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FAQ's
INTRODUCTION TO JET DRIVES
| Inboard jet pumps come in
different sizes to match up correctly with boater needs and the
motor selected. Pumps are designed as single stage, two stage and
three stage (the number of impellers determines how many
"stages" in a pump). (Click image to enlarge) |
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Outboard
jets are an extremely popular power choice for jet boats,
particularly those in the 14-20 foot range. Major outboard
manufacturers offer outboard jet motors as standard issue now.
During the early years they were created by simply replacing the
propeller gear case with a jet drive. (Click image to enlarge) |
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Principles of Operation
The jet drive should have been installed in
your boat with a correct impeller to match the engine supplied with the
jet drive. There is no requirement to change this impeller in an
effort to increase out of the hole thrust or obtain better top speed.
Your jet drive is easy to maintain.
There are few parts in a jet drive. The direct-drive shaft has a
thrust and tail bearing. The impeller is fixed to the shaft and
completely enclosed. The intake grate screens out most trash...but
if tough weeds, string or a small rope pass the grate, and remain in the
impeller, these are easily removed through a hand hole which is normally
covered.
With no gears and so few parts, overhaul of
a jet drive may not be necessary for several years, or hundreds of hours
of use. Parts are largely interchangeable and readily available.
Access is simple and there's a minimum of downtime.
The engine is a heavy-duty automotive type,
expertly modified for marine use. Maintenance is much the same as
you would expect with a car.
Jet Drives compare favorably with other
types of propulsion on fuel consumption. Any engine uses excessive
gas when pushed toward maximum RPM. At skiing speed a large V-8 can
compare very favorably on fuel costs for a day of cruising, skiing or
picnicking.
With RPM reduced to 70% of maximum, fuel
needed is reduced to only 32% of maximum, while speed is maintained at 66%
of maximum.
Thus at two-thirds full speed, fuel use is
cut to less than one-third, resulting in twice as many miles traveled per
gallon. Since jets use ordinary automotive grade gasoline without
expensive mixing with oil, by seldom exceeding 50 MPH you can have a day's
fun for little, if any, greater cost than running a smaller I/O or
outboard.
A jet handles quite differently than the
traditional prop and rudder. What makes a jet different, makes it
better! It doesn't depend upon hull movement to attain full power.
A prop unloads as forward speed is attained, which lets the engine rev to
full power that is only available at full boat speed. With a jet,
you hit the throttle and take off tight now, with full power. When
you reverse a jet drive, you reverse it right now, with full power.
When you turn, the jet, plus the rudder, you swing around in a super tight
circle.
You can move a jet boat sideways into tight
docking situations by switching from forward to reverse while coordinating
steering.
This is not unsafe. Without
underwater appendages, your jet drive propelled boat will immediately
return to a straight line and coast to a stop if the power is cut quickly.
Use of a rudder is recommended if you want to have more control, even
under power off or low thrust conditions. You will learn to keep a
little throttle on when slowing from high speed so you always have a power
steering thrust force available.
"At Whitewater Marine we are fully
versed in the operation of Jet Drive as well as the operation of the
conventional Stern Jet Outboards. We can help you get the the maximum
performance out of which ever drive system you choose!"
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