Anchor handling involves a number of special marine operations. The high tensions experienced in chains and wires may cause high heeling moments and may cause high transverse and/or astern movements of the anchor handling vessel. The vessel’s motion through the water may also be affected by high hauling speed on the anchor handling winch or as result of any loss of bollard pull. The vessel may be pulled astern at speed by the tension in a heavy anchor arrangement. Any simultaneous loss of thrust, for any reason, on the vessel may lead to a rotation which would lead to considerable extra transverse forces. Environmental conditions will also influence the operations. For these reasons the vessel’s stability needs to be closely monitored.
Anchor Handling activities
- Planning and risk assessment
- Verification of Vessel Stability
- Preparation for the Anchor Handling Operation
- Checks of machinery and equipment to be used
- Loading and stowage of equipment
- Radio communications between the deck and the bridge
- Rig move meeting with the ship's crew
- Equipment being transferred to the rig
- Personal protective equipment
- Safety on deck & safe areas
- Taking the pendant wire from the rig
- Connecting the work wire to the pendant wire
- Decking anchors
- Chain being recovered to the ship's chain lockers
- Use of buoys to run anchor cables over sub-sea structures and pipelines
- Lowering anchor in 'drop' position
Anchor Handling Vessels
There are three main categories of anchor handling vessels, the North Eurpean Anchor Handling Tug, the American Anchor Handling Tug and the Anchor Handling Tug and Supply Vessel (AHTS.) The stern of the vessel is open to the sea, allowing anchors and other equipment to be deployed and recovered easily. It is normal to have a stern roller positioned at the stern of the vessel. A winch house containing towing wires, winches and anchor handling equipment is situated on the forward section of the after deck.
The work wire is stored in the winch and used for deployment or retrieval of anchors, in addition to towing operations. Work wires on vessels vary with different lengths, diameters and characteristics.
The winch usually contains both anchor handling drums and towing drums. The drums are normally connected to the same drive system. The anchor handling winch should have multiple gears to allow high pulling power at low gears. An arrangement with variable braking power should be present, allowing the winch to pay out work wire when the tension is excessive. The winch system may either be hydraulic, electric or diesel driven. The direction of rotation is normally overwind, so that the work wire has a small downwards angle towards the stern of the vessel.
The shark jaw is a device for connecting and disconnecting chain and wires, in addition to securing chain sections on the deck.
The system is protected by patent in countries world wide
Types of Anchors
- Delta flipper type anchors
- Stef Shark anchors
- D'Hone Special anchors (all sizes)
- Pool TW anchors
- Ac-14 anchor
- Danforth Anchors
- Hall anchor
- Spek Anchor