Chris
There is no locking mechanism on any of the Seal or Parker boats, however I owned a Parker21 for a few years before moving to our current Parker 275 and the absense of such a thing has never bothered me. I have never heard of either boat inverting, let alone to such an angle that the keel would fall into the boat. However, even it it did, this would not stop the boat from righting itself as most of the balast is built into the hull, not into the keel.
Regards
Don Harvey
Don Harvey