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Features of a jet
driven - advantages and disadvantages
Boat Articles, Guides, Commentary and archival articles & helpful information
Features of a jet-driven
Boats propelled by a jet drive unit are famous for their instant responsiveness and maneuverability, A beginner should operate the boat at a low speed until the operator feels comfortable and is aware of its limitations and response to movement of the wheel. One of the unexpected features of a jet driven boat is the ability to turn the boat without any "way on" (forward motion). With only a limited amount of practice, the boat may be turned through ISO degrees within its own length; backed into a limited space against the wind; and even "walked" sideways into a tight berth. This "sideway" movement is accomplished by giving the throttle short bursts for increased rpm, while shifting from forward to reverse and coordinating the steering at the same time.
It is not necessary for a jet drive boat to be moving in order to achieve its full thrust potential. A jet drive boat can develop full drawbar thrust even if the boat is anchored or secured. The boat is able to pick up water skiers as quickly as the individual's skill and strength will permit. If a ski line remains out while retrieving a downed skier, do not attempt to maneuver the boat in reverse with the gate down. The ski line may pass under the boat and enter the suction piece.
Shallow Water Operation
Under normal conditions, a jet drive boat may be operated in waters approximately one foot shallower than a propeller driven boat. Actually, it is possible to maneuver the boat directly onto a slopping beach. A rock gate is available as an accessory by most manufacturers to prevent the ingestion of rock and small pebbles, If the boat is to be operating continuously in shallow waters.
Caution must be exercised when moving the boat off a beach to avoid sucking in mud, sand, pebbles, or rocks through the intake. Such ingestion could cause damage to the impeller, the vanes in the pump bowl, or clog engine cooling passages. The engine cooling passages must be flushed with clear water on a regular basis. This is accomplished by simply opening the drain valves on the engine block and connecting a garden hose to the thermostat housing. Such an easy maintenance practice should become a habit and will prevent accumulation of debris which could restrict engine coolant water flow and cause overheating. On a jet drive installation, an accurate engine temp era tue gauge is an essential early warning device.
Almost all jet drives are equipped with a hand hole cover to gain access to the bowl and impeller. This opening may be inside or outside the boat, depending on the manufacturer, The opening permits quick and easy removal of weeds or other floating debris ingested through the suction piece opening. If the hand hole cover is located INSIDE the boat the cover may be below the water line. Therefore the cover should only be removed when the boat is on the beach or out of the water. A hand hole opening extension may be purchased from some manufacturers to permit removal of the cover while the boat is in the water. Carry about a foot of stiff wire aboard for use in probing into the impeller to dislodge debris where fingers cannot reach.
Some manufacturers offer a hand hole extension, at modest cost, as an accessory to raise the cover above the water line. If the hand hole cover Is on the outboard side of the transom, the cover may be removed and the bowl and impeller cleaned while the boat is in the water.
The nozzle or deflectors are moveable to port and starboard. Therefore, unlike a propeller driven boat, the boat does not have to move through the water in order to have "steerage way". A steering cable connects the helmsperson's wheel to a tiller arm mounted on the nozzle housing. When the wheel is rotated clockwise, the nozzle or deflectors will move starboard directing the ejected water in that direction the stern moves to port - and the bow to starboard the desired new courses Naturally when the wheel is rotated counterclock- wise, the opposite is true and the bow moves to port. With the engine operating and water being ejected from the nozzle, the stern of the boat may be moved to port or starboard with the boat making little or no forward motion. Imagine the maneuverability pos- sible in tight places. Actually the boat may reverse direction entirely through 180 in its own length. It is also possible to move the boat sternward into a limited space against the wind or even "walked" sideways into a confined berth.
Gate As mentioned earlier, a gate referred to as a "reverse gate", a "deflector gate", a "reverse bucket" and other terms, is installed in such a manner to swing down over the sischarge nozzle. The gate is controlled with a cable or hydraulic system from the helmsperson's position. When the gate is in the fully raised position, the boat is said to be in FOR- WARD, allowing all water from the nozzle to be discharged sternward the boat moves forward. When the gate is swung down just part way, some of the discharged water moves sternward and the other portion of water is deflected downward and forward under the boat. Positioning the gate in such a manner places the jet drive in a NEUTRAL condition, because the water moving aft equals the water moving forward and the boat is static. jet boat book