ballast and righting moment and moi

[s vernon]

It is interesting to contemplate building a new boat. Some important choices to make. I have always been a max righting moment fan, but there are a lot of very successful skippers who seem to be going with low moment of inertia at the expense of righting moment.

The Carr lead is long and low while the DB lead is slightly shorter and slightly higher. Max righting moment and higher moi versus less righting moment and lower moi.

Any thoughts?

Scott

[Doug Wotring]

which ballast setup does what?

quick physics leson is needed here

Thanks

[s vernon]

Carr - longer lower - higher righting moment and higher moment of iniertia. With a higher moi the boat will keep hobbyhorsing longer once it starts, in very little wind and chop. The boat wants to keep going straight rather than being willing to turn when commanded to do so or when a slight windshift causes the boat to seek a different line (upwind) on its own due to balance (change) between the center of effort of the sails and the center of lateral resistance of the hull. (Probably getting too deep.)

DB - slightly shorter and higher - slightly lower righting moment and lower moi. With a lower moi the boat responds quicker to turning commands of the rudder or a small windshift.

The difference in boat personality between the two styles of lead may be subtle or it may be very obvious. (?)

I have the 2 types of leads in 2 different boats. 95 std with long low and Ozmun with short high. They both are fast boats. I am going to have to try to sense the differences in racing situations.

AMYA magazine #115 has a very good article by Rod Carr concerning this subject.

Scott

[Doug Wotring]

Thanks Scott,

excelent Saturday afternoon lesson

would like to hear what you find out on your two boats