Gemini's have for a long, long time been Class A certified. I've been to Portugal visiting Alex on Giulietta and seen them there.
4 that I know of of them have circumnavigated, many have done trans-oceanic voyages.
Like any guy will tell you, it's not about the length, it's how you use it.
I don't know if they are or not Class A certified and if not, if they are certifiable. I have searched and found nothing about that and that's a pretty good advertising piece of information. Maybe you have found it?
Having done circumnavigations means nothing. I have said that a guy with a 22ft mono-hull has circumnavigated nonstop and a Corsair 27 had done that also (I saw the boat once in Dusseldorf). Both boats are not Class A boats.
As we have seen it is possible to certificate relatively small multihulls as A Class boats. Tropiccat gave the example of the 32ft Tomcat and I can give the example of the Dragonfly 32. Both are not the typical mainstream multihull.
Anyway I am sure that even if certifiable in class A these type of boats are pretty limit in what regards the needed stability criteria to be certified.
You can also circumnavigate or cross oceans in a mono-hull that passes closely the stability requirements for a Class A boat and we would be talking about boats like the Elan 31 or the Vancouver 28 but even if the boats have offshore potential I would not choose one to cross the Atlantic, much less to circumnavigate.
Class A stability requirements for classifying boats as no limited boats represent a minimum that many find to be too low and a minority finds also that boats that don't pass those requirements are still suitable to cross oceans.
The safety and stability limits each one is willing to accept in what regards a boat to cross oceans, I mean for you or me to cross oceans
is a personal choice and I would say it should be an informed one and that's the point of the EC classification regarding seaworthiness.
Personally I would say that what makes it comfortable for me, regarding mainstream design, in what regards monohulls is a 38/40ft boat. In what regards multihulls I would say 42/45ft. Of course that is a personal evaluation based on the risks I am disposed to take. Any small boat crossing an Ocean represents a risk, smaller or bigger depending on the boat. But everyday we take risks and without have a notion of it, we are always choosing what is acceptable and what is not.
I am talking about mainstream designs. Some boats, monohulls or multihulls can by designed to improve slightly its stability characteristics regarding equally sized designs. It is the case of the Dragonflyies or the Tomcat that have the stability of a slightly bigger mainstream designed multihulls.
I would say that in what regards improving a boat stability for its length has a bigger scope in monohulls than in multihulls because multihulls rely exclusively on beam and weight in what regards stability while monohulls rely also in a significantly lowered CG through ballast deep on a keel.
That's why size is so important in what regards a multihull seaworthiness.
Jobberone said all that in a much simpler way
Others would say it's both length and beam as well as how its used.