A B737 CREW; ON A VISUAL APCH TO RWY 01 AT KMSY; NOTICED A 100 FT CHANGE IN THEIR RADIO ALTIMETER AS THEY PASSED OVER A SHIP IN THE RIVER.

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VISUAL APCH TO RWY 01 ON FINAL; ON ILS COURSE AND GLIDE SLOPE. I NOTICED OIL TANKERS PARKED IN THE RIVER WITH ONE PARTICULAR TANKER PARKED WITH THE BRIDGE EXACTLY IN LINE WITH FINAL APCH. R ABOUT 400 FT ON THE RADIO ALTIMETER; IT JUMPED TO 300 FT. I ASKED TWR IF THEY KNEW THE TANKER WAS THERE AND THEY SAID THEY DO IT ALL THE TIME. WHY? THERE WAS PLENTY OF ROOM IN THE RIVER TO PARK OTHER THAN DIRECTLY ON FINAL. DOES THE FAA KNOW THIS? DOES THIS AFFECT THE TERPS? WHAT IF ANOTHER TANKER HAS A HIGHER BRIDGE WITH TALLER ANTENNAS? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: A KMSY TWR SPECIALIST REVEALED THAT THIS ON GOING PROB HAD BEEN ADDRESSED BY THE PARTIES INVOLVED; THROUGH PROPER CHANNELS; WITH NO DETERMINATION OF A SOLUTION AT THIS TIME. THE COAST GUARD FEELS THE RIVER WAS THERE BEFORE THE ARPT SO THE SHIPS HAVE A RIGHT TO BE THERE. THE FAA'S CONCERN IS; HOW MUCH CLRNC IS PROVIDED FOR ARRIVING ACFT. IT WAS STATED THAT THE HEIGHT OF THE SHIPS VARY DEPENDING WHAT TYPE CRANE IS BEING USED TO LOAD/UNLOAD THE VESSEL.