If you plan to switch between prop and jet, depending on water conditions, winter, summer, etc., purchase a second cooling water pump so that each, the prop and jet drive, have one installed and you don’t have to transfer the pump back and forth. What?...now you want constant displacement? To further define the term jet drive, there are basically two types: an outboard jet drive and an inboard jet drive. In addition to fuel, the aircraft have lower charter, insurance, and maintenance costs thanks to more reliable engines and fewer moving parts. And with electronic multi-point fuel injection, you get lots of responsive power with fuel-sipping efficiency. Jet boats are not problematic to run compared to prop and you can decide to buy an inboard jet or outboard jet. It's really pretty simple. The logic for airlines is that a jet engine can fly a plane faster between destinations, and thus the aircraft will burn around the same as a slower prop plane. An outboard jet is simply a standard outboard with an aftermarket jet pump bolted to where the prop unit sits. Each time the jet disengages, the prop is left scrambling to regain its depleted energy, and the jet is maneuvering to prevent the prop from ever being able to fully recover. 2021 Reflex Reefrunner. A good example of this is the recoil felt on the shoulder when firing a rifle, or the thrust felt when holding a powerful firehose. ), Brake power required for Water jet propulsion, Converting Yamaha Traditional Prop to Jet Drive. This means that regional airports that might not even have a concrete runway (especially in developing areas of the world), are perfectly safe to land on with a turboprop. Multiple engines are normally used to get higher speeds maneuverability and have redundant systems. This begs the question about efficiency. Be in the know. Large interior space: It has a large amount of space in the cockpit. 2) The v-drive must overdrive the gear ratio, while spinning a relatively small diameter prop (due to prop being under the boat) with a typical 15 pitch. A modern turboprop engine produces incredible power to weight compared to earlier era engines, while staying exceptionally light. Also, because the jet drive impeller is contained within the pump, there’s no propeller to pose a danger when swimming around the transom of the boat. I looked at the diagram (I had seen it before, too), and I still don't know why efficiency and speed aren't related. Propellers and piston engines are getting quieter and even more efficient. Why so? More complicated and heavier than turbojet. Ok, now the jet boat has twice the range or carrying capacity, which makes it the better choice as the propboat cannot meet the transport capacity needed. Mercury Introduces V12 600hp Outboard. This topic can be as deep as an ocean, and to approach it in the simplest way possible, we will need to avoid any in-depth technical knowledge that might be beyond those without aerospace engineering degrees. Because it extends below the keel of the boat, the outdrive and its propeller are susceptible to damage if they impact the bottom or an obstruction in the water, like a rock or tree stump lurking just below the surface. Vospower PP100 Jet + 300HP in 7.5 m RIB - a reasonable combination. 2021 Jeanneau Leader 12.5 WA. Fuel efficiency, on the other hand, would again be directly related to the drive efficiency multiplied by the engine efficiency. If we go back to my V-drive vs. Jet example, according to the diagram, the V-drive should be slower, because the conventional propeller prop efficiency shows a sharp decline after 20 knots, and crossing over with the jet drive at 50 knots. Because of their unusual-ness in the broader aviation world, many pusher designs are relatively famous. http://www.boatdesign.net/forums/showthread.php?t=17003, http://www.ultradynamics.com/sections/educational/why.asp, http://www.ultradynamics.com/sections/control/index.aspoffer, http://boatdesign.net/forums/showthread.php?t=11254, http://www.yachtforums.com/forums/technical-discussion/4470-jet-drive-vs-prop.html, (You must log in or sign up to reply here. A waterjet is essentially a pump inside a very short pipe. A turboprop engine has a propeller that you would find on the first aircraft; however, the similarities to those piston engines end there. I also question that diagram, or perhaps I'm not reading it correctly. On longer journies, the jet engine becomes more fuel-efficient, which added to the speed, makes the aircraft desirable. Turboprop: Efficiency . Pumps work differently than propellers; they don’t show the same limits. The prop issue doesn't worry me so much as my daughter has been on a prop boat her whole life and knows the rules. The safety and space savings of the jet … Let’s examine. I would certainly like to know where this data was derived, because it doesn't seem to apply to small high performance boats. The performance of a 360hp prop boat over jet is quite the difference too. Journalist - Working in news media for over a decade with outlets including 9News and the Discovery Channel, Nick is an airline marketing specialist with a Masters level education. Honda Marine Introduces Three New Jet-Drive Outboard Models. The propeller in front of the engine becomes less efficient with faster-moving air. Other examples include: Burt Rutan’s Long EZ and its variants, the Convair B36, the Cessna 337 (a push-pull configuration), the Velocity family of homebuilts, a wide variety of military unmanned aircraft, and perhaps the strangest looking of the bunch… Why would the prop need nearly twice the torque to so the same job? While piston engines have distinct divisions between the four engine cycles, turboprops seemingly blur the line between each. the jet aircraft syndrome). We will never see a propeller driven aircraft fly as fast or fly as high as a jet. Fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts. This engine is able to develop very high thrust at low air speeds because the propeller can accelerate large quantities of air at zero forward velocity of the airplane. Air is drawn into the intake and compressed by the compressor. The most interesting comparison is that between the outboard jet and the propeller. Please Support us by turning off your adblocker. That being said, the first big (and obvious) difference between the two engines is the traditional propellor. Other pod drive models push the boat in traditional fashion, with propellers mounted behind the drive shaft unit. Well, part of it is that turboprops are less efficient at higher speeds and higher altitudes, and jets are more efficient at both (obviously to a point, but airliners don't fly fast or high enough to decrease their efficiency again). 1. Discussion in 'Jet Drives' started by Michael1, Oct 6, 2007. Smaller, lighter, cheaper jet engines continue to be developed. jet drive crafts will run in less than 6 inches of water. Sign up to our daily aviation news digest. How a Waterjet Works A waterjet generates propulsive thrust from the reaction created when water is forced in a rearward direction. Turboprop engines fly at speeds 20 to 30% lower than that of turbojets in the same category. This makes them excellent for short-range flight. Also, while the jet's appendage drag is less, since no gear case is being dragged through the water, this may result in increased wetted surface of the hull, since it offers no ability to trim the boat. Thus a turboprop engine is the engine of choice for smaller and light aircraft where fuel capacity and profitability is more limited. What more speed with a jet drive? What exactly is the difference, and which is the better engine choice for aircraft? The efficiency of a jet is far poorer than a prop. 2. More of the engine horsepower is going towards moving the boat, and less toward heating water. Based in Sydney, Australia. The turboprop uses the power of a jet engine to turn a propeller. Jet Boat Options: Jet Drive or Sterndrive . By having more efficient engines, an airline can fly a more extended range and utilize more of its fleet for destinations. A turboprop engine is a turbine engine that drives an aircraft propeller.. 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