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Quixotic said..
if true: "I believe it has to handle 40 kt winds and 4 metre waves", that is woefully insufficient for an ocean going boat, IMHO. I would not set out to cross an ocean in a boat with those limitations.
Seems like CE Category B "offshore" is up to 40 knot winds and 4 metres significant wave height.
Cat A "Ocean" is winds exceeding force 8 (40 knots) and waves of more than 4 metres, but not hurricane conditions.
Unclear from anything I can find as to whether "more than force 8" but "not a hurricane", means they are thought to be able to survive force 9-11 winds (ie from strong gale to violent storm) and corresponding significant wave heights.
There are also differences in minimum AVS requirements based on ISO 12217 - apparently for Cat B it is minimum of 95 degrees for boats 7.5 tonnes and over, increasing to 122 degrees for boats of 2 tonnes or less, whereas for Cat A it is minimum 100 degrees for 15 tonnes and over, increasing to 123 degrees for 3 tonnes and less.
None of this appears to go to structural specifics about keel attachment/design. However, I understand CE tends to be tied to ISO standards.
There're ISO standards for small monohull (up to 24m LOA) hull structure ISO 12215, including appendages (ie keels) - ISO 12215-9, so presumably these are picked up in CE, though it is not easy to see specifically how, as ISO docs are not available unless you pay (~$A400 for just 12215-9) and it is also not easy to see how they are used by the various certifying organisations that certify a design / sample boat as meeting the requirements. There may be an engineer out there who can shed light on this?
To be fair tho' 12215-9 does cover different types of keels (fixed single, dual, canting etc) in different materials (metal, wood, FRP) and also load cases covering 90 degree knockdown, longitudinal impact and vertical pounding.
For those with particular views on keels, these ISO standards are stated as not meant to be the basis of design for racing boats...