Rolling along.
IMHO - For a typical semi displacement trawler that is not ballasted & with an A/B Ratio of over 2.6 to 1 here is what my experience has been:
For most Semi-Displacement Trawlers with out any sufficient ballast down in your keel, chances are you will not recover from a roll of much over 60 to 70 degree roll. The designer has calculated where that point of no return is & it varies from boat to boat. This has to do with the interaction of the center of buoyancy & center of gravity relationship to each other as the boat heals over & the specific design of the particular boat your looking at.
Without sufficient ballast in your keel, the non ballasted semi-displacement trawler boat with an A/B ratio over 2.6 to 1 can be more stable upside down than it is right side up should you turn turtle. That means it will not self right should it get beyond that point.
of course there are exception like the Dutch boat shown in the video of the "Elling E-4" -- but they also use shaping to encourage self righting & have a lower A/B ratio. BTW - One more thing when it happens in the real ocean, it is not like shown in the video in a quiet bay, it can be quite violent !
My Current boat - The Kadey-Krogen 42 Trawler - which is a ballasted true full displacement hull, has an approximate A/B Ratio 2.2 to 1 & is only stable to about 85 to a max of 90 degrees of roll.
Which BTW is pretty good for a Trawler, as most all Semi-Displacement type trawlers are way less tolerant in their roll axis.
Of course other Full displacement boats with ballasted keels like the Willard's, Nordhavn's & Diesel Duck's, & the like, etc. are in that same neighborhood as the Kadey-Krogen.
Even though this boat has a displacement of 39,500 lbs., They recommend never have more than 750 lbs. up on the fly bridge or on the boat deck or that will upset the center of gravity enough to affect your max recoverable roll angle & make that then under the wanted self righting recoverable angle of roll of 85 degrees, if weight over that 750 lbs. is up there. Yes, I was told this is calculated with 1/2 tank fuel & 1/2 tank water. Filling both gives you about another 5 degrees I am told - but never tested. However, I have never asked the designer the specifics of the details except the interior is empty of everything not factory installed.
So center of gravity is big a key element.
How much roll under those maximums you can comfortably tolerate is up to the crew to decide. When your at 60 or 70 degrees your almost walking in the walls. Anything over 80 degrees you are on the walls. BTW - not recommended.
Most crew get pretty uncomfortable past 30 to 35 degrees.
Good Luck.
Alfa Mike
