Production Planning and Control

Scheduling methods used in shipbuilding are unique to each yard and generally reflect practices developed from experience. An overall schedule which is most useful to both management and production departments is one which highlights major tasks and events, and which shows the sequence of work and the relation of the various tasks to each other and to the whole project.

The basic principle in network flow is the task-to-task relationship. That is, task С cannot start until its two prerequisite tasks A and В are completed. There is, of course, the usual task-to-time relationship for each task. These principles have always been employed in one form or another throughout industry, but the computer has now made it possible to utilize to the fullest these principles in network form.

Network Flow Scheduling technique is often used for controlling large, complex, and possibly non-repetitive projects. Examples of the technique are PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method), both of which provide a means of representing graphically the different operations that make up a project. These networks can be revised to show the effects of adjustments to a schedule necessitated by changes in design, delays, etc. It is also possible to treat the network statistically in order to obtain an idea of the probable longest and shortest times for completion of a project.

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Preliminary Planning in Shipbuilding

Preliminary planning is done at the time of bidding and before contract signing. The first step is to determine dates for such key events as keel laying, launching, and delivery. Due to uncertainties of the final design, the material market, and the general labor situation, it may be desirable to modify these dates in order to provide a margin of time in meeting definite commitments. This is a management prerogative.

Key dates are usually shown on a shipway schedule chart; these dates become increasingly critical when the number of shipways is decreased. Estimating the shipway schedule for new designs is difficult, especially if development work is necessary of if new facilities are required. Experience is extremely valuable in this connection because there is seldom time for any in-depth analysis.

For any efficient operation, whether the plans are prepared in the shipyard or by a subcontractor, the engineers and draftsmen must work closely with the building yard. The only way to minimize potential problem areas and to ensure a maximum degree of success is to consider each step in the construction and scheduling process, no matter how trivial the step may appear. This applies to machinery installation and outfitting as well. It is imperative that a design engineer be familiar with all of the pertinent factors affecting production, such as maximum size and weight of plates, sub-assemblies. and erection units. But most important is the time and effort needed to plan construction at the very beginning of the design stage.

In order to provide some flexibility in design and construction, specifications are often written to give the con¬tractor reasonable options, such as to use a casting, a forging, or a weldment for a stern frame or to use either radiography or ultrasonic testing for weld inspection. In other cases, the specification will describe the construction method or system preferred by the contractor.

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