Photo: TotalChoosing MacGregor as a partner at an early stage of projects lets our clients take advantage of our creative thinking, which adds value to their projects.
For more than one hundred years MacGregor has developed innovative solutions for the marine and offshore industry. We mitigate potential risks associated with new ideas by including proven technology in the designs.
For Total's Moho Nord project in the Republic of Congo, the development team opted for a Floating Production Unit (FPU) with an off-deck mooring system. Off-deck mooring involves mooring lines leaving the vessel at deck level and not directed down through an underwater fairlead.
MacGregor was chosen to deliver the Pusnes mooring system for Moho Nord. There are existing floating production vessels with off-deck systems but what makes the Moho Nord system unique is that the chain jacks (Pusnes Dual Chain RamWinch, DCRW) can handle 2 chain sizes. The DCRW for Moho Nord is designed for 76mm and 157mm chain. The MacGregor design team put ground-breaking engineering into the Pusnes dual chain RamWinch development which opens a new market for this type of chain jack.
To take care of the FPU’s liquid cargo handling requirements, MacGregor delivered a combined Pusnes loading and offloading system for condensate and utility, along with a tandem mooring system for shuttle tankers loading from the FPU. The loading system is used for offloading condensate and for loading methanol, low dosage hydrate inhibitor (LDHI) and xylene.
The delivery included a bunker hose reel, a 300m floating hose and a hawser handling system to maintain the tandem-moored vessels at a safe distance during loading operations.
The hawser is attached to a releasable hawser-handling winch, which compactly combines mooring, handling, storage and emergency release functions into a single unit. To maintain the highest levels of safety, all operations are carried out without any manual-handling of the hawser.
The mooring and loading/offloading systems share a common hydraulic power unit, resulting in the cross-utilisation of products. This delivers weight savings and reduces costs for the customer.
A chain jack that handles 2 chain sizes is advantageous where operators use smaller chain sizes during installation to bring the larger diameter top chain up to the same chain jack for final tensioning. In order to accommodate the variation in line direction, a Bellmouth Chain Guide (BCG) was developed specifically for the DCRW.
The BCG ensures correct entrance of the installation chain with connecting links during hook-up operation. In addition, it is of great importance that this design reduces the risk for Out-of-Plane-Bending (OPB).
Each DCRW is supplied with four hydraulic cylinders, one main cylinder (Rocker cylinder) and three auxiliary cylinders (two Chain Stopper Cylinders and one Rocker Pawl Cylinder).The DCRWs cylinders are used to operate the winch's main functions which are - Pay Out, Haul In, and Park. The principle and interaction of these cylinders is based on MacGregor’s popular Pusnes RamWinch which was developed in the late 1990s.
The unique design with only one rocker cylinder ensures safe operation during all phases without the risk of cylinder jamming that can be experienced with solutions requiring 2 main cylinders.
Designing a winch able to handle the various connection links between the smaller installation chain and the bigger platform chain required considerable engineering in close co-operation between the manufacturer of the mentioned connectors and our engineers.