A B757-200 PILOT REPORTS THAT HIS ACR IS DISPATCHING ACFT WITH UNREALISTIC MIN FUEL LOADS.

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DISPATCHED WITH CLEARED FUEL 13.1 -- BLOCKED OUT WITH 13.6. NORMAL S/E TAXI; NO TAKEOFF DELAY. MINIMAL DELAY IN CLIMB TO FL380. IN CRUISE; FO POINTED OUT THE FMC PLANNED FAT WAS 4.7; INSTEAD OF FPF PLANNED 6.3!! CHECKED FMC FOR OBVIOUS ERRORS -- NONE. ACARS DISPATCH WHO REPLIED THAT HOWGOWZIT NORMAL AND THAT IT WAS PROBABLY FMC DATA ENTRY ERROR! AS WE DON'T ENTER THE FOB ANYWHERE OTHER THAN ACARS; THIS SEEMED UNLIKELY. HOWGOZIT CONTAINED ONLY TWO FIXES; ORIGIN AND DESTINATION; SO NO WAY TO CHECK AGAINST THAT. RAN SUSPECTED FUEL LEAK IRREGULAR PROCEDURE AND THIS DID NOT SHED ANY LIGHT ON THE PROBLEM. CALCULATED VS TOTALIZER VARIED FROM ZERO TO 500 LBS. ENDED UP LANDING WITH LOW FUEL EICAS MESSAGE ON ROLLOUT; L MAIN SHOWED 2.1; RIGHT MAIN 2.6; TOTAL 4.7. AT GATE; TOTALIZER STABILIZED TO 5.1. SENT ACARS MAINT LOG ITEM FOR SUSPECTED FUEL LEAK AND/OR FUEL GAUGE ERROR. MAINT CHECKED AND CLEARED THE ITEM OVERNIGHT; SAYING THAT THE TANK DRIPS AGREED WITH THE GAUGE FOB. MY SUSPICION NOW; IS THAT THE DISPATCH BURN FIGURE OF 6.8 IS TOTALLY UNREALISTIC FOR THIS SEGMENT. WE FLEW THE ROUTE EXACTLY AS FILED; AND LANDED SOUTH INTO ZZZ. WE JUST BURNED ABOUT 20% MORE THAN PLANNED; EVEN WITH THE S/E TAXI AND NO DELAYS. THIS WOULD NOT BE THE FIRST TIME THE DISPATCH COMPUTER WAS OUT TO LUNCH -- A FEW MONTHS BACK THEY FILED ME A RTE AT FL410 WITH AN ATOG AROUND 190K; AND THE FMC STATED REPEATEDLY 'UNABLE CRUISE ALTITUDE!' WHEN I CALLED THE DISPATCHER THE NEXT DAY; HE WAS NON-PLUSSED AND SAID THE DISPATCH PERFORMANCE DATABASE IS 'NOT NECESSARILY THE SAME AS THE AIRCRAFT'S FMC DATABASE!' HELLO? I'M ALL FOR FUEL SAVINGS; BUT IF WE'RE GOING TO BE FLYING ALL OVER THE PLACE WITH NO ALTERNATES AND MIN FAT; WE DAMN WELL BETTER HAVE ACCURATE BURN/PERFORMANCE DATA PROGRAMMED INTO THE DISPATCH COMPUTERS; DON'TCHA THINK??