A C172 PLT EXPERIENCED A LOSS OF PWR AND MADE AN OFF ARPT LNDG NEAR SUT.

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FLEW FRIENDS TO MYRTLE BEACH (GRAND STRAND) FOR LUNCH. RECEIVED WX BRIEF FOR THE DAY AND FILED FIRST LEG VFR FLT PLAN WITH FSS FROM ALBERT ELLIS ARPT IN JACKSONVILLE; NC (OAJ). LANDED WITHOUT INCIDENT AT GRAND STRAND. TOOK OFF FROM GRAND STRAND ABOUT XA20 AFTER FILING VFR FLT PLAN WITH FSS. FLEW AT 1000 FT; NO SIGNIFICANT WINDS AND NO PROBS NOTICED. ENG WENT TO UNDER PWR SIT WITHOUT ANY WARNING OR APPARENT REASON. ENG DID NOT SPUTTER OUT; SO I THOUGHT WE MAY HAVE A CHANCE TO MAKE IT TO BRUNSWICK COUNTY ARPT. I COMMENCED WITH THE EMER PROC TO TRIM THE ACFT TO BEST GLIDE SPD AND FOUND THE NEAREST CLRING TO LAND AT IN CASE I COULD NOT MAKE IT TO BRUNSWICK COUNTY. TURNED TOWARDS BRUNSWICK COUNTY AND HAD IT IN SIGHT STRAIGHT AWAY; BUT IT WAS EVIDENT THAT WE COULD NOT MAKE IT. THE RPM WERE STUCK UNDER 500 AND DID NOT RESPOND TO THROTTLE MANIPULATION. I THOUGHT ABOUT ATTEMPTING A RESTART BUT THE ENG WAS STILL ON. I TURNED TOWARDS THE CLRING AND WE SET DOWN WITH SOME DAMAGE TO THE ACFT BUT ALL 4 PEOPLE ON BOARD WERE OK. THE FAA HAS DETERMINED THAT THIS IS LABELED AN 'INCIDENT' AND NOT AN 'ACCIDENT' DUE TO THE LACK OF SUBSTANTIAL ACFT DAMAGE.