Shipbuilding Erection Scheduling Support Tool
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Transcript of Shipbuilding Erection Scheduling Support Tool
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Erection Scheduling Support Tool
Kees Meijer, Delft University of Technology, [email protected]
Jeroen Pruyn, Delft University of Technology, [email protected]
John Klooster, IHC Krimpen Shipyard, [email protected]
Abstract
This paper gives an overview of a method, developed to estimate planning data for the erection phase
in a very early stage of a shipbuilding project, allowing the planning department to quickly assess
numerous possibilities and make founded strategy decisions. The tool offers the possibility to
investigate several strategic options like pre-erection and block assembly. Validation against
conventional erection schedules proved this method to be quite accurate.
1. Introduction
In 2006, the shipbuilding company IHC Merwede restarted the yard facilities of the former Van der
Giessen de Noord yard. This yard had ceased production activities only three years earlier. The
shipbuilding industry seemed to flourish again after darker times so new possibilities for investments
appeared. The new company IHC Krimpen Shipyard is blessed with a great location, unique facilities
and an enthusiastic staff. Together with the economic prosperity this cleared the road for production
innovation.
In cooperation with the department of Ship Production at the Delft University of Technology, IHC
Krimpen Shipyard started searching for ways to tackle one of the greatest challenges in shipbuilding:
prediction of production. Clearing out uncertainties will probably never be an option, but being able to
estimate quite exactly the time needed for various operations would certainly lead to a higher
efficiency which would lower the costs, creating higher profits. In this context, previous work
developed a high-level simulation model of the production process at Krimpen Shipyard. This
simulation was then used to make a production capacity assessment, Van Rijssen (2007).
This paper describes the next step in creating tools to assist in making early stage (pre-contract)
estimations and support strategy decisions, the search for a tool to automatically generate an erection
schedule in the pre-contract phase. At this moment research is also carried out to develop the same for
the section building phase of the production process.
2. Planning in Shipbuilding
Building a high-tech vessel consists of a sequence of numerous complex activities. Planning and
scheduling of this production process is a very challenging task. The complexity of planning in the
shipbuilding industry can be visualized by several typical properties. First of all, reproduction of
schedules is impossible. Not only is the product different for every project, but also the conditions
regarding floor occupation, deliveries from third parties, and other projects call for a different
approach every single project. Secondly, because of the urge to implement the just-in-time principle,
it is not enough to make sure all information is available on time, but more important: production
must be in total harmony with engineering. Finally, a shipbuilding project planning has to deal with a
large number of parties, all working on the same vessel, all requiring space and time to do their
activities. Taking these considerations into account, it is rather safe to say, planning in shipbuilding is
more complex and of higher importance than in many other comparable industries.
2.1. Master planning
The first planning activity is done in a very early stage. Before the contract is signed, estimations of
several key points in the process have to be made. These milestones of several sequential projects of a
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yard form the master planning. Some of the key moments in the development and production of a
vessel are:
1. Signing the contract
2. Keel laying
3. Launch
4. Delivery
The contract will state these milestones. They are not only important for both parties because they
guard the progress of the project, but the stated dates also stand for the payment of part of the contract
price. Finally the master planning is used by management to keep track on the order book and
investigate possibilities for new tenders.
The planning department will of course use information provided by earlier projects to estimate the
throughput time of the total project. Comparable weight and complexity will most likely result in a
comparable lead time, supposing the conditions for production are also the same. In the absence of
any comparable project, more in depth production figures extracted from earlier products should be
used. A certain margin, proportional to the uncertainty of the used method, is used to make sure
production will be able to meet the set standards.
2.2. Erection Schedule
When it becomes clear that the contract will be signed, the planning department will start scheduling
the project in more detail. The vessel is therefore divided into sections and grand blocks. The main
outline of the production stage is given by the erection dates of those sections and blocks on the
slipway. These dates, and thus also the erection sequence is stated in the erection schedule. The
importance of this part of the planning is supported by the fact that delays in this schedule most likely
will have serious consequences for the master planning.
The erection sequence can be seen as the backbone of the erection schedule, Yoon and Varghese
(2007). Changes in plan regarding the sequence of erecting blocks will most likely affect a great deal
of the erection schedule. Theoretically, the erection sequence defines the total throughput time of a
project on the slipway, and so also the number of projects a yard can handle in a certain amount of
time.
Fig.1: Erection activity taking place at IHC Krimpen Shipyard
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But not only is the erection schedule inspired by the erection sequence, also the section building
activities are dictated by the activities on the slipway. The erection sequence decides when a section
should be ready, and consequently, also the start date of construction and the delivery date of material
and components. Thinking through this matter, the conclusion is that the erection sequence eventually
dictates all other activities on the yard. The urge to find a good erection sequence in a very early stage
is thereby explained.
3. Erection Scheduling Support Tool
Automatically finding the desired erection sequence is part of the process in this tool Lee (1995). But
before this algorithm is initiated, the user has to provide the model with all needed input. Rather than
developing a fully automatic planning tool, the choice has been made to include a great deal of user
interaction. This has the intention to involve as much of the users knowledge as possible into the
scheduling process.
By running the process several times while changing variables, this way experience in cause and
effect can be gathered and several scenarios can be investigated allowing the yard to pick a robust
planning rather than the fastest one. Reasonably experienced users can create a decent erection
schedule in less than 2 days. At this point in time the goal is to be able to get a good revision 0
planning, perhaps slightly improving it, as users can investigate alternatives rather rapidly. At the
basis of the tool however are still the same assumptions. Improving on that is something for later
study.
3.1 Working of the model
The available input in the stage when the model is meant to be used consists of a general arrangement,
together with a list of all sections with their locations. To make a first estimation of total throughput
time, this information should be enough.
For reliable information on required personnel, also the weights of sections have to be known. In this
stage that will most likely be an estimation. A system has been developed to allow a great deal of user
interaction in order to state the estimated amount of work needed for a certain section, while on the
other hand providing easy first estimations.
Fig.2: Rhino visualization of output
If the focus is put on generating a realistic erection schedule as a ground for further planning
activities, then more information is needed regarding the nature of the product and production. These
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preferences are translated into boundary conditions for the model. Taking all boundary conditions into
consideration, a scheduling algorithm delivers a feasible planning of the erection phase. Implemented
boundaries are discussed in the next section.
Delivered output of the model consists of the erection schedule, showing the dates and lead times of
all erection activities. To visualize the sequence of erection chosen by the model, Rhinoceros is used.
3.2 Various options
In shipbuilding the yard has many strategic possibilities at its disposal. The fact that every project
requires a different approach forces the yard to be quite creative in its scheduling activities. Pre-
erection is one of those options which have a great influence on the erection schedule. Other strategic
choices involve the amount of blocks to be built as well as the definition of closing decks.
Pre-erection
Pre-erection is the situation where a project is already (partly) being erected while the previous project
is still on the slipway. This strategy involves the transport of the already erected part of the vessel to
the slipway, once the previous vessel has been launched. The model offers the possibility to insert the
part of the vessel which should be pre-erected. It will then make sure that part is erected and ready for
transport when the previous project has been launched. It will not (yet) be able to consider pre-
erection together with the other vessel under construction
Block definition
The designation of the several parts of the construction of a vessel at the yard can vary per yard. For
now let’s assume that a panel is the smallest constructed part. Two or more panels are called a section
and several sections can be assembled to a block. There is a trend going on, where the number of
these steps is optimized to get as close as possible to standardization of production activities, without
losing the advantages of building huge blocks at once. The preferred number of steps will most likely
depend on the available space and facilities. However, the model offers the possibility to quickly
assess the outcome while varying the number and size of the blocks to erect.
Closing decks
To allow components to be lowered into the ship while it is being erected, some sections should be
erected later. These sections are called closing decks. In the model this is a property which can be
given to all sections, creating the possibility to erect them much later in the process.
Component scheduling
Scheduling components means, making sure the delivery date of the concerned component will be
before the date of placement. Preferably, the two dates do not differ too much. However, one of the
greatest risks of scheduling is the delay of a key-component. To avoid this risk from infecting the
whole schedule when this occurs, it is probably wise to keep a certain buffer zone between the two
dates. The model offers the possibility to enter a number of components as input with their delivery
date. Additional input needed is the blocks which are a condition for the placement of the component
as well as the blocks which have the component as condition to be erected. The resulting schedule
will take this information into account and make sure the concerned section is still accessible when
the component arrives.
Resource leveling
The user has the choice to implement resource leveling into the desired schedule. The model will then
level the resource personnel to a stated level by shifting some erection activities forward in time. This
measure might lengthen the throughput time of the project, but will give a much more even workload.
Fig.3 shows an example of the outcome when resource leveling is applied. It shows the amount of
personnel needed per week over a certain period.
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Fig.3: Effects of resourcelevelling. Amount of personnel was levelled around 40.
4. Validation
In order to validate this tool against the regular used methods, the output of the tool is compared with
the first version of the actual erection schedules of various projects. These schedules have been made
in the same phase for which the model is also intended, and are therefore suitable for validation.
Although there is no reason to reject the tool if the outcome does not come anywhere near the first
real erection schedules, if they do have some resemblance, it is safe to say that the tool delivers
schedules of equal quality compared to the initial schedules of the yard.
The comparison is made in two steps. First the general data of the schedules have been compared.
Looking at the date of the launch as suggested by the tool and by the real schedule, they lie
surprisingly close to each other. Maximum difference was one week on a total throughput time of
almost a year.
The second step in this validation was made by comparing the chosen sequence of the two methods.
The following example shows the validation as it is carried out with the first schedule of the vessel
‘Well Enhancer’ as built at IHC Krimpen Shipyard. A relatively small well intervention vessel built
up from 44 sections. Fig.4 shows for each section the difference in position in the sequence between
the two methods. Here the model only looked at steelwork, no components were yet implemented. A
positive difference means that the model scheduled the erection to take place earlier than the date as
scheduled by the yard. Most minor differences can be neglected, while big differences are in need of
an answer.
Fig.4: Differences per section in position in the erection sequence of first outcome
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The three major differences need an explanation, to accept the validation:
A. This section is the bulwark. The model ‘sees’ this section as a whole and thinks it is only
possible to erect this section when all deck sections have been erected. In reality, it can be
erected partly already much earlier. The negative value is thereby explained.
B. This section is a closing deck. As the model does not see the need to keep this deck opened,
this section is erected quite early in the process by the model.
C. This is the bulbous bow of the vessel. Just behind it, the bow thrusters are placed, requiring
the installation of important components. This could be the reason it is scheduled later by the
schedule of the yard.
Until now, this example has shown that the model is able to generate a reliable throughput time and
deliver a quite reliable sequence. However, to be able to use this for actual scheduling, the possibility
should exist to adapt the first outcome of the model in order to create a decent schedule. Assuming the
first effort of the yard can be seen as a decent schedule the model should be able to deliver a schedule
very close to it, with some adaptations done by the user. Looking at the example of the ‘Well
Enhancer’, several measures can be taken. By adding various key components and changing the
conditions of the bulwark the differences reduce to what is shown in Fig.5. All differences in this
graph are below the threshold for this ship. This threshold is based on the amount of sections in a
regular ring section.
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Fig.5: Differences per section in position in the erection sequence after taking measures
5. Conclusion
This paper shortly presents a model to automatically generate an erection schedule for vessels in a
very early stage. It gives very acceptable results in a short time and offers various opportunities for
the user to adapt the results to find the eventual desired erection schedule. The concepts used to set up
the model are extracted from the methods which are applied in reality to set up a first erection
schedule. The specific strength of this model is the ability to build a range of erection schedules from
scratch as a basis for further planning activities and strategic decisions, and thus enabling more robust
scheduling. Further investigation is going on to develop a similar tool for the section building
activities. Together with the already existing simulation of the production activities, these tools will
form one pre-contract decision support system for the planning department of the yard.
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References
VAN RIJSSEN, B.F. (2007), Production capacity assessment of a new shipyard, Delft
LEE, J.K.; LEE, K.J.; HONG, J.S.; KIM, W. (1995), Intelligent Scheduling Systems for Shipbuilding,
AI Magazine 16/4
YOON, D.Y.; VARGHESE, R. (2007), Looking-Forward Scheduling Approach Applied in Pre-
erection Area of a Shipyard, J. Ship Production