Water Offtake; Conventional Water Pickup - Hamilton Jet HJ212 Installation And Service Manual

Installation and Service Manual
Hull deadrise angle
0°
5°
10°
15°
20°
25°
30°

Water Offtake

The jet unit is fitted with a water offtake which may be used as a supplementary water supply (e.g. for deck
wash).
If used as part of the engine cooling circuit, the designer / builder must satisfy
themselves that the available flow is sufficient for the cooling requirements.
To fit a hose to the water offtake, cut the bung from the end of the connection.
The water offtake provides water at approximately 7kPa (1psi) at 600rpm and 550kPa (80psi) at
approximately 4000rpm.
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 unit water offtake can be used for a deck cleaning hose but the pressure is not high enough to be
used for a fire hose.
If a gearbox or clutch is fitted to the engine, a conventional hull water pick-up and
engine raw water pump must be used.
Make sure 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 unit.

Conventional Water Pickup

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: 112110 Sandtrap.
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.
Mainshaft angle relative to keel
B1 (shaft angle in plan view)
0.0°
0.4°
0.9°
1.3°
1.7°
2.1°
2.5°
B2 (shaft slope in elevation)
5.0°
5.0°
4.9°
4.8°
4.7°
4.5°
4.3°
3-9
Design Basics