Ah, the sponson. There is an elegant simplicity to this increasingly popular watercraft part that belies its cutting edge design. It doesn't take an engineering degree to see how a sponson works, and that's true whether it's the stock part that came with your watercraft or an aftermarket version you've added recently. The outer edge provides bite in turns, the inner section provides lift and stability. It's as simple as that.
But is it really?
"Well, yes and no," said Brian Bevins of Beach House Express, one of the leading manufacturers of aftermarket sponsons. "It is a pretty straight-forward part: pretty easy to manufacture, pretty easy to install, and the results are instantly noticeable, as long as it's designed properly.
"What most people don't understand, though, is how much is actually going on with a sponson, in terms of shape, angle and positioning, and how much all of those can affect the ride of the craft. And it's not just handling. They also have a big impact on lift, acceleration, stability, riding style, you name it."
It's that wide range of effects that has made the sponson the important part it is to the modern watercraft. On a purely functional level, probably no other single part has played as big a role as sponsons in the quantum leaps in performance we've all enjoyed over the past few years.
"There's no way we'd have the speeds we have now without them," Bevins said. "The boats would just be too hard to ride."
Now, sponsons aren't the only reason new runabout models have topped the 60 mph mark, but they have allowed them to do it safely. In addition, they've made the boats easier and more enjoyable to ride because of the added stability and improved handling and turning ability.
Yet despite their importance to the quality of the ride, sponsons remain a misunderstood and often overlooked feature for consumers, particularly recreational riders, who often associate aftermarket sponsons with racing.
That's too bad because nearly every watercraft enthusiast will benefit from a better understanding of the sponson. In addition to the increased control and predictability, sponsons can also dramatically improve a three seater's ability to tow skiers or turn a jumpy two seater into a comfortable long-distance cruiser.
A History Lesson
First, a little history. While the aftermarket sponson craze is something of a recent phenomenon, sponsons have actually been used in the watercraft market for quite awhile. Even classic Kawasaki stand-ups employed basic block sponsons to improve stability and lift. A few aftermarket companies offered block sponsons for runabouts — almost exclusively on Sea-Doos — in the late 1980s, but again, their purpose was to provide better stability and lift and reduce porpoising rather than improve handling. Sea-Doo incorporated stock, block-type sponsons on its GT hull design, but their inclusion was to improve acceleration rather than handling.
Sponsons didn't become a tool for better handling until 1993, when Sea-Doo widened their existing GT sponsons and added a curve. The new sponsons improved the handling on the GTs so much that it attracted the attention of Ferd Keyes, the father of racer Jaimie Keyes, who added them to his daughter's race boat. Word spread quickly, and within months nearly all of the top Sea-Doo riders had added them to their boats, and the week before the IJSBA National Tour got underway, Kawasaki rider John Stevens added them to his PJS-built Xi, turning what Stevens himself described as a "scary unrideable boat" into a craft that completely dominated racing for the next two years.
From then on, sponsons became an integral part of watercraft design, though there was some trial and error at work. The first hooked sponsons Sea-Doo used on its performance two-seaters would sometimes submarine and make the boat rock suddenly and unpredictably to one side or the other. In 1995, Yamaha added large hooked sponsons to WaveRaider in an attempt to get the craft to stick better in turns, placing them in the normal position at the back of the craft and forgetting about the step built into the back part of the hull. As a result, much of the potential benefits of those sponsons — improved control and sharper turning — was lost because they didn't come in contact with the water. The next year, they positioned the sponsons forward about six inches, which was more in line with the real pivot point on the hull, bringing about a significant improvement in handling.
Those two misses point to the subtleties involved in designing sponsons. In addition to basic design, sponson designers also have to think about positioning, angle and size, as well as the specific design of the hull.
There are essentially three types of sponsons available on the market today — the basic block type; the hooked or winged type and the paddle or rudder type.
The block type is simplest and looks like a child's building block. Usually, the front end is round or pointed to allow water to flow over it more efficiently. This is the type that first appeared on personal watercraft, but it's becoming rarer every year. Its main function is to provide additional lift on the back of the hull, mostly during acceleration. They can also help provide better side-to-side stability at speed and reduce porpoising by providing a bit more hull surface at the rear of the craft.
Winged or hooked sponsons are the most prevelant type on the market today, mostly because they are the choice of every original equipment manager. Like the block type, they can provide added lift during acceleration, as well as better side-to-side stability and reduced porpoising, but their biggest advantage over the block type is the improved handling they offer. The outside edge provides grip in turns, allowing you to turn sharper and faster without fear of the back end sliding out. They can also provide a pivot point for the hull in turns. One of the most overlooked benefits of these types of sponsons is that they have allowed riders to lean into turns more, which has made watercraft easier to push to their limits.
Paddle or rudder type sponsons, which use a flat paddle-shaped rudder attached vertically to a block type sponson, do essentially the same thing, but the effect can be even more dramatic because the flat paddle or rudder portion of the sponson provides a sharper and more pronounced edge to catch the water. So far, the original equipment managers have steered away from this type of sponson (pun intended) because they can provide extremely aggressive handling characteristics. Engineers and hull designers from a number of manufacturers have told us that the decision to stay away from the paddle sponsons has been made by their various legal departments because of their concerns over lawsuits. However, as anyone who has used a properly set-up type of this sponson can attest, the improved predictability and control is startling. We've personally ridden a number of makes and models with these sponsons installed and have yet find a set up that doesn't improve on the stock hull.
The paddle or rudder type of sponson is also popular with aftermarket manufacturers because they lend themselves to adjustable designs. That doesn't mean hooked sponsons can't also be adjustable — Yamaha's sponsons on the GPs demonstrate that — but the paddle type is easier because your dealing with flatter surfaces and edges for the most part.
That adjustability is important because sponsons are a lot like a running shoe - one size doesn't fit all. The original equipment managers design their sponsons and position them on the hull with the average rider in mind, and generally lean toward the stable and forgiving side, so if you're looking for more aggressive handling, changing your the set-up of your sponsons is a good first step.
The key factors in the positioning of sponsons are the angle of the sponson, how deep or low the edge cuts into the water, how far forward or back the sponsons are placed on the hull, and the overall size of the sponson.
The angle is most important when it comes to lift and stability, though it can also have an effect on handling. Generally, the more the sponson angles up toward the front of the craft, the more lift it provides, but if it's angled too far up, it won't grip the water as well in turns. On the other hand, if the sponson is angled to far down, water can start flowing over it and create control problems.
How far the sponson goes into the water is mainly determined by its up and down position on the hull. Generally, the further down the sponson is placed, the more aggressive the handling. However, if it's too far down, the sponson can catch unexpectedly and abruptly, particularly in rough water. Because of that, being able to adjust your sponsons up or down is an important feature. The height of the sponson also affects the amount of lift it provides, both during acceleration and at speed, affecting acceleration, stability and control. The trade-off here is drag, which reduces overall speed.
The position of the sponson from front to back plays a big role in the handling mainly by shifting the pivot point in turns. The old Yamaha WaveRaider hull was a good example of this. In its first incarnation, when the sponsons were placed far back on the hull, the craft would enter turns gradually and then cut sharply when the sponsons caught the water in back. By moving the sponsons forward, that effect was lessened.
Understandably, the weight of the rider plays a big role in determining the proper setting. When it comes to handling, heavier riders generally don't need the sponsons positioned as low as lighter riders because the watercraft naturally rides lower in the water, but lower sponsons also provide better lift, which helps heavier riders, so it ends up being a trade-off.
In the same way, riding style is also important because it determines where your weight is located. Ironically, active, athletic riders will often find they don't need as aggressive settings because they use their body weight to help with handling, weighting the inside (or outside depending on the craft) during turns or standing up and weighting the back when riding in rough water.
But just as one sponson doesn't fit all types of riders, the same is true different watercraft models. The XP Limited and XP are good examples. Because of their hull design, their sponsons need to be shorter because the flow of water off the hull is directed onto longer sponsons, which creates too much lift on the back end and counteracts any benefit the longer sponsons might have for handling. Conversely, on a big hull like the old GT, the original smaller sponsons had little effect on either the handling or the stability of the craft.
Down The Road
According to our sources within the industry, the biggest changes in sponson design over the next several years will come in terms of increased adjustability. A couple of companies are already working on systems that use levers to adjust while you're underway. Kawasaki is using a similar system this year on some of their factory race boats and we should see some systems for consumers at Havasu this year.
Cost, however, will keep those on-water adjustable systems out of reach of many recreational riders. However, we'll probably also see more use-specific sponsons — such as towing sponsons which keep the back end from slipping out when the skier cuts — in the near future.
Whatever the case, sponsons aren't going away. They proved themselves to important for that. Amazing, considering how elegantly simple they first appear.