[Jeff_H]

This whole business of motion is a very complex subject, but increasing the moment of interia slows the motion of a boat but increases the kinetic energy so that a boat with a heavier mast will roll (or pitch) more slowly but through a wider angle.

Most of us have gotten the basics of Motion Science from Marchaj''s book on seaworthiness or from someone who learned it from Tony''s book, BUT a lot has been learned since that book was written.

Probably the most critical factors in terms of comfort at sea, (beside length) is the height of the center of gravity (low is good), moment of interia, and the shape of the hull. But when you tall about a large moment of inertia above the the momentary roll axis, you are increasing the roll angle in order to gain a slightly slower motion. When you talk about a carbon spar, that lowers the center of gravity and moment of inertia pretty dramatically and so results in a smaller angle of roll or pitch albeit at a slower rate.

In studies of seasickness, there are clearly two factors that affect whether people get seasick, the amount of motion (roll or pitch angle) and the speed of accellerations of the motion. Individuals have differing tollerances to both. Some people have a small tollerance only for larger angles of motion while others have only a smaller tollerance for quick motion and still others have a small tollerance bor both.

There is a common misunderstanding about motion that any way that you can get greater inertia is good for seaworthiness and comfort able motion, so you see people moving weight to the bow and stern or up the mast. While these may slow motion slightly they can also decrease seaworthiness by making a boat more prone to pitchpole, take serious water over the deck and roll through dangerous angles. Now then adding weight deep on the keel, both increases inertia,and increases dampening and therefore reduces both roll rate and angle. But like everthing else there is a bit of a trade off to that as well.

Jeff