same installed power and for

the same trip, is proportional to the total specific fuel consumption of the

Specific fuel consumption

The specific fuel consumption is defined as the fuel consumption in fuel mass per unit of engine real horsepower. Since, in a ship the Main Engine but also

other operations require an amount of auxiliary machinery that use part of

the produced power, it is accepted that the specific fuel consumption should

be the total one, that is the fuel consumption required for all of the

operations on-board, but refers to the maximum continuous shaft power with the simultaneous determination of the operating conditions of all of the rest

of the machinery. The specific fuel consumption is also given for various values of the power and operating conditions, which must be explicitely

defined. 1.0 0.9 0.8 0.7 0.8 0,5 0.4 0.3 0.2 0 2 4 6 a 10 12 14 16 18

SHP RATING OF PROPULSION PLANT (THOUSANDS)

Fig. 4.4 All purpose fuel consumption vs SHP rating ofpropulsion plant

For a Diesel engine, the accepted variable is the specific fuel consumption of

It is measured in the

20 22

III

RECIPROCATING STEAM ENGINE

II/

111111

r.iiTI , , 1

LP 4

litalijill-girl

DIRECT-DRIVE

gifrwiqlsAMI

maeasi

NEER

-14".=119 gil GEARED I DIESEL DIESEL. MEM _ COMBINED AND STEAM i GAS TURBINE TURBINE I DIESEL-ELECTRIC --

-for the operation of the ship generators. Since the latter consume a different

kind of fuel,

the proper transformations must be carried

out. The

consumption of oil(s) must also be taken into account.

When we reach the final values of the total specific consumptions for

alternative designs, we must consider the sort of fuel used for each one, since the fuel lowest heat value, Ho , and the price for each fuel is different. That

is, all fuel lowest heat values and fuel prices must be referred to a certain Ho

and a certain price, and then the comparison can take place.

The curves of Fig. 4.4 [Marine Engineering, 1992] refer all to a fuel with the

same Ho, but the differences in the fuel prices have not been taken into

account.

The consumption of the auxiliary machinery, of the machinery that support the crew, and the consumption for special needs (such as tank cleaning, load

heating in tankers, passenger support in cruisers,, etc.) have not been

considered.

_{These prices are much better lately for every type of Main}

Engine, but especially for Diesel engines (low-speed and medium-speed

coupled with gear boxes). Table 4.1 [loannidis, 1985] contains the relative fuel prices for various propulsion alternatives.

Table 4.1 Relative fuel prices Propulsion Plant Gas Turbine (fossil fuel) Medium-Speed Diesel/ Gas Turbine (Diesel fuel) Low-Speed Diesel/ Medium-Speed Diesel (residual fuel) Boiler & Steam Turbine/ Low-Speed Diesel (residual fuel) Relative price of used fuel 1.60 152 1.C6 1.00

Maintenance cost

This is the area for which fewer reliable data exist. One reason is that engine

manufacturers on purpose give values lower than the actual, while on the

other side, their data are hard to measure and/or check. Furthermore, neither

do the ship owners want to release such data that would allow the accurate determination of their cost of transport. (General Electric,1984) gives the

following relative data (Table 4.2):

Table 4.2 Relative Cost of Transport (RCT steam engine = 100%)

We observe that the maintenance cost of a propulsion system with a Diesel engine is about three times that of a Steam Turbine.

It is also true that when a power plant operates with a lower power than the one given by the engine manufacturer the maintenance cost decreases. The

quantitative relation between the two, however, is hard to establish. Diesel Engine 2,8 to 3.9

4.2 Procedure

Here we will develop a method according to which one can choose one of

many design alternatives that satisfy completely the technical requirements of the problem. Therefore, in our case, we accept that all the system alternatives

satisfy completely the requirements of the combination ship-propeller. We must also point out that since most ship operations (other than propulsion) depend on the kind of propulsion system, we accept that at every point we

consider the entire installed energy generating system of the ship [loannidis, 1985].

The method can be applied also to other engineering problems where an economical comparison must take place. It must be noted, however, there are

cases, where the costs associated with a type of propulsion plant are of

secondary importance, because the ship's mission makes a particular type of

propulsion plant mandatory. Such is the

case with

strategic-missile

submarines, which must have nuclear propulsion to permit extended periods

of underwater operations [Marine Engineering, 19921.

Normally, three kinds of costs must be evaluated: initial costs (e.g., installed

costs), recurring costs (e.g., fuel, maintenance, and crew expenses), and

contingency costs (e.g., most aspects of reliabilty, possible costs for corrective

maintenance). By applying the present-value concept, the costs to be incurred

in the future can be discounted and compared on a common baseline to

establish the most advantageous alternative.

We will proceed now with the method description [Ioannidis, 1985]. _{Let us}

suppose that we have two system alternatives A and B that satisfy the

propulsion and other energy requirements of

a specific ship. These

alternatives may be different in many points and this difference may not

The following variables are important to our analysis:

kp = capital costs , $/a

i = interest rate , 1/a

ri

= power plant purchase price , $

RV = power plant rest value , $

V = power plant life cycle , a

ki = insurance and maintenance costs not influenced

by the operating hours per year , $/a

maintenance costs proportional

to the operating hours , $/h

mb fuel consumption , kg/h

kb fuel price per unit weight $/kg

°

ML = oil consumption , kg/h

lube oil price per unit weight , $/kg

operating hours per year Ida

power plant capital costs , $/a

engine effective power kW

be= "lb = engine specific fuel consumption , kg/kWh

Pe

it = m'p = engine specific lube oil consumption ,kg/kWh

a

total costs per year

cc

energy production costs , $/kWh

Pe H

weight of transported goods

to = round trip duration , h/trip

4 = Htc= number of round trips per year , trip/a

ki =

H =

kp =

Pe =

The operating hours per year, H, may be different for every alternative

because one may be more reliable than the other.

The weight of the

transported products may also vary since a heavier propulsion plant means

fewer products can be carried and vice versa.

It is

possible that the two alternatives

_{differ in one of the above}

characteristics. In this case the comparison is very easy. There are also other simple cases. They may for example differ just in the fuel consumption and

fuel price. Then the criterion is the product mhkb (in $/kWh). They may also differ in all elements but the initial acquisition price, the life cycle and the weight of carried load. In this case, the criterion are the propulsion plant

running costs, which are defined as the sum of

the insurance costs and costs of maintenance that is not influenced by the

operating hours per year factor (ki)

the fuel, lube oil consumption costs and that part of the maintenancecosts

which is a function of the operating hours per year (km).

kr =k,+ (mb-kb+k,-mi+ k,,,) H (1)

The life cycle of the propulsion plant and its initial purchase price are not

running costs and at first glance cannot be compared to the rest. In order to transform them we need to know the interest rate used for the purchase. Its values range from 1% to 20% per year. The interest rate stands for the costs involved in borrowing money in order to purchase the propulsion plant (1).i

each year).

We observe that the amount D after years becomes:

which means that D and f).(1+01 are equivalent in two different moments in time. We can thus define as the present value of an amount Df after 1 years,

the amount:

(2)

If we examine now the case where at the end of each of the following

years, equal amounts of A $ are paid, the present values of the amount to be paid is: A A A A

n

_o + + 1+i (1+02 (1 + i)3 0 + iY A no =

11++'++-+---+(i+ov-`}

0000

(1+" 0 A

(1+ if 1 A (1+ if -I

no 0 ± iy 0 + i) 1 i (1 + i)v

for v > .0

: i

while for small v and i : A i = A

i

In case

that amounts A are not equal we can

carry out suitable

transformations.

Assume now a realistic scenario where an installed plant is used for v years, after which it is sold for RV ($), and replaced with a similar one costing the same amount IT ($). This is repeated every v years. In a similar analysis as above, the present value of the amounts payed throughout the life cycle of

the propulsion plant is:

II = II + fl RV RV flRV+ 0 + iy 0+02v

n

11 RV

{0

0

1++0' +(l+i

0 + iy =Li+ 01-iy

{1-

1

0-

}

n RV

1 0 n - RV Ho + (1+ i)v

The inflation rate could have been taken into account if it had been known

during the propulsion plant life cycle. However, the additional accuracy in the

calculation would be counterbalanced by the inaccuracy of an inflation

estimate.

Applying the aforementionned reasoning, we can determine the annual cost

(that is the fixed amount that needs to be paid every year) for the purchase

of the initial propulsion plant and all the remaining ones that will eventually

replace it. The amount that results is then comparable to the running costs.

Therefore, for the purchase of all the propulsion plants we need:

today

after Iyears

D-RV

after 21 years D-RV etc.

RV will be paid in a number of yearly payments that tends

_{to infinity.} Consequently, the approximate required amount is RV *i expressed in $/a (as found from (3), for _{large). On the other side, amount D - RV (and all of the}

following), will be paid after i years in yearly installments (according _{to (3),}

if we solve for A and replace Do with D - RV) of:

RV). i + iy

(l + i)v

--2v +

(4)

-Therefore, the entire amount paid every year, that is the annual capital costs, will be:

(ri

-

RV)- i + i)v= if - RV }

kp = i RV +

(1+ iy

-

+ i)v

-After the calculation of k. we can give a general expression for the total

annual operating cost, which will be valid for the same weight of transported

goods of both alternatives A and B. Quest for Minimum it can now be the unique quantitave economical criterion for the choice of alternative power

plants:

a = kp+

Or

a = i

fl+

fl -RV k, + m,,

k, + km) H

(6)

It can be seen from the above that the alternatives are favorable where all

the values are small, except for R V and 1.

Assuming that the real installed engine power is Pe during the H operating

hours per year, then the reasonable criterion for power plant selection is the

lowest ratio of the total annual operating costs:

a

1

P, H

H (5)

{n+Ort

) I P,)} K

(1+ i) 1

+be kb+1,ki+m-

Pe (7)

However, in the case of a merchant ship, we are more interested in the costs

of product transportation. Since different engines may result in different

+ iy

k

The lightship is also an increasing function of the power plant weight. Therefore, for a comparatively lighter power plant, and for a constant ship displacement, the deadweight will be greater (i.e. the ship's goods transportation capability will be greater). Consequently, for merchant ships, the criterion is the minimum ratio of total annual operational costs per total weight of transported goods and per round

trips per year:

a

1 IT-RV }

1{11+ + k,

+ (m,

k, + m,,

k, + k)

(8)

W

_+iy

wE

Here, we must note that the above relations give the part of the cost that

concerns the purchase, operation, and maintenance of the power plant. There

is, of course the part of the cost due to the purchase, operation, and

maintenance of the vessel. Finally, the number of the crew members also

depend on the kind of the power plant. For the purpose of this thesis, these

last two elements have not been taken into account.

In order to clarify the way the choice is made, we give

now a graphical

method [loarmidis, 1985] for the selection of the best alternative.

We can examine the influence of the operation coefficient and other cost parameters. We define two auxiliary variables X and Y:

X---(m k + ;11,,

W"

+ km)

where

X = transportation costs depending on the operating hours per year

Y = transportation costs independent of the operating hoursper year

7 to 11-RV Y=

\

W -Him. + 0+ iy

-

1} ,, sit