Charles' victory was enough to give him third overall, five points behind Russell Peters, with Jeremy Robinson as tactician, the runner-up, and eight points behind Smith.
This is the eighth year of the Ultra 30s and Smith has won every time except 1995, when Peters broke his domination. This year, even a move by Peters to have Smith's boat declared illegal came to nothing.
With Smith here were three of his Silk Cut crew ahead of next month's Whitbread Race - Neal McDonald with him on Frontera, Jez Fanstone with Owen on Hoya and Jan Dekker with Charles on United Airlines.
The nine-man crews of the 30ft Ultras showed how far their ability to control these difficult boats, each with racks on which the crews sit out to balance them, has developed.
In a gusty and shifting wind off the Royal Ulster Yacht Club there were plenty of anxious moments for the spectators, but the old days of capsizes returned only once, Owen and crew going for a swim in the first race.
He came back to take the second race of the day, while the improving Charles scored three wins in a weekend of eight races which took the fleet first to Jordanstown Lough, then Carrickfergus and Bangor.
John Merricks and Ian Walker, who may race Ultras next year in a series which could see an additional grand prix staged in London, are in Israel competing in the 470 dinghy World Championship. The duo, who came second last year in Brazil, qualified for the finals after finishing fifth in group A, as did Nick Rogers and Steve Irish, 12th in Group B.
FRONTERA ULTRA 30s GRAND PRIX (Belfast Lough): 1 G Charles (United Airlines) 35pts; 2= L Smith (Frontera) and E Warden Owen (Hoya) 34; 4 R Peters (DBS) 29; 5 P Newlands (Mobil) 20; 6 R Yeoman (Save & Prosper) 15. Final standings: 1 Smith 22pts; 2 Peters 19; 3 Charles 14; 4 Owen 13; 5 Yeoman 9; 6 Newlands 7.