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).
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.
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!”