Originally Posted by LtBrett
I don't think I've done as good a job as the book at explaining negative stability. It's not practical to make a sailboat with no negative stability, if it's even possible.
They would if the mast
fills with water
. Plus all the unsecured crap in your cabin
, your water/fuel tanks
, even your "new" underwater hull
profile have shifted your center of gravity substantially and changed its relationship with your center of buoyancy (google metacentric height).
Bottom line, if you are turtled, a wave, whether the initial wave or a subsequent one, has to overcome your negative stability to right you.
I know what metacentric height is. I haven't dug out my copy of Derrett's, but I doubt he covers small yachts. A small ballasted mono has a big chunk of lead/iron/concrete in its keel
- you would have to have an awful lot of stuff come loose to change the CG enough to significantly affect the stability. The water
in the mast
is neutrally buoyant, so it doesn't change the CG when immersed.
In Blue Stocking's example, an exceedingly wide vessel essentially became a catamaran
when inverted. It would have a lot of negative stability as it would need to be tipped over enough to move M down past the CG. My theory is that when a large enough wave came along it started sliding down the face of the wave, the sail's drag caused the boat
to start tripping and when the keelbulb was far enough over it created a positive righting moment.
This is the sort of example I'm looking for. Thanks.