How to maintain safe stability onboard container ship during laden voyage
As the nature of container ship operation, it’s tread to be lack of stability, due to Top Heavy Load, the Master shall always take special attention for her stability. Also the Master should remind factors to cause reducing stability more such as Alternating course with Big angle of Rudder, Towing by tugs at the scene of Berthing / Un-berthing, etc.
Parametric rolling occurs because of the fine hull form of large post-Panamax container
ships. The large bow flare and wide transom increase the effect. The phenomenon occurs
because of changes in the waterplane area, which can cause large changes in GM as
waves pass. At times, GM can become negative. A large initial GM will provide large righting
levers that can lead to violent rolling.
In principle, IMO designated criteria of minimum GoM for Container ship should always be considered.
Course and speed factors during rough sea conditions:
During bad weather if a ship keep maintain her course into head seas and swell, she may encounter pitching and rolling
heavily. Rolling in head seas may be associated with the phenomenon known as ‘parametric
rolling’ which occurs because the ship’s waterplane area changes as waves pass along the
ship’s length.
Maximum rolling can occur when a wave’s length is comparable to the ship’s
length. At the instant when the ship’s midship is supported by a wave crest, with the bow
and stern in a wave trough, there is an instantaneous loss of waterplane, sudden and
massive loss of righting force and the ship may roll to very large angles. As the wave passes
along the ship’s length the situation is reversed, strong righting forces are exerted and the
ship rights herself but only to roll again as the next wave passes. Effectively, the ship
performs simple harmonic motion but with violent rolling.
During the conditions of very severe rolling, containers stowed on deck can be subjected
to massive separation forces, forces that are likely to exceed the combined strength of the
securing system. Parametric rolling may be prevented by alteration of course or change
of speed.
Make a good stowage plan and maintain Safe loading
While making stowage plan When Master observes deviating from the safe criteria as specified in ships class approved loading manual, even though applying the best Ballast and Fuel layout, the Terminal planner / Central planner must be informed and cargo stow plan appropriately modified. Stability may similarly affect securing equipment. If the vessel is excessively stiff she may be subject to a short rolling period, creating greater loads on all equipment and fittings. Also it has a great influence on “Lashing strength for containers on deck.
Fig:Container ship prior departure
A ship can capsize because of the variation of the metacentric height GM, or of the righting
arms GZ, in head or following seas (parametric resonance) or due to the loss of control
in severe following or quartering seas (broaching-to phenomenon). Nonetheless, a ship
can capsize even in port if the metacentric height is negative.
Check items upon completion of repair works
Upon completion of the repair works the vessel is to sail from the yard in a safe
condition as soon as possible. It is essential however, that adequate function tests
and inspections are carried out under the supervision of superintendent of all safety systems and
systems that had been disturbed during the repair period.
A suitable checklist is to be compiled in order to ensure that all critical equipment,
such as key navigational, propulsion, steering, cargo, ballast, fire and gas detection
systems are tested. Also to be included is the replacement of bottom plugs, anodes,
sea chest valves correctly set and ensuring echo sounder and Doppler transducers
are cleared and written confirmation that all personnel are adequately rested before
departure.
Loss of containers due lashing failure
Suitable checklist to be completed by
the Master under the supervision of the Fleet Superintendent after completing
repairs, before and during flooding and prior to departure from the repair facility. A
further checklist on testing of safety automation and protection devices
is also to be completed). The completed checklists are to be sent to the management
office in advance of sailing.
Prior to departure from a repair / dry-docking facility, it is imperative that the vessel
emails / faxes to the management office the completed and signed forms. Entries
must be made in the deck and engine room log books upon completion.
Damage Control Information (DCI) - The Damage Control Information is a part of onboard
documentation. The documentation should be clear and easy to understand. It should
not include more information than this directly relevant to damage control, and should
be provided in the working language of the ship.
The DCI is intended to provide the ship’s officers with clear information on the ship’s
watertight subdivision and equipment related to maintaining the integrity of the
watertight boundaries, so that in the event of ship damage causing flooding proper
precautions can be taken to prevent progressive flooding. The DCI should consist of:
Damage Control Plan, Damage Control Manual, External Watertight Integrity Plan and
Internal Watertight Integrity Plan.
Our additional pages contain some more useful resources
Ship Encountering Parametric Roll In A Seaway The term parametric roll for a container ship is used to describe the phenomenon of large unstable roll motion suddenly occurring in the head or stern seas. Due to its violent nature, the large accelerations associated with the onset of the parametric roll cause concern for container ships' safety. Possible consequences include loss of containers, machinery failure, structural damage, and even capsize....
Action by vessels navigating in congested water Ships navigation is referred to the voyage practices, focusing on the process of monitoring and controlling the movement of the ship from point "A" to point "B". Choosing the most optimum route while transiting through traffic-congested water is even more challenging. Specifically, due to the presence of many vessels in the vicinity, a repeated risk of collision exists....
Action by vessels navigating in an area of restricted visibility Ship navigation under restricted visibility circumstances is one of the most challenging tasks while accomplishing a safe voyage. The visibility is mentioned as restricted in cases that have been observed fog, heavy rain, or dust storm, all hazardous conditions to navigate. Ship navigation in such conditions doubles the likelihood of a collision or grounding. It calls for the use of specialized equipment and requires some actions to be taken by the time the ship's officer gets information of relevant weather conditions......
How to confirm stabilty condition? In the northern hemisphere during hurricane season, extreme weather is a common phenomenon. A big storm can run havoc even on the largest containership by tearing off its deck lashings. Most modern ships are designed to survive in harsh conditions and stay on schedule. Nevertheless, facing storms at sea is routinely an unavoidable part of life at sea. Each year substantial weather damages incur huge financial liabilities on ship operators.
......
How to maintain watertight integrity? To maintain Water tightness, Seaworthiness, Fire integrity and Security of the vessel, it is important ships personnel ensure all openings to hull below water line and above waterline ( weathertight & watertight doors etc.) are adequately secured.
......
Guide to watch officer for ships navigation ? Bridge watchkeeping is the most critical activity conducted at sea. Upon the watchkeeper's diligence rests the safety and security of the ship, her entire crew, the cargo, and the environment. It is a demanding activity, requires support, encouragement, motivation, self-discipline and a high standard of professionalism. Ships master must ensure that all watchkeepers understand the use of safety related equipment, prior to them keeping a watch......
Heavy weather countermeasures for prudent navigator Encountering extreme weather conditions at sea along major trade routes is a common phenomenon. Depending upon geographical location and seasonality of revolving tropical storms, a ship, therefore, need to prepare well to survive in harsh conditions. Both heavy weather and tropical storms demand of crew's preparation and immediate response.
How to navigate vessel safely in heavy seas ? Encountering extreme weather conditions at sea along major trade routes is a common phenomenon. Depending upon geographical location and seasonality of revolving tropical storms, a ship, therefore, need to prepare well to survive in harsh conditions. Both heavy weather and tropical storms demand of crew's preparation and immediate response.
Meeting rough sea conditions by containerships In heavy weather conditions where it is unsafe for ship crew to venture out on the deck for purposes of checking deck cargo securing, Master shall consider his ship handling options and heave to if required. The aim should be ensuring the safety of the vessel and its cargo.
.....
Checklist for calculating stability and hull strength for cargo ship
In heavy weather conditions where it is unsafe for ship crew to venture out on the deck for purposes of checking deck cargo securing, Master shall consider his ship handling options and heave to if required. The aim should be ensuring the safety of the vessel and its cargo.
......
Container Ship navigation - passage planning guideline Before proceeding to sea, the Master shall carefully check the Passage Plan, made after receiving the voyage instruction from the Charterer or the Company. Passage plan shall be made from berth to berth acting on the principle of Safety-first, while also taking operating efficiency into consideration.
The passage plan shall be prepared normally by the Second Officer, signed for approval by master and for understanding by all officers, before departure.Based on this Guide, the Master shall collect necessary information and review the Plan including Emergency Contingency Plans.
Navigation in cold districts and countermeasures Ocean water freezes just like freshwater, but at lower temperatures. Freshwater freezes at 32 degrees Fahrenheit, but seawater freezes at about 28.4 degrees Fahrenheit, because of the salt in it. Due to the presence of many hostile conditions, any merchant ship, while entering a freezing sea area, significant challenges are being encountered concerning safety and reliability of navigation.
Safe anchoring - planning and operational guidance for cargo ships
For the safety of the ship, strict anchor watches must be kept when the ship is at anchor. The principal reason for keeping anchor watches by one or more sailors is to maintain the safety and security of the vessel. Anchor watches to be maintained following the Masters's orders. This should include regular inspection of lead and weight on-chain.
How to deal with a damaged anchor?
.... When a part of the anchor chain breaks, it may be due to wear and corrosion or to over-stressing of its weakest part. Typically a ship owner arranges for anchors and chain damage inspection in a dry-dock, full range length, and can take a note on weakest links. A common defect is loose studs that reduce chain strength significantly. In all cases, the class surveyor should be consulted, and defective/ wasted chain be renewed as per surveyors' strict guidelines. It is a ship owner's routine expenditure for anchoring arrangement.
How to recover a lost anchor ?
.... After the anchor and chain are lost, the Master should make an initial report to the management company. After that, from time-to-time, the Master should report further developments. The Master should report the circumstances that led to the loss of the anchor and chain so that the Company can determine whether the general average is affected.
What is stranding ? Investigation of possibility of self-refloating and urgency of danger
.... Stranding means when a vessel has run aground, it is accidental. In consequence, the double bottom area of the vessel will probably suffer considerable damage, especially if the ground is rocky. This is physically the same action as beaching, but with the significant difference that beaching the vessel is an intentional action and under comparatively controlled conditions, whereas stranding is accidental.
What are the emergency procedures for loss of anchor and chain?
.... After the anchor and chain are lost, the Master should make an initial report to the management company. After that, from time-to-time, the Master should report further developments. The Master should report the circumstances that led to the loss of the anchor and chain so that the Company can determine whether the general average is affected.
Securing your vessel for sea passage - when to check and what to check Many maritime accidents are caused by the mistakes of ship personnel for inadequate sailing preparation. To avoid recurrences of the fatality deck and engine department must be well prepared before a vessel’s departure for a voyage at sea. These arrangements may include many complexities, and this is the reason why a bunch of things should be recognized and prepared delicately to ensure a smooth voyage passage and safe navigation.
Shipping industry recognizes environmental protection as one of its highest priorities and that every effort should be made to conserve and protect the environment from marine, atmospheric and other forms of pollution.
Our articles are based on various shipboard activities,prevention of pollution,safe operation & maintenance procedure. We welcome any feedback from our visitors.
For any comments or suggestions please Contact us Site Use and Privacy - Read our privacy policy and site use information. Terms and conditions of use
