ship handling

Home page|| Tanker Notes || Container Ship Operations || Ocean Navigation ||



Container Ships Motion in a parametric roll - Adverse affects of such phenomenon

The term parametric roll is used to describe the phenomenon of large unstable roll motion suddenly occurring in head or stern seas.
Due to its violent nature, the large accelerations associated with the onset of parametric roll cause concern for the safety of container ships. Possible consequences include loss of containers, machinery failure, structural damage, and even capsize.

Parametric roll is a “threshold” phenomenon. This means that a combination of environmental, operational and design parameters needs to occur before it is encountered. These are:

Ships Motion in a parametric roll

1) The ship would be traveling with a small heading angle to the predominant wave direction (head or stern seas).
2) Wavelength would be comparable to ship length.
3) Wave height would be large.
4) The ship’s roll damping characteristic would be low. If unfavorable tuning occurs between wave encounter period and natural or twice natural roll period of the vessel, then parametric roll motion can be experienced.



Large containerships are particularly vulnerable to parametric rolling.
This is because they have hull forms with pronounced bow flare, flat transom stern and wall-sided mid-ship section.

Such features contribute to the variation of the ship’s stability characteristics due to the constant change of the underwater hull geometry as waves travel past the ship.

Consequences of a Parametric Roll

Parametric roll is an extreme condition for container securing since it combines the effect of large roll and pitch amplitudes. This scenario imposes significant loads on container securing systems.

Such extreme roll angles exceed those usually adopted during machinery design. Possible consequences on machinery operation of the ship heeling to very large angles include loss of cooling water suction, exposure of lubricating oil sumps– and hence shut-down of the main engine.

The following points should be borne in mind:

a) Parametric roll is a relatively rare phenomenon occurring in head or following seas, which is characterized by rapidly developed, large, unstable ship rolling.

b) Risk control options exist in both design and operation of container ships that can effectively reduce the likelihood of a parametric roll occurring.

c) Reducing the likelihood of its occurrence is considered a more effective approach than mitigating the consequences.

d) Masters should be aware that, when conditions for parametric rolling exist, the action of putting the ship’s head to the sea and reducing speed could make rolling worse.

e) The North Pacific in winter is known to be an area where conditions for parametric rolling exist.



References

Motion of containership & various risk factors

How to confirm stabilty condition ?

How to maintain watertight integrity?

How to navigate vessel safely in heavy seas ?

Guide to watch officer for ships navigation ?

Heavy weather countermeasures for prudent navigator

Meeting rough sea conditions by containerships

Affects of Shearing forces, Bending moments and Torsional moment for containership

Risks of heavy weather with containerized cargo onboard



Ships turning circle and manoeuvering characteristics

Ship manoeuvering-turning circle advices
A deeply laden vessel will experience little effect from wind or sea when turning, but a vessel in a light or ballasted condition will make considerable leeway, especially with strong winds. ....

Various factors affecting ships turning circle while manoeuvering
When a vessel fitted with a right-hand fixed propeller, she would benefit from the transverse thrust effect, and her turning circle, in general, will be quicker and tighter when turning to port than to starboard. ....

External factors that affecting ships turn
The deeper a vessel lies in the water, the more sluggish will be her response to the helm. On the other hand, the superstructure of a vessel in a light condition and shallow in draught is considerably influenced by the wind. ....

Ships navigation -Factors Affecting Turning circle diameter
Merchant ships usually turn in a circle having a diameter of about 3–4 times the length between perpendiculars (LBP). The larger the rudder, the smaller will be the Turning circle diameter(TCD). During the TCD manoeuvre, the ship will experience transfer, advance, drift angles and angle of heel (see Figure )....



More shipboard operation and safety matters

Safe anchoring - planning and operational guidance for cargo ships

Anchor watch check item - deck officers guideline ....

How to deal with a damaged anchor? ....

How to recover a lost anchor ? ....

What is stranding ? Investigation of possibility of self-refloating and urgency of danger ....

What are the emergency procedures for loss of anchor and chain? ....

In case of damage to anchor and chain when to claim for '' general average"? ....

Ships arrival in ports - check item prior entry

Ships navigation in restricted visibility check items

Rules of ships navigation in restricted visibility

Ships navigation in confined water - matters that require attention

Securing your vessel for sea passage - when to check and what to check

Collecting Information and Data for Passage Planning






Other info pages !

Ships Charterparties Related terms & guideline
Stevedores injury How to prevent injury onboard
Environmental issues How to prevent marine pollution
Cargo & Ballast Handling Safety Guideline
Reefer cargo handling Troubleshoot and countermeasures
DG cargo handling Procedures & Guidelines
Safety in engine room Standard procedures
Questions from user and feedback Read our knowledgebase
Home page




ShipsBusiness.com is merely an informational site about various aspects of ships operation,maintenance procedure, prevention of pollution and many safety guideline. The procedures explained here are only indicative, not exhaustive in nature and one must always be guided by practices of good seamanship.

User feedback is important to update our database. For any comment or suggestions please Contact us
Site Use and Privacy - Read our privacy policy and site use information.
//Home //Terms and conditions of use

Copyright © 2015 www.shipsbusiness.com All rights reserved.