"DSK" wrote in message

Maxprop wrote:
.... Beneteau has, but does not distribute, graphic studies of net
displacement vs. stability for all of its boats built after the mid-90s.

I wonder if they assume that the center of gravity stays the same?

No indication of CoG movement on the graphs I have, but I'd assume that it
would have to change, unless one puts all the additional weight in the
bilge.

Not sure if the French gov't. requires them or what, but I think they are
all just computer models depicting the safety margins of their boats.
I've seen the ones that apply to boats in the size range that interests
me, and frankly it's a bit scary. Bottom line: don't overload a 39'
Beneteau. And I'd suspect the same admonition might apply to similar
boats, such as Jeanneaus, DuFours, Catalinas, Hunters, etc.= the plastic
fantastics.


Probably true of any boat that is shaped like a normal sailboat. The only
way to be able to keep stability constant is to load all the weight
increasingly lower down so as to maintain the relationship between the
centers of bouyancy & gravity. Actually, as the beam/disp ratio drops, the
lever arm between CG and CB needs to increase... very unlikely!

Not sure I comprehend that concept, but I'll assume you know what you're
talking about here.

... What was interesting is that there seemed to be an over-center
point, beyond which the stability of the boat fell off precipitously. It
was not a smooth curve, rather it peaked, then plunged.

Maybe like a sine wave, with the peak for the point at which the gunwhale
immerses?

Sounds a bit extreme, or tongue-in-cheek.


... I'm surprised that boat builders don't publish a *do not exceed*
load figure for each boat, even if they don't want those graphs out and
about.

Ever hear of the Plimsoll marks? For commercial ships, these figures are
published and are supposed to be kept by the captain. For naval vessels,
they keep a whole book of figures on stability.

No, never heard of them, but it might be a good idea for recreational boats
to keep such figures handy as well. Then again, perhaps it's difficult to
exceed those critical figures in terms of load.

Yep. Everything is a trade-off. That's why life is such a good metaphor
for sailing....


Aw, heck, I want it all, dammit. g


If you figure out how, let me know.

Still working on it. No solution in sight.

Max