OK, you asked for it. Prepare to be confused:

Mast design starts with the transverse righting moment. That is the force
in foot pounds required to overcome the initial stability and heel the boat.
It is usually measured at 30 degrees. 30 degrees is where the sail area
perpendicular to the wind starts to reduce faster than the wind speed
increases so it is about the point of maximum stress. The calculations
require finding the center of gravity and the center of buoyancy and the
metacenter at the heel angle. The Metacenter is the point at which a
vertical line through the COB crosses the centerline of the hull. The
horizontal distance between the COG and the COB is the lever arm. The
righting moment is the mass * the acceleration of gravity (32'/s/s)* the
lever arm.

The actual mast section depends on the righting moment at 1 degree and 30
degrees, the number of spreaders, baby stays, runners and several other
factors. I am not even going to try to get into that.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

wrote in message
oups.com...
Is this simply the moment of inertia of the mast and objects along it
or is it some kind of definition specific to yachts. Does it include
the contribution due to sails and rigging? If not, moment of inertia
is a fairly simple concept. If it is the simple physics definition,
let me know and I'll show you how to estimate it (or even calculate for
simple cases).