Block baskets

Fabrication process and delivery

Not only were there several designs and engineering challenges that needed to be addressed, but also the entire fabrication process and delivery to the client needed to be safeguarded. As always our engineering team was up for the challenge and after an initial orientation phase, the design and engineering works started in earnest.

 

The objective of the block baskets is to support the lower blocks of the crane in the stowed position, and also provide access to the lower blocks for inspection and maintenance purposes. In close cooperation with Allseas, the design was agreed upon. The design needed to take several major design restrictions into consideration; such as actual positioning and clearance issues with other equipment on the vessel and access for inspections and maintenance. Once the design was in place, the actual engineering process could commence. Considering the relatively large weight of the main and auxiliary blocks, 200 tons and 50 tons respectively, and the significant environmental survival conditions (significant survival wave height Hs =14m) resulted in rather complex FEM models being generated of both block baskets. Once the FEM models were completed, the actual process of generating all the fabrication drawings was started.

 

As with everything on Pioneering Spirit – the biggest construction vessel in the world – the block baskets are gigantic. The main and auxiliary block baskets have outer dimensions (L, B, H) of approximately 8.0m x 10.0m x 9.0m and 4.0m x 5.0m x 5.0m respectively. The total weights of the baskets are approximately 45 tons and 12 tons respectively.

 

Both baskets have been fully outfitted with ladders, stairs and railings. All walkways have been fitted with composite offshore grating. These gratings require less maintenance and are lighter, more slip and corrosion-resistant than regular steel gratings. The main hoist block basket has almost 80m2 of walkways while the auxiliary block baskets walkway area is limited to 12.5m2.

 

The actual challenge started once the engineering was completed and approved by the client. Although having completed several fabrication orders in the past, fabrication on such a large scale and implementing the building specifications of Allseas was something that was new for Saltwater Marine Services. We needed to develop new procedures and update existing processes in order to meet the high standards that were expected. From detailed material tracing to welder qualifications and weld specifications, every aspect of the fabrication process was documented. Extensive quality assurance and control procedures were implemented in order to track and guarantee quality during the fabrication. The block baskets were coated with several layers of 2 component paint, which also needed to be taken into account during the QA/QC process.

 

Our client was at the building yard several times a week for on-site inspections to ensure that our procedures were implemented correctly and to ensure a smooth progression of the works. The final products were inspected one last time and found to meet all requirements. All that was left to do is transport the block baskets from the building site in Hardinxveld-Giessendam (NL) to Schiedam (NL).