Max steady heel angle to prevent downflooding in squalls

[Jure]

I have problem to find appropriate equations to calculate Max steady heel angle to prevent downflooding in squalls (graph) (part of requirements for sailing yachts) for 30, 45 and 60 NM/h squalls. I am working with MaxSurf Stability module (I already check in Maxsurf stability module), I would like to validate/check Maxsurf is ploting graph correctly (or I did a mistake with some inputs in Modeler module).
Can you please provide equations for following graph.
Thank you for your answer in advance.

 

[jehardiman]

Jure, welcome to the forums.
What criteria are you using/told to use to generate a graph that looks like that? Generally downflooding in a gust is calculated/displayed on the righting arm curve and expressed in energy (i.e. area under residual righting curve) because of seaway considerations.

 

[Center 24]

Curves of maximum steady heel angle to prevent down flooding in squalls.

There is a work on the Internet. There are formulas and examples of calculations (pages 14-15 and 23-24):

Delfs Jespersen.Tall Ships’ Stability. Copenhagen 2015/2020.

If we apply the criteria as shown in the figure, Maxurf v.20 counts correctly.

 

[jehardiman]

Delfs Jespersen.Tall Ships’ Stability. Copenhagen 2015/2020.

Hummm. That's a rather bass ackwards way to do it.
https://irp.cdn-website.com/5ae73933/files/uploaded/TS+Stability+pamphlet-UDJ-v10a.pdf

 

[Center 24]

The calculation is based on this source:

MCA Stability Information Booklet Large Yacht Unit

More details in the article:

Barry Deaki. The Development of Stability Standards for UK Sailing Vessels. April 1990

 

[jehardiman]

Having written operation manuals, I understand the difficulty of developing actionable guidance to inform the operators when they are approaching the limits of the design envelope. Nobody wants another MV ROCKNES or SV CONCORDIA or SV BAYESAIN. I'm just not sure that graph is the proper way to plot it; it would require constant reference and plotting in the changing environment because it is not referenced to sail configuration (in and of itself neither here nor there but most sailors I know don't think like that.) Why not a simple chart with sail configuration vs maximum steady wind speed?. See the TSBC report on the CONCORDIA.
Marine Investigation Report M10F0003 - Transportation Safety Board of Canada https://www.tsb.gc.ca/eng/rapports-reports/marine/2010/m10f0003/m10f0003.html

 

[ropf]

Could someone explain to me the difference between a squall and a gust, please?
(In the German translation, both is the same)

 

[jehardiman]

Could someone explain to me the difference between a squall and a gust, please?
(In the German translation, both is the same)

A squall refers to a small concentrated weather event, usually along a front line, generally associated with rain and a marked change in wind velocity and/or direction lasting over several minutes. Microbursts and downdrafts are often also associated with squalls. Squalls that contain visible clouds/rain are just termed "squalls" or rarely "black squalls". Squalls/downdrafts that are not associated with rain are often termed "white squalls" and are much harder to visually spot.
A gust is any rapid change in wind velocity that lasts just a few seconds, usually associated with near-earth turbulent mixing.
Squall - Wikipedia https://en.wikipedia.org/wiki/Squall
What is a Microburst? https://www.weather.gov/bmx/outreach_microbursts
The Gust Front - Understanding Downdrafts in Thunderstorms While Boating https://www.spinsheet.com/news/gust-front-understanding-downdrafts-thunderstorms-while-boating

 

[ropf]

Thanks @jehardiman