B747 FLT CREW HAS PRECAUTIONARY SHUTDOWN OF THE #4 ENG. DECLARES EMER AND DIVERTS TO NEAREST SUITABLE ARPT.

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ENRTE TO EDDF FROM DOV WHILE IN VMC AND ON AN ATLANTIC TRACK; A PRECAUTIONARY SHUTDOWN OF THE #4 ENG WAS PERFORMED AS PER COMPANY PROC. WE INITIATED A 15 NM OFFSET TRACK PRIOR TO RECEIVING OFFICIAL CLRNC IN ORDER TO AVOID POSSIBLE TFC CONFLICTS AS WE DRIFTED DOWN TO FL310. AFTER CONSULTING WITH DISPATCH VIA SAT-PHONE REGARDING DEST WX; FUEL BURN AND CONSEQUENT LNDG FUEL; I ELECTED TO LAND AT BOS. MY REASONS FOR CHOOSING BOS VERSUS OTHER POSSIBLE OPTIONS WERE: 1) THE ABILITY TO COMMENCE THE APCH WITH SUFFICIENT FUEL RESERVES TO AFFORD US ADDITIONAL OPTIONS SHOULD THE FIRST APCH (FOR WHATEVER REASON) PROVE UNSUCCESSFUL; 2) ITS LACK OF ATC CONGESTION; 3) OVERALL ARPT SUITABILITY; 4) ADEQUATE WX FORECAST; 5) MY PERSONAL FAMILIARITY WITH THE ARPT AND ITS APCHS. UNDERLYING THE ABOVE WAS MY OWN RELUCTANCE TO CONTINUE TO EDDF AND ARRIVE THERE WITH POTENTIALLY UNSUITABLE WX AND LOW ON FUEL THEREBY SEVERELY LIMITING AVAILABLE OPTIONS. BOS APPEARED TO BE THE SAFEST; MOST REASONABLE CHOICE AT THE TIME.