Flotation calcs are always interesting. Getting something to float at a certain attitude is even more fascinating. How much is generous flotation worth if it causes or allows the boat to turn turtle? And, now that we're thinking of the unthinkable, why is it that blues and greens are the popular bottom paint colors? Wouldn't day-glow orange be the color you would want if your boat was floating upside down? Maybe even orange reflective bottom paint? (Patent #1). And since boats commonly turn turtle, wouldn't an automatic pop-up safety grab bar on the bottom be a good idea? (Patent #2).
But, back to flotation. I did a lot of kayaking with storage float bags. Two weeks worth of food, clothing, etc., in waterproof stuff sacks fitted to the shape of each compartment. I still think of that in my little Limpet. Bedding, clothing, etc. are stored in dry bags and fastened down. There is some inconvenience in opening a dry bag to get the coffee out, and some inconvenience in putting things back into a dry bag and connecting to the hull. A flotation bag that floats away isn't worth much. And, again based on kayaking, the power of surging water will quickly scour the inside of the hull of anything not fastened down.
The hull flotation collar looks good, but (based on past research about saxophones, of all things) that concept has been the subject of various patents for over 60 years (because of torpedo sinkings in WWII). It provides some comfort in pictures and on paper. Not so practical in real life.
It seems to me that the biggest difficulty is how to compensate for the weight of the outboard. Every picture I've seen of a floundering pleasure boat shows the bow remaining above the surface, probably because of trapped air which might soon be gone. Knowing that the outboard will become the unintended anchor, why not have full compensation at that point? Something like an inflatable collar on the outboard leg. Right where it is needed most and out of the way behind a cosmetic cover (like airbags in a car). It would deploy automatically upon complete submersion (Patent #3).
There may be such a product already, and the fact that the Flamingo OMFD (Outboard Motor Flotation Device) isn't known to every boater generally might mean that it doesn't work. But maybe it would. And maybe even a design that kept the outboard operational despite partial submersion of the hull (Patent #4).
Marco Flamingo