On April 28, 1993 at 0915 Hawaii standard time, a Bell 47G-2, N1437, experienced a hard landing while attempting to land on a tuna boat which was located about 200 miles north west of Western American Samoa. The pilot was conducting a local visual flight rules aerial observation flight. The helicopter, operated by San Diego Fisheries, San Diego,California, sustained substantial damage. The certificated airline transport pilot and the passenger were not injured. Visual meteorological conditions prevailed. The flight originated from the tuna boat at about 0845 hours. The pilot reported in the Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2, that before departing on the tuna boat the helicopter had been parked at the airport in Pago Pago for about a month. On April 25, 1993, the pilot flew the helicopter in the airport local area. On engine shutdown, the pilot and owner determined that the weights were missing from the vertical stabilizers; they had been relocated on the vertical stabilizer. The pilot and owner also found that the main rotor blade tips began to delaminate. The owner resealed the main rotor blades with a metal epoxy. The subsequent engine run-up revealed no unusual vibrations. The pilot flew the helicopter several times after the repairs were effected, with no problems. On April 28, 1993, the pilot, together with his passenger, departed the tuna boat on a practice flight. When returning to the tuna boat, the pilot was unable to "slow the helicopter down to land" and effected a go-around. The passenger radioed the tuna boat and requested that the boat slow down to about 5 knots. On the second approach the pilot was able to slow the helicopter to about 10 knots, but was unable to bring the helicopter to a hover. During the approach, at about two feet above the helipad, the tuna boat pitched upward and the helicopter front skids collided with the landing pad and landed hard. During the hard landing, the main rotor blade severed the tail boom assembly. The pilot also reported that the examination of the helicopter after it was returned to the airport revealed that the severed main rotor wooden spar contained dry rot and extensive rust. The pilot stated that the rotor blades repairs that the owner effected before departing on the tuna boat were still intact.