BANNER TOW PLANE ENCOUNTERS FOG AND TURNS BACK TOWARD LAND. HIS BANNER COLLIDES WITH SECOND TOW PLANE.

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DURING A BANNER TOW OP OVER THE OCEAN ON CAPE COD; MY ACFT TOWING A 30 FT BY 100 FT BILLBOARD WAS INVOLVED IN A COLLISION WITH MY BOSS'S ACFT. THE VISIBILITY WAS POOR AND DETERIORATING IN HAZE AND FOG. I WAS THE LEAD ACFT WITH MY BOSS APPROX 1 MI IN TRAIL. WE DECIDED THAT WE WERE GOING TO TERMINATE THE TOW ON THE S SIDE OF THE CAPE AND CLB UP TO 1000 FT AND GET VECTORS TO THE N SIDE OF THE CAPE TO GET AS MUCH OF OUR ORIGINAL RTE DONE AS POSSIBLE. AFTER PASSING ONE PARTICULAR BEACH; I WAS TO TURN R OUT OVER THE OCEAN; THEN TURN L OVER LAND (VISIBILITY WAS BETTER 1/4 - 1/2 MI INLAND). I ENTERED A FOG BANK HIDDEN BY THE HAZE. AT THAT POINT I LOST ALL OUTSIDE VISUAL REFS. WHILE STRUGGLING TO STAY UPRIGHT DUE TO VERY LIMITED INSTRUMENTATION IN A PA-25; I CALLED MY BOSS TO TELL HIM I HAD LOST ALL IDEA OF MY LOCATION. I CONTINUED MY R TURN TO GET BACK OUT OF THE FOG. I DID NOT REGAIN ANY VISUAL REFS UNTIL I WAS ON A COURSE PERPENDICULAR AND APCHING THE BEACH. I AGAIN RADIOED MY BOSS TO TELL HIM THAT I WAS COMING BACK AT THE BEACH WHICH WAS NOT WHAT HE EXPECTED ME TO DO. I WENT TO FULL PWR TRYING TO CLB ABOVE HIS EXPECTED FLT PATH. AT THAT POINT HIS ACFT COLLIDED WITH MY BANNER. TWO ROPE HOOKS AND A BANNER WERE TAKEN OFF MY ACFT. THE BILLBOARD IMPACTED THE C-172'S R WING AND SHREDDED INTO 2 PIECES; 1 ABOVE AND BELOW THE WING. HE DROPPED HIS BANNER TO LIGHTEN HIS DRAG LOAD. HE WAS UNABLE TO MAINTAIN ALT AND MADE A FORCED LNDG ON AN UNOCCUPIED PART OF THE BEACH WITH NO INJURIES OR MAJOR DAMAGE TO THE ACFT. I WAS PRESSURED TO CONTINUE WHEN I FELT UNCOMFORTABLE AND I SHOULD HAVE BEEN MORE FORCEFUL ABOUT TURNING BACK EARLIER. I SHOULD HAVE CLBED ABOVE 500 FT AND TURNED L TOWARD BETTER VISIBILITY AND GREATER DEFINITION BTWN LAND AND SKY. NEEDED BETTER RADIO COM AND COORD. HE NEVER HEARD THE 2 IMPORTANT CALLS. WAS PROBABLY TALKING AT THE SAME TIME.