AN ACR WDB MADE A GAR TO AVOID WAKE TURB.

Narrative

THE WX AT BOSTON WAS GOOD; HOWEVER; THERE HAD BEEN STRONG WINDS ALL DAY. THE APCH TO RWY 33L WAS NOT UNUSUAL UNTIL APPROX 200 FT WHEN WE GAINED 10 KTS OF AIRSPD FOLLOWED BY ANOTHER GAIN OF 5 KTS. THE FO BLED OFF THIS INCREASE IN A NORMAL MANNER AND THE APCH WAS CONTINUED UNTIL AFTER I HAD CALLED 20 FT AT WHICH TIME THE ACFT STARTED A HARD ROLL R. IT REQUIRED FULL AILERON CTL TO STOP THE UNDESIRED R ROLL. WHEN WE EXITED THE CONDITION; WE EXPERIENCED ROLLS IN BOTH DIRECTIONS DURING THE RECOVERY. WHEN THE ROLLING STARTED; I ORDERED A GAR; ASSUMED CTL AND RETURNED TO LAND AT BOSTON ON RWY 33L. WHEN WE BEGAN THE APCH; THE TWR GAVE WINDS OF 310 DEGS AT 19 KTS. WE WERE FOLLOWING A DC9 BY APPROX 4 MI AND TFC WAS DEPARTING ON RWY 27. THE ROLL WAS FROM WINDS OF SOME SOURCE OUTSIDE THE ACFT BECAUSE THE ACFT FUNCTIONED NORMALLY AFTER THE RECOVERY. THE R GEAR TOUCHED THE RWY SOFTLY DURING THE GAR. I ENTERED A LOG ENTRY REQUESTING AN INSPECTION FOR ANY POSSIBLE ABNORMALITIES AND NONE WERE FOUND. I BELIEVE WE EXPERIENCED A WINGTIP WAKE VORTEX FROM AN ARRIVING OR DEPARTING ACFT. SUPPLEMENTAL INFO FROM ACN 271390: I WAS 180 DEGS OUT OF PHASE WITH ACFT -- LIKE THE DUTCH ROLL MANEUVER IN A SIMULATOR. I COULD NOT CTL ACFT; AT LEAST UNTIL PWR WAS ADDED. I HAD BOTH HANDS ON YOKE AND IT WAS ALL I COULD DO TO TRY AND LEVEL THE WINGS. I PROBABLY SHOULD HAVE GONE AROUND SOONER AND THE 15 KT AIRSPD INCREASE ON SHORT FINAL MAY HAVE BEEN A PRECURSOR OF WHAT HAPPENED NEXT.