Reliability of delivery in theory and practice. A theory developed and verified for Reefer Ships in practice

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Reliability of Delivery in Theory and Practice

A theory developed and verified for Reefer Ships in practice

August 1999 D.E.J Knops OVS 99/09

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-RELIABILITY OF DELIVERY

IN

THEORY AND PRACTICE

A theory developed and verified

for Reefer Ships in practice

D.E.J Knops

Delft University of Technology

Faculty Design, Construction and Production

Sub-Faculty Mechanical Engineering

Section Marine Engineering

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ACKNOWLEDGEMENTS

Dear reader,

This report contains my master thesis study at Delft University of Technology. Before you take notice of this report, I would like to thank the people who made it possible for me to complete my study Mechanical Engineering.

From Delft University of Technology, I thank SC. Santema: D. Stapersma and H. Grimmelius

for their guidance and support during my final year of studentship. I am very pleased that I got the opportunity to combine the technical with marketing aspects of marine engineering in my master thesis. It has been an instructive year for me in every respect.

I would also like to thank the people of Seatrade in Antwerp and Groningen and especially Jeroen Vermeer, Michiel Schaap, Bert de Ruiter and Henk Schuur. I would like to thank them for their co-operation, guidance and enthusiasm. They supplied me with a lot of information and knowledge. It was a great experience to fulfil the final stage of my study at Seatrade.

Furthermore would like to thank A. Nijsen of MAN Rollo B.V. in Zoetermeer and H. Lophuaa

of the faculty Technical Mathematics of Delft University of Technology. II appreciate their help very much.

Last but not least I want to thank my family and friends. They supported me from the beginning to the end in a way few people can.

Den Haag, 24 August 1999 David Knops

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TABLE OF CONTENTS

SUMMARY

In the world-wide trade market, logistics play an important role due to a high level of co-makership. The just-in-time system is frequently implemented in the logistic chain.

Transporting cargo by ship is an important chain part in the logistic chain. If a just-in-time

system is implemented, a predictable time of arrival and a reliable delivery should be demanded in the shipping business.

This report describes a theory developed about the reliability of delivery in shipping and the

results of verifying this theory in practice for Reefer ships. There has been focused on the differences between ships equipped with a 2-stroke or a 4-stroke main engine.

The theoretical part of this study makes clear that several factors can influence the reliability of delivery. One of these factors is failure of machinery and one of the most important pieces of

machinery in a ship is the main engine. Differences in design and usage of a 2-stroke or 4-stroke main engine could influence the performance of a ship and so the reliability of delivery. The practical part of this study deals with the following questions: is there a difference between

the actual and the initial estimated transportation time, is this difference related to the length of

the distanceci sailed or the ship that sailed the leg? Furthermore it is questioned if there is a difference between distances sailed with ships equipped with a 2-stroke or 4-stroke main engine? And finally, what is the present reliability of delivery for Reefer ships?

The data for verifying the theory in practice is obtained from Seatrade Reefer Chartering NV in Antwerp. This data contains information about actual transportation times of distances sailed, called legs, from January 1998 till June 1999. In order to obtain data about relative long legs, the data is filtered. Calculations are carried out to determine the difference between the initial estimated transportation time for a leg and the actual transportation time it took to sail the leg. This difference is called the transportation time difference. The difference between the theoretical service speed a ship should sail and the average actual speed sailed on the leg is also calculated.

It is also investigated which ships sailed the legs and the results are that Reefer ships of different sizes and with different theoretical service speeds, sailed the investigated legs. For these legs the distribution of ships equipped with a 2-stroke or a 4-stroke main engine is fifty-fifty. The percentage of legs in which an offhire at sea occurred is 4%. In these offhire at sea legs, the number of ships equipped with a 4-stroke main engine is considerably higher than for ships equipped with a 2-stroke main engine. For about 86% the reason for an offhire at sea is main engine failure.

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SUMMARY VI

For the reliability of delivery in practice the following gets clear. In a logistic chain with a just-in-time system, the receiver of the cargo sets the amount of just-in-time the cargo may arrive before or

after the initial calculated time of arrival. This is called the time of arrival margin. If this is

considered to be half a day, the overall reliability ofdelivery for all legs investigated is about

62%. The reliability of delivery for the legs sailed with a 2-stroke main engine is about 4% higher than for the legs sailed with a 4-stroke main engine.

Not attaining the time of arrival margin can have financial consequences. Profit can be lost and the chances on cargo claims increase. There are several options to improve the reliability of delivery. Adding extra time to the estimated transportation time, which is calculated by means of dividing the distance by the theoretical speed results in a more realistic estimation for the estimated transportation time. If a time of arrival margin of half a day is allowed, this results in

an overall reliability of delivery of 81%. Forthe remaining legs, which do not attain the time of

arrival margin, reducing the legs with an offhire at sea is a solution to minimise their share in this. Applying a well balanced maintenance policy, installing the more reliable 2-stroke main engine or creating more redundancy could do this and thus improve the reliability of delivery.

Installing a power-buffer of 30% to increase the speed in order to compensate a delay is expensive regarding to the extra profit, which could be made. Reducing the relative service

rating of the main engines can also create a power-buffer. This could be profitable to do for ships equipped with a 4-stroke main engine.

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INTRODUCTION 1

1 INTRODUCTION

With the increase of the world-wide trade market, the demand for more and efficient

transportation rises. The just-in-time system is frequently implemented in the logistic chain and demands a predictable time of arrival and a reliable delivery. In the world-wide trade, shipping is often involved in the logistic chain and therefore a reliable delivery should be demanded in the shipping business.

In a previous study the technical differences between the 2-stroke and the 4-stroke marine diesel engines were investigated. It made clear that the choice for a 2-stroke or a 4-stroke main engine could influence the performance of a ship and thus the reliability of delivering cargo.

If the demands for predictable time of arrivals and reliable deliveries are to be fulfilled in shipping, it is useful to investigate the present reliability of delivery

In this report a theory is developed which describes the most important issues for a reliable delivery and this theory is verified in practice with data obtained from Seatrade Reefer Chartering NV in Antwerp.

This report deals with the following questions:

Is there a difference between the actual transportation time and the initial estimated transportation time of a distance sailed?

Is this so called transportation time difference related to the length of the distance?

Is this transportation time difference related to ships equipped with a 2-stroke or a 4-stroke main engine?

What is the present reliability of delivery for the Reefer ships sailing in the Seatrade shipping pool?

The structure of this report is as follows. The theory developed about the reliability of delivery and the possible influencing factors, are explained in chapter 2. The data obtained and the conversions made in order to create workable information about legs sailed are described in chapter 3. In chapter 4 information about the ships, which sailed the legs, is described and this chapter also compares the amount of failure of 2-stroke and 4-stroke main engines. Chapter 5 describes the data survey carried out to determine the transportation time difference and the

reliability of delivery in practice. Furthermore, the differences between the legs sailed with a 2-stroke or a 4-2-stroke main engine are shown and a zoomed in view on the legs sailed through the Panama Canal is given.

Chapter 6 deals with the possibility of compensating delays so the time of arrival can be attained. Finally, conclusions and recommendations can be found in chapter 7.

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RELIABILITY OF DELIVERY IN THEORY 2

2 RELIABILITY OF DELIVERY IN

THEORY

2.1 Introduction

This chapter explains the theory developed about the reliability of delivery. It gives the

parameters involved and the factors, which can influence the reliability of delivery. It describes how new economics of production involve new developments in the manufacturing and

transportation sector. It gives an insight in the logistic chain with a just-in-time system and the

importance of attaining the time of arrival and reliability of delivery.

Paragraph 2.2 displays the share of the shipping business in the Netherlands. An insight in the new economics of production and how these effect the logistic chain is given in paragraph 2.3. In paragraph 2 4 a logistic chain with JIT system is described and the parameters involved are

defined. Paragraph 2.5 describes the realistic logistic chain with a time of arrival margin How

the reliability of delivery is situated in this realistic logistic chain and the factors, which can influence the reliability of delivery, are described in paragraph 2.6. Paragraph 2.7 underwrites

the importance of attaining the time of arrival margin and the reliability of delivery How

feedback is obtained for the theory developed is described in paragraph 2.8. And paragraph 2.9 contains the chapter conclusions

2.2 Import & Export in the Netherlands

World-wide, cargo is being transported by means of three kinds of transport modes: over land.

over water and by air. When we focus on the Netherlands, it can be stated that transport over water (when measured in cargo mass) has the largest share lathe import and export markets

[source CBS 1997]. This can be seen in figure 2 1.

Although from 1983 till 1996. the share of import and export by land increased and the share of

import and export over water decreased. The latest trend indicates that transportation over water gains share again and that transportation

over land loses share This is a profitable outlook

for the shipping business.

Table 2.1 displays the average shares in cargo mass per transportation mode over the years 1983 till 1996.

Table 2.1: average shares import and export

Figure 2.1: Percentage of cargo import and export per year in NL ___.nd limper?) ome.41 (.00,0 Imair end (export/ wpm) 411lexporti ?93 1984 1985 1988 198? 199 8 19013 /99 0 1991 /99 2 1993 199, 1995 19913 0 0% BO% i".11.1999y. TO% 80% 6..." 50% 80% 3 0% 20% 10% ...,---...._.... ,4,--,-...i, '''' ''.'''''''''a...-..4...-"''-0% Al

OH. .M. .111.11.. .. .111

import

export

land 18,1% 39,3%

water

81,8% 60,6%

air

0,1% 0,1%

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The average share of transportation over water for the import is 81,8% and for export is 60,6%. These are the largest shares of the transportation modes and underline the importance of the merchant shipping business in the Netherlands.

When a zoomed in look is created on the transportation over water, one can see that the 81,8% import share is build up out of 70,1% sea shipping and 11,7% inland-shipping. For the 60,6% export market share, these figures are 24,7% for sea shipping and 35,9% for inland shipping. Table 2.2 displays these figures.

Table 2.2: average shares Import and export

It can be concluded that shipping is an important transportation mode in the Netherlands. When looking at the import and export shares, one can conclude that cargo enters the Netherlands by sea shipping and leaves by inland shipping and road transportation. Shipping will be involved in many logistic chains.

2.3 New Economics of Production effect the Logistic

Chain

In all kinds of business there is a constant renewal of production methods. Today many businesses face new economics of production due to a globalisation of the market. Better and faster communication methods are available and the price and quality differences all over the world get clear. Production nowadays involves a higher level of co-makership enabling manufactures to get more specialised, produce a smaller variety of products and buy more products or semi-products from other manufacturers. This amplifies the globalisation and an

increase of the world-wide trade is the consequence. This increase of the world-wide trade offers also new opportunities and demands for the transportation sector.

To gain competitive service and total cost advantages from the new economics of production, the transportation sector developed the door-to-door intermodal services in the logistic chain. The transportation sector can take over all the transportation required and is able to specify its services to the needs and demands of the manufacturers. This enables manufactures to focus on their skills, the actual manufacturing of products.

import

export

sea 70,1% 24,7%

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Mostly a logistic chain is split up into many chain parts, so there are many doors in a single door-to-door service. Figure 2.2 displays systematically a total (intermodal) logistic chain consisting out of several chain parts. I ntermodal means that it can contain different transportation modes, like road and water transportation.

logistic chain part

total logistic chain

Figure 2.2: Intennodal logistic chain

The first sender of the cargo is situated at the 'begin' of the total logistic chain and the final receiver of the cargo at the 'end'. In between there are many senders and receivers with their own "doors" at each begin and end of a chain part.

Delivering cargo from and to all these "doors" in the total logistic chain can take relative more time than in a logistic chain containing only one sender and receiver. To obtain the highest benefit from the door-to-door services in a whole logistic chain with several chain parts, the

just-in-time (JIT) system has been developed. The main issue in this system is to deliver the

cargo exactly on the moment desired.

So besides the changes in the manner of production, transportation and logistics have an important share in the new economics of production. Changes in the logistic chains are necessary to benefit from the door-to-door intermodal services.

2.4 Explaining the Just-in-Time (JIT) System

The Just-in-Time system is a system, which can be implemented, in a logistic chain. It strives to minimise the costs, which have to be made for stock, storing and transhipping of cargo in a logistic chain. By delivering the cargo on the moment desired (just in time), less stock, storage and transhipment is necessary.

2.4.1 Just-in-Time features

STOCK AND STORAGE MINIMISATION

When zooming in on a single chain part of the total logistic chain, the JIT system can be

described as follows. Cargo is transported from the sender's to the receivers door and this is

done in such a way that the receiver gets the cargo on the moment desired, so the stock quantity and storage period can be minimised. Which yields a reduction of costs.

When getting the cargo too early, the receiver will have extra stock and the storage period gets longer than necessary. When receiving it too late, line fallout can be the consequence.

Because this can occur at all senders and receivers in the whole logistic chain, not fulfilling the JIT terms can be expensive because, a lot of extra stock, longer storage periods or line fallout can be generated in the whole logistic chain.

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TRANSHIPMENT MINIMISATION

When dealing with door-to-door intermodal services, usually several transportation modes in the whole logistic chain are used. Each transportation mode in the logistic chain is called a chain part. The most common transportation modes are:

land (road, rail) water (shipping) air (aviation)

Switching the cargo from one chain part to the other chain parts requires a transhipment action. Because transhipments are considered to be expensive, compared to the actual transportation costs, one wants to minimise the number of transhipments in a logistic chain. Another reason to minimise transhipment actions is that in general, there are two

transhipments necessary when switching chain parts and consequently a storage period in between the two transhipments is necessary. For instance, the cargo is first unloaded from the arriving 'transporter' and than stored. After storage it is loaded on the departing 'transporter' and transportation continues. In an ideal working JIT system, the cargo could be unloaded from the arriving 'transporter' and directly be loaded on the departing 'transporter'. So a second transhipment is not necessary and this reduces not only the number of transhipments but also terminates a storage period of the cargo.

An ideal JIT system does not exists in a realistic logistic chain and so storage of the cargo between two chain parts can mostly not be avoided. But when keeping in mind that the highest efficiency in a JIT system can be obtained by a minimisation of (necessary) storage periods and transhipments, this yields that one should strive to attain the planned (calculated) time of arrival and time of departure of the cargo exactly.

2.4.2 Logistic chain layout with a JIT system

Because mostly the logistic chain contains several chain parts, zooming in on a single chain part can provide insights, which can be applied to all the chain parts in the logistic chain. By doing so the door-to-door service contains two doors, one of the sender and one of the receiver.

Figure 2.3 displays a zoomed in view on a logistic chain part.

time of departure

time of arrival

time of departure

transportation storage transportation storage transportation

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RELIABILITY OF DELIVERY IN THEORY

6

The following definitions will be used in this report.

Storage + Tranship Time

Time of Departure (ToD)

Time of Arrival (ToA)

Distance OM

Theoretical Service Speed (vtheo)

Actual Transportation Time '(fl)

= the amount of time

it takes to store and tranship

the cargo in between two chain parts

= the moment (date, hour)

the transportation of

the cargo starts

= the moment (date, hour)

the transportation of

the cargo ends

= the distance travelled between departure and arrival

= the theoretical service speed which can be

attained by a ship

Estimated Transportation Time (TTest)= the estimated

amount of time it takes to

transport cargo from the place of departure

to the

place of arrival

= the actual amount of

time it takes to transport

cargo from the place of departure

to the place of arrival

Transportation Time Difference (TTdif)= the difference between the actual transportation

time and the estimated transportation time

It is assumed that a (logistic) chain part beginsin the middle of the (start) storage* tranship' time and ends in the middle of the (end) storage + tranship time. This is a common assumption

in Logistic Engineering.

Though the highest efficiency in a JIT system can be obtained by a minimisation of necessary storage + tranship time, this survey will not investigate what the minimal necessary storage + tranship time is. It is assumed that other surveys more specialised in Logistic Engineering are able to determine these minimal necessary storage + tranship time. The scope of this survey will be on attaining the time of arrival at the end of the transportation time, which lies between two storage + tranship times.

The storage + tranship time is considered to be a 'black box' and the minimal necessary amount of time this black box takes is considered to be known and fixed. So the time of arrival has to be attained.

Not attaining the time of arrival is caused when the actual transportation time differs from the estimated transportation time. This difference is called the transportation time difference. When the actual transportation time is longer the following departing 'transporter' will have to wait for the cargo and possible will not be able to attain it's time of arrival.

When the actual transportation time is shorter than the estimated transportation time, the arriving 'transporter' will have to wait for the departing transporter. Though the time of arrival is attained, it is inefficient and thus it is stated that also in this case the time of arrival is not attained either.

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2.4.3 Backward calculation in a logistic chain with a JlT system

When a JIT system is implemented in a logistic chain, the final receiver of the cargo is the one who specifies the time of arrival of the cargo because, for example he wants to minimise his stock. When this time of arrival has to be attained, this yields a backward calculation to determine the first time of departure in the logistic chain. Because the logistic chain mostly consists out of several chain parts, the times of arrival and departure of each chain part need to be determined in a backward order.

As described, first the final receiver in the total logistic chain specifies the final time of arrival. Than the estimated transportation time is calculated. When cargo has to be transported from a

sender to a receiver, the distance (D) is specified and the estimated transportation time (TT)

can be calculated by means of equation 2.1 in which ytheo is the theoretical service speed.

TT, =

vo,e,

Equation 21

From this estimated transportation time, the time of departure can be determined. Then taking into account the given and fixed storage + tranship time, the preceding time of arrival can be determined.

For each chain part in the total logistic chain, repeating the calculations yields the backwards calculation and will have to be carried out to determine when the cargo has to be send by the first sender in order to attain the final time of arrival.

Of course. this calculation can only be done when the estimated transportation time and the storage + tranship time in between the chain parts are known. When the backward calculations for the total logistic chain is done, it is assumed that once the estimated transportation time of a chain part is calculated, it can not be not be changed anymore. This includes that the time of arrival and the time of departure for each chain part are determined and fixed, otherwise the calculations of the preceding chain part can not be carried out.

So when the storage + tranship time is assumed to be known fixed and the estimated transportation time per chain part is calculated and fixed. All times in the whole logistic chain are known and the cargo can be transported.

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RELIABILITY OF DELIVERY IN THEORY

SUMMARISING

Applying the backward calculation on a single chain part yields the following calculation chronology.

1. First the time of arrival (TA) is specified.

2 Subtracting the estimated transportation time (TT) from the time of arrival yields the time of departure (ToD).

3. When for some reason, the actual transportation time differs form the estimated

transportation time the time of arrival (ToA) will not be attained. If possible, the transportation speed needs to be changed to compensate.

So speed is an .ad hoc" tool to compensate for the transportation time difference.

Figure 2.4 visualises the chronology of specifying time and speed in a chain part when a JIT system is implemented.

distance / theoretical service speed

1: time of arrival

estimated transportation time

2: time of departure

Figure 2.4: Calculation order of a logistic chain with J1T system

delay

3: transportation speed

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2.5 Time of Arrival Margin

Because the ideal JIT system with an exact time of arrival does not exist, there needs to be a margin around the time of arrival. This margin will be called the time of arrival margin (ToAM).

Time of Arrival Margin (ToAM) = allowable amount of time the cargo may arrive

before or after the initial calculated time of

arrival

What the allowable time of arrival margin is depends on the type of cargo, the market

demands, the competition and what the storage + tranship time accepts. Because the time of storage + tranship time is given, it is assumed that also the time of arrival margin is given. The time of arrival margin is symmetrically situated on both sides of the time of arrival and this yields that the total amount of time around the time of arrival is two times the time of arrival margin. Figure 2.5 displays a zoomed in view on the estimated transportation time (R-est), the

time of arrival (TA) and the time of arrival margin (ToAM).

ToA

ToD

--)o 2x ToAM

TT

<

>

logistic chain part

Figure 2.5: Zoomed in view on a chain part with ToD, ToA, and ToAM

The time of arrival margin creates a time-buffer. It gives the amount of time the actual transportation time may differ from the estimated transportation time. The probability (of a transporter) to deliver the cargo within the time of arrival margin is called the reliability of delivery.

ToD

logistic chain part storage transportation storage transportation

+

tranship

+

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2.6 Reliability of Delivery

Attaining the time of arrival margin is important in a JIT system, which can be expressed by the reliability of delivery.

Reliability of Delivery =

probability to deliver the cargo within the (2x) time of

arrival margin

It is the chance of delivering cargo within the time of arrival margin. The higher the reliability of delivery, the more frequently cargo arrives within the time of arrival margin. It can be displayed

by the following equation where Ti = ToA - ToAM and T2 = ToA + ToAM.

Reliability of Delivery = P{T1< actual ToA < T2}

Figure 2.6 displays a zoomed in view on the estimated transportation time (TTest), the time of arrival (ToA), the time of arrival margin (ToAM) and the reliability of delivery.

RELIABILITY OF DELIVERY

logistic chain part

.4 014

Figure 2.6: Zoomed in view of a chain part with Reliability of Delivery

Instead of attaining the exact time of arrival in the ideal JIT system to minimise the stock, storage and transhipments cost, in a realistic JIT system this can be translated into attaining the time of arrival margin. The probability of doing so is expressed by the reliability of delivery, which can be seen as a performance indicator of the transporter.

The reliability of delivery is related to the transportation time difference. For instance if this transportation time difference frequently exceeds the time of arrival margin the reliability of delivery is low. By trying to reduce these large transportation time differences, the reliability of delivery can be improved.

What causes this transportation time difference will be investigated in order to make realistic calculations for the estimated transportation time and if required, the possibility of a speed increase to compensate for the difference.

logistic chain part ToA ToD 2x ToAM

)(

TT ToD storage tranship transportation storage tranship transportation

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2.6.1 Two groups of factors influencing the reliability of delivery

When reliability of delivery is pursued, one needs to know which factors influence the reliability of delivery and how they can be manipulated.

As stated before, the transportation time difference between the actual transportation time and the estimated transportation time can cause the time of arrival margin not being attained. In order to make a realistic calculation of the estimated transportation time, it is useful to create an insight on which transportation time differences can occur and whether they can be

manipulated or taken into account when calculating the estimated transportation time.

The transportation time difference can be caused by several factors. These factors can be split up into two groups. Those, which can be manipulated, and those, which can not. Manipulating in this context means: changing factors in such a way that they can contribute in attaining the _N4

1S.1

time of arrival margin.

FACTORS WHICH CAN BE MANIPULATED

-kJ

Z

The following factors can be manipulated.

Failure of machinery is a factor, which can be manipulated. The chance of occurrence can -0,

(

be minimised for example by good and sufficient maintenance.

..--Professionalism of a crew can be manipulated. Well-educated crews can be hired or

ic

'education can be provided.

In this survey the main engine is considered to be the most important piece of machinery in a ship. It supplies the ship with power for propulsion and sometimes electrical energy necessary

LI

for operating. Because it is the most important piece of machinery its reliability is considered to

NI!

be an important factor in the reliability of delivery.

'-.. .. In a previous survey [Knops, 1999] some insights into differences between 2-stroke and

4-stroke marine diesel engines are obtained. The reliability of these engines is also described and assumed to be unequal.

FACTORS WHICH CANNOT BE MANIPULATED

The following factors cannot be manipulated.

The weather is a factor, which cannot be manipulated. Though it can be predicted, this is only at a relative short time before departure.

Currents can not be manipulated, but can be well predicted.

Time for passing through special corridors cannot be manipulated Usually the average

time is known, but there are a lot of unpredictable factors.

The occurrence of accidents cannot be manipulated. Efforts can be made to minimise thel

chance, but not all accidents can be excluded, unpredictable events do occur. Amount of time customs takes for checking cargo cannot be manipulated.

Port services cannot be manipulated. Transhipment actions like loading and unloading of

/ 7

ships are usually performed by local enterprises and the time it takes can mostly not be

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Besides taking into account the expected extra time, one can try to reduce the unexpected extra time. For the remaining unexpected extra time, which cannot be reduced, there remains the possibility of a speed change in an effort to attain the time of arrival margin.

The following sub-paragraphs will focus on the possibilities to reduce the chances on an unexpected extra time.

2.6.2 Factors which influence the failure of machinery

The reliability of machinery can be manipulated so the changes on unexpected extra time can be reduced. The design which involves the number of parts and number of critical parts, the usage which involves the level of load and third-party products and the maintenance, which involve level, policy and quality can be distinguished.

NUMBER OF PARTS

Developing machinery with simple parts and structures can increase the reliability of machinery. Usually the more complex machinery is, the less reliable it gets because more can go wrong

Approaching a piece of machinery as a system consisting out of several parts, the more parts it has, the lower it's reliability gets. This reliability of a system

when reliability of all parts (Rime) is the same and failure of one part means failure of the system, can be written as follows [Smit, 1988]:

R_system -number of parts in systemR_parr

Equation 2.2 1.0 0,9 0,8 E 0,7 tit' 0,6 -6 0,5 0,3 0,2 0,1 0,0 100 200 300 400 500 600

number of parts in system

-4).- 0,9999 -6-0,999

Figure 2.7: Reliability of system versus number of parts in system

The value of Rsystern, as derived in equation 2.2, has been plot in figure 2.7. Three Rpad values have been chosen: a high reliability of 0,9999 a middle of 0,999 and a low 0,98 reliability per part. Consider the middle Rpart = 0,999 line, one can see that when 250 of these parts are used in a system its reliability gets below 0,8. For all three values of Rpart, increasing the number of parts decreases the reliability of the system (Rsysteni). The lower the value of Rim, the faster the reliability of the system decreases.

Not for all systems, failing of one part means failure of the whole system, but this approach underlines that the complexity of machinery has its influence on the reliability. After all, there is a lot of machinery, which does depend on the functionality of one (critical) part.

The following can be said about the difference between 2-stroke and 4-stroke marine diesel engines. It is known that 4-stroke engines have more parts than 2-stroke engines. This higher number of parts suggests that the 4-stroke main engine is less reliable than the 2-stroke engine.

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CRITICAL PARTS

Designing machinery is a process where a lot of calculations have to be made. Mostly these calculations focus on a part, which is critical for the functionality of the piece of machinery (a critical part). The level of over-dimension can compensate for the possible faults and uncertainties in the calculations. Over-dimension of critical parts in the machinery increases the reliability of the machinery.

Again something can be said about the difference between the 2-stroke and 4-stroke main engines. In the design stadium, it is tried to keep the 4-stroke engines as small and light as

possible. So an over-dimension of 4-stroke parts is mostly not desired and this suggests that these engines could be less reliable than 2-stroke engines

LEVEL OF LOAD

When developing machinery, an operating point for the machinery has to be set. Machinery can operate correctly under a certain load, which has been determined by the developer.

Under that load, the lifetime, the time between overhaul (TBO) and the level of maintenance needed can be determined.

When the machinery is operating at loads exceeding the determined maximum the reliability of the machinery will decrease. Also the lifetime, the TBO and the level of maintenancewill

change.

Also for this issue, the 4-stroke engines can be less reliable than the 2-stroke engines. Because the 4-stroke engine design strives for small and light engines, the service rating of these engines is frequently set to a relatively higher rating than for 2-stroke engines. This can cause a less reliable 4-stroke engine.

THIRD-PARTY PRODUCTS

Besides the determined level &load, also the third-party products are determined. These

products like lubricating-oil, fuel-oil and water are often required for operating the machinery. When developing machinery, the requirements of these third-party products get specified. Mostly they have to be of a certain quality for having the machinery operate correctly. When using third-party products of inferior quality, the reliability of the machinery will decrease. Something can be said about the third-party products involved for the 2-stroke and 4-stroke engines. Modern 4-stroke engines burn HFO in stead of the higher quality MDO. Because 2-stroke engines burn HFO more easily than 4-2-stroke engines this could result in a lower reliability for the 4-stroke engines. It must be noted that due to better refine processes nowadays, the quality of HFO gets lower. This could increase the difference in burning HFO for 2-stroke and 4-stroke marine diesel engines.

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LEVEL OF MAINTENANCE

Every piece of machinery has a lifetime and so has every part in that machinery. To keep the machinery functioning correctly, maintenance is required. The level of maintenance influences the reliability of machinery. Well-maintained

machinery is more reliable than poor maintained machinery.

Usually, machinery failure can be characterised by figure 2.8. The failure rate (h) is plotted versus the lifetime [Smit, 1988].

During the burn-in period, machinery has a failure rate, which is relatively high but decreasing (DFR). The relative high failure rate is caused by some faults in design or construction, which are usually corrected in this burn-in period. For the operating life period, the failure rate is constant (CFR). Failures in this period are due to chance mechanisms. The ageing period is characterised by an increasing failure rate (IFR). In this period failure of machinery is caused by deteriorating processes.

MAINTENANCE POLICY

The maintenance policy influences the reliability of machinery. Choosing a well balanced policy for each life time period can increase the reliability and maintenance efficiency. Of

There are two main types of maintenance distinguished [Smit, 1988]. Preventive maintenance (PM)

Corrective maintenance (CM)

Preventive maintenance (PM) is maintenance carried out before failure and corrective

maintenance (CM) is carried out after failure of a part. Preventive maintenance can be split up into two sub-policies and each of these can be split up into two executing forms. Figure 2.9 pictures this [Vut-inie, 1994].

Life

Periodic

Block

Figure 2.9: Maintenance policies

The difference between periodic PM and on-condition PM is that for periodic PM, the

maintenance is executed, following a specified schedule. The schedule is only effective if the

failure predictability is high and can include 'life or 'block' replacements. Life replacements

take account of failures and the maintenance-schedule gets changed. For block replacement the maintenance-schedule doesn't get changed if failure occurs.

Discrete Maintenance Policy On-condition burn-in CFR operating life

Figure 2.8: Failure rate versus time

Continuous IFR aging time I Preventive (PM) Corrective (CM)

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On-condition PM is executed when monitoring or inspection of a part shows that the condition is falling below specified standards. The monitoring or inspections can be carried at discrete moments in time (Discrete condition PM) or continuous (Continuous condition PM). On-condition PM is only effective when monitoring or inspection can detect potential failure. When reliability of machinery is pursued the maintenance level and policy will have to be adapted to the failure rate periods for an optimal functioning of the machinery. A said before, not for all systems, failing of one part means failure of the whole system. By determining which parts may fail and which may not without influencing the reliability of machinery, the

maintenance policy can be adapted and a higher maintenance efficiency can be obtained.

The most economical balance between PM and CM, which provides the highest-level of

machinery reliability has to be determined QUALITY

Besides the maintenance level and policy, the maintenance quality plays a role in the reliability of machinery. To obtain a high reliability, maintenance must be of a high quality. The crew executing maintenance needs to be well educated so maintenance tasks are performed correctly. Spare parts used, need to be at least of the same quality and when failure of a part is considered to be too frequent, the spare parts design needs to be of a higher quality. Also the available engine-room space can contribute to the maintenance quality. The more space the easier the maintenance can be carried out which results in a higher quality (and less time).

is easier to perform maintenance than for a 4-stroke engine. This can cause a higher reliability Because the 2-stroke main engine has less parts and is more robust than a 4-stroke engine, it for the 2-stroke engine.

BACK-UP SYSTEMS

Apart from directly influencing the reliability of the machinery by means of the design, usage or maintenance, one can influence it indirectly. Installing back-up systems, which take over after the machinery fails, can do this. The function will remain and so indirectly the reliability increases by means of an increased redundancy.

Installing plural pieces of the same machinery has the same effect, increasing the redundancy increases the reliability (of the function).

2.6.3 Professionalism of the crew

There is very little known about the professionalism of the crew. What is clear is from experience is that skills and motivation of the crew can make a big difference in the performance of a ship.

Using the ship and machinery correctly causes less errors and less failure of machinery. This involves good seamanship like navigation, steering and not exceeding given maximum level of loads of machinery, but also correctly carrying out of maintenance and repairs.

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2.7 Importance of attaining the Time of Arrival Margin and

Reliability of Delivery

2.7.1 How it used to be

In the shipping business there used to be an endeavour for high transportation speeds and

short transportation times. There was a tendency of the faster the better and no real attention

was paid to the reliability of delivery. Over the year's ships sailed faster and low fuel-oil prices amplified this tendency.

With the new economics of production, involving door-to-door intermodal services and JIT systems, the endeavour for minimisation of stock, storage periods and transhipments should be more actual. One should no longer be interested in how fast the cargo travels, but in the time of arrival of the cargo. New demands, like the time of arrival margin and the reliability of delivery have to be investigated. Of course for some cargo types there remains a maximum of the transportation time due to a vulnerable character or to minimise costs (like interests) for having cargo at sea. This results in a minimal theoretical service speed, which is considered to be given.

As said before, the focus of this survey is on the shipping business. The allowable time of arrival in the shipping business has not yet been investigated. Shipowners can't exactly tell how important it is to have cargo arriving on time. Furthermore, little is known about the reliability of delivery. Arguments like "when weather permitting" or the uncertainties of the seas are frequently recalled upon.

2.7.2 Tools supporting the reliability of delivery

A few articles make notice of what could be called an growing interest in the reliability of delivery.

"With the development of door-to-door intermodal services and the advent of just-in-time (JIT) supply systems, punctual delivery of cargoes is more than ever a priority both for shippers and for shipowners." [Kindred, 1990]

New tools have been developed to support the shipping business operating in a JIT system to achieve a reliability of delivery level. For instance, the possibility of electronic data interchange (EDI) and a 'penalty-box' system are tools, which claim to support the shipowners and

shipmasters.

ELECTRONIC DATA INTERCHANGE (EDI)

"They (the shipmasters) are concerned because delays may result in their inability to meet letter of credit deadlines or charter commitments. In addition, the trade journals are full of advertisement and articles promoting speedy transit times and use of electronic data interchange (EDI) for tracing shipments, reflecting the business community's concern for reliable delivery." [Kindred, 1990]

EDI involves a direct electronic connection between the 'transporter' and the sender or receiver. The sender or receiver is able to have the 'real-time' position of the shipment. But in fact, EDI does not directly support to increase the reliability of delivery level of the shipment, it can only give an insight in were a delay is caused.

For example, one of the most common causes of delay is customs checking the shipment, which the shipowner can not influence. So EDI can only create a transparency, which enables

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PENALTY-BOX

When a production business wants to have a certain reliability of delivery level, it can put pressure on the shipowner, which is transporting the shipment by applying a 'penalty-box'

system. This involves that every time a shipment is not on time, the shipowner gets placed in

the 'penalty-box' and is warned. Once a shipowner deteriorates below the reliability of delivery

level, the production business will terminate the relationship with this shipowner.

This 'penalty-box' system does not directly support the reliability of delivery in a JIT system. But it tries to eliminate the problems for the receivers and senders of the shipments. The

shipowner gets the responsibility to develop his services in such a way that the reliability of

delivery is achieved.

Although these systems seem to advocate reliability of delivery, as well EDI and the

'penalty-box' system do not directly support the reliability of delivery.

2.7.3 Time of arrival margin per cargo and ship types

To get an insight in the allowed time of arrival margin, it is assumed that different types of

cargo require different time of arrival margins. Each type of cargo is transported with a specialised type of ship.

Table 2.3 distinguishes three main kinds of cargo and the ship types used in merchant

shipping to transport each type of cargo. This has been done in a previous survey [Knops, 1999]. The ship types used for the transportation of people (Passenger ferries and Cruise liners) are excluded because they differ too much from the cargo ships used in merchant shipping. In the table the cargo is split up in three main categories and several sub-categories, For each sub-category the type of ship and the average service speed is given.

Table 2.3: Average service speed for ships transporting bulk cargo. unit cargo or cooled cargo

The following can be concluded about the average service speed. The average service speed does vary per type of cargo. The average service speed for the bulk cargo ships is 14 knots,

for the unit cargo ships the average service speed varies between the 13 and 19 knots and for

the cooled cargo ships, the average service speed is 17 knots. So bulk cargo is transported with a relative low speed and unit cargo (except Dry cargo ships) and cooled cargo with a

relative highspeed.

cargo

ship type

average service speed

solid Bulker 14 knots

bulk cargo liquid Tanker 14 knots

gas Gas-Tanker 14 knots

containers (TEU) Container ship 19 knots

unit cargo trailers RoRo 17 knots

"unit" Dry cargo ship 13 knots

cooled cargo cooled "unit" Reefer 17 knots

'

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The following assumptions about the time of arrival margin, reliability of delivery level and transportation speed per cargo type in shipping will now be developed.

BULK CARGO

Bulk cargo has usually a low value per weight and is a raw material or semi-product, which h to be manufactured into a final-product. After arrival in a harbour it is relatively easy to transhi and store ashore. The receiver, which is mostly a manufacturer, is often situated near by the harbour so the bulk cargo does not have to be transported any further. Whether this

manufacturer is situated near by the harbour because there was a harbour or the manufacture was already there and so a harbour was build can not be said. But fact is that they are often situated near each other.

Concerning these arguments, a large time of arrival margin and low reliability of delivery level would be sufficient for bulk cargo

When trying to explain the relative low service speed for Sulkers, the following can be said. From a previous survey a charter rate of $0,15 per ton per day is obtained [Wijnolst, 1995]. This charter rate is drawn from a database and is an average price for transporting a ton of bulk cargo a day with a 66000 DVVT Bulker in 1992.

Compared to charter rates of other types of cargo, the bulk cargo charter rate is low. This can be explained by the low value per weight of bulk cargo. The transportation costs have to be in accordance with the value of the cargo transported. The Wijnolst survey concluded that the charter rate is not related to the size or the speed of the ship. So the charter rate is fixed and the shipowner will have to comply with it. This demands relative low transportation costs, and consequently a low charter rate. This low charter rate can be achieved by designing a ship with an optimal cargo space and also an optimal ship speed.

Mostly an optimal cargo space will have a poor effect on the ship resistance, which will be relative high. That on its turn will have a decreasing effect on the service speed, which will be relative low because not too much propulsion power will be installed to reduce costs.

UNIT CARGO

Unit cargo is usually of a high value and consists of final-products that can be sold immediately to the consumer's market or can directly be used in a production line. When arriving in a harbour it has to be further transported in the logistic chain. Because it is valuable cargo, storage, stock and long transportation times have to be avoided.

Due to its high value, the need for further transportation and possible depending production lines. JIT terms have to be maximally fulfilled and so a small time of arrival margin and a high reliability of delivery level would be required for unit cargo.

An explanation for the relative high service speed can be the following one. From a previous survey a charter rate of $0,85 per ton per day is obtained [Wijnolst, 1993]. This charter rate is draw from a database and is an average price for transporting a ton of unit cargo a day with a 1000 TEU Container ship in 1992. The Wijnolst survey concluded that the charter decreases when the sip size increases.

Within Container ships, there is a relation between the ships size and the service speed namely, larger ships sail at higher speeds. So the charter rate is related to the ship size and service speed.

Compared to the charter rate of bulk cargo, the unit cargo charter rate is high, but also the value per weight of unit cargo is high. This demands a high transportation speed due to investment payback time and interest losses for the time at sea. The higher service speed will involve higher transportation costs, which are allowed due to the higher value of the cargo.

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COOLED CARGO

Cooled cargo can be considered as vulnerable cargo. It can immediately be sold to the

consumers market and because it is perishable, long storage has to be avoided so it has to be 1

(immediately) further transported after arrival in a harbour.

Because cooled cargo can decline by time, a small time of arrival margin and a high reliability of delivery level would be required.

A high service speed is used to transport cooled cargo. The main reason for this high service speed is the limited self-life of the cargo. Further more the cargo can be sold directly the to consumer market, at a 'hause', the cargo can bring up a lot of money.

In the reefer business, the charter rates are given in dollar per cubic feet per 30 days. From a reefer chartering business, an average charter rate of about $0,65 per cubic feet per 30 days is obtained. When assuming that a 40 cubic feet corresponds with 1 DVVT this yields that the average charter rate is $0,87 per ton per day. This relative high charter rate can be explained because during transportation, the cargo needs to be kept at a certain temperature. A lot of equipment is necessary to create this temperature and extra fuel-oil is required for delivering power to this equipment.

The following table gives an overview &the time of arrival margin and reliability of deliver of

the three types of cargo distinguished.

Table 2,4: Overview of time of arrival margin and reliability of delivery

2.8 Theory Feedback

By developing these thoughts about the reliability of delivery, the desire raised to verify the theory with some real data. An abstract of the theory together with some costs indication of the total costs of ownership of marine diesel engines was sent to several shipowners in the Netherlands. Some reactions were received about the theory and mostly involved the costs aspect.

A possibility for applying some real data to the theory was given by Seatrade Reefer

Chartering in Antwerp. During almost two months, data about distances sailed by Reefer ship was gathered and the theory could be filled with data. The results of this period are described in the following part of this report.

time of arrival margin

reliability of delivery

service speed i

Bulk cargo

large low low

Unit cargo small high high

Cooled cargo small high high

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2.9 Chapter Conclusions

Globalisation of the market caused by a higher level of co-makership demands changes in the logistic chain. Door-to-door services are developed and beneficial when a JIT system is implemented. The final receiver sets the time of arrival and a backward calculation for the total logistic chain is necessary. For each chain part a calculation for the estimated transportation time has to be made and speed is the resultant of the transportation time difference.

The focus in the logistic chain is on attaining the time of arrival margin. The probability of arriving within the margin is called the reliability of delivery.

The reliability of delivery can be influenced by two groups of factors:

1. Factors which can be manipulated:

failure of machinery

professionalism of a shipping crew

2. Factors which can not be manipulated: weather

currents

sailing through corridors accidents

customs port services

Both groups of factors can produce extra time during transportation. Sometimes extra time is known and can be taken into account in order to make a more realistic estimated

transportation time calculation.

Of the factors, which can be manipulated, the failure of machinery can be influenced by design, usage, maintenance and back-up systems. The main engine is an important piece of machinery in a ship and it is assumed that there are differences between the reliability of 2-stroke and 4-2-stroke marine diesel engines. Concerning the design, usage, maintenance and back-up systems the following can be concluded about the differences between the two engine working principles:

Design:

When the number of parts increases, the reliability of machinery decreases. The 2-stroke engine has fewer parts than a 4-2-stroke engine and so could be more reliable. When critical parts increase, the reliability of machinery decreases. The 2-stroke engine is more robust than the 4-stroke engine and so could be more reliable. Usage

When the level of load increases, the reliability of machinery decreases. The 2-stroke engine runs mostly at a relative lower service rating than the 4-stroke engine and so could be more reliable.

When the third-party products (fuel-oil) quality is low, the reliability of machinery is low. The 2-stroke engine can burn HFO more easily than the 4-stroke engine. A low quality fuel-oil will have less effect on the 2-stroke engine and so it could be more reliable.

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Maintenance:

When the level of maintenance increases, the reliability of machinery increases. This should be the same for both engine working principles.

When the maintenance policy is a well balanced between preventive and corrective maintenance, the reliability of machinery during operation will increase. This should also be the same for both engine working principles.

When the maintenance quality increases, the reliability of machinery increases. Because the 2-stroke engine is less complex, it is easier to perform maintenance than for a 4-stroke engine. So the 2-stroke engine could be more reliable.

Back-up systems do not directly increase the reliability of machinery they create a redundancy, which can compensate for failure of machinery.

Professionalism of the crew can be influenced by education. It can have large effects on the reliability of machinery and the performance of a ship.

JIT systems in logistic chains get more important but the time of arrival margin and reliability of delivery were never investigated for shipping.

Three types of cargo are distinguished and the time of arrival margin and reliability of delivery are assumed to be different for each type of cargo.

The height of the speed is considered to be less important than the reliability of delivery. The theory about the reliability of delivery has to be investigated in practice. This can be done for cooled cargo at Seatrade Reefer Chartering in Antwerp.

1. Bulk cargo: large time of arrival margin and low reliability of delivery

2. Unit cargo: small time of arrival margin and high reliability of delivery 3. Cooled cargo: small time of arrival margin and high reliability of delivery

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3 DATA SURVEY

3.1 Introduction

In order to get some insights in the reliability of delivery in practice, a data survey is carried out at Seatrade Reefer Chartering in Antwerp. This chapter describes which data is obtained from

different databases and experience of some employees. It further describes how the data is conversed into workable information about legs sailed.

Paragraph 3.2 gives some information about Seatrade Reefer Chartering. Paragraph 3.3 describes the conversions and calculations made to obtain the workable information about the legs sailed. In paragraph 3.4 the filtering process which was carried out in order to obtain al reliable database is explained. An insight in the types of commodity transported is given in paragraph 3.5. The chapter conclusions can be found in paragraph 3.6.

3.2 Information about Seatrade Reefer Chartering

Seatrade was founded 1951 and at that time owned several Coaster between 600 DVVT and 900 DVVT. They sailed mainly in Western Europe and transported dry cargo. In 1962 the first Reefer ship was build and a successful business of transporting cooled cargo began. New markets were found in transporting frozen fish and cooled fruit and nowadays Seatrade ships sail all over the world.

The modern ships have capacities of 2190 DVVT to 15200 DVVT and with about 150 ships in the pool, Seatrade belongs to the largest Reefer companies in the world.

Seatrade Reefer Chartering NV in Antwerp is the branch office of Seatrade Group INC.

Curacao NA.. The business manages a shipping pool of Reefers and arranges the cargo for

the ships in the pool.

Different shipowners have their cargo arranged by Seatrade Reefer Chartering as like the

fleetmanagement department of Seatrade Group, called Seatrade Fleetmanagement Byin

Groningen.

3.3 Gathering Data

In chapter 2 the importance of attaining the time of arrival in order to attain a reliability of delivery in a JIT system has been discussed. It is stated that the functioning of the main engine has a large influence on the reliability of delivery and it can be manipulated. Also it suggested that there is a difference in reliability between 2-stroke and 4-stroke marine diesel engines. To find out what the reliability of delivery is, how time of the arrival margin is attained and the difference in performance of the 2-stroke and 4-stroke engines in practice, data about the following factors is required.

the transportation time difference, the time of arrival margin,

the pursued reliability of delivery level,

differences in performance for the two engine working principles, speed increase to compensate for delays,

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This data can be obtained from databases and interviews with employees at Seatrade Reefer

Chartering NV in Antwerp and Seatrade Fleetmanagement BV in Groningen.

3.3.1 Database conversions

At Seatrade Reefer Chartering, information about legs is stored in a database, which contains

information about portcalls.

A portcall is a stopover of a ship at a certain port and a leg is the distance sailed between two portcalls. The database contains information of about 9000 portcalls between January 1998 and June 1999. All legs sailed between two ports are included and do not have to be only laden legs or only legs between a loading and a discharging portcall.

Because the information is about portcalls and not legs, merges, conversions and filtering are applied to the database to obtain information about the legs sailed in between the portcalls. By doing so insights into the actual and estimated transportation times can be obtained.

In order to obtain some workable 'leg data out of the database with 9000 portcalls, merges,

conversions and filtering are applied to the database. The merges with other databases yield a

new database containing the following information about legs instead of portcalls

name of ship, the deadweight and the main engine working principle installed,

name of start-port and end-port of the leg, the country and the area they are situated in, action carried out at start-port and end-port,

commodity loaded, discharged or aboard,

local time of departure from start-port-pilot-station and local time of arrival at end-port-pilot-station.

A pilot-station is the place at sea where the pilot comes on board of the ship to guide her in the port and leaves the ship when she has left the port.

In this database, the names of the portcalls are real ports like "Rotterdam" but also given in the database is the name "offhire at sea".

An offhire at sea means that the ship is not performing during sailing of a leg. The ship is not fulfilling her task she is hired for, mostly transporting cargo. Mostly the reasons for the offhires at sea are known and stored in an other database called the offhire database.

After a filtering process of the offhire database (see Appendix 1 (offhire database)), the percentage of main engine is calculated. This results in a percentage of offhires at sea caused by the main engine is about 86% of all offhires at sea. This emphasis the statement that the machinery, especially the main engine is of large influence for the reliability of delivery. So when speaking of an offhire at sea, one can be 86% sure that is caused by a main engine

problem.

In this stage of the survey it is clear that the offhire at sea database contains more ships equipped with 4-stroke main engines than 2-stroke main engines.

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DATA SURVEY 24

3.3.2 Calculations carried out in the database

TRANSPORTATION TIME DIFFERENCE

Because this survey is investigating the time of arrival, the differences between the actual transportation time and the estimated transportation time, called the transportation time difference (Thai), has to be calculated.

The transportation time difference is calculated by subtracting the estimated transportation (TTest) time from the actual transportation time (T T act).This yields the following equation:

:TT =

, dif Tract

Equation 3.1

How the actual transportation time and estimated transportation time are calculated will be explained next.

ACTUAL TRANSPORTATION TIME

In order to calculate the actual transportation time of a leg in the database, a conversion needs to be made. In the '9000 leg database' the time of departure from the start-port-pilot-station (ToD) and the time of arrival at the end-port-pilot-station (ToA) are known in local times. The actual transportation time of a leg can be calculated by subtracting the time of departure

from start-port-pilot-station form the time of arrival at the end-port-pilot-station. However because these times are given in local times, in order to obtain the (real) actual transportation time, first they need to be converted into GMT times.

By adding or subtracting the time difference between the local time and GMT time, the time of

departure in GMT time (ToD(Gm-n) and the time of arrival in GMT time (ToA(Gm-n) are obtained.

Subtracted these times from each other yields the actual transportation time (TT). The

following equations display the actual transportation time calculation, which is also visualised in figure 3.1

ToA(GmT) =ToA(1,,)±timedifference ToD(Gmr) =ToD(Io,)±timedifference

iTTact = ToA(Gm-r) - ToD(Gmr)

Equation 3.2

When converting the local times into

GMT times the difference between ports keeping summertime and those, which do not, is not taken into account. By doing so the actual transportation time (flaps!) has an inaccuracy of 1 hour (= 0,0417 day).

When a start-port is situated in a area

keeping summertime and the end-port is not, the actual transportation time is 0,0417 days longer. And when the start-port is not keeping summertime and the end-port does, the actual transportation is 0,0417 days shorter.

Whether this possible 0,0417 days inaccuracy is negligible depends on the size of the

transportation time difference

(TTda)-ToD(Grvm

transportation

Figure 3.1: The actual transportation time (7-1)

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ESTIMATED TRANSPORTATION TIME

At Seatrade Reefer Chartering, when a leg has to be planned in the voyage registration database, the estimated transportation time (TTest) is calculated this way.

The estimated transportation time of a leg is calculated by dividing the distance from port to port by the theoretical service

speed (vthec,), recall equation 2.1.

irest

V the°

Although the actual transportation time (TTact) of a leg at Seatrade is measured from pilot-station to pilot-station, the distance (D) used to calculate the

estimated transportation time (nest) is

measured from port to port.

Because the pilot-stations are situated on the leg-route at sea before the port, the distance from pilot-station to pilot-station is shorter than the one from port to port. Figure 3.2 visualises these differences.

ToD(Gm-n

transportation

-rest with D (= port to port)

Figure 3.2: The estimated transportation time incorrectness

So the estimated transportation time is calculated longer than the actual transportation time for sailing from pilot-station to pilot-station. Why this calculation method is carried out this way is not clear.

A calculation of the estimated transportation time with the port to port distance (D) is not correct. Because sailing from port to pilot-station or vice versa, is not done with the theoretical service speed (vtheo) but with a lower manoeuvring speed. This yields that when the port to port distance is used, it is not realistic to use the theoretical service speed. Further more the

waiting time for the pilot to arrive onboard and leaving the ship is not taken into account. A possible explanation could be that Seatrade wants to create a time-buffer to compensate for unexpected extra time during transportation. But than it has to be assumed than the customer is interested in the time of arrival at the pilot station and not at the port.

If the customer is interested in the time of arrival at the port, the time of arrival in the database is not the right one. Some extra time has to be added to this time of arrival at the pilot-station to obtain the time of arrival at the port.

TOA/GmT,