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Angle of Vanishing Stability
I am reading the book "Adlard Coles' Heavy Weather Sailing" by Peter Bruce. In the chapter "The stability of yachts in large breaking waves", it tells about an experiment done on boat models in a water tank, that measures the AVS of various boat shapes. One of the outcomes of this experiment is that adding a coachroof to a boat without one may move the AVS further towards the 180 degree, or alternately, two boats of the same height above water line, one with high freeboard and no coachroof and the other with coachroof and lower freeboard, the later shows much less inverted stability.
The reason for this phenomenon is that the coachroof, when submerged in the water, adds buoyancy and raises the center of buoyancy to higher point with regard to the vessel.
This may raise some thoughts:
1) An inflatable boat stowed on deck may cause the same effect and thus contribute to the stability of the boat.
2) We can take this idea a step further and install a balloon on deck. Such a balloon can be empty in normal sailing and automatically inflated when the boat is inverted. If this idea is right, I suppose I would have not been the first one to raise it. So why don't we see such systems on boats ?
Btw, I have a picture of the said page from the book but I don't know if I am allowed to display it here.