Hamilton Jet HJ241, Manual

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1.2
1 INTRODUCTION & PRODUCT DESCRIPTION
1.1 T
HE
H
AMILTON
W
ATER
J
ET
S
YSTEM
HJ-241 / HSRX
EQUIPMENT DESCRIPTION:— The Hamilton HJ
Series is a range of highly efficient single stage
waterjets suitable for propelling craft typically up to
20 meters in length and 30 tonnes displacement, at
speeds up to 50 knots. HJ Series waterjets are
generally directly driven by high speed diesel
engines. The HM Series are larger single stage
waterjets suitable for vessels typically up to 50m in
length and are generally driven by high speed diesel
engines via a reduction gearbox.
Mounted partly inboard at the stern of the vessel,
the Hamilton waterjet consists of a totally integrated
package with steering and reverse mechanisms and
jet mounted control system hydraulic equipment.
Water is drawn into the waterjet through an intake
screen at the base of the intake, which is mounted
flush with the hull bottom. The pumping unit
(im stator) increases the pressure or "head"
of the flow, which is then discharged at high velocity
at the nozzle. The reaction to this high velocity jet
stream provides the net thrust force, which is fully
transmitted through the intake to the hull bottom.
A single piece balanced steering nozzle precisely
directs the jet stream as commanded by the helm,
providing high turning forces to either port or
starboard. An independent split-duct type reverse
deflector, usually hydraulically actuated, directs the
jet stream back underneath the hull to provide
powerful astern thrust. The reverse nozzle may be
set to a "zero speed" position (where the ahead and
astern thrusts are balanced) at which point full
steering is still available. Infinitely variable forward
and reverse thrust may be selected by varying the
position of the reverse duct and combined with the
highly efficient steering, results in unparalleled
vessel control and manoeuvrability.
A vessel fitted with a Hamilton waterjet has the
minimum possible draft, with no protruding
underwater appendages. This allows operation in
shallow waters and in water with floating debris
that may foul or damage a typical propeller driven
vessel and also means increased safety for
personnel working in the water near the vessel. The
waterjet unit is an ideal form of propulsion for
vessels working in a marine mammal environment.
1.1.2 Main Components
INTAKE AND INTAKE BLOCK:— The Intake
represents the main structural body of the Jet Unit
and is an integral part of the Hamilton Jet design.
The Intake is cast from high silicon aluminium alloy
and is capable of transmitting the full net thrust
force of the Jet Unit to the hull bottom, and not to the
transom or to the engine via the drive shaft. The
Intake casting has a lower flange which mounts to
an Intake Block, which is welded or bolted into the
vessel hull. All Hamilton waterjets include an Intake
Screen that is carefully engineered into the waterjet
design so that operational parameters such as
cavitation resistance are unaffected by its presence.
OIL COOLER:— The Intake has an integrated Oil
Cooler for the hydraulic control system. This is
connected to a Jet mounted Hydraulic Power Unit
(JHPU) via hoses.
THRUST BEARING AND WATERSEAL:— The thrust
force generated by the pressure differential across
the waterjet Impeller is reacted by a Thrust Bearing
inside a Bearing Housing attached to front of the
Intake. No additional external thrust bearing is
required. Aft of the Thrust Bearing on the waterjet
Mainshaft is a mechanical face type Water Seal
which prevents water from entering the vessel and
Bearing Housing.
COUPLING:— A Coupling is mounted on the
Mainshaft forward of the Bearing Housing. A
variety of Couplings are available to suit the type of
driveshaft flange used. The driveshaft to the
waterjet must have axial and radial flexibility.
IMPELLER:— The Impeller design employed in all
Hamilton waterjets is a highly refined mixed flow
type capable of pumping large volumes of water at
relatively low pressures, permitting high propulsive
coefficients to be achieved at fast vessel speeds with
outstanding resistance to cavitation. All Impellers
have been designed using sophisticated flow
analysis software. The cast stainless steel Impeller
runs within a replaceable stainless steel Wear Ring
located in the rear section of the Intake or within an
Impeller Housing attached to the rear face of the
Intake (on larger HM Series Jet Units).