Curve of Downflooding Angle

I have been asked to provide a set of curves I do not usually present as in a standard Stability Booklet. The required curves are to describe the heeling angle which ranges up to where the lower edge of a non-watertight opening becomes submerged.

They require this to be as a function of either displacement of draught.

Any suggestions to what would be the best way to obtain the results for this in Maxsurf Stability?

TIA

Fin Evans

Naval Architect

  • hi Fin,

    There is no built-in analysis mode to calculate this. Essentially you have to do a large angle stability analysis at each condition and pick the immersion angle for each condition, then plot the data.

    If you input data is displacements and LCG then simply set up loadcases for each of these conditions. The VCG will possibly cause the vessel to trim (which could then have some small effect on the immersion angle), as a second order effect, so you should consider how you are going to select this value also.

    If the input data is draft and trim, then you first need to do an upright hydrostatics (or specified condition) to get the displacement and LCG.

    The set up the loadcase with the displacement, LCG and VCG and run the analysis for each condition and pick out the immersion angle.

    If this is something you have to do frequently, you may want to consider writing a script in Excel to automate it. Its probably best to work out the steps manually before you tackle writing a script, however.

    hope this helps,

    Pat

    Answer Verified By: Fin Evans 

  • Hi Pat,

    Many thanks for your response.

    We will go back to the class society, who is looking for these curves, and explain to them that it is a "long winded" process to produce said curves.

    Out of curiosity, is this a feature that Bentley would/is looking to incorporate into the stability software in future updates?

    Many thanks,

    Fin Evans

  • Hi Fin, can you send me the class document that explains exactly whats required (trim range for instance? fixed/free trim? VCG?) and I can add it to the wish list. We can certainly consider adding this feature but its difficult to give a timescale since we have a lot of requests and limited resources :-)

    It might be something we could add to the Cross-curves, KN analysis - Ill take a look

    Answer Verified By: Fin Evans 

  • Pat,

    ClassNK (Japan) have not given any range in which to complete the task with. I have attached the comment from class, along with the snip-it out of the rule set to which the comment refers to.

    NKClass (Class society)

    ClassNK Comment(Class comment)

    ClassNK Rule Set(Class rule set extract)

  • Hi Fin,

    I think what you need is provided when you do a KN analysis: