A Ballast Procedure
for 15 tanks
Scope
of work
Planning and supervision of shifting buoys into and out of the water, coordinating method, timings and on-site execution.
Methods & Software
Executed with AutoCAD and E4 to support drawings, method development and calculations.
Engineering
scope
On-site supervision with procedure planning, barge stability calculations, ballasting procedures and consolidated reporting.
Unexpected assignment
Designing a Ballast Procedure – Floating a 255-Ton SPM Buoy onto a Barge: Sometimes an unexpected call can bring exciting adventures – this was exactly the case when SAL Engineering was contracted to prepare a complex loading operation of an SPM buoy in Nigeria, West Africa.
A call on a Saturday morning from one of SAL’s long-established clients in Nigeria, Wellman Group, urgently requesting support to calculate and design a complex ballasting procedure to load an SPM buoy onto a barge, led to a remarkably swift process – from contract signing to design development and on-site execution in only ten days.
Unlike what SAL engineers normally deal with, this was not a lifting operation, but rather a float-on / float-off procedure that required a completely different approach.
The challenge
The project centered around a 255-ton SPM buoy, normally used for FPSO/FSO mooring at sea, which was due for refurbishment after years of service and was to be replaced with a reconditioned unit. The buoy had been towed to Port Harcourt, a remote port in the river delta of south-eastern Nigeria.
To bring the buoy ashore for refurbishment – and to later return the refurbished one to the water – it had to be floated onto an 82-metre self-ballastable barge and then skidded from the barge to shore and vice versa. SAL Engineering’s scope was to calculate, design, and supervise the barge’s ballasting procedure, which required partial submersion of the barge to allow the buoy to float onto it.
Chris Lyovwaye, Managing Director of Wellman Group, explains: “We made our own initial engineering plan, but I was not convinced we could execute the operation safely. I contacted SAL Engineering for an initial assessment, and after assigning them to conduct the detailed engineering design, a new light was brought to the project.”
Execution and engineering precision
To achieve the required submersion, the aft section of the barge was lowered about 5.5 metres below the surface by taking in 6,800 tons of water into its ballast tanks. This required complex calculations to define the exact sequence of water intake across the barge’s 15 ballast tanks. Beyond hydrostatic stability, the engineers also had to consider structural stresses, as the barge could potentially bend under the immense forces of the water and the buoy during submersion and re-floating. A further critical concern was avoiding capsizing, which demanded precise control of the ballasting process.
SAL Engineering delivered a 132-page ballasting procedure and deployed Special Engineer Philipp Ludewigs to Port Harcourt for ten days to supervise and support the on-site execution. Ludewigs concludes: “It was a special operation with a very short lead time, but also an exciting project – quite different from what we usually handle. It truly demonstrates the wide range of services that SAL Engineering can offer independently.”