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Jet Yachts...

Discussion in 'Popular Yacht Topics' started by alloyed2sea, Sep 8, 2004.

  1. tantetruus

    tantetruus New Member

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    Do variable gullets exist?

    What about dirt like seaweed etc?

    Wouldnt it be more logical to "connect" the gullets directly to the waterjet?
    I might imagine that when the bow ries with speed, the waterjet has to be trimmed accordingly since otherwise it would be pointing down instead of at the back. Also, in forementioned situation, the gullet in the hull might rise so much with the hull that waterintake might be at risk.

    When connected to the waterjet the latter problem wouldnt occur?
  2. YachtForums

    YachtForums Publisher/Admin

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    Not really, although it is possible to mechanically reduce the volumetric area of the cavity without having having an adverse effect on laminar flow. I've done a considerable amount of analysis in this area and it yields great improvements in efficiency, but the mechanical means of altering the gullet would not prove economically viable. This is best left to specially built craft with unlimited research budgets, such as the Navy. ;)

    This is one of the reasons that pump designs are kept relatively simple. The less moving parts, the less chance for debris corrupting the same. Pump housings, specifically stators, can become contaminated with debris, but no more than any other appendage on a hull, i.e. props, rudders, shaft struts, etc. For the most part, because jetpumps are recessed up inside the hull, they are less prone to picking up debris, such as seaweed, lines, etc.

    The intake gullet IS connected to the jet pump. It is the "housing" that channels water to the entrance of a pump. Or from another persepctive, it is the housing the impeller "draws" water from.

    I think I understand what you're describing. Yes, if the bow is rising, the expulsion orifice of the pump (assuming it is fixed; in a neutral position) would be pointing down. This is actually benefical, because this induces negative trim into the bow, helping the boat to come on-plane. Ultimately, a jet pump should have the ability to induce negative or positive trim, in the form of a trimmable nozzle or thrust deflectors. This is a more effective way of adding trim into a hull, as opposed to trim tabs, which must have sufficient speed (read: water pressure and lift) to effect trim changes.

    On your second question... yes, hull lift can effect the performance (efficiency) of a jet pump. Large yachts generally don't have to contend with this, as they run with so much wetted surface and have so much weight, they are not prone to exiting the water at higher speeds. Smaller and lighter craft are much more susceptable to the problem of ventilation. This is when a boat achieves sufficient speed that the hull exits the water in rough, varying water conditions. At this point, the intake gullet is prone to ventilation, or "breaking" vacuum. Without vacuum, the pump can not draw water into the intake gullet and thus ventilation occurs. The result is a loss of efficiency and a loss of speed.

    One of the benefits of jet pumps and the vacuum they create is "artificial weight". Because the intake vacuum (remember; negative pressure) is pulling down on the hull, it not only helps to keep the hull planted in the water, it can provide a better ride in varying conditions because this simulates increased weight.
  3. YachtForums

    YachtForums Publisher/Admin

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    The NEW “Adler”...

    Some of you might remember a 116’ Baglietto of the same name, well.. this is the successor to the throne.

    "Adler", which means Eagle in German, was designed by Gary Grant (see link).

    http://www.amsgrant.com/files/ams01.html

    Designed in 1999, but only recently finished, it is 136' in length and is reportedly seeking the 50 knot threshold, using a pair of Paxman 18-cylinder diesels driving KaMaWe waterjets.

    The owner, an experienced yachtsman who didn't want to use an established yard to build the boat, took a hands-on approach to developing the boat. He wanted a super-clean profile, which meant virtually all of the boat’s deck-fitted equipment, including the radar antenna, personal watercraft, tender, horns, spotlights, and even the satellite domes, were to be hidden from view.

    This yacht is TRULY a one-off custom. Plugs for the mold were CNC machined and the hull was laid up in a combination of fiberglass and carbon fiber. Everything from the materials utilized to the labor contracted was specifically chosen to bring about a state of the art yacht. Word is, he hired the best-of-the-best to build and finish the yacht and much of the fitting and finishing work took place at Lauderdale Marina. Looks like a remarkable job...

    These pictures were taken in April, while Adler was docked at the Hall of Fame Marina in Ft. Lauderdale. I'm told the boat is currently under-going sea trials.

    Attached Files:

  4. tantetruus

    tantetruus New Member

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    Incredibly complicated ánd interesting stuff!

    This changes my view on Seadoo's forever. :D
  5. Codger

    Codger YF Wisdom Dept.

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    There was a variable intake for waterjets in development during the mid 90s. All that I saw of it was a paper-napkin drawing during a conversation that I probably shouldn't have been having. Looked like a NACA duct with a flush spring loaded slider. As speed increased the plate moved aft and reduced the opening size. There was a drag vane inside the throat that was part of the actuator mechanism. Sorry, that's all that I recall about it.
  6. YachtForums

    YachtForums Publisher/Admin

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    Yes, I'm familiar with the system. In the end, we developed an inner liner that was positioned on the top of the gullet (and only the top). It used a soft durameter plastic that was flexible enough to pull away from its seated housing as vacuum increased, creating a bubble shape. Because pumps run fully loaded at idle to medium speeds, the pressure of the water kept the "skin" pressed firmly into its housing.

    As speed increases sufficiently, water can not make the abrupt turn into the intake gullet as quickly as it can at slower speeds. The result is, a negative pressure air pocket is formed on the top of the intake cavity. This negative pressure zone pulled the skin away from its seated position, thus reducing the volumetric area of the intake cavity, which ultimately increases vacuum and therefore efficiency at higher speeds. The beauty of the system was... no moving parts. :)
  7. YachtForums

    YachtForums Publisher/Admin

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    On the subject of intake gullets, which are only one aspect of jet-pump integration and configuration, I should expand on the venturi...

    Of all the components that make up a jet pump, the venturi is by far the most critical component in dimension, shape and size. It is the final stage of acceleration that water will receive prior to expulsion. The venturi, for those of you not familiar, is the shroud located just after the stator blades (directing vanes) and the part of the jet pump that the steering nozzle or thrust deflectors are most commonly connected to.

    The exiting size of the venturi's orifice is generally half the size of the dimensional area of the intake gullet footprint, or a 2-to-1 reduction. Quite simply, the venturi is a reducer or compressor, and in the case of water, which can not be compressed, it is an accelerator. As I've said, venturi's function on the principal that a reduction in size of a flow path will cause water to accelerate if the same volume is to be realized at the other end of the reduction. The venturi is one of the most important links or stages in jet pump design. Without it, the jet pump as we know it... would be rendered benign.

    By increasing or decreasing the size of the venturi's exiting orifice, where the water is expelled, you can effectively control backpressure, velocity and the intensity of the exiting thrust. Each are inter-connected and controlled via the inner bowl camber (rate of compression), entrance and orifice dimension, and time of reduction (travel).

    Increasing the venturi's expulsion size will decrease backpressure, and allow water to be processed more rapidly, thus moving the hull (mass) forward at a faster rate due to more available thrust, but sacrifices top speed because of reduced compression. Decreasing the venturi's expulsion size will create more backpressure, which results in less water being processed, but increases the velocity at which it exits. This results in higher speeds, but does not give the mass of water necessary for greater acceleration. Venturi designs are usually a compromise to give maximum acceleration and top speed.

    The real reason that an adjustable venturi is necessary and holds so much value is that because pumps do not run fully loaded at higher speeds. They ventilate, thus inducing air into the equation. Because the amount of water available for compression at higher speeds is reduced, due to the introduction of air, there is less water density available for thrust. By reducing orifice size, density is enhanced, thus speed is increased. This technology is really not new. The original inception, whose origins date back to the Messerschmitt 262 and the "movable onion", were the forerunners to afterburning turbo-jets. Because flow-is-flow, whether it be water or air, some theories cross-platform. The only difference is air can be compressed and water can not. Oh yeah, one is quite a bit denser than the other too.

    In early 1984, our research team began conceptualizing and theorizing the potential of an adjustable venturi and later developed the V.G.V. (variable geometry venturi) This unit operated on the principles mentioned above but utilized hydraulics to control orifice diameter, which was necessary given the huge amounts of thrust created on the research vehicles we developed. In 1987, a very unique material was made available, current regulated (electrical stimuli), that lined the inner walls of a venturi (or bowl) and controlled exact camber and orifice dimension. This material has future applications i.e., artificial limbs, robotics, etc. Unfortunately, it is under regulation for now and there is no access to it.

    Controlling rate of compression realized significant performance and efficiency gains. This is one of the most important aspects of venturi design. By shortening the length of the venturi and increasing the rate of compression (along with a larger exiting orifice) it would generate increases in mass velocity. And sub-sequently, increasing the length of the venturi and reducing the rate of compression (along with a smaller orifice) would yield increases in speed, primarily due to reduced drag and increasing the density of flow available. Inner wall flex and fluctuation is critical as well. The reason that I mention flex is because it is conceivable to utilize a material with built in flex to accomplish some desirable characteristics.

    Other aspects of venturi design are critical as well. Orifice length is an example. By elongating the orifice, you can effectively "true" the trajectory of water, similar to the difference between the accuracy of a pistol and a rifle. By "truing", I'm referring to the explosion that water experiences during rapid collision within the bowl. This results in a very diffused spray pattern exiting the venturi. Elongating the exit will give water a chance to "compose" itself and thus travel in a true path resulting in tighter expulsed trajectory.

    One of our first VGV’s was an adjustable venturi that utilized inner bowl “feathers” actuated by an aperture that closes concentrically. While it was mechanically a very cool-looking contraption, much like the afterburning tail-feathers on a fighter jet, it was hydrodynamically incorrect. The reason is simple, while it reduced orifice size it also increased the rate of compression while failing to control trajectory. Properly configured and controlled, the device had great merit.

    Original design's of Bernoulli's work (remember your physics) and the principals behind a venturi are still applicable today. If you are familiar with his work and you happen to be familiar with the development of the SR-71 BlackBird (Lockheed), you have witnessed the future of venturi optimization. God Bless Kelly Johnson, he was so far ahead of his time.

    A properly designed venturi can yield significant acceleration gains and top speed gains. A really good design will become exponentially more efficient with speed. In other words, the faster you go.. the more efficient it becomes! Venturis work on thrust and pressure. Wherever you have thrust you have the potential to create vacuum. Wherever you have pressure, you have energy. And in the case of venturis, that pressure can control a multitude of variables… and this entire process can be executed with NO MOVING PARTS! ;)
  8. tantetruus

    tantetruus New Member

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    2xHeesen

    Of course everybody remembers Octopussy (39,4 mtr.) by heesen which Heesen's site claims 53 knots (not bad considering 1988...)
    But they also produced Bonita (36,8 mtr.) at also 53 knots (1995 this time).
    Both used Kawema's.
    Of course, the Adler is longer (41.45 mtr.) but given the age difference...
  9. YachtForums

    YachtForums Publisher/Admin

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    Good additions Tantetruus!

    In keeping within Alloyed2Sea's original guidelines, (100+ feet and 30+ knots) we should probably include Pershing's 115' Silver Bullet...

    Twin MTU 16V 4000 M90 for power, producing 3700 hp. With the optional 2720 Kw gas turbine driving a center mounted waterjet, you have 115' of pure luxury producing a 55 knot top speed. (48 knot cruise)

    There's a full review located here...

    http://www.yachtforums.com/forums/showthread.php?t=2582

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  10. tantetruus

    tantetruus New Member

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    ok, in that case...;

    The Wally 118; cruising at 60 knots... (eh, thats according to wally of course..)

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  11. JonS

    JonS Senior Member

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    Everytime i see Adler I can't help but stare! It is a beautiful craft, one of the most eyecatching yachts in recent years.

    Also included in that bracket are the two above.. 115 Pershing and 118 Wallypower, also consider Baglietto 115 [hull number 10192] seen below.

    I did a lot of work in my last year of uni working on perceptual length and using subtle curves and straight lines to extend the visual length of a boat. All be it, i was working on a 37 footer, but these craft were the inspiration behind such ideas. Beautiful. :)

    Also attached below for reference is the original Adler from 1987 that Carl mentioned on the previous page.

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  12. YachtForums

    YachtForums Publisher/Admin

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    Found an interesting page listing over 60 yachts that range in speed from 30 knots to 60+ knots... and most of them are over 100 feet in length! :cool:

    [Click Here]
  13. alloyed2sea

    alloyed2sea Moderator

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    Secret knowledge = secret power

    Hey!
    Thatz my super secret source of internet information.
    Not a bad guide, eh?
  14. superyachtie

    superyachtie New Member

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    Sunseeker Preditor 108' @ 42knots

    Triple Arneson surface drives

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  15. Steven H

    Steven H New Member

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    Anyone knows if this one got past the studfy/concept phase or is in a "design-ready-waiting-for-owner-with-deep-pockets" state ?

    http://www.amsgrant.com/files/ams18.html

    Some interesting features actually on that one. I just wonder what the function of the tower is other then "watch-the-world-fly-by-at-80knts". Maybe a remote helmstation since at that speed extra long-range visibility is desirable...
  16. Ben

    Ben Senior Member

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    About Ecstasea....

    "At the heart of Ecstaseas awesome propulsion package are four MTU 16 V4000 M70 engines, two per side. Each pair of diesels is connected on a single shaft to Wrtsilla 4-blade controlled pitch propellers, some 2.6 meters in diameter and weighing 3,200 kg each. A Maag custom-made gearbox allows the captain to switch between engines at will, depending on the load required.

    Booster power is provided by a GE-LM 2500 turbine: geared to an eleven-to-one double-planetary gearbox (again custom-made by Maag), this offers a staggering. 30,843 hp at 3600 rpm. The turbine comes out in a carbon fiber shaft 7.7 meters long and 0.7 meters in diameter, which drives the Lips LJ210E water jet. Some 2.10 meters in diameter, the jet pipe is the largest in the world and pumps no less than 50 m of water per second. To compare, this is roughly three times the volume flow into the River Rhine as it enters the Netherlands. The total length of Ecstaseas drive train is 26.5 meters. The overall result is a maximum speeds of just over 33 knots."