A mooring chain handling and tensioning system has been developed as an alternatative to the other on-vessel mooring equipment for the FPSO (Floating Production Storage Offloading) type vessels. The mooring chain handler is intended for use on any vessel that is anchored with a pre-laid spread mooring system. A comparable vertical windlass type mooring system and a chain jack type mooring system are also reviewed.
The mooring chain handler can accommodate any deck location, requires only one chain locker and can accommodate all turndown sheaves. A vertical windlass compromises the location of the single windlass to accommodate the additional chain lockers and locations of the turndown sheaves Chain jacks are limited by the intermittent pull and also require additional vertical shaft guide sheaves. The mooring chain handler does not require additional guide sheaves and has uninterrupted power-in power-out unlimited variable speed.
The mooring chain handling & tensioning system requires only two (2) chain handlers and four (4) moveable turndown sheaves to handle up to twenty (20) mooring lines per vessel. As a result, the initial investment, maintenance, and installation costs are substantially reduced and the operation, safety, and reliability significantly improved.
The mooring chain handler, located on the centerline of the vessel, can rotate in a horizontal plane about the center of a single chain locker allowing it to line up with the individual turndown sheave locations. This makes it practical to safely handle multiple mooring chains with a single piece of equipment.
The integral messenger wire winch, located directly behind the chain, guides the chain to the front of the mooring chain handler reducing the need for handling equipment such as cranes, davits, winches, etc.
The platform chain and messenger line is connected and disconnected at the front of the mooring chain handler eliminating the need for a special windlass wildcat normally used to pass the wire rope messenger line, connector, and platform chain.
The mooring chain handler (Fig. A1) is a horizontal shaft type wildcat mounted in a frame that rotates on a circular foundation. The wildcat is centered directly above the chain pipe. The mooring chain handler can be rotated about the center of the chain pipe to lead the chain in any direction. The wildcat maintains the same degree of chain wrap for any horizontal orientation.
The messenger line winch (Fig. A2) is located above and behind the modified wildcat. The wire rope lead is always in line with the mooring chain lead. The chain handler is designed for 20% of the chain breaking strength. The winch drum is sized to handle the required length of wire rope messenger line.