Anchoring is one of the very frequent operations onboard ships. A number of variables and external factors influence the duration and location of an anchoring operation. While the type of seabed is of utmost importance during anchoring, soft muddy grounds or clay bottoms are best preferred. It should be taken care that the anchoring bottom is free of power lines, submarine cables, pipelines or rocks.

Various methods on anchoring include consideration of direction and strength of wind, current and tidal stream. Often good local knowledge helps a mariner determine required manoeuvres and actions to be taken while anchoring.

The two most prevalent methods for anchoring are –

i) Let Go

ii) Walk back Under Power

1) Let Go: This method is used in over a wide range of vessels including smaller crafts and pleasure yachts to larger vessels with tonnage varying up to 1,00,000 GT. The principle followed in this method is to let go or let the anchor slip with cable under its own weight from the hawse pipe. The weight on the cable, windlass brake holding power and momentum of the vessel are factors to be controlled by the vessel to ensure the anchor digs in and the cable is subsequently laid to extend backwards. While approaching the anchoring position the speed of the vessel over ground is brought to zero using engines and helm and at the same point anchor along with the cable is allowed to run out under its own weight.

Once the flukes touch the bottom or chain touches the ground the engines are moved astern or ahead according to the prevailing conditions of wind and current to attain astern momentum with respect to ground, which will stretch the cable. It can be paid under controlled application of brakes to control the length of cable from running out completely. Often under such conditions combined effects of wind and current vessel will tend to swing and fall astern as well.

Attention to be paid to the preferred direction of swing and the anchor on which side to be used. Care should also be taken to not allow the full cable to run out under weight or to allow the cable to pile up which can result is developing kink or twist in the cable. During approach to anchoring grounds it is a general practice by shipmasters to lower the anchor to water level so that when the brakes are released the cables is paid out freely. After a long sea voyage sometimes the anchor might get stuck in hawse pipe and not release down from the hawse pipe under its own weight. As a proactive and good seamanship practice one should always check the condition of the windlass brake liner before use.

On several occasions, often on old ships, due to repeated use brake liners were found completely worn out or below required thickness, consequently reducing the braking power significantly which led to cable running out completely under its own weight resulting in loss of anchor and cable both.

Uneven loads or excessive astern momentum after applying brakes can damage the windlass and its seat and foundation. Engines should be used to counter the excessive momentum of the ship and the state of the vessel loaded or in ballast should be always kept in mind while using engines. Prolonged kicks might develop sufficient momentum in a loaded vessel to drag anchor or even snap the cable. A loaded vessel is found to be more responsive to effects of current or tide whereas a vessel in ballast drifts substantially due to wind. Combined effects and directions of local conditions can be helpful while doing preparation for anchoring.

2) Walk Back Method: Most of the companies have their own guidelines for anchoring large ships such as VLCC’S or ULCC’S which should be followed without fail. Walk back method of anchoring is recommended and used mostly on vessel’s above 1,00,000 GT. The working principle is the same however cable is paid out using the windlass at a fixed speed. Upon approaching the anchoring position the speed upon ground of the vessel is brought gradually to zero and the anchor is lowered in water.

As it touches the bottom more length is paid and engines are given astern to develop slight astern movement to lay the cable nicely as the flukes of the anchor dig in the seabed. This method usually is of longer duration than the let go method; however it provides ship master’s with better control over the amount of cable paid and weight upon the windlass. It is important that correct assessment beforehand of tidal conditions, gusty winds or strong coastal currents are made by ship master to accommodate for the movement of vessel as the cable is paid out. In general design speed of windlass is about 30-35 feet/min., which is approximately 0.3 knots over the ground.

Also a windlass is designed to lift up to 3 -4 shackles along with the weight of the anchor. Walk back method prevents piling up or twisting of cable, which is paid under power and thus provides better control to master or pilot to ensure the anchor holds in and does not drag. However speed over ground of vessel must be diligently controlled to avoid excessive loads on windlass, which is being used with gear engaged.

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Surrounding circumstances and conditions are probably the greatest variables when the ship is at sea. It may become necessary all of a sudden to drop anchor in an emergency in case of steering failure, probable collision, manoeuvring in shallow waters etc.

Usually, letting go (dropping of anchor) is done to reduce the speed of the vessel as swiftly as possible to prevent any forthcoming mishap. When such an action is taken at sea, there’s barely any time to walk back the anchor which means the action to be taken by the responsible officer is to be firmly made in limited time.

Letting Go (Dropping) Ship Anchor in an Emergency

The following points must be kept in mind when letting go anchor in an emergency:

1. The Officer must be at the forecastle with a portable VHF, a torch and their paraphernalia to release the bow stoppers. While clearing away anchor in the previous operation, the brakes as well as the bow stoppers must be checked for efficient operation.

2. The Ship sides must be checked for boats, skiffs, tugs, barges and other such obstructions, especially below the anchor; obviously, this is to be done to prevent harm to a third party.

Watch: Ship Anchor Drops on Tug Boat

3. The Officer must be in constant parley with the Bridge to relay and receive orders to and from the Master. This includes information about where and which anchor to let go and how many shackles as well.

4. The Officer must open the take and let the anchor run out directly from the hawed pipe, as and when the required information is received. There’s no time to walk back anchor in this case due to probable imminent danger.

5. The cable must be checked at all time to count the number of shackles passed as per orders from the bridge.

6. In case there’s too much cable paid out without keeping an eye on it, the anchor tends to hold tight causing the cable to part by the vessel’s momentum.

7. In case there’s less cable paid out, the anchor won’t really make the required full contact with the seabed, defeating the very purpose of dropping it in the first place.

8. The number of shackles paid out is normally in the region of two to three times the depth of water. The whole point of this emergency operation is to enable the ship anchor to drag along the seabed bottom, providing maximum resistance to the movement of the vessel without causing damage to the anchor or the vessel.

9. The Officer undertaking the operation must be at all times aware that there is another anchor at his disposal which might need to be used.

As with any emergency operation, dropping anchor under the circumstances requires swift action that can prevent any imminent danger. The handling of the vessel and her anchor will differ as per the characteristics but the above points give a general direction to the procedure that is required in such a case.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

9 Points to Remember When Dropping Ship Anchor in Emergency appeared first on Marine Insight - The Maritime Industry Guide

A merchant vessel is said to be having a “dragging anchor” when the vessel drifts without holding power inspite of being anchored. Dragging anchor has been the reason for several accidents such as collision, grounding, or stranding.

Merchant vessels stay at anchorage for various reasons:

• Waiting for berthing prospectus
• Cargo discharge and loading
• For carrying out maintenance , hatch cleaning
• Waiting for Instructions from owners or charters
• Quarantine etc.

The main reason for a vessel dragging its anchor is because of rough weather conditions. In such situations, it is extremely important for seafarers to collect all necessary information to familiarise with the situation and prevent dragging of anchor as much as possible. Some important parameters that needs to be considered are:

• Prevailing weather condition of that particular area
• Safe position for anchoring the vessel
• Wind and tidal behaviour of that area
• Contact information of port authorities in case of assistance required etc.

At most ports, it is inevitable for a vessel to wait at anchorage and the time at anchorage can be for days or even weeks. During such times, the master and ship crew should identify possible dangers to the ship and make all the necessary preparations.

A vessel dragging anchor is a threat to its own and also to other vessels in the vicinity, often leading to an emergency situation such as collision, grounding or stranding, depending on the manoeuvrable condition of the ship.

In such situations, a quick assessment of the situation can only be achieved by a vigilant bridge watch, contingency plan to tackle any emergency, quick response and good judgment of the situation. It may take some time to weigh the anchor and restore the vessel to its full manoeuvrable condition, but no serious accident should happen if there is enough sea room and time to do so.

Following points should be considered by a seafarer prior anchoring where dragging anchor is predicated:

• Take on heavy weather ballast, taking in to account the stability of the vessel and depth of water below the keel
• Pay out more anchor cable depending on the size of the vessel and weather condition
• Keep a safe distance from other anchored ships, shoals and other dangers, leaving room for manoeuvring
• Weigh anchor and shift the vessel to different position away from the vicinity of other vessels, provided prior permission is received from VTS of that area, port authorities and owner’s orders
• Increase the efficiency of the bridge team by adding an extra lookout
• Keep the main engines standby for manoeuvrability

How to assess the vessel is dragging its anchor?

• Check the ship’s position at frequent intervals, to confirm if the vessel is outside the swinging circle. Use all available means, both visual and electronic equipment such as GPS, RADAR and ECDIS, to make the appraisal of the situation. If the vessel deviates from the circle, it is likely to be dragging its anchor
• The bow cannot stand against the wind
• Check anchor chains for slipping, a small pole with a cloth as flag like arrangement can be tied to the links to understand the slipping of anchor chains
• Extra vibration and weight on anchor cable
• Check the speed over ground (SOG) when the vessel is swinging, the SOG can increase variably and this should not be misinterpreted
• Check the course recorder for figure of eight motion locus
• Also monitor the position and distance of vessels nearby. In case if they are dragging counter measures to be taken to safe guard own vessel

What actions to be taken if the vessel has started dragging anchor?

• Master to be informed, do not hesitate to call him at any time of the day, his experience and decision making authority is vital in any give situation
• Inform engine room and start the main engine with the permission from the master and give power to windlass if it is not already given. Make the vessel ready for manoeuvring
• Stop all cargo operations and prepare vessel for manoeuvring. Let go cargo barges and crane barges if they are alongside
• Inform and alert Vessel traffic system (VTS) and other vessels nearby about the condition and inform about the actions taken. Seek permission for re-anchoring
• Start heaving up the anchor and once the vessel’s manoeuvrability is restored, shift the anchorage position where drifting can be safer or take to the open sea
• Deploy more cablse or drop a second anchor (not recommended for big vessels) before the speed of dragging of the vessel increases. This can stop the small vessel from dragging anchor at very early stage before the ship is pressed to leeward side with increasing speed
• Use bow thrusters, main engine and steering to manoeuvre. 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.
• If the scenario permits, let the vessel drag in a controlled manner. But this is not recommended in areas where offshore work such as oil and gas operations are being carried out, which can result in damaging the submerged pipe lines, cables etc.
• Release the bitter end and let go the anchor completely, when weighing of anchor is not possible. A ship without minimum of 2 anchors is not considered to be sea worthy, a careful assessment is to be made prior making this decision
• Call (tugs) for assistance. This is possible only if the weather permits

Most accidents collision or grounding happens while the vessel is at anchor mainly because of no early prediction of dragging anchor. Time plays a vital role in area of high vessel density and this time lapse results in difficulty in restoring the manoeuvrability of the vessel. Ensure that proper contingency plan is set in place to control such incidents and avoid arising of any emergency due to dragging anchor.

Over to you..

Do you think this article need additional points?

Let’s know in the comments below.

What To Do When Your Ship Is Dragging Anchor? appeared first on Marine Insight - The Maritime Industry Guide

Mariners consider anchoring a ship to be an art. In fact, it’s also a form of science for it involves a sense of pivot, around which, a ship turns and imparts the stalling force to the ship.

While berthing a ship alongside a jetty or a pier in tidal or windy conditions, the role of the ship’s anchor is extremely vital.

Preferably, a ship must always approach the berth or a jetty stemming the tide (reduce the effect of the tide by cutting it) to ensure better control of the vessel. If the opposite is done when the ship is berthed, i.e. if the ship approaches the berth or jetty with the tide at its stern, the rudder effect is minimized as the tide plays with the stern.

Related Read: What Are “Let Go” and “Walk Back” Ship Anchoring Methods?

To turn the vessel, which is coming up the tidal estuary along with the tide, the anchor is dropped on the side towards which the vessel has to be turned. If the vessel is planned to turn on the starboard wheel, the starboard anchor is dropped. Likewise, if it’s planned to turn on the port wheel the port anchor is dropped.This is done to avoid the anchor chain going across the stern of the vessel after the swing.

But before dropping the anchor, the ship’s speed is reduced to around 3 knots or less to minimize the chances of chain damage or damage to the ship’s equipment and hull.

For a ship having a normal right-handed propeller, which comes up with the tide, the starboard anchor is dropped so as to take the advantage of the canting, i.e., swinging of the stern due to transverse thrust ( which is essentially a sideways force acting on the stern of the vessel moving forward or astern). The ship is brought up with the help of the anchor ( i.e. her way has stopped and the vessel is riding only on her anchor).

Related Read: How Dredging Anchor is Used for Maneuvering Ships?

Generally for obtaining maximum holding power of the ship’s anchor, the total anchor rode (The vessel is attached to the anchor by the rode, which is made of chain, cable, rope, or a combination of these) should be 4 to 7 times the depth of the water the ship will be anchoring in.

If the anchor is designed to hold on the horizontal pull (like fluke or claw type anchors), more chain is paid out to give a lower angle of pull and the sag of the chain will give enough catenary effect to hold the ship. The final position of the vessel is assessed beforehand so as to keep enough leverage of the swing.

Once the anchor drag has stopped, the helm is kept hard over to the starboard and the tide starts pushing to the starboard quarter, turning the ship 180° to the starboard facing the tide. Once turned, the anchor is slowly weighed up. Then, by stemming the tide the ship is brought close to the jetty at an angle of 20° – 25° and the head rope is passed.

If a tugboats are available to assist the berthing, it is placed on the stern side in the quarter of the opposite end to the ship’s side that is coming alongside. Pivoting the bow with the head-rope, which has now gone ashore and is ‘bar-tight’, the ship is brought alongside the jetty with the tug gently pushing the stern till the time the stern-line is safely ashore and the second officer has started heaving in.

Related read: What are Anchor Handling Tug Supply Vessels (AHTS)?

If the head rope becomes too tight, minor slack or adjustments are given from the shore to prevent it from parting. If there is no tug in the vicinity, a jollyboat takes the line ashore from the stern. If the jollyboat is also unavailable, the ship’s stern is brought closer to the jetty with the help of the engines, with repeated slow kicks while pivoting the bow with the head-rope.

A pilot feels blessed if the ship has a bow and stern thrusters in such cases. These equipment tools make the job of a pilot much easier.

Have questions? Let us know in the comments below.

How a Ship is Berthed Using An Anchor? appeared first on Marine Insight - The Maritime Industry Guide

Ship’s anchors can be used not only for berthing but also during maneuvering through channels and other similar areas with restriction in movement. Dredging anchors is a method which is used to assist a ship in maneuvering during unavailability or inability of tugs to assist as required.

A dredging anchor sniffing the bottom of the ship would hold the bow steady while allowing a ship to move fore and aft, this would shift the ship’s pivot point forward. Then, to overcome the anchor’s drag, propulsion is used giving good steering at low speed.

Today, modern ships have bow-thrusters to control the bow while going ahead or astern. While piloting in the narrow confines, in restricted waters or maneuvering vessels in somewhat constricted space, bow thrusters or tugs can be handy.

Sometimes ships have to cross stern first (i.e., moving backward) through the restricted channel between ships or buoys, using engines and bow thrusters. Now since the stern cants (moves laterally sideways) while a ship comes astern due to transverse thrust, a towing tug is employed in this case at the stern and the engine is used sparingly just to adjust any deviation in the desired direction of motion.

At the bow of the vessel, a checking tug is also deployed to control it and prevent it from swinging waywardly. The checking tug also comes in to play in stopping the momentum of the ship lest its engine doesn’t respond in time.

Now what happens when there is neither a bow thruster nor a tug to check the bow? The towing tug is necessary as the ship will invariably deviate with every second of the engine running astern due to the transverse thrust. In such an emergency situation the anchor becomes the rescuer.

The anchor is dropped at short stay where the cable is almost vertically down up to the anchor and taught. The anchor barely digs in when the ship is put to astern and the anchor is dragged over the sea bed. The pivot is shifted to the bow near the howse-pipe, making it easier for the towing tug at the stern to exert more moment of force as its distance from the pivot has increased. Also, the bow is prevented from “Yawing”.

The objective of this operation is to drag the anchor over the soft mud (like the drag-heads of the suction dredgers) and not to dig the anchor deep into the mud. Otherwise the cable will come under huge strain and can part when engine is run astern or when the towing tug tows. The machineries involving the anchor on the forecastle, like the windlass, the bow-stopper or the brakes can also get damaged.

Ideally the length of the cable should not be one and a half to two times than that of the depth of the water. Moreover, it is generally advised to have a thorough knowledge of the sea or river bed before performing this operation. Recent survey charts in this case can become extremely helpful.

Do you know any other way in which ship’s anchors are used for maneuvering ships? Let us know in the comments below.

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How Dredging Anchor is Used for Maneuvering Ships? appeared first on Marine Insight - The Maritime Industry Guide