Found this on the net for Seafarer 24:
Ballast. Fixed lead ballast, total weight 1,200 lbs (c/b), 1,400 lbs (keel). Hydro-dynamically streamlined fiberglass centerboard on centerboard model weight 342 lbs. incorporates 207 lbs. additional lead ballast and is worm gear winch operated to provide positive continuous position control at all times. Centerboard swings up if it hits an obstruction and can be removed for painting from the outside the boat without any risk of leaks. Lead ballast custom cast and weighed by Seafarer, structurally laminated to hull and centerboard.
So, at least it (the centerboard) is not as heavy as I imagined, it sounds quite good actually. I could go to new areas and find all the hidden thin water and rocks, without sinking!
Real good for lakes, where charts are non existent or very poor. Lots of unmarked granite even in the big lakes I have charts for.