Information about PWC's & Outboard Engines needed...

TSI AV · Feb 9, 2008

Hello everyone.

I'm looking for technical information abt wave runners and outboard engines.

Of course, I did some googling, but all kind of information (descriptions, drwgs, trouble shooting, schedules, books to buy) is still very welcome.

Best regards,

Andrei

YachtForums · Feb 9, 2008

Andrei,

I've been away from this for over a decade, but in another life I was a consultant to Bombardier on the development of a little boat known as the Sea Doo. It's doubtful you'll find the following comparisons useful in choosing between today's crop of PWC's, but maybe you'll find something helpful from my observations. Remember, I wrote this over 10 years ago...

PERSONAL WATERCRAFT HULL DESIGN: SPECIFIC VARIATIONS AND TRAITS...

BOMBARDIER SP, SPI, SPX, XP (2 SEATERS): Original Sea Doo’s (pre 1993 XP) used a 22 degree deadrise hull with four “step” shaped strakes that were conducive to good lift and hull aeration, while providing predictable tracking and excellent grip when cornering (leaning to the outside). These same hulls featured a light hook at the rear of the hull to reduce porpoising. Current generation Sea Doo’s utilize a 22 degree deadrise hull with four “V” shaped strakes. The V-shaped strake is intended to add more lift and reduce wetted running surface, while adding grip when cornering. As reality would have it, the V-strake sacrifices the smooth predictable handling characteristics of the original Step strake, so Bombardier reduced its size slightly on the most recent hulls. The “hook” was also removed from this hull, which resulted in porpoising. The 95XP and newer performance hulls are 3” longer at the transom and the rake of the bow has been decreased by several degrees to give a hull with a wetted running surface that is equivalent to a hull that is 4” longer. This helped reduce porpoising and added longitudinal (lengthwise) stability. All of the 2-seaters feature a 6’ wide running pad. And ofcourse, the new performance hulls feature parabolic sponsons!

The intake gullet (gullet, housing, area, etc.) on Bombardier’s Sea Doo is a model of laminar flow perfection, given the speed, weight and displacement of their runabout models. While room exists for refinement with any design, I believe that Bombardier’s “original designers” set the standard by which other would be judged.

BOMBARDIER GT, GTS, GTX (3-Seaters): The Sea Doo GT series features a progressive deadrise hull with no strakes. This hull has a deeper deadrise at the bow and shallower deadrise at the transom. This combination gives a hull that slices and displaces water at the bow, for a smoother ride through rough water, while the rear of the hull is wider with a shallower deadrise for greater stability, given its purpose to carry 1-2 extra passengers. This hull is also referred to a hook & pivot design, because the forward Deep-V will create a hydrodynamic slot to hold a designated track through the water, while the shallower transom (rear) of the hull will pivot around the forward axis of the front part of the hull when turning (due to vectored thrust from the jet-pump nozzle). The result is a hull that is capable of turning very sharply, even though it is significantly longer than its 2-seater counterpart. The GT series has a Center of Gravity that is quite forward. This is most noticeable with one rider on board, as the hull more or less “plows” through the water. But with two or more riders, as it was designed for, it becomes more C.G. correct, which results in better pump priming.

The 3-seater has a deep V-hull forward of the intake gullet. This V displaces water outwards and away from the intake gullet while underway, resulting in exponentially less efficiency with increased speeds. The addition of any loading grate (especially the Magna-Flow) will increase high speed efficiency, substantially. And that translates into verifiable increased speed.

BOMBARDIER SEA DOO HX: This hull is really a good combination of several proven concepts. First, a deep deadrise hull will give a smoother ride due to slicing and displacing. Second, a shallow deadrise transom will allow a “hook & pivot” configuration when turning. Third, the partial forward cathedral design with a narrow beam works like a water-ski with a parabolic tunnel. This allows carving & cutting. Each one of these designs has favorable attributes and they have done an excellent job at mating them. However, a deep deadrise hull wants to corner flatter to build hydrodynamic pressure or a “berm” on the outside deadrise. At the same time it uses its keel as a slot through the water to hold a desired path. This is why all of the 22 degree deadrise 2-seaters work so well. In contrast, the cathedral design generates its grip when banked over. It also induces a turn without as much need for vectored thrust. Each one of these characteristics will work best at a given speed, but there will be a threshold at which these two forces work against each other, and the result will is a craft that feels unstable in high speed sweepers. The chines on the HX are “hard” toward the bow and soft toward the transom. This is also contributes to the “bite” this hull produces toward the front, and lack thereof toward the rear. These same “hard” chines create a slightly concave area (somewhat cathedral) at the fore section. Contrary to logic, a concave surface does not always develop lift, sometimes it creates a vacuum. This vacuum can be felt in the form of instability during high speed sweepers.

Because lift moves back as speed increases, the HX loses a some of the stability that is available at mid-speed due to the forward girth of the hull. With lift mostly transferred to the transom at high speeds, the rub-rail mounted sponsons begin to loose some of the grip they provide at medium speeds (due to increased hull lift) and thus do not add as much grip as desired at high speeds. The Deep-V generates the greatest grip at this point (when banking), but the narrow beam at the transom which allows the smooth transition into banking angles, now allows the transom to wash out easily. (Insert plug for ULTRAC HX Skegs here!)
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YachtForums · Feb 9, 2008

Continued...

YAMAHA WAVERUNNER: 500, 650, LX: This hull falls between the categories of a flat bottom hull and a shallow “V”. The deadrise on this hull is less than 12 degrees. This design affords good stability at rest or idle speeds, but lacks the deadrise depth for aggressive handling and smooth ride. Because the pump placement is generally close to the same plane as the rest of the hull, ventilation occurs easily in less than ideal water conditions. This configuration is not conducive to higher speeds as the pump constantly becomes “un-primed” or “un-hooked”, and the hull creates excessive water tension (drag). In cornering with this hull, air is easily inducted from the sides of the hull, especially given the amount of sliding associated with a shallow deadrise design. This causes the pump to become un-hooked because inducing air into the intake area will break vacuum, and ultimately, far less grip is available when this occurs. Handling and intake vacuum are closely related.

YAMAHA VXR: This is basically the same hull as the original WaveRunner, but it features a sharper V at the bow. This gives a slightly smoother ride and allows a little greater speed in rough water because it slices through water, as opposed to slapping, but accentuates the hook & pivot configuration with no measures to control the pivot portion of the equation. The result is.. the bow will track, but the transom will not follow suit. This is one reason that aftermarket plates with skegs were popular for this craft. (Especially ULTRAC Hidrofins)

YAMAHA WAVERAIDER: This was the first implementation of “step-ventilating” technology for a PWC. This design induces air under the hull to help reduce drag. Yamaha did not pioneer this technology. The original concept was pioneered by Harry Schoell, a prominent marine architect and Naval engineer. This system was patented as the "Duo-Delta-Conical" concept and has been adapted by many of the leading performance yacht builders around the world. It is also referred to as Step-Ventilation. One of the benefits of this design is it induces trim into the hull when lift is present at the bow.

This design is really two hulls in one; a forward Delta Conic hull section
having a conical entry with a delta constant planing area. And after the main hull section, a constant planing area displacing a delta pattern when on plane. The forward hull creates a bow wave that surges under the hull (rooster tail), causing the aft section of the hull to ride on this wave of higher pressure. As speed increases, this wave moves aft, lifting the stern and creating greater leverage against bow rise (anti-porpoising). This system gives quicker planing, much like an cavitation plate mounted lifting wing (Doel-Fin, Stingray, etc.) It essentially gives a longer hull without the penalty of increased wetted surface.

The WaveRaider hull features this technology in the form of a recessed step just past the intake gullet to help aerate the trailing aft section of the hull, thus reducing drag, at a point of highest pressure on a hull. This results in increased speed, but sacrifices handling at a point on the hull where a large percentage of handling properties are normally derived. This hull also features several strakes toward the front portion of the hull to help deflect spray down & away and aerate the water passing under the hull, again for increased speed, but it diminishes handling by sacrificing grip. This hull features a progressive deadrise design for wave displacement toward the bow and a slightly shallower transom for increased lift at high speeds and better stability. This design falls into the hook & pivot category, but lacks adequate displacement at higher speeds to enable predictable turning and handling.

The Big-Bore version of this craft makes the hook & pivot even worse, because the increased weight of the 1100 triple, given its forward placement in the hull, sacrifices weight at the transom and thus decreases wetted surface at an area crucial to grip, resulting in a hull that slides out easily in turns and creates a tendency to hunt at high speeds. This is mostly due to the lack of a good tracking appendage toward the rear of the craft.

The dimensional footprint of the Raider’s intake area is comparatively smaller than any other PWC vehicle available. The benefit here is enhanced vacuum. At higher speeds, a smaller intake housing (volumetrically speaking) will create more suction, and thus bring up more water, resulting in greater thrust. Couple this with the step-ventilating hull and you have the single most important reasons for the amount of speed this hull can achieve.

YAMAHA BLASTER: This is a cathedral with a flat “V” design. The cathedral hull features channels that force air and water to travel backwards under the hull, as opposed to displacing outwards. This helps generate lift and aeration. The channels are a by-product of the longitudinal appendages referred to by Yamaha as chines, but really fall into a category of skegs. The actual chines on this hull are reversed, thus allowing the hull to ride deeper in the water when banked over. This adds grip because it creates two 90 degree corners at separate planes. This same configuration creates parabolic areas at the chine allowing this hull to carve much like a water-ski. Vectored thrust from the steering nozzle accentuates the carving ability of this hull and produces excellent cornering, but can feel a little quirky at times due to its short hull length. A longer hull will make for more predictable turning. The single largest drawback to the Blaster’s hull is a flat cathedral design does not lend itself to optimum pump priming at higher speeds. This is coupled with an abrupt transition into the intake intake gullet that creates a very disruptive laminar flow pattern to the impeller.

KAWASAKI ZX: The ZX series features a very deep deadrise hull (23-24 degrees) with multiple strakes. Given the depth (angle) of this hull and greater than average weight, it yields a very smooth ride with predictable handling, due to the amount of wetted surface for ride control. The new 1100 ZX features an air induction system to aerate the aft portion of the hull. This is accomplished via an inlet from the bilge that draws air under the hull, based on the vacuum created by a raised strake located just forward of the exposed air inlet hole on the bottom of the hull. This is an innovative form of hull aeration, but only serves to aerate a small portion of the hull, which might be just right, because too much aeration sacrifices handling. (ref: WaveRaider) The ZX has a fairly linear laminar flow shape leading up to the intake gullet. While this design will enhance surface tension and make for a very smooth laminar transition up to the intake area, it will allow ventilation to a much greater degree at high speeds in rough water. This hull relies more on its own weight to keep the pump primed, rather than intake housing vacuum, which is critical for a lighter hull, such as a Sea Doo. This is the single most important reason that the Nu-Jet impeller works well on this vehicle. The Nu-Jet does not have over-lapping blades, and thus does not produce as much vacuum as other impellers.

KAWASAKI SS & XI: This was the industry giant’s first attempt at creating a vehicle to compete (on the race course and in market share) with Bombardier. This was their first Deep-V hull. It was evident that Kawasaki knew little or nothing about hydrodynamics due to the implementation of a Progressive Pad and Box Keel hull design. In other words, the pad became progressively wider from the front keel to the transom. The result of this configuration was a hull that developed an extreme amount of lift at the rear of the craft, thus causing the nose to plow. It created a large amount of spray off the bow and a hull that would not stay centered at high speed. The narrow hull accentuated the problem, but the box keel made it worse. In addition to this, the intake gullet was as archaic as the original 440 & 550 Jet Ski’s. It is the most abrupt and disruptive laminar transition (and pump placement; height) of any vehicle in the market. Some of these problems were addressed when the XIR was introduced.

POLARIS SL, SLT: Both the 2 and 3 Polaris model hulls are similar to Bombardier’s hulls, with the exception of the 2-seater using step strakes and the 3-seater using one set of step shaped strakes just offset from the center of the hull. While the hulls are very similar to Sea Doo’s, (more like a direct copy) their increased weight offers a noticeably better ride in choppy water, but does not offer the aerobatic prowess of the lighter Sea Doo’s.

NICHOLS: Now out of the PWC manufacturing business and working for Mercury, Greg Nichols developed some very interesting designs with extensive use of carbon fiber and billet aluminum. (and a V-4 engine) The hulls he developed were a Tunnel-V design. This design has incredible potential as proven in Formula One Grand Prix Boats. However, it does not work well with jet-pumps. Tunnel V’s develop extreme lift (surfacing hulls) at speed and this does not keep the pump down beneath the waterline. In today’s world of romp & play in a wide variety of water conditions, this is not a versatile design. But if Oval style racing were the norm, this would be hard to beat, if the pump could be placed deeply enough to offset the lift created by the tunnels and sponsons. Tunnel V’s have incredible cornering capability due to the outside sponson building a hydrodynamic berm when cornering and the inside sponson working like a rail to hold the combined sponsons in a designated track. This could be accentuated by vacuum at an intake housing to make great cornering, even better! Allthough it might require a steerable rudder to offset the straight line track that Tunnel “V’s” naturally follow.

CONCLUSION...

There are many elements that make up a hull’s bottom. The shape of the bottom’s sections, how rapidly the sections sharpen as they move forward, and they blend toward the transom. A good hull has the right blend of design elements and it the designers job to create a hull that incorporates the best features and performance for a given application. Hence, the rapid development of specific class PWC’s, i.e., runabouts, cruisers, sportcraft, stand-ups, etc.

Despite having to meet general performance goals, every PWC has its own personality and quirks. Performance can best be rated as Power-To-Weight. Personality can be cosmetics, ergonomics, special features and lay-out. Quirks will most often manifest themselves in the form of handling. This is why hull design is crucial to the overall package. The perfect PWC hull does not exist, because each person will place emphasis on different areas. But we can all agree on one thing... we’re all having a “hull” of a lot of fun!
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Information about PWC's & Outboard Engines needed...

TSI AV Senior Member

YachtForums Administrator

YachtForums Administrator