ISO 12217-1:2015 - Recess size

Hello everyone,

I came around one problem considering calculation of point 6.5 Recess size in ISO 12217:2015 standard for DC B.
I am working on stability calculation for open motor boat (some thing similar to Axopar 37 Sun Top). Boat has two cockpits, one infront (i first 1/3 of LH) and one covers rest of the boat, from stern to 2/3 of LH from transom fwd. Aft cockpit is assumed as open to sea acc to ISO 11812:2020 standard - step height (retention height) is 90mm above cockpit bottom level.
But, when calulcating retention level (acc to ISO 12217) for calculating SM freesurface, retention level comes up very high (almost as hight of sides - 1.3 m above cockpit bottom level.). This results in huge GMt reduction in % acc to any of simplified methods.
Does anyone know how boats like Axopar 37 and similar complies with this clause?

Thank you,

Best,

Tom

 

Although it is not an answer to your question, you may be interested in applying Option 3, which does not require the study of point 6.5.
If I manage to answer your specific question, I'll let you know. In any case, such a large reduction in GM seems strange. Check that you are using the correct dimensions in each variable. That is a very common mistake given the gibberish that the ISO establishes with the units.

 

I would need to see a General Arrangement of your boat but, if it is similar to Axopar 37 Sun Top, this one cannot be considered as a "fully enclosed boat", therefore, for category "B" only option 3 can be applied, which does not require checking chapter 6.5. Maybe that will help you get your boat to DC "B".