HAMILTON WATER JETS

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HAMILTON WATER JETS
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Nature

• Newtons 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 Waterjet
Position of the bucket for Ahead
Neutral Astern
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Steering a Water Jet

• By changing direction of water stream as it
  leaves the jet unit

Waterflow
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Going Astern

• By lowering an astern deflector into the jet
  stream
• reversing the direction of the force generated

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Emergency Crash Stop

• Warn crew to hold on
• Move Astern Deflector to Reverse position while
  at speed (at full revs)
• 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 waterjets control functions can be used
• in combination
• separately
• to 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
  Units 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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Cavitation
Cavitation causes a loss of performance and
results in serious damage to the waterjet
components.
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Cavitation
Cavitation 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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Cavitation
Cavitation can be prevented by 1 Increasing the
jet intake pressure i.e. Increase boat speed
but do not increase power 2 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

• At high planing speeds, shallow water operation
  is not a problem until the vessel is nearly
  grounded.
• At slow displacement speeds, avoid using high
  RPM in shallow water.

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Shallow Water Operation

• Idle over a shallow area into deep water before
  accelerating.
• 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.