Hamilton Jet HJ241, Manual

Page: 47 / 202

3.13
3 DESIGN BASICS
3.5 W
ATER
O
FF
-T
AKE
HJ-241 / HSRX
3.5 WATER OFF-TAKE
The Jet Unit is fitted with a Water Offtake which may
be used as a supplementary water supply (e.g. for a
deck wash).
If it is used as a part of the engine
cooling circuit, the designer / builder must satisfy
himself that the available flow is sufficient for the
cooling requirements.
The water offtake point is located on the starboard
side of the Intake. This is fitted with a bung which
can be converted to a 22mm dia x 30mm long hose
tail by cutting off the end as shown on the basic Jet
Assembly drawing HJ24101000.
This will provide water at a max pressure of 550kPa
(80psi) at full power. The water may be fed directly
to the engine without the need for a raw water pump
provided:-
The pressure from the water offtake at idle is sufficient
to cool the engine,
and ,
The engine can withstand the full pressure from the jet
offtake.
To be sure of correct flow for engine cooling, a
conventional water pick-up and the engine raw
water pump should be used. The Jet water offtake
can be used for a deck cleaning hose but the
pressure is not high enough to be used for a fire
hose.
CONVENTIONAL WATER PICK-UP.
Alternatively a cooling system separate from the Jet
Unit can be fitted to the engine maker’s
specifications. The water pick up points must NOT
be directly ahead of the Jet Unit intakes and should
be well to the side of the area forward and the same
width as the intake opening.
SANDTRAP:— - (Optional Raw Water Sand Filter).
Refer to Drawing HJ-241-12-000 Sandtrap & en-
gine Cooling.
High pressure water from the Jet is piped into the
sand trap before feeding into the engine cooling
system.
Sea water (raw water) fed into a centrifuge, drops
out foreign matter (sand, shells, stones, etc) into a
clear perspex bowl, which can be easily, visually
inspected. Opening the Dump Valve, while water is
being fed in, drops out the collected material into the
dump line which carries any collected material
overboard via a skin fitting, through the hull side or
Transom.
C
AUTION
If a gearbox or clutch is fitted to
the engine, a conventional hull
water pick-up and engine raw
water pump must be used.
C
AUTION
Ensure that the engine cooling
water pick up is not directly
ahead of the Jet Unit Intake, but
well to the side to avoid turbulent
water flow into the Jet.