Pros and cons of stress overload

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Pros and cons of stress overload

I have the same thoughs as Wildone: Poor efficiency, poor handling, but good for shallow running.


When you say "stop on a dime" do you mean by spinning out like jet skis? I doubt that would work on a normal sized vessel. I just found this article from Yachting Magazine that confirms what I have been told about efficiency, handling and the ability for even a large boat to reverse thrust and stop quickly.

Going Propless Water-jet drives, long a curiosity, are now turning up on almost everything. By Chuch Husick Published: Today's water jets are the end result of developments that date back to the first century B.

William Hamilton later, Sir Hamilton developed the modern water jet in New Zealand in the early s by modifying an American invention, the Hanely water jet, relocating the jet nozzle so that the stream of fast-moving water was expelled above the waterline, thereby eliminating all drag-inducing underwater appendages.

Pros and cons of stress overload

A water-jet drive provides a number of advantages when compared with the conventional screw propeller. The absence of propellers, prop shafts, support brackets and rudders reduces drag, making jet drives particularly efficient at medium and high planing speeds.

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Since the drive train can be contained entirely within the hull, a jet-drive boat can, when necessary, operate in water only a few inches deep. The water jet's ability to propel a hull without an exposed propeller is what makes the PWC practical and can be a significant safety factor for people swimming near a boat, as well as for marine life.

Jet drives steer the boat with vectored aimed thrust, providing unmatched maneuverability, including the ability to precisely hold a boat in a fixed position against the effects of current and wind.

The jet drive avoids the asymmetric thrust produced by propellers mounted on inclined shafts.

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The vectored thrust capability of a jet drive also provides efficient astern thrust typically 60 percent of forward thrust and instantly available reverse thrust for very rapid braking at any speed. The load imposed on the driving engine does not vary with boat speed or wave impact, protecting the engine from possible overspeed or overload.

In high-speed applications jet drives can be quieter and smoother than propellers. Today's yacht may depend entirely on water-jet propulsion or it may use a conventional propeller drive with a jet providing an auxiliary power source for high-speed dash operation.

One of the notable examples of this application was seen in the yacht Fortuna, built by Palmer Johnson for King Juan Carlos of Spain in Twin diesel-driven props were augmented by a gas turbine-powered water jet to propel this foot yacht to more than 50 knots.

In such installations the jet nozzle is fixed in position to deliver forward thrust. Water jets intended for use over the entire speed range of the vessel are fitted with steerable discharge nozzles and flow diverters to provide the vectored thrust needed for maneuvering.

Some yachts are propelled by three jet drives, the two outboard units equipped with thrust vector control for steering, and the center fixed jet used when maximum speed is required. Water jets are manufactured using a variety of structural materials, including aluminum, stainless steel and composites to match the wide variety of environments in which they are used.

Pros and cons of stress overload

In a typical installation most of the jet-drive nozzle is aft of the vessel's transom, allowing the engines to be placed far aft, which further reduces the intrusion of the power plant on the accommodation. In relatively low-power installations the jet's pump may be directly coupled to the engine, with the flow diverters used to provide neutral thrust when the boat is stationary.

However, this method has the disadvantage of churning up the water around the boat and, depending on water depth, the seabed.

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Jet-drive power ranges extend from well under hp to the 33, hp GE gas turbine-powered Lips water jet made by Wartsila, which also buildshp diesel engines installed in the foot yacht Ecstasea. KaMeWa, a part of Rolls-Royce turbine engines, not carsoffers jets with power ratings up to 50 megawatts 67, hp.

Water-jet-drive systems require the same careful application analysis and testing as a conventional prop system. Critical evaluation areas include design cruise speed, matching the drive to the shape of the hull, and maneuverability requirements.Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement.

Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component [1].

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