Are you referring to the more-or-less horizontal line across the keel in the photo?
I'm not specifically familiar with that model Hunter but, speaking generically, the line in that photo appears to be the seam between the lower cast (lead or iron, probably) ballast portion of the keel and the upper "keel stub." The upper keel stub would be part of the molded fibreglass hull. The lower ballast portion of the keel (below the line) would normally be bolted to the keel stub.
What you see there is not unusual at all. Although, many folks do try to fair out that seam between the two sections of the keel so it is less conspicuous.
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Pacific Seacraft Crealock 31 #62
NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT