Stingray Boats Article - "Z" Difference

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"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.