A structural design methodology to reduce structural complexity to improve coating application and performance in water ballast tanks

Abstract

The introduction of the IMO Performance Standard for Protective Coatings (PSPC) for dedicated water ballast tanks (WBT) has increased the importance of the coatings applied in these tanks. Typical structural configurations within Water Ballast Tanks (WBTs) have a high degree of complexity; these spaces contain a large extent of edges, corner details and welds, which are commonly cited as areas most likely to suffer coating failure. However there is no quantitative measure of complexity as an indicator of how difficult a structure is to coat reliably. The concept of ‘structural complexity’ is considered with the intention of improving the in-service performance of applied coatings by proposing ships structures that include the coating process as a design consideration. As a means to try and provide a quantitative measure indicative of how easy a structure is to coat, the idea of ‘structural complexity’ is developed based on fundamental structural features. This measure is then used to understand the influence that different stiffener profiles and stiffener spacing may have on the coating process if structural configurations are sought that have reduced complexity. Investigation of the principal developments of the coating process indicates that any improvement is unlikely to be driven by coating technology or process alone. If improvements are to be made the suggestion here is that they should be driven by improving the design of the structure to be coated. The intention is to promote a ‘design for the coating process’ methodology to achieve this. The global ship and structural design process have been reviewed, where the classical approach looked at the relationship between weight and strength. This work concurrently considers the implications of different structural configures on not only weight and strength but also ease of coating. The relationship between the topology of the structure and the physical task of applying paint to it has formed the foundation of a ‘design for coating’ methodology, where the influence of structural complexity on all aspects of performance is considered with equal merit. A coating cost estimator has been developed in order to demonstrate the potential savings that could be realised by considering the coating process during the design phase. A simple optimisation routine has been used to seek solutions for minimum, complexity, weight, steelwork and coating costs. This allowed the balance to be explored between the completing aspects of the steelwork and coating processes. These alternative design solutions have been assessed using mathematical computational methods to ensure that the designs provide adequate structural performance.