SHIPTALK: Dragging Anchor And How To Prevent It

 “Dragging anchor” happens when a vessel drifts without holding power with no regards to the vessel being anchored; causing many collisions and stranding. So why does the anchor drag in the first place? This is due to a combination of wind, waves and tidal forces exerted on the cable system holding the cable which leads to breakage of the anchor from the ground. 

At this point, there exist few methods of addressing the issues; starting from establishing the vessel’s position. 

Below are the facts which will help the process; checking a ship’s position to confirm whether it is placed outside of its turning circle; monitoring by visual and electronic means to confirm whether the vessel remains within swinging circle defined by the scope of anchor cable and distance from forecastle to the bridge.

 If a deviation from the circle occurs, the ship is dragging anchor and therefore appropriate actions should be taken. However, such deviations could also occur due to weather conditions therefore there are more traits a ship dragging anchor exhibits; including a bow which cannot stand against the wind alongside ship’s sides not changing against the wind. Slacking and vibrating chains is also a known trait. 

Anchoring therefore requires more attention since such a phenomenon appeared within the industry. The first measure required is to determine whether the location is a suitable anchoring spot by checking depths. Then, make a circular excursion around where you intend to drop your anchor while checking the depths of your swing area

1. Check the type of bottom

 

2. Check the state of the tide and the range

 

3. Check the weather

 

4. Know your wind and current and when each is likely to change

 

5. Select your anchor and flake out your rode and chain. 

After determining that the spot is appropriate for anchorage, slowly drop the anchor until you feel it hit bottom.

 

Give the rode some resistance to aim the anchor, and then pay out the anchor rode as slowly as the boat is backing. This lays the rode in a straight line along the bottom – not all piled up. (If there is no wind or current, your helm person may have to help a little with the engine – just in reverse at idle speed. Work out hand signals.)Usually the boat will turn across the wind/current. When you have reached approximately 1/3 of your intended scope, cinch off the rode and wait until the boat straightens out. Do not use engine throttle at this time – just the momentum of the boat. This accomplishes three things: a.

 

It straightens the rode you’ve paid out; b. It starts to set the anchor gently; c. And, if the boat doesn’t straighten out, it tells you that the anchor is dragging and you need to pick another spot.

Assuming the boat straightens out, uncinch the rode and start paying it out – again, as above, only as fast as the boat is backing. When you reach 2/3rds the length of your intended scope, cinch off the rode again. 

After a few moments, the boat should again start straightening out, indicating that the anchor is holding. You have just gently nudged the anchor a little deeper. As before pay out the rest of the scope and again, cinch it off. Let the boat straighten out again. It should be gently setting even deeper. 

Now, take a look around you. Line up two objects along the shore abeam of the boat. Watching these two objects, signal the helmsman to gently give the boat some throttle in reverse. Watch those two objects. 

They should appear no longer lined up. Your catenary should straighten. Indicate to your helmsman to return to neutral. The boat should slowly move back forward as the catenary slacks and the objects you have selected on shore should realign. Now your anchor is ready to be set hard.Indicate to the helmsman to set, or snub the anchor with a hard reverse. If you’re not sure, repeat step 6 before snub.

You may want to snub more than once if you’re in a hard bottom or an unknown bottom. Once set, kill the engine. Or at least, turn it off. 

Use your hand-bearing compass to take bearings off several objects around you. It is helpful if one or more of them is lighted so you can check after dark. Wait 15 or 20 minutes and check your bearings again. About half an hour after sunset, TURN ON YOUR ANCHOR LIGHT! And record it in the log that you did so. 

(A well-organized logbook, with each page signed by the Captain, can be a legal document in court. If another vessel runs into you at O: dark: thirty, and claims you didn’t have your anchor light on, you can point to your log and show that you did. If you have a history of logging these things, it adds more credence to any testimony.)However, the above steps concern the preventive measures against dragging, but what if your vessel is already at sea and dragging anchor? Firstly, the master should be informed in order to set the appropriate objectives and tasks for the crew. Then, the engine room should be informed to start the up the main engine which will increase the vessel’s manoeuvrability. 

While navigation procedures run, all cargo operations must be stopped and all VTS (Vessel Traffic Systems) must be informed to avoid potential accidents while permission to re-anchor is obtained. When your vessel’s manoeuvrability is restored, pull up your anchor to place in a position where either drifting could be safer or lead to open seas. Bow thrusters, main engine and steering must be used to manoeuvre the vessel; as it becomes more difficult to weigh anchor when the vessel is pressed more to the leeward side and takes considerable amount of time. Use bow thrusters for stemming the wind.

 Do not override the anchor especially in shallow waters as the vessel may impact on the anchor during pitching. Finally, tugs must be called in if they are available.  

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