Talk:Ship stability

Do we think that finite element is used? It may be finite difference, but I am pretty sure that the water is not modelled quite so accurately as FEA, it is just iteratively computed, so not even FD perhaps. Antony 119.11.113.211 (talk) 08:56, 12 August 2008 (UTC) --- Again, I agree. Cruise ships are not as vulnerable to capsize as the original auther would have us believe. In addition, the angle of heel is not an indication of stability- a ship may lie at 20deg very comfortably and never capsize even in the roughest seas. I have added the required stability section as a start. I'm not convinced it should be merged with the other page- I think conditions and general stability constitute different topics.--Dj245 14:04, 2 July 2007 (UTC)

I don't see how this article adds any value to the growing number of articles on Naval Architecture that seem to be saying the same thing different ways - I suggest removing it. The article attempts to cover too many topics at once. There are also errors in the text : The fins, paravanes, etc. are active and passive roll control devices. They do not improve or detract from stability they merely reduce roll amplitude. Finite Element Analysis is used to calculate stresses in structure not stability. I could go on. Jmvolc 02:55, 27 August 2007 (UTC)

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First of all, some of the other pages on naval architecture are much worse. See Stability conditions (watercraft) for a good example. That one appears to be written from the perspective of a deck officer- the words "chief mate" appear frequently throughout the article. I'm not sure where to begin to start fixing that one. fins, vanes, and other such devices affect the perceived stability of the vessel. It could also be argued they affect dynamic stability. Static heeling loads are not affected by these systems but shock loads such as waves are. I think they deserve to be included. Stress calculations of complicated structures is only one application of FEA. Finite element analysis is used in many other applications. Splitting the object up into many small elements and then solving simultaneous equations is a FEA analysis.

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Breaking the object up into many small elements then solving simultaneous equations describes _many_ methods. The Finite Element Method is a _specific_ method, and not one that is employed here.

Further, breaking it up that way is not the technique used by all or even most hydrostatics packages. For example, Orca works directly with the NURBS surfaces with no tessellation to do the necessary integration. Various other methods don't create polygonal meshes.

The claim is quite simply, patently wrong and it's a shame it stayed up for the better part of a decade. Cody-b (talk) 14:58, 18 June 2013 (UTC)

Merge discussion

Please conduct merge discussion at: Wikipedia_talk:WikiProject_Ships#Stability. Regards, The Land (talk) 17:50, 28 December 2007 (UTC)

Add-on stability systems

The section gives wrong information. Active roll stabilizers are not intended to give stability but just to reduce roll motions for crew and passengers comfort. Roll stabilizers intend to reduce uncomfortable roll accelerations (due to larger GM / more stability). Manoj nav (talk) 13:07, 21 August 2009 (UTC)

Required Stability

- Replaced reference to "CargoMax" and "MACS3" with general reference to "commercially available" software. In the years since these two programs were mentioned a number of other commercially available computer based systems for measuring stability on ships have been developed. Seems biased to mention only these two without listing all the others. Mtheadmama (talk) 07:17, 3 June 2012 (UTC)

I believe the section on Calculated stability conditions is partially incorrect.

This is specifically relevant to the image. I am not a ship designer but it is my understanding that it is more stable for the CG (center of gravity) to be above the CB (center of buoyancy). This way the corrective torque caused by the vertical misalignment of the buoyancy and gravity is not further amplified by the CG being below the CB. The amplification could lead to extreme wobbling in some cases due to resonance.

Hopefully someone more knowledgeable on this can provide further insight.

JustinJustin (talk) 20:48, 6 November 2017 (UTC)

No the CG must be below the centre of buoyancy in order for the ship to have stable equilibrium aka float the right way up. Greglocock (talk) 00:41, 7 November 2017 (UTC)

I don't think so though. That conflicts this article https://en.wikipedia.org/wiki/Metacentric_height You can see this explains the righting moment in a simple way https://www.engineeringtoolbox.com/centre-gravity-buoyancy-d_1286.html That shows why the CG can be above the CB and the ship will still be stable.

Here is another streamlined and good writeup about it. https://www.marineinsight.com/naval-architecture/ship-stability-introduction-hydrostatics-stability-surface-ships/

I don't have any marine engineering textbooks at home but from everything I know working in hydrodynamics and all that I have read it seems that having the CG above the CB is normal and part of the design (especially for larger ships).

-Justin

You are right, CG is usually above the CB for large ships, my bad. Greglocock (talk) 20:04, 29 January 2018 (UTC)