[Donald Blount]

Fortuna (41.5 m) this year, after five years in service, exceeded 70 knots (85+ MPH) during sea trials which is the reported design speed/bench mark condition for The World Is Not Enough as a finely finished yacht. I remain interested in the technical progress and challenges others, such as The World Is Not Enough, are attempting to extend the performance boundaries for high-speed, seaworthy motor yachts.

[tantetruus]

I wonder why a jetengine almost automatically implies a waterjet..
Given the problems you described with the vacuum and the extreme position of the flaps i might have thought that something like arneson drives would have been more logical.

Has there ever been an attempt to use both diesel engines ánd jetengines to produce electricity and let the electricity drive for example the arneson drives?
This option is used in dieselelectric trains to avoid transmission problems...

[YachtForums]

Originally Posted by tantetruus

I wonder why a jetengine almost automatically implies a waterjet...

It usually doesn't, except in the case of some yachts, where speed is a primary consideration. Turbines generate a favorable amount of power for their size and weight. They also produce excellent torque, which jetpumps demand, as the venturi increases backpressure against the impeller prior to expulsion. Jet pumps work on the principle of accelerated flow, or the Venturi effect. The venturi reduces the volumetric area in which water can pass. Because water can not be compressed, water must accelerate in order to pass the same amount of volume through the expulsion orifice.

Originally Posted by tantetruus

Given the problems you described with the vacuum and the extreme position of the flaps i might have thought that something like arneson drives would have been more logical.

This is a subject better discussed privately (as we have). Certainly, surface piercing drives are an option, but they slightly increase draft over a jet-pump application. One of the protocols for the M-140 was operating in the shallow waters of the Caribbean and keeping draft to a minimum. Typically, surface piercing drives don't offer the low-speed maneuverability that would be favorable for handling a yacht of this size. Because of their "surfacing" nature, these drives are not deployed as deeply as conventional shaft driven props and are less efficient for achieving plane. Once on plane, surface drives can offer reduced drag and increased RPM's, as the prop is not running completely submerged. Surface drives are best left to high speed apllications, which is not normally associated with "yachts" (atleast luxury yachts), where the majority of time is spent idling, cruising or maneuvering. For most yachts, they don't achieve on-plane speeds that would truly benefit from surface drives.

Originally Posted by tantetruus

Has there ever been an attempt to use both diesel engines ánd jetengines to produce electricity and let the electricity drive for example the arneson drives? This option is used in dieselelectric trains to avoid transmission problems...

Lurssen's new "Air" is using this platform, diesel electric power connected to Pod Drives. But this is not new, large cruise ships and freightors have adapted this technology in recent years. We'll have a full feature on Air in the coming weeks.

As for using diesel generators, driving electric motors that are connected to surface drives... I don't recall this ever being done before. I would imagine the power demands would make this prohibitive for any length of time. Further... in the quest for increased speed, weight is a primary consideration. This sounds heavy.

[tantetruus]

The inner workings of these technics are kinda virgin territory for me (bloody obvious from my questions)) but fascinating nevertheless.

Another part of waterjets i dont know is how the waterintake works?

[YachtForums]

Originally Posted by tantetruus

The inner workings of these technics are kinda virgin territory for me (bloody obvious from my questions)) but fascinating nevertheless. Another part of waterjets i dont know is how the waterintake works?

Let me begin with some jet-pump fundamentals...

To better understand how the intake gullet works, we need to take a closer look at the jet-pump and the impeller. The impeller itself will only scatter water, and is highly inefficient. But, when placed within a "shrouded" environment, it becomes a ducted propeller. This shrouded configuration produces greater efficiency than its open, non-shrouded counterpart. The reason is simple. The duct controls water and forces it backwards as opposed to a propeller which allows water to slip outwards.

Impellers (and jet-pumps) work on the principal of positive and negative pressure, or a push/pull concept. As a blade rotates, it pushes water back (and outwards due to centrifugal and accelerated force). At the same time, water must rush in to fill the space left behind the blade. This results in a pressure differential between the two sides of the blade: a positive pressure, or pushing effect on the blade face and a negative pressure, or pulling effect, on the backside of the blade. This action occurs on all the blades around the full circle of rotation.

Thrust is created by water being drawn into the impeller and accelerated out the back. However, due to the spiraling effect (vortex) of water leaving the trailing edge of the blade it must pass through stators (straightening vanes) to "true" its trajectory. Stators also increase velocity by "catapulting" water, similar to the way a "kick" works on the trailing edge of a propeller blade. To further enhance velocity, water passes through the venturi before finally exiting the pump as thrust. As we discussed earlier, the venturi works on the principle that a restriction or reduction in line size will cause water to accelerate if the same volume is to be realized at the other end of the restriction. This is where you get the "jet" in pumps. Finally, a steering nozzle is used to vector or deflect thrust for yaw direction.

Impeller design and efficiency is strongly linked to the other components that make up the jet-pump, i.e., the intake gullet, its volumetric area, the laminar transition of the intake housing, stator blade area (including angle of trajectory), venturi rate of compression, venturi "bowl" area, exiting orifice dimension, mass and weight of the hull, and pump placement or depth within the same.

The intake gullet is the recessed area within the hull leading up to the entrance of the jet pump. This area plays a vital role in jet pump efficiency. There are a multitude of factors that determine its length, size, shape and depth. Much of this has to do with the operational parameters the vessel was designed for, such as hull speed and displacement.

For instance, a larger vessel with greater displacement may choose an intake gullet design with a more gradual rake leading up to the jet pump entrance. This maximizes the amount of water available for acceleration. In this scenario, intake gullet vacuum is not as critical because the weight of the hull (and the depth of the pump) will keep the intake cavity primed. In contrast, a light, high speed hull that rides closer to the water's surface, may use an intake gullet with a more aggressive rake and a reduced intake gullet area. This decrease in cavity size, increases the vacuum (or negative pressure zone) at the intake, which helps reduce ventilation brought on by a higher speed planing hulls that operate near the water's surface.

Several variables effect water flow to the pump, including the speed and density of the impacting water due to the forward motion of the hull when underway, and the amount of negative pressure created by the intake housing under operation, which is directly relevant impeller pitch, rpm, and blade area.

Ultimately, the best intake gullet design would be variable in size. In other words... larger for acceleration and smaller for high speed operation, to maximize intake vacuum when aeration is present.

There are a myriad of other factors to consider as well. In the end, it depends largely on the application.

[tantetruus]

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?

[YachtForums]

Originally Posted by tantetruus

Do variable gullets exist?

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.

Originally Posted by tantetruus

What about dirt like seaweed etc?

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.

Originally Posted by tantetruus

Wouldnt it be more logical to "connect" the gullets directly to the waterjet?

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.

Originally Posted by tantetruus

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.

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.

[YachtForums]

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.

[tantetruus]

Incredibly complicated ánd interesting stuff!

This changes my view on Seadoo's forever.

[Codger]

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.

[YachtForums]

Originally Posted by Codger

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.

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.

[YachtForums]

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!

[tantetruus]

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...

[YachtForums]

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

[tantetruus]

ok, in that case...;

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