Procedures for mooring operations#

Note

Based on (translated and slightly modified by ØF) the document PROSEDYRE FOR RIGGARBEID PÅ F/F KRONPRINS HAAKON written by senior engineer Kristen Fossan (29.06.2018).

Mooring: Instrument-carrying construction of length 1-3000 m that is lowered to the sea floor and held in place there by a metal or concrete weight denoted an anchor.

Mooring deployments#

Anchor-first deployments#

Advantages

  • The mooring can be pulled up and adjusted to the desired target depth.

  • Only a small hole in the ice is required if deploying in ice.

  • The vessel can remain stationary.

Drawbacks

  • The mooring line must be able to carry the full weight of the mooring.

Procedure#

  • Kevlar or other material constituting the mooring line is spooled onto a winch strong enough to carry the weight of the anchor.

  • Pieces of chain are be inserted where instruments will be placed (AWI shackle / ring shackle).

  • All elements that will be attached to the mooring (instruments, floats, etc) are laid out on deck.

  • Toolbox meeting with all involved parties before starting deployment.

  • The anchor (or the anchor plus the first group) is lowered into the deep until the first chain appears.

    • The lower half of this chain is shackled to the side of the vessel or to another winch.

  • The chain is opened and the desired instrument group is shackled to kevlar and lifted up using the main crane.

  • The mooring is further lowered until the next chain appears, and the process is repeated.

  • When the entire mooring is out, an acoustic release is attached to the top of the mooring. The mooring is then lowered until the anchor hits the bottom.

    • If the depth is correct, the release is opened and the mooring deployment is complete.

    • If the depth is wrong, the mooring is lifted from the sea floor, and either the mooring length is adjusted or the ship moves to a different location with different bottom depth.

  • The position of the mooring is noted on mooring diagram along with all details.

Anchor-last deployments#

Advantages

  • The mooring line does not have to be able to carry the full weight of the mooring.

Drawbacks

  • The vessel must either move or use a small boat or similar to extend the mooring.

  • No possibility of adjusting mooring depth after deployment.

Procedure#

  • Kevlar or other material constituting the mooring line is spooled onto a winch strong enough to carry the weight of the drag of the mooring in water.

  • The top of the mooring is attached t the mooring line and liften into the ocean.

  • Kevlar is paid out until the next instrument group is to be attached.

  • The mooring is shackled to the ship and instruments are attached to the mooring line. Pull in a little so that the shackle can be loosened and then pay out until the next instrument group.

    • Repeat until only the anchor and release is left.

  • When only the anchor and release are left on deck, these are shackled to the mooring. Typically, a second release is used to lift the anchor and mooring release and lower them into the water.

  • Now, the vessel moves to the desired location, and the second/upper release is triggered to drop the mooring.

    • The anchor will fall approximately vertically and drag the rest of the mooring along with it - like a diving sea snake.

Mooring recoveries#

Procedure#

  • The ship moves to the assumed location of the mooring.

  • Try to locate the mooring (using the release transponder and ideally also an echosounder or similar).

    • Assess whether the mooring looks ok.

  • Position the vessel in the desired position in relation to the mooring.

    • A good rule of thumb is that the mooring should be 200 m from the bridge at a 45 degree angle.

    • The mooring can be long, so be careful of getting tangled in the propellers!

  • Activate the release.

    • If all is ok, the mooring will release and appear at the surface after a time period depending on buoyancy and depth.

    • If the mooring floats do not appear, the mooring must be dredged up.

      • This is usually a good approach, but there is greater risk of damaging equipment.

  • Attach to the top of the mooring and bring the mooring on deck.

    • The instrument groups are unshackled and cleaned before they are brough inside for servicing.

    • The kevlar is spooled onto the winch.

Trawl-safe bottom landers#

Metal shell with buoyancy that protects the instruments and acoustic release. Kept down by metal- or concrete frame.

Typically deployed by lowering down to the sea floor and releasing.

Recovery:

  • Acoustic release is activated.

  • The frame should pop up when released from the weight as it is positively buoyant.

  • Concrete frames are usually left on the bottom. Metal frames are typically recovered.