Recently, Malta Shipyards re-instated two handymax bulk carriers operated by Torvald Klaveness to ‘better than new’ condition using an innovative new technology.
Until recently, re-instating tank tops was an expensive and time-consuming process involving the cropping out of old tank tops and replacing them with new plating and longitudinals. However, thanks to Intelligent Engineering’s patented Sandwich Plate System (SPS) overlay technology, the existing thinned tank tops of the Klaveness vessels were used as one side of the new composite.
In selecting this sandwich solution, Klaveness made significant repair and operational savings. Project schedule and risk were minimised and the reinstated cargo holds are better suited for their purpose than their predecessors. DNV, which carried out extensive analysis prior to execution, is delighted to support customers at the forefront of new technology.
Since they were built at the end of the eighties, the Klaveness self-discharging Bauta and Ballangen bulk carriers have served their owners well. Frequent maintenance of the double-bottom tanks had ensured that the coating systems were in good condition. However, the constant wear and erosion from cargo and handling equipment led to the steel tank tops coming close to the minimum allowed thickness. Rather than re-assess alternate loading possibilities, Klaveness decided to reinstate the tank tops.
“There were three key reasons for using SPS overlay,” says Sverre Grønn, technical manager at Klaveness. “First, the need for a predictable schedule for the work was essential. Second, we avoided to clean and then re-coat the double bottom ballast tanks, saving considerable inconvenience and work. Last, but not least, the final tank tops would be more durable and resistant to damage than their predecessors, minimising future deformation, allowing for easier discharge and cleaning.”
Klaveness approached DNV for approval of the use of SPS overlay. DNV’s major concern was not the sandwich design itself, but its termination at the base of the hopper tanks and stools. As the double bottom is a major contributor to longitudinal strength, the transfer of stresses between the conventional structure and the sandwich was seen as a possible hotspot for future through-life fatigue. DNV conducted a detailed Finite Element Method (FEM) analysis, and working together with Intelligent Engineering, a satisfactory solution was found.
Stuart Rolland, COO Intelligent Engineering observed, “Torvald Klaveness avoided lengthy deviation and time out of service by conducting the repair at Malta Shipyards rather than travelling to the Far East. The repair took 23 days rather than an estimated 56 to crop and replace the tops, and deviation was eight days each way rather than 30. With charter rates as they currently stand, the opportunity costs savings could not be ignored.”
The work was conducted at Malta Drydocks in conjunction with IE’s field engineers. 3,025m2 of SPS overlay on Bauta was completed in just 23 days in a number of steps:
- Cleaning and grit blasting of the tank tops
- Attachment of perimeter bars and top plates
- Injection of polyurethane elastomer, which cures to form a solid core within three hours.
Intelligent Engineering and DNV have over the past five years enjoyed a growing cooperation. Several SPS applications have been looked at and several projects have been completed. The Klaveness project is the biggest so far and the experience gained has paved the way for future projects.
Date: 2005-06-06