PLT OF SMA ON FLOATS ENCOUNTERS FLT CTL ANOMALIES AND MAKES EMER LNDG ON WATER.

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I FILED AN OUTBOUND AND RETURN INBOUND FLT PLAN. THE TKOF SEEMED NORMAL; THE PLANE RESPONDED NORMALLY TO ALL CTL INPUTS. I CLBED TO APPROX 1800 FT AND CHKED IN WITH APCH AS NORMAL. I CLBED TO 2500 FT AND THROTTLED BACK TO A CRUISE SETTING. AFTER FLYING AT CRUISE ALT FOR 5 MINS OR SO; THE PLANE BUFFETED SIMILAR TO FLYING THROUGH A LIGHT CHOP. THE NORMAL SOUND OF AIR RUSHING BY THE PLANE INCREASED 2-3 TIMES NORMAL; AND THE NOSE OF THE PLANE PITCHED DOWN VERY QUICKLY. WHEN I CORRECTED THE PITCH USING ELEVATOR; THE NOSE PITCHED UP MUCH HIGHER THAN IT SHOULD HAVE FOR THE AMOUNT OF INPUT THAT I HAD USED FOR THE CORRECTION. A LOUD FLAPPING NOISE WAS CLEARLY AUDIBLE. I WAS CONVINCED I HAD LOST SOME FABRIC FROM THE TAIL AREA; PROBABLY FROM AN ELEVATOR. I WAS UNABLE TO SEE ANY OF THE REAR OF THE PLANE IN THE TAIL AREA. I WAS CONCERNED I WOULD LOSE CTL AT ANY TIME. MY PLAN WAS TO REDUCE ALT AND AIRSPD. IF I DSNDED AT TOO FAST AN AIRSPD; I FELT I COULD LOSE MORE FABRIC; BUT I WANTED TO LAND AS QUICKLY AS POSSIBLE. I THROTTLED BACK AND BEGAN A DSCNT TO LAND. I CALLED APCH AND RPTED THE PROB. THEY ASKED ME IF I WANTED TO DECLARE AN EMER; AND I RESPONDED YES. I WANTED HELP IF I CRASHED WHILE LNDG. I FOUND A COVE THAT WAS LINED UP INTO THE SE WIND OF THE DAY. I KEPT A HIGHER THAN USUAL AIRSPD ALL THE WAY TO TOUCHDOWN. A LOT MORE ELEVATOR CTL WAS NEEDED THAN NORMAL TO KEEP THE NOSE UP IN THE PROPER LNDG ATTITUDE. THE TOUCHDOWN WAS GOOD. I TURNED BACK TOWARD THE COVE WHILE TAXIING; AND ATTEMPTED TO REACH APCH SEVERAL TIMES TO LET THEM KNOW I WAS DOWN AND SAFE; BUT WAS UNABLE TO REACH THEM. WHILE DOING SO; I NOTICED A LARGE PIECE OF MATERIAL FLOATING ON THE WATER THAT WAS SIMILAR IN COLOR TO THE COLOR OF MY FUSELAGE. I STEERED TOWARDS IT; AND NOTICED IT WAS LIGHTER IN COLOR; AND MELTED. I WAS UNABLE TO TELL HOW LARGE IT WAS; BUT AT A MINIMUM; IT WAS 4 FT WIDE AND CURLED UP IN THE WATER. IT LOOKED LIKE THE PLASTIC USED TO SHRINK WRAP A BOAT FOR WINTER STORAGE. I IGNORED IT BECAUSE I WAS STILL CONVINCED I HAD LOST TAIL FABRIC; AND SHUT DOWN THE PLANE TO STAND ON THE FLOATS AND LOOK THE REAR OF THE PLANE OVER. A PLANE FLEW OVERHEAD AT A LOW ALT AND CIRCLED. I WAVED TO LET THEM KNOW I WAS OK; AND GOT BACK INTO THE PLANE TO TRY TO REACH HIM ON THE RADIO. I HEARD HIM TALKING TO APCH; AND I WAS ABLE TO TELL HIM I WAS OK; DIDN'T NEED ANY EMER ASSISTANCE. HE RELAYED THE INFO TO APCH. I GOT BACK OUT TO LOOK THE PLANE OVER; CHKED ON BOTH SIDES; AND DIDN'T SEE ANYTHING THAT LOOKED UNUSUAL. I RESTARTED THE PLANE AND TAXIED TO A NEARBY SHORELINE; BEACHED THE PLANE AND GOT OUT TO CLOSELY INSPECT THE ENTIRE PLANE. I SAW NO DEFECT ON THE PLANE AT ALL. I BEGAN TO BELIEVE THE PIECE OF PLASTIC I SAW HAD SNAGGED ON MY PLANE DURING TAXI OR TKOF AT HOME; AND HAD CAUSED THE PROB. I WANTED TO TEST FLY THE PLANE. I CALLED APCH BY CELL PHONE AND GOT A XPONDER CODE TO FLY BACK HOME. THE TKOF WAS NORMAL; CLB WAS NORMAL; THE UNUSUAL NOISES AND PITCH OSCILLATIONS WERE GONE. I WASHED DOWN THE PLANE AT HOME; AND INSPECTED IT AGAIN; NOTHING WAS NOTED AS UNUSUAL. IT IS MY OPINION THAT THE PLASTIC PIECE I SAW WAS THE CAUSE OF THE WHOLE INCIDENT. IN RETROSPECT; I DO FEEL THAT I OVERREACTED BY DECLARING AN EMER; BUT AT THE TIME; AND THE WAY THE PLANE WAS BEHAVING; I WAS SURE I WOULD NOT BE ABLE TO CTL THE PLANE AT THE SLOWER LNDG SPD IN THE FLARE. I WANTED ALL THE HELP I COULD GET. I AM SURE I CAUSED SOME ANXIETY AT TRACON; BUT WAS VERY IMPRESSED WITH THE RESPONSE THEY GAVE TO HELP LOCATE ME; SEND HELP; SEND A PLANE OVER TO LOOK FOR ME; AND TO HELP ME GET BACK HOME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR EXPERIENCED A SUBSEQUENT EVENT ALMOST IDENTICAL TO THIS THE NEXT TIME HE TOOK THE ACFT OUT. MADE ANOTHER LNDG IN A COVE. THIS TIME HE WAS ABLE TO DETERMINE THAT A PIECE OF TAPE APPLIED BY THE PREVIOUS OWNER SPANNING THE WIDTH OF THE FORWARD WINDSCREEN TO SEAL THE JOINT BTWN THE WINDSCREEN AND THE FUSELAGE FABRIC HAD COME LOOSE ALL ALONG THE FORWARD EDGE AND WAS PEELING UP AND BACK. HE SURMISED THE TURB CAUSED BY THE 'SPOILER LIKE' PROTRUDENCE WAS DISRUPTING NORMAL AIRFLOW OVER THE HORIZ STABILIZER; THUS DIMINISHING ITS EFFECTIVENESS AND CAUSING THE NOSE TO DROP. THIS REQUIRED THE USE OF NEARLY FULL UP ELEVATOR TO MAINTAIN PITCH CTL. AFTER TEARING THE TAPE OFF; THE AIRPLANE ONCE AGAIN FLEW NORMALLY. RPTR DID NOT STATE WHETHER THE ANOMALY AND FIX HAD BEEN ENTERED AND CERTIFIED IN THE ACFT LOG.