Jet Boat Accident Caused by Bolt Failures
The New Zealand Transport Accident Investigation Commission (TAIC) has released its final report into the contact of the jet boat Discovery 2 with a canyon wall in February 2019, noting that safety depends as much on mechanical factors as it does on crew training and operating conditions.
The commercial jet boat was steering at speed through bends in a narrow section of the Shotover River in Skippers Canyon. The steering failed, as did the reverse thrust, and the boat continued under momentum. She was travelling at 20 to 30 km/h when she hit a rock face. One passenger was thrown partly overboard and suffered a broken leg. The other passengers received minor cuts and bruises. All were evacuated by helicopter.
The jet unit's steering failed because three of the four stud-bolts holding the steering nozzle onto the tailpipe assembly had broken. The stud bolts broke due to fatigue cracking which occurred because nuts on the bolts were not tightened to the manufacturer’s recommended torque.
TAIC says that the nuts weren't tight enough because the operator's hazard focus was less on mechanical matters than on operating conditions and driver training.
TAIC says jet boat operators should have a regime to follow the manufacturer's maintenance instructions and guidance. Operators need to identify and take extra care to maintain critical components that, if defective, would pose significant risk.
The report is available here.