Network Planning Application for Scheduling of Marine Diesel Engine General Overhaul Activities

There are many sub-tasks and tools in general overhaul activities, so that a planned and systematic arrangement are needed. In systematic general overhaul planning can use the Network Planning method. Scheduling by the Network Planning method describes a task into a network. The Network Planning has two commonly used techniques, namely CPM (Critical Method Path) and PERT (Program Evaluation and Review Technique). Therefore, in this study, scheduling will be carried out by the Network Planning method, CPM and PERT techniques. By using network planning in overhaul activities, it is hoped that it will be able to identify deviations and critical paths in the sequence of work processes so as to prevent delays in completing work.


Introduction
Diesel engine is an auxiliary engine that is used as a provider of electricity needs on ships when the ship is being in operation.Diesel engine maintenance is used to maintain the continuity of the availability of electricity on the ship.The use of diesel engine operated over a long period of time certainly requires overhaul action as the maintenance after the use of auxiliary engine during 20000 running hours.
In general overhaul activities, there are many sub-tasks and tools so that a planned and systematic arrangement is needed.General overhaul activities that need to be planned include work order, resource allocation, and duration of working hours.Then the results of the work allocation arrangement can be made into the planning of the estimated time and order of work.A project can be defined as a temporary activity that lasts for a limited period, with the allocation of specific resources, and are intends to produce a product or result whose quality criteria were defined [1].
A project requires a technique used to manage an activity ranging from planning, scheduling, to controlling the project.The success or failure of the implementation is often due to the lack of planned project activities and ineffective control so that project activities are inefficient, resulting delays, decreasing quality of work, and swelling implementation costs [2].
A project should have proper planning even the used scheduling method to avoid or overcome delay problems by using Network Planning.In principle, network planning is used to plan the completion of various kinds of work, using the network as a planning tool can be compiled good planning [3].Network Planning is in principle a dependency relationship between parts of work (variables) that are depicted into the network diagram.Thus it is known which parts of the work should come first, which work does not need to be rushed so that tools and power can be shifted to other places for efficiency [4].
Network Planning Methods is a management technique that can use to assist in project planning and control.There are two methods commonly used in this method, namely Critical Path Method (CPM) and Program Evaluation Study and Technique (PERT) [5].The PERT and CPM techniques have many similarities, although they have been developed separately, the main difference lies in the fact that the CPM technique is based on deterministic estimates for the duration of activities while the PERT technique is based on probability estimates for the duration of the activities [6].
The CPM technique is carried out by compiling a network of work identified against the activities and using a simple time estimate on each activity indicating the duration of implementation, while the PERT technique is used in scheduling, organizing and coordinating parts of activities in a project.The PERT technique requires three estimated times for each activity (Optimistic, Pessimistic, and Most Likely).From the three estimated times, it will be used to determine the expected time then (te) [7].In addition to being applied to project and production planning, network planning can also be applied to general overhaul activities of diesel engine.The general overhaul activity of diesel engine has many sub-tasks that have the potential for irregularities in the sequence of work processes.Structured planning is needed to deal with the uncertainty of project conditions so scheduling the implementation of a project is very important.In diesel engine overhaul activities, structured planning is needed to obtain an effective work sequence scenario.
The purpose of this study is to plan and schedule project activities effectively, to solve the problem, is the late completion time of the general overhaul of marine diesel engines by using the CPM and PERT methods to design network planning.With effective network planning, a more planned work schedule to get effective work sequence scenarios.

Methodology
The data used is a list of general overhaul tasks and per-task completion times obtained by measuring during general overhaul activities.

Data Processing
At this step was a continuation of the data collection stage that had been carried out, such as: a. Making a breakdown of activities b.Determining the time for each activity c.Determining the relationship between activities

Making Network Diagram
At this step, network diagrams were made.The activities making up the project are defined, and their technology dependencies upon one another are shown explicitly in the form of a network diagram [8].After the breakdown of activities was arranged and the duration and relationship for each activity had been determined, a network diagram was made.

Determine of Critical Path using CPM and PERT Technique.
At this step, the determination of the critical path was carried out using the CPM and PERT technique.In the process of identifying critical paths on network diagrams in the CPM technique, there were several terminologies and calculation formulas used, including [9]: a. Forward Computation Formula : EF = ES + t b.Backward Computation Formula : LS = LF -t c.Float/Slack Total Float Formula : S = LS -ES For the PERT technique, after compiling a network diagram with the value of time expected as the duration of the calculation, the critical path was obtained.From the diagram, a critical path would be obtained.In the PERT technique, the emphasis was directed to trying to get the best period of time (in a more accurate direction).The assumption of the approach in the PERT technique was expressed in the calculation of the following formulas [10]:   1. Activities that were identified to be critical paths were activities that had a float value equal to zero.The activities that were said to be critical paths are:

Analysis Using CPM Technique a. Network Planning Diagram
Activities having a certain float or were not equal to zero are identified as non-critical activities, then the implementation of such activities in the relevant line may be postponed or extended to a certain extent.So that the activity could be delayed in its implementation as long as the value of the float is.Activities that were identified to be non-critical were: D5 -E6 -E10.3. The completion of the general overhaul of the diesel engine using the critical path CPM technique was 83,4 hours.From Table 4 above, it is obtained: 1. Activities that were identified to be critical paths were activities that had a float value equal to zero.The activities that were said to be critical paths were: A1 Activities having a certain float or were not equal to zero are identified as non-critical activities, then the implementation of such activities in the relevant line may be postponed or extended to a certain extent.So that the activity could be delayed in its implementation as long as the value of the float is.Activities identified to be non-critical are: C4 -C5 -C6 -E10.3. The completion of the general overhaul of the diesel engine using the critical path PERT technique was 84 hours.6 above, it could be seen that the use of the PERT technique obtained a work completion time of 84 hours where the time was 10,4 hours faster than normal time scheduling.The use of PERT technique also had a time efficiency of 11,02%.

Conclusion
Based on data processing and the results of analysis and discussions on general overhaul marine diesel generator, the critical path obtained by the CPM and PERT methods is different.This is because the time usage in the network planning diagram is different.In the network planning diagram of the CPM method is based on deterministic estimates for the duration of activities while the PERT technique is based on probability estimates or duration from te (time expected).From Surraya Aulia's research the critical path obtained by the CPM and PERT methods is the same.
Scheduling using the CPM technique had a completion time of 83,4 hours while scheduling using the PERT technique had a completion time of 84 hours.Scheduling with CPM technique shortened the work completion time by 11 hours compared to normal time while scheduling with PERT technique shortened the work completion time by 10,4 hours.
The scheduling with the best effectiveness is chosen taking into the shortest the work completion time.From the results of the comparison of the time between the CPM technique completion time with the normal completion time and the PERT technique completion time with the normal completion time, it could be concluded that the most effective scheduling was to use the CPM technique.

7 3. 2
Analysis Using PERT Technique a. Determining the expected time (te)

Table 1 .
Scheduling with CPM Technique

Table 2 .
Total Float CPM Technique

Table 3 .
Expected Time

Table 4 .
Total Float PERT Technique

Table 5 .
Scheduling using CPM TechniqueFrom Table5above, it could be seen that the use of the CPM technique obtained a work completion time of 83,4 hours where the time was 11 hours faster than normal time scheduling.The use of CPM technique also had a time efficiency of 11,65%.

Table 6 .
Scheduling using PERT Technique 11From Table