THE PLT & OBSERVER WERE ON A FLT TO RESCUE 2 DUCK HUNTERS, STRANDED IN A BOAT THAT BECAME STUCK IN ICE, 500 TO 600 FT FROM SHORE. AFTER REMOVING THE RGT DOOR, THEY PLANNED TO PICK UP 1 HUNTER AT A TIME ON THE RGT SKID WHILE THE OBSERVER HELD ONTO HIM THRU THE OPEN DOOR. AFTER CIRCLING IN GUSTY WINDS, THE PLT WAS ABLE TO HOVER AT THE BOW OF THE BOAT. AS THE 1ST HUNTER CLIMBED ONTO THE RGT SKID, THE HELICOPTER BANKED TO THE RGT, AND SUBSEQUENTLY, ENTERED A SPIN TO THE RGT.HOWEVER, THE PLT REGAINED CONTROL & CONTINUED TO THE LANDING AREA WHILE REMAINING IN A CONSTANT RGT TURN. AS HE ENTERED A 5 FT HOVER TO LAND, THE ACFT PITCHED FORWARD. THE PLT PULLED THE COLLECTIVE TO GAIN ALT, BUT THE ACFT ENTERED A RGT ROLL & TURN, AND SUBSEQUENTLY STRUCK SEVERAL TREES & CRASHED. AN INVESTIGATION REVEALED THE CG EXCEEDED THE FORWARD LIMIT BY .33 INCHES & THE RIGHT CG LIMIT BY 5.2 INCHES. THE ACFT WAS NOT EQUIPPED FOR LATERAL LOADS & NO LATERAL CG LIMITS WERE LISTED IN THE FLT MANUAL. THOSE EQUIPPED FOR LITTERS (LATERAL LOADS) WERE RIGGED WITH ADDITIONAL CYCLIC CTL.