# IMO Weather Criterion (K-factor)

Discussion in 'Stability' started by athvas, May 29, 2013.

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### athvasSenior Member

Does any one know how to calculate the K factor for vessels having bilge keels. For ships having round bilges k is taken as 0. My doubt if vessel has round bilge with bilge keels on its sides. what will be value of k. It is mentioned to calculate the area of bilge keel. do we need to calculate the area of both sides of the vessel or one side. Plz clarify my doubt. Also plz explain the term 'b' and 'a' in weather criteria (b area should be greater than a). what actually b' means and a' means the definition.

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### TANSLSenior Member

#### Attached Files:

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• ###### Area a-b.jpg
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### athvasSenior Member

Thanks for you response. But the definition of area 'b' and area 'a' is not given in that.

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### TANSLSenior Member

See picture in my previous post

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### athvasSenior Member

From the graph, it can be defined as

b- Area between intersection of GZ curve and stead gust wind heeling lever and downflooding angle or 50 deg

a - Area between intersection of GZ curve and stead wind heeling lever and angle of roll due to windward.

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### TANSLSenior Member

In the figure on the first page of the file "Weather Criterion.pdf" you have, clearly defined, areas "a" and "b".

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### athvasSenior Member

Dear TANSL

As per IMO Weather Criteria Calculations,
Vessels having no bilge keels have high angle of roll to windward due to wave action compared to the vessels having bilge keels. Does Weather Criteria improves for all vessel fitted with bilge keels ?

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### TANSLSenior Member

The factor k, which is equal to or smaller than 1, decreases the value of angle "teta1" (heeling angle due to waves) which lowers the area "a". The greater the area of ​​the bilge keel, the lower the value of "K" and thus "a". So, effectively, bilge keels improve compliance with the wind criteria.
Vessels having no bilge keels have k = 1.

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### athvasSenior Member

Thanks TANSL,

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