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Thread: Sponson Science

  1. #1

    Sponson Science

    Does any one have the latest on sponson science. Considering the hull design is changing every year.

    Has any one ever made them wider (stick out further) or experiment with different shaped fins? I want to make a set some but I need to better understand how they work.

  2. #2
    abracadabra's Avatar
    Join Date
    Oct 2008
    Wellington, FL United States of America
    Quote Originally Posted by OTBT View Post
    Does any one have the latest on sponson science. Considering the hull design is changing every year.

    Has any one ever made them wider (stick out further) or experiment with different shaped fins? I want to make a set some but I need to better understand how they work.
    As far as I understand their job is for the most part to keep you from spinning out when turning and to give you some horizontal stability when going on a straight line. The key is to make them with the least possible drag and yet efficient, Julio...

  3. #3
    Can yo help with my RPM questionin my other (IC Cap). Here it is below.

    Question: The ski previously would only hit about 7,200 est RPMs. Now it looks to be hitting 7,800-900 and the engine is "hunting" (The rythm (not sound) a diesal engine makes when idling). Is the ski hitting the Rev limiter?


  4. #4
    abracadabra's Avatar
    Join Date
    Oct 2008
    Wellington, FL United States of America
    Quote Originally Posted by OTBT View Post
    Can yo help with my RPM questionin my other (IC Cap). Here it is below.

    Question: The ski previously would only hit about 7,200 est RPMs. Now it looks to be hitting 7,800-900 and the engine is "hunting" (The rythm (not sound) a diesal engine makes when idling). Is the ski hitting the Rev limiter?

    I'm going to need more info. What mods o you have? You could be picking up RPMS due to not having an intercooler leak anymore. Are you running a RRFPR? I had that problem one time due to too much gas at idle, Julio...

  5. #5
    I put it all back together and the ski now doing 63.9 GPS, Sea Temp 67, Flat salt water, sitting up-right
    2008 SHO
    Riva Charger Wheel
    Removed Intake Ribbon
    Modified air filter (wire screen, from 2007 Sea Doo IC)
    Removed fins from the IC core
    R&D Intake Grate
    Removed wall inside waterbox
    Removed Resonator from rubber exhaust
    Cut extra lip in rubber exhaust pipe
    Cut out flapps in the exhaust end pipe (exit hull)

    BOV for rough water riding
    Proper Air Filter
    New Impellar (Don't know what to get?)
    All I want is the ski to be able to do 70-75mph. Bermuda is mainly rough salt water riding. So trying to go +80 mph on a ski is pushing it!

    For now it runs very nice, love it!!

  6. #6
    Connecticut CrazyA's Avatar
    Join Date
    Nov 2005
    Quote Originally Posted by OTBT View Post
    Does any one have the latest on sponson science. Considering the hull design is changing every year.

    Has any one ever made them wider (stick out further) or experiment with different shaped fins? I want to make a set some but I need to better understand how they work.
    It's an old article, but it certainly goes into the "science" of sponsons.

    When the original extension plate for the Bombardier Sea-Doo was introduced by Pro-Tech (as in Yamaha), it was met with much enthusiasm, because it was one of the first aftermarket accessories available and it helped cure a problem. The purpose of the plate was two fold; to allow quicker planing with less bow rise and to reduce porpoising. To further enhance its use, 6mm skegs were added to help tracking and give grip when cornering. Some designs went a step further adding channels or deeper skegs.

    All of the above were effective, but mostly for 1988-1990 Sea-Doos. As of 1991 & 1992, Bombardier incorporated a "hook" into the bottom of the hull. This "hook" can be found in the last 4 inches of the hull where it meets the transom. If you use the straight edge of a ruler and place it up against the bottom of the hull, you will see how the hull takes a down turn toward the transom. This is an old trick used by powerboat manufacturers to give lift toward the rear. This enables faster planing and reduced porpoising. It has also been known to reduce speed on many full-size boat hulls!

    As of 1993, under the influence of Novi Engineering, Bombardier adapted an enlarged "V" shaped strake in place of the conventional "Step Strake" in an attempt to gain more lift, thus reducing wetted surface and increasing speed. The result was a hull lacking the finesse and predictability that had popularized their craft in the market. Within a couple of months, Bombardier's engineers observed pro runabout racer Jaime Keyes utilizing a set GTX sponsons and promptly running away with the races she entered on the Florida World Cup. They quickly made a set of symmetrical sponsons a warranty upgrade for all of the 93XP's to basically put a band aid on a bad hull design. The addition of these sponsons made a very large improvement in the handling of this craft. Their placement on the side of the hull near the transom helped generate lift at the rear, thus keeping the bow down and reducing porpoising. This same location also increased the width of the hull at the rear, thus adding more lateral stability. This simple appendage helped tame the beast.

    This embarrassing situation coupled with the total failure of Novi Engineering designed Sea Doo's (4 boats valued at $250,000) at the World Championships in 1993 put an end to Bombardier's relationship with Novi. What they discovered at the same event was a group of guys that had been quietly building a better mouse trap. You might remember a Black GTX (3-Seater) that stunned the watercraft racing community by leading two pro-mod heats and winning pro-mod slalom. Guess who designed the hull, pump, impeller, venturi, stinger (that's a hint), nozzle and intake grate. A certain aftermarket company had supplied the prototype parts to see how well they would do against the world's best. This was done with a 650cc motor running against 750cc 2-seaters.

    That same year saw John Stevens dominate the IJSBA tour on his KawaDoo and some of the manufacturers began to see that speed does not always win races... handling plays an important role too. The Steven's boat had a hull configuration very similar to Bombardier's hull. The reason this hull worked so much better than the Sea Doo's it was competing against is because it was narrower. The narrow hull decreased displacement, which allowed the hull to ride deeper in the water. This inturn kept the pump down in the water through choppy race conditions, thus maintaining thrust while building greater deadrise pressures when cornering.

    Within months, the interest in sponsons soared in the media and with racers. They became the bolt-on choice of racers because they made a big difference in handling. Handling was evolving as an important role in winning races. With a greater emphasis on this area, Bombardier's engineers began experimenting with sponsons and discovered a design that would not only add lift at the transom, thus reducing porpoising, but would add grip when cornering. This sponson was incorporated into the 94XP and subsequent high performance models. The only drawback to this design is that water can choose to flow under or over the sponson depending on rider weight and speed (lift). If water flows over the sponson it is pushed down until pressure under-neath forces the sponson up thus producing a lateral rotation to the other side of the hull. When this scenario occurs it induces an oscillation or high speed broach that feels like chinewalking or an inability to keep the hull centered (laterally) at high speed.

    The irony in this whole evolutionary process is that sponsons have been in existence for almost twenty years, but only gained recognition a short time ago. Kawasaki's Jet-Ski's have utilized outboard mounted tabs for years to aid in lift and stability. While they were somewhat crude by today's standards, they were the precursor to current day sponsons.


    The two sponson designs that are prevalent today are Symmetrical and Parabolic.

    SYMMETRICAL Sponsons are more of a bolt-on lifting device that increase the "footprint" of the hull at the transom. This design adds lift to the transom, helping to control porpoising and adds lateral stability which reduces chinewalking and oscillation.

    PARABOLIC Sponsons (winged) utilize an outrigger turned down or hooked wing that serves the same purpose as a symmetrical version except the wing catches water being displaced outward and channels it backwards, thus producing more lift. The wing portion of this sponson effectively creates a skeg, and we all know what skegs do... add grip!

    The placement of the skeg (sponson) in relation to the thrust line (distance to) can have a significant effect on a boats turning capability. Vectored thrust from your steering nozzle uses the skeg as a pivot point to create leverage against the rest of the hull. The skeg creates a hydrodynamic slot in the water (or a groove) and begins to follow this track. The thrust exiting your steering nozzle forces the rear of the boat to pivot around the track of the sponson. The result can be a hull that wants to make a progressively tighter turn once a turn is commenced. This is similar to driving a grocery cart backwards. Everything is fine if a straight line is maintained, but once you begin to turn, the back wheels want to spin around the axis of the front wheels (which are stationary in direction like the sponson).


    Recently, a new aftermarket sponson design has gained popularity. This unit resembles more of an outrigger and skeg combination that is more clearly defined. The "outrigger" portion of the sponson serves as a lifting and stabilizing surface. The "skeg" portion of the sponson features a vertical plate mounted perpendicular to the outrigger that can
    be adjusted up or down. The vertical adjustment of this plate determines how effectively the sponson will contribute to handling and cornering. The deeper you set the plate, the more aggressive cornering will become.


    Sponson placement on the hull has very pronounced effect on ride, stability and handling. The angle of attack, the design and the size are also critical factors. This is also compounded by the weight of the hull, the weight of the rider and the lift the hull generates at different speeds.

    A sponsons most important role is that of a stabilizer, much like hydraulic trim tabs on a performance boat. With full size boats, the ride of the hull can be adjusted by trimming the tabs up to reduce wetted surface and gain speed or trimming the tabs down to allow quicker acceleration with less bow rise coming on plane. The trimmed down position can also be favorable for smoother ride characteristics in rough water. If this all sounds familiar, than you're relating it to the variable trim system or V.T.S. on your personal watercraft. The V.T.S. can effect sponson performance as well. Adjusting the trim will adjust the angle of attack of the hull and thus the incidence of the sponson.

    The factory placement of sponsons is generalized. Much like an impeller has been chosen to give the best acceleration and speed given the powerplant incorporated. Moving the sponson down will create more lift. This would be an advantage for a heavy rider, but would make the hull feel "loose" on a light rider. The lift created at the rear of the hull from moving the sponson down will cause the hull to run with more wetted surface, because it pushes the bow down. This will reduce speed, but can make for a better ride in certain conditions. Positioning the sponson higher on the hull will reduce lift at the rear and thus allow the hull to run with less wetted surface, resulting in increased speed. However, this
    can reduce the sponsons effect on lateral stability and as an anti-porpoising device.

    By moving the sponson fore and aft, another set of variables is created. A rearward placement will increase turning response because it reduces the sponson-to-thrust line ratio. This reduces the leverage or fulcrum effect. A forward placement will increase leverage and dampen steering response, which can help control pivot progression. This location is actually more advantageous because it adds a grip in a more critical location and allows more predictable turning, but it fails to provide lift toward the rear of the hull where it was originally intended. A properly designed hull can significantly contribute to the effectiveness of a sponson.

    The incidence the sponson is set at can also have an impact on handling. A positive incidence will increase lift, this can be helpful for quicker planing, but will disrupt laminar flow when cornering. A negative incidence will "suck" the hull down. This is great for cornering, but will cause a variety of unwanted handling characteristics in a straight line. The angle of attack will also be effected by the overall design of the sponson, i.e., the shape of the leading edge, the length, thickness, taper, etc.
    Sponsons create drag. It is so significant and verifiable that in some cases, with certain designs, the craft will loose upwards of 3-4 mph. This is the penalty we pay. As the old adage goes: " what is speed, without handling ". If racing were not closed circuit sponsons would not be as popular as they have become. In drag racing watercraft (if such a thing existed), these appendages would be a major disadvantage. However, with applied hydrodynamics, drag can be minimized and performance enhanced.

    Future sponson design may be "active". It may be mechanically, hydraulically or hydrodynamically adjusted. It will provide lift during acceleration, thus eliminating bow rise. It will maintain a slightly positive incidence for straight line tracking (to keep water flowing underneath) and graduate to a negative angle of attack when cornering to "suck" the hull down to the water for more grip. This same design will incorporate channels between the sponson to allow a release of pressure when cornering. This will allow smoother rolling transitions from side-to-side.

    By the way, future sponsons will be a fixed configuration that accomplishes all of the above. ULTRAC is proud to announce the release of the AERO-SLOT; MODULAR ADJUSTABLE SPONSON SYSTEM!

    If you're familiar with the Odyssey Sponson, which ULTRAC designed (Odyssey was our Canadian Distributor who ran to the market with our concept because we were finalizing development work on a Naval contract.

    The Aero-Slot's feature a semi-symetrical airfoil with a reflexed trailing edge that developes increased lift over the factory sponsons to offset the drag created by the vertically adjustable plate (sponson). This airfoil was developed for speeds in the 50 -70 mph range and creates very little laminar disruption over and under the foil. This foil creates excellent lift coming on-plane, for reduced bow-rise, and was designed to work as a super cavitating foil, which reduces hydrodynamic drag. When you lean over into a corner, the angle of attack of the foil forces the foil to pull itself under water, thus creating downforce when cornering for added grip.

    The vertical plate, or sponson, creates a hydrodynamic slot above the foil that entraps water, much like the popular laterally placed foils on hi-performance waterski skegs, that help keep the rear of the ski from sliding out, by providing downforce. As we all know, the sponson portion below the base mount, or airfoil with the Aero-Slots, is providing grip. It also gives a leverage point against thrust exiting the steering nozzle. This is why the plate is moves further back as it moved down, to decrease the thrust line to sponson ratio, which results in faster turning. (it can also result in pivot pregression, which is not good)

    The Aero-Slots use an aluminum airfoil for greatest strength and injection mold sponson for reduced weight. By the way, some manufacturer's may try to convince you that a textured finish makes for better water flow on their sponsons. This is pure hype. If this was true, why wouldn't we do this to the rest of our hull, which has far more wetted surface than the sponsons. I've even read where some fool slammed certain sponsons due to weight, when in fact, outboard weight adds stability at high speed and more predictable handling.

    Carl Camper, President

  7. #7
    Thanks and your avatar photo is awsome!!!
    Thanks guys

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