"Z" Difference
Hot Boat Magazine
- June 1994

NOTE: the 656zp has been redesigned as the 220LX

In HOT BOAT'S Annual Awards Issue this past April, Stingray's 656zp was named Compact Boat of the Year for 1994. The fact that Stingray won the award was not particularly surprising since the South Carolina-based boatbuilder has been winning accolades for its various models for quite some time. What was surprising, however, was the margin of its victory. Normally, Boat of the Year competitions are close. This time, however, it was a cakewalk for the Stingray entry as the 656zp far outdistanced its rivals and was the clear-cut winner in its class.

According to our test-team drivers, the 656zp was the sleeper of the year.." a well-mannered family bowrider sportboat that simply didn't have any faults and did nothing wrong, especially when it came to performance."

So how did Stingray do it? They use the same MerCruiser packages everyone else does, and their boats are priced so reasonably that it often makes their competition wince. So what's the secret?

Actually, it's no secret at all. In fact, the Stingray difference even has a number - U.S. patent number 5,063,868. This is how Stingray's exclusive Z-plane hull design is registered with the U.S. Patent Office, protecting it against imitators.

But let's back up for a minute and review some of the basics about vee-bottom hull design. First of all, Stingray can't take any credit for coming up with the original concept of the modern-day vee-bottom. That was done nearly 40 years ago by naval architect C. Raymond Hunt, who is considered the father of the classic roe-hull. Until Hunt came along, planing hulls of that era had a relatively shallow vee-entry at the bow and a long, hard chine forward. Hunt changed that trend by significantly deepening the forward sections of the hull and maintaining a constant amount of deadrise (vee) all the way back to the transom. The result was a smoother-riding, more manageable boat in rough-water conditions.

Essentially, the typical vee-bottom is a variation of the standard-planing mono-hull. Unlike a displacement-type hull that simply pushes water out of its way, the planing hull achieves greater speed and more efficiency by "lifting" out of the water as it gains speed. What happens at a certain speed is that hydrodynamic forces overcome the static buoyant forces and the hull reacts by moving forward and up, out of the water. We commonly refer to this condition as planing.

Once the boat is on plane, drag (friction caused by the remaining wetted hull surface) becomes the determining factor (along with available horsepower/thrust) in how fast a boat will go.

Most vee-bottom hulls are measured by the amount of deadrise. Deadrise is calculated by measuring the angle on each side of the hull bottom at the transom. Imagine, if you will, looking at your boat's transom from directly behind the boat while it is out of the water. Next, picture a horizontal line at the lowest point of your keel running out to each chine. The gap or angle formed by this imaginary line is measured in degrees. If the angle is small, such as eight to ten degrees, the hull would be regarded as a shallow-vee. If it's ten to 16 degrees, it's a full-vee. And when you begin to exceed 18 degrees up to 24, you are now talking about a hull that qualifies as a deep-vee.

As you have probably noticed, the vast majority of vee-bottoms have angular strakes that protrude from the otherwise smooth running surface. These strakes run longitudinally, from bow to stem, and are placed in a variety of locations depending upon the make and size of hull.

At planing speeds, strakes serve several purposes. Primarily, they are there to provide additional lift, acting somewhat like an extra chine and helping to get more hull out of the water, thus reducing drag and increasing overall performance. Strakes also tend to break up the flow of water beneath the hull to eliminate some of the surface tension that develops between the water and the bottom. Furthermore, strakes can generate tiny air pockets and bubbles, sometimes referred to as vortices, to assist in this process.

About five years ago, Stingray was designing and building its line of family sportboats, using this same vee-bottom technology. The boats performed well, but Stingray President Al Fink was not completely satisfied. "We've always taken a lot of pride in the way our boats perform," said Fink. "But to us, performance means more than just top speed. I was looking for a way to improve the turning characteristics of our boats. Like most vee-bottoms, there was a tendency to occasionally catch a chine in a fast corner, which can surprise a novice driver. Our testing also indicated that it was possible to induce propeller ventilation [slip] if too much power was applied or too sharp a turn was attempted. In both cases, I wanted to develop a better hull design to eliminate those shortcomings."

After many months of computer-assisted engineering, the Stingray design team came up with what they thought would be a reasonable solution in terms of a new vee-bottom hull configuration.

ZP hull illustration In a nutshell, the Z-plane hull design essentially incorporates the hull strakes into the bottom, rather than having them appear as external appendages that have been added on after the hull surface was completed. If you study the accompanying diagrams, you will see that the Z-plane has only two angles instead of the conventional three found in a typical roe-bottom with nonintegrated strakes.

Initially, it was thought that the new Z-plane design would probably sacrifice a little top speed in order to achieve the better overall handling, especially in the turns. "We assumed that because we were reducing the amount of lifting potential that the boat might run a little slower," said Fink. "We never really intended that the Z-plane bottom would give us extra miles an hour on the top end too."

As the testing phase began, it became immediately evident that Stingray was on to something big. Not only did the boat turn better and lose the tendency to ventilate the prop, but it also ran faster with the same amount of horsepower.

When the Stingray design team started to analyze the data, they found that the integral Z-plane strakes were delivering an undisturbed flow of water beneath the hull and to the propeller. What was happening was that the minuscule air bubbles and tiny vortices created by conventional vee-bottom strakes had disappeared. And, although some hull designers feel that aeration under the hull is an advantage in optimizing top-speed potential, Stingray was finding that cleaner, less disturbed water flow was actually more of a benefit.

"It didn't take long for us to realize that the lack of air entrapped beneath the hull provided a much more positive feel for the driver, both in cornering and while running at full throttle," commented Fink. "Consequently, we got the best of everything. Our boats still ride beautifully in the water without the need for excessive trim, and the propeller has optimum bite to deliver maximum thrust and efficiency."

But Stingray didn't stop there. "We also recognized the fact that a notched transom design would also enhance our performance," said Fink. "It's been proven in all types of racing that a notch, or cavity, in front of the lower-unit gearcase will allow you to mount the drive unit higher [more vertically out of the water] thus reducing gearcase drag and generating more performance. And as expected, because the Z-plane design was not disturbing the water flow to the prop, the advantage of raising the drive unit to a higher X dimension worked perfectly. Our time to plane off was quicker and so were our full-throttle speeds."

So how does all of this relate directly to how Stingray performance compares to similar family sportboats? The numbers don't lie. Over the past five years, Stingray has kept copious records regarding published boat performances of all major boat brands. With almost no exception, Stingray models have achieved the fastest top speeds with given stock engine packages in virtually every size category.

For example, Stingray's 606 (20' bowrider) has been radar-tested at 55 mph with a stock 4.3LX (V-6) MerCruiser. The next two closest 20-foot bowriders hit the list at 51.4 and 50.3 mph respectively. In the 21-foot category, Stingray's 656 (21' 5"), powered by a MerCruiser 5.7L small-block V-8, was caught at 59.3 mph by a Mercury Boat House Bulletin report. The next nearest 21-footer on the list came in at 57.6 mph, while the average performance with that particular power plant is in the low-50-mph range. And If you want to see if the z-plane works in even larger hulls, Stingray's 719 (23' 6") family cuddy cabin cruiser with a little 4.3LX (V-6) MerCruiser tells the story. With that package, the 4,000 pound Stingray still makes a top speed of 44.1 mph. A check of the official record won't show another 23-plus-foot cruiser with a 4.3LX over 40 mph.

Although mile-per-hour numbers are usually how boats are judged, Stingray has taken the time and energy to convert some of these speed figures into actual dollar savings at the gas pump. Depending on the models/brands used for comparison purposes, Stingray claims to save boaters with standard 5.7L stern-drive power as much as $650-$900 per year (based on 100 hours of annual operation) just in fuel costs. The numbers become pretty significant if you boat a lot.

Maybe the Z-plane isn't quite the hull-design breakthrough that the original modern-day vee-bottom was but it certainly has had a positive impact for Stingray owners around the world. The next time you decide to pick on that "unassuming-looking" family boat, you better make sure it doesn't carry the Stingray Logo. If it does, you could be in for the chase of your life.

Hot Boat Magazine
June 1994




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