A dragging anchor is one of the many unwelcome incidents a ship may encounter during its operational life at sea. Sometimes the anchor may drag, something that may not be in control of the crew. So, what rests for the crew to do is to recognize the signs of a dragging anchor: Early identification is the key to avoid accident-related to the dragging anchor situations.
The most frequent anchor-related incidents occur when the anchor drags and the vessel drifts without holding power, which could lead to collisions, groundings or strandings.
But let us take things from the beginning.
Why do ships anchor?
An anchor is -usually a metal- device, used to connect a vessel to the seabed, to prevent it from drifting due to wind or current.
Anchors achieve holding power either by “hooking” into the seabed or sheer mass or both.
The reasons that a ship stays at anchor vary:
- Cargo loading and unloading
- Undergoing maintenance or cleaning
- Waiting for instructions from owners- charters or waiting for berthing
In the current shipping trade operations, waiting at anchorage is inevitable for ships at most ports of the world. This “waiting time” at anchorage can be days or even weeks.
What is dragging anchor?
A “dragging anchor” means the ship drifts without holding power even though it has been anchored. This can lead to less or more serious incidents, as collisions, groundings or strandings.
3 indicators the ship is dragging anchor
- The bow cannot stand against the wind.
- The ship’s side against the wind has not changed.
- There are extraordinarily large vibrations coming from the anchor chains.
Why it happens?
Simply put, “when an external force exceeds that of the anchor’s holding power, it will drag”.
Heavy weather is among the common causes of shipping accidents, but the most common cause of dragging anchor.
#Tips: How to know when the ship is dragging anchor
- Know position of the anchor by noting down the position of the ship when the anchor is dropped.
- Press the MOB button on the GPS when the anchor is dropped.
- Set the anchor alarm to make good use of available electronic aids.
- Check the ship’s speed; If the ship is moving with the flow of the current, it is possible that its anchor is dragging.
- Watch the anchor chain in water; As the ship is falling back, anchor is expected to hold the ship and stop it from falling back.
- Flag on the anchor chain; If the flag falls down, this could be the first indication of anchor dragging.
Do’s and Don’ts to avoid dragging anchor
|Use anchor watch function of the ECDIS as a supplement to GPS anchor alarm.||…set the anchor watch on ECDIS without testing it.|
|Know the weather and bear in mind the wind direction.||…anchor on a lee shore even if the chart has an anchor symbol on it.|
|Be aware in advance: Study charts, consider the seabed, check the charted depth.||…forget to doublecheck there will be sufficient chain for high water.|
|Always keep a proper watchkeeping.||…underestimate the importance of extra lookout.|
|Make the deep draft.||…keep close distance from other anchored ships.|
Do’s and Don’ts when dragging anchor
Sometimes, even if everything is done right, dragging anchor may still occur, so the next best practice is to do everything to minimize significantly adverse impacts:
|Use bow thrusters, main engine and steering to manoeuvre.||…override the anchor.|
|If dragging is inevitable, let the vessel drag in a controlled manner.||…do so when you know oil and gas operations are being carried out in the vicinity.|
|Deploy more cables.||…drop a second anchor unless the ship is small.|
|Always inform the Master and the main engine and call assistance tug.||…forget to inform alert VTS and other vessels nearby of the condition.|
|Stop all cargo operations.||…maintain cargo barges.|
MOORING PROCEDURES: Read in this series
A little flash of history
- The word derives from Latin “ancora”, which itself comes from the ancient Greek word “ἄγκυρα” (ankura).
- The most ancient anchors were probably rocks and many rock anchors have been found dating from at least the Bronze Age.