B737 FLC ISSUED OVERWATER CLRNC WHILE FLYING A NON-OVERWATER ACFT.

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OUR FLT RELEASE FROM FLL-BWI READ AS FOLLOWS: '(SEE FILED RTE) FLL...PBI...A699...PERMT...AR7...DIW...FKN...BWI.' WE HAD NEVER SEEN THIS ROUTING BEFORE AND WERE GOING TO QUESTION THE USE OF AN ATLANTIC RTE DUE TO OUR REQUIREMENT TO REMAIN WITHIN 50 NM OF LAND ENRTE. HOWEVER; CLRNC DELIVERY AMENDED THE FLT PLAN TO READ: FLL9...ZAPPA...PERMT...ILM...J40....RIC...OTT4...BWI. WE INTUITIVELY RECOGNIZED THIS AS A ROUTING CLOSER TO LAND; CONTAINING NO ATLANTIC ROUTES; AND BELIEVED ATC HAD CAUGHT THE ERROR. AFTER DEP; WE LOOKED MORE CLOSELY AT THE NEW ROUTING AND ASKED ATC TO VERIFY THAT ZAPPA WAS WITHIN 40 NM OFFSHORE. ATC CONFIRMED IT WAS. ENRTE TO PERMT; WE ASKED ATC WHY WE WERE BEING ROUTED AS WE WERE AND IF THEY WERE AWARE OF OUR REQUIREMENT TO REMAIN WITHIN 50 NM OFFSHORE. AFTER CHKING; ATC SAID THERE HAD BEEN NO ATC AMENDMENT AND WE WERE BASICALLY ROUTED AS PLANNED BY DISPATCH. I AGAIN ASKED IF OUR ROUTING WOULD KEEP US WITHIN 50 NM OFFSHORE TO BWI. THE CTLR REPLIED HE WASN'T CERTAIN AND HAD LIMITED CAPABILITY TO VERIFY THIS. AT THAT POINT WE ASKED FOR; AND RECEIVED; A VECTOR BACK TOWARD THE COAST WHILE WE CONFIRMED THE VALIDITY OF OUR RTE. SOON AFTER; WE WERE CLRED DIRECT CRAIG AND REROUTED OVER LAND ON THE RTE WE NORMALLY USE. THE REST OF THE FLT WAS UNEVENTFUL. SUBSEQUENTLY REVIEWING THE PLANNED RTE IN DETAIL; IT BECAME APPARENT THAT; HAD WE FLOWN AS PLANNED; THE ROUTING ON THE RELEASE WOULD HAVE TAKEN US TO A MAX DISTANCE OF 165 NM FROM SHORE. ONLY BECAUSE THE SHORE WAS NOT OBSCURED BY CLOUDS AND WE CHKED THE ROUTING; DID WE CATCH THE MISTAKE IN TIME. I CALLED DISPATCH ON BWI ARR TO ASK ABOUT THE ERROR AND SPOKE TO THE DISPATCHER WHO PLANNED THIS FLT. SHE WAS VERY CONCERNED AND AT A LOSS TO EXPLAIN THE ROUTING. SHE SAID THE ONLY WAY TO INPUT THIS ROUTING WAS MANUALLY; AND SHE HAD NOT DONE THIS. SHE WAS VERY HELPFUL AND SAID SHE WOULD FOLLOW UP THE INCIDENT.