[PUP] Let's design the perfect passagemaker - Lets start ....

[Mike Maurice]

> .  The boat I am building has a
> positive righting moment (think that is what it is called).  If knocked over
> by "a big one" it will right itself.

Alan,
All boats have positive righting moment. If they did not they they would 
immediately turn turn turtle.

The issue is how much righting moment to resist turning turtle, AND,
At what point does the righting moment vanish, also known as the point 
of vanishing stability. The graph of this is a curve and is known as the 
curve of vanishing stability.

There are rough rules of thumb for the desirable number of degrees 
rolling before this point is reached. A bluewater boat, sail or 
otherwise should have at least 120 degrees and 140 is better.

Such a vessel when inverted will tend to not return upright within the 
cone of 40-60 off of vertical degrees and to stay inverted until wave 
action causes it to roll beyond that cone.

In other words, if a boat rolls over in a flat calm sea, it may not ever 
roll back upright. If the sea is rough and it rolls over, the greater 
the chances are that it will roll back upright. The chances of this 
happening are increased if it has a large number of degrees of ultimate 
upright stability as the cone in which it will be trying to escape the 
upside down mode will be small.

All this ignores the possibilities of down flooding occurring or the 
contents changing position, while inverted.

Mike

_____________________________________
Capt. Mike Maurice
Tigard Oregon(Near Portland)