November 2020 Safety of jet boats with systems that use studs to hold steering nozzle housing in place
This safety update is for
- New Zealand commercial jet boat operators
- Maritime NZ authorised persons and surveyors
- Maritime NZ maritime officers, investigators and technical advisors
Jet boat steering systems
Jet boats rely on water flow propelled through the jet nozzle which pivots to steer the vessel. Failure of steering components or a sudden engine failure can leave a jet boat travelling at speed without any way of manoeuvring.
The jet boat operates by forcing water through the jet unit and discharging it through the nozzle at high velocity. The water enters through the intake, is propelled through the impeller and out through the nozzle as a jet stream. Steering is achieved by changing the direction of the stream of water as it leaves the jet unit.
The reverse bucket assists with slowing the jet boat down and enables it to move backwards if required. This is also known as the astern deflector. It needs to move freely to operate correctly.
Importance of studs holding steering nozzle housing in place
The nozzle housing attachment to the tailpipe is a critical safety component. It is very important that this is serviced and maintained according to the manufacturer’s requirements.
Risk to safety
It is the nature of commercial jet boating in canyons that the vessel travels very fast and close to rock walls. Jet boats operating on braided rivers or other river environments can also contact river banks or run aground at high speeds. Steering failures in either situation have the potential to result in many casualties.
A failure of the jet boat’s steering system at any speed is a risk to safety. Failure of studs holding the steering nozzle housing unit in place may result in the unit coming away from the tailpipe and obstructing other parts of the steering system.
These diagrams show where the studs are located that hold the nozzle housing to the tailpipe. The two red circles in Figure 1 are the port side studs.
What you should do
As part of your regular maintenance programme, you need to physically check the steering nozzle housing of your jet boat as detailed by the manufacturer. If any repair or maintenance of the water jet unit requires the nozzle housing to be removed from the tailpipe and refitted, make sure that this is done only by an appropriate person and that they do the following:
1. When refitting the nozzle housing to the tailpipe, make sure that the recommended torque has been applied to any fastening system. Refer to the manufacturer’s product manual for recommended torque settings and use a calibrated torque wrench (shown below).
2. Where a thread locker (such as Loctite) is specified on a fastener, use the type recommended by the manufacturer. Refer to the manufacturer’s product manual.
3. As best practice, once any nut or bolt has been tightened to the manufacturer’s recommended setting, use an anti-tamper paint (shown below) to allow a visual check of the nut or bolt to ensure that it has not moved.
4. Make sure components critical to the safe operation of each jet boat (such as the steering nozzle housing) are serviced by appropriate persons. An appropriate person includes the manufacturer and authorised service agents or the distributor. They could also be an employee or owner with the appropriate training, experience and relevant qualification to work on these safety critical components.
5. It is best practice to have a second appropriate person verify and sign-off any service of components critical to the safe operation of each jet boat.
6. Before you start servicing any components critical safe operation, make sure that the version of the manufacturer’s product manual you are using as a reference for servicing is verified as the version recommended by the manufacturer for your jet boat (make and model).
7. Do not, under any circumstances, use a gasket material on flanged joints unless this is specified by the manufacturer.
8. Make sure that pre-use servicing checks are done daily. Follow the maintenance service intervals as detailed in the manufacturer’s product manual. Be aware that silt and other characteristics of the water the jet unit is used in, and the type of use the jet unit has may mean the service intervals should be more frequent.
If you are unsure, talk to the supplier or manufacturer of your jet boat.