Erection Scheduling Support Tool Kees Meijer, Meijer, Delft University of Technology,
[email protected] Jeroen Pruyn, Pruyn, Delft University of T echnology,
[email protected] John Klooster, 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 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. 2. 3. 4.
Signing the contract Keel laying Launch 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 a ll 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. Preerection 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 preerection 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 t he 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 Preerection Area of a Shipyard , J. Ship Production
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