Could be voids
With the exception of the 1971-75 O'Day 23, all of the O'Day Keel/Centerboard models had the keel molded as part of the hull, the ballast was lead ingots that was placed inside the keel (between cb trunk and sides of keel) then fixed in place with thickened resin. It is possible that there might be a few small areas where the resin did not enter before curing took place. These might also be areas of blistering or delamination. After 25 years the flexing of the keel may have allowed the fiberglass skin of the keel to separate from the encapsulated ballast, not a major problem unless water has found it's way in, freeze/thaw cycles if you boat in an area with cold Winter seasons of haulout may worsen the problem. I'd give Rudy a call at D&R Marine for advice, or consult a local boatyard for repairs. D&R Marine (508) 644-3001
