hamilton water jets
DESCRIPTION
HAMILTON WATER JETS. Nature. Newton’s Third Law of Motion “Every action has an equal and opposite reaction”. . Water jet - Main parts. Cast aluminium pump u nit and intake transition duct Stainless steel impeller Astern deflector Steering nozzles. Water Jet Advantages . - PowerPoint PPT PresentationTRANSCRIPT
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HAMILTON WATER JETS
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Nature
• Newton’s Third Law of Motion – “Every action has an equal and opposite
reaction”.
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Water jet - Main parts• Cast aluminium pump unit and intake transition
duct• Stainless steel impeller• Astern deflector• Steering nozzles
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Water Jet Advantages • Supreme manoeuvrability
– Turn around axle without touching the wheel
– Speed zero possible, without switching gears• While steering capability is kept
– Simplicity– Better low speed manoeuvrability and
better acceleration– Precise steering control.
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Water Jet Advantages • Safe for persons in water
– No moving parts extending under boat
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The WaterjetPosition of the bucket for:Ahead Neutral Astern
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• By changing direction of water stream as it leaves the jet unit
Steering a Water Jet
Waterflow
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• By lowering an astern deflector into the jet stream – reversing the direction of the force generated
Going Astern
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Emergency “Crash” Stop
• Warn crew to hold on• Move Astern Deflector to
Reverse position while at speed (at full rev’s)
• Notes:– Emergency stop should only
be used in extreme situations.– Engine damage can occur
because of lubricating oil moving to front of carter
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Zero Speed
• By lowering the astern deflector partially in the jet stream so ahead and astern thrust is equal
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Waterjet Operation• A waterjet’s control functions can be used
– in combination– separatelyto create precise vessel control and
manoeuvrability in all low and high speed situations
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Throttle
• Increasing rpms results in– increased acceleration– increased maneuverability
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Comparison between jets and outboards
• Waterjet seems to react slowly– Activate steering by giving quite a bit of
rudder and turning back to central position straight afterward
– Activate stopping by buckets full astern and back to neutral position straight after
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Backing up
• Steers other way round, compared with outboard motors / cars etc.– No banana-ing– During turn no turning of wheel when
changing from ahead to astern
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Steering
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Moving sideways(multiple jet installations only)
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Debris Problems
• Blockages and Debris– Any debris caught in the Intake Screen,
Impeller or Tailpipe stator vanes can affect the Jet Unit’s performance
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Detecting Debris
• Vibrations• Noise in the jet (sometimes)• Increased rpms, but less power
– Loses grip on the water• Less speed at high revolutions
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Unblocking a Jet Unit
• Backflush the blocked Jet– if a reversible gearbox is used
• Slow or stop engine driving the blocked Jet– Bucket up– Reverse on other engine (if fitted) to create
backflow
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Unblock Jet Unit
• Operate the manual Intake Screen Rake (if fitted)
• Remove Inspection Cover on Intake – Clear manually
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Vessel not stopping
• Boat goes ahead, unless buckets in reverse (double jet)– One of buckets is not moving, due to
broken cable• Solution
– Stop motor at side of broken bucket– Unclutch jet unit
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CavitationCavitation causes a loss of performance and results in serious damage to the waterjet components.
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CavitationCavitation can be caused by…
• Hump Conditions• Overload• Weight too far aft• Bad weather or sea conditions• Blocked intake screen• Blunt or damaged impellers• Excessive impeller tip clearance• Poor installation
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CavitationCavitation can be prevented by…
1 Increasing the jet intake pressure– i.e.: Increase boat speed but do not
increase power2 Reduce rpm
– less throttle– coarser impeller, i.e.. less rpm
(steeper pitched blades)3 Reduce flow plus fit a smaller nozzle
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Shallow Water Operation
Avoid pumping stones, sand and debris through the Jet Unit as this will blunt and wear the Impeller. The following diagrams illustrate good and bad practice…
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Shallow Water Operation
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Shallow Water Operation
a) At high planing speeds, shallow water operation is not a problem until the vessel is nearly grounded.
b) At slow displacement speeds, avoid using high RPM in shallow water.
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Shallow Water Operation
a) “Idle” over a shallow area into deep water before accelerating.
b) If any debris has been picked up in the intake screen, momentarily stopping the engine should allow the debris to drop away from the screen.
Do not run the Jet if the vessel has run aground. Damage may occur to impellers.