# Intact stability – weather criterion windspeed

DELFTship forum General Questions Intact stability – weather criterion windspeed

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• #37714
Malte Schilling
Participant

Hello Delft community,

I want to influence the windspeed in the weather criterion (IMO MSC 267 (85)), that for example the windspeed in for the mast is less than for the hull. Therefore I can set different wind Speed in defined heights (see Picture).

As can be seen at the Picture i just Need to Input height and according windspeed.

But where does the height in this menu refer to? Baseline? Waterline? Center of defined wind silhouette?

• #37715
Marven
Keymaster

The wind speed is measured above the water plane, not the base line

• #37716
Malte Schilling
Participant

Thank you for the fast reply.

If I have a ship with the main dimensions of :

depth to maindeck: 10m
superstructure height (maindeck–>Topdeck): 5m
mast height (Topdeck–>mast end) : 5m
height overall: 20m
draft: 3m

For the hull a wind preasure for the weather criterion should be 504 Pa (as usual) and für the superstructure I want to reduce the wind preasure to 300 Pa and for the mast to 150 Pa. (These are just some randomly chosen values!!!) How do I put it into the inputmask shown above?!

• #37721
Marven
Keymaster

In general the wind speed picks up when the height above the water plane increases. So a lower wind pressure for the superstructure does not seem very realistic.

You can try the following:

The wind pressure is calculated simply by dividing the required pressure [in Pa] by 9.81 m/s2.
So 300 Pa equals 300 / 9,81 = 30.58 kg/m2.
If you enter this in the rightmost column of the input screen then the corresponding wind speed is calculated by delftship.

But beware: The program first calculates the center of effort of your wind silhouette, then the height of this point above the water plane and finally wind pressure for that height. This windpressure is then applied to the entire silhouette.

• #37722
Malte Schilling
Participant

i know that the wind speed increases over the height above waterplane, but this is not my Intention.

The mast of a ship has another drag coefficient (0,6) than the hull (1,0), but in Delftship I cant define individual cd´s for the wind silhouettes of the hull or mast or anything. So I thought not to change the cd and keep the wind preassure fixed, but to fix the cd and change the wind preassure for the heights(i.e. height of mast).

Or is there another way to set different cd´s to the windlateralplane.

• #37723
Maarten
Keymaster

You have a good point- and it is on our to-do list to set a drag coefficient per silhouette item. While we can not say exactly when this feature will be included, I expect it will be this year.