I think they are mostly rubrails. When I am on plane they are submerged and throw some spray. But unlike a bow spray rail mine are "V"ed where they meet the hull, probably so they can't get hung up on a dock at low tide. I don't think Hatteras would do this if the rails were intended to provide lift.
Mine are wood, and thrubolted to the hull. After much searching for a master cabin leak I learned the sealant on these bolts will someday fail and admit water, but only at speed.
On my 50MY I have a second, main set of rubrails just below the portholes from stern to the forward cabin. This was dropped from the 53MY and only the aft ones used. This could be done because the 53s have another 1.5 inches of lip at each deck rubrail, increasing your beam from my 15'7" to 15'10". This means your rails don't get scraped as much as mine do.
