Stingray Powerboats
3 Liter Lightning

Trailer Boats - March 1999
Land & Sea's Stern Jack and Torque Shift Prop can substantially improve the performance of a 3.0L sterndrive
Stingray 180RS - 3 Liter Lightning

Shown are the components of the Stern Jack kit. Some outside labor may be necessary to have the power trim cylinder extension welded in place. Land & Sea's variable-pitch Torque Shift prop (right) offers top speeds approaching the finest stainless fixed-pitch props, and a holeshot that can't be beat.

Land & Sea produces unique products designed to make a boat go faster. Two of these have some very wide ranging applications. The Torque Shift prop was the first successful shifting prop on the market. It is one of the fastest props and still compares in top-end speed with some of the finest fixed-pitch props available. Nothing comes close to the Torque Shift prop when it comes to low-end grunt. The Torque Shift prop fits a variety of sportboat applications, adapting to most V-6 outboards and most MerCruisers, SX Volvo Pentas and OMC stern-drives.

Less well known but an equally effective performance-enhancing device is the Stern Jack, an 8-inch extension that goes between the gimbal housing and upper gearcase on a sterndrive. The effect of this extension is to move the sterndrive leg back and extend the lever arm of the drive over the trim range. Trimmed down, the unit sits an inch lower in the water for a better low-end bite. Trimmed up, the unit not only trims 1 1/2-inches higher at full trim, but the setback allows the prop to operate in less turbulent water, and the trim system has additional leverage to lift the hull.

In some high-performance applications, the Stern Jack alone is worth an additional 3 to 5 mph in top speed and holeshot is also improved. We didn't get that much with the four-cylinder engine and we didn't expect to. The performance increase, nonetheless, was still satisfying. The Stern Jack is available only for MerCruiser Alpha and Bravo sterndrives.

Our purpose here is to show what can be done with a modestly powered boat to improve both its ski towing ability and top speed. The boat we used is a Stingray 180 powered with a 3.0L four-cylinder MerCruiser with an Alpha I drive.

The improvements we made do not come at a low price. The Torque Shift prop retails for $799 and the Stern Jack for the Alpha drive is $1995. The Bravo drive Stern Jack is $2495.

This brings us to a very important point. If you need more speed and power for towing heavy skiers, moving heavy loads or simply because you want to go faster, the least expensive way to increase performance is to buy a larger engine when you buy the boat. Adding performance after the fact is costly.

The Stingray 180 was run with full fuel and two people with test gear (approximately 400 pounds), and the engine was equipped with power steering.

Our initial test with the Stingray was with a stock 23-inch-pitch MerCruiser aluminum prop. This prop produced a top speed of 47.7 mph at 4400 rpm and acceleration from 0 to 30 mph took 9.9 seconds. Acceleration was definitely on the sluggish side and the performance of the prop was less than exceptional. It had a tendency to ventilate easily in turns and release suddenly when over trimmed. The next prop tried was a 21-inch-pitch Mercury aluminum. This prop topped out at 47.5 mph, but rpm was over the 4500 rpm recommended limit by 200 rpm.

Acceleration was much improved with a 0-to-30 mph time of 7.5 seconds. The 21-inch was a much better prop in its ability to hold in turns and when trimmed. There was far less ventilation.

The Torque Shift prop comes in several variations. The first we tried was Part No.144-126. This prop starts out with a low pitch of 11 inches and its top pitch range is adjustable from 19 to 26 inches. With the top end pitch set at approximately 23 inches, we recorded a top speed of 50 mph.

This prop did not do well on hard acceleration. Nailing the throttle produced excessive slippage (ventilation), and 0-to-30 mph times went up to 7.5 seconds. Feathering the throttle off the line allowed the prop to bite better and we whittled the 0-to-30 mph time down to 7.2 seconds, a noticeably stronger kick than either of the fixed-pitch props.


We then tried Torque Shift prop Part No.144-132. This prop has a low pitch of 14 inches and the high-pitch position is adjustable from 23 to 32 inches. Adjusted to hold at approximately 23 inches at the high-pitch position, we recorded an identical top speed of 50 mph at 4600 rpm. Nailing the throttle with this prop did not cause either the prop to break loose or excessive ventilation, and our 0-to-30 mph times dropped to 7.0 seconds.

With our initial tests complete, it was back to the shop for the installation of the Stern Jack. Installation is not difficult, but it does require some special tools that a good mechanic will have but will probably not be found in the tool kit of the average do-it-yourselfer. These tools are the U-joint press and a stud-removing tool. In addition, it will be necessary to modify the power trim rams with extension kits. This can be done at your local welding shop, by Land & Sea, or through an exchange program with Land & Sea, depending on the condition of your rams. The kit is complete with all necessary parts including studs, seals and gaskets, drive shaft extension, shift shaft extension and extensions for the power trim rams. The kit also includes Loctite, Never Seize and a check valve for the sterndrive oil reservoir. The instructions are very detailed.

With the Stern Jack installed, a process that requires approximately 21/2 hours once the modified components are assembled, it was back into the water.

Our first test in the second phase was again with the 23-inch aluminum prop. This time we recorded a 51.3 mph top speed at 4700 rpm for a 2.6 mph improvement over our initial run and a gain of 100 rpm on the tachometer. Acceleration times from 0 to 30 mph went down slightly from 9.9 seconds to 9.8 seconds. Prop ventilation was still a problem and it was obvious that this prop was not taking maximum advantage of the Stern Jack or the Stingray hull, which is one of the few 18 footers capable of breaking the 50 mph barrier with the 3.0L engine.

The 21-inch prop, while not as fast on the top end, showed a greater speed improvement with a top speed of 49.8 mph with the engine cranking along at 5100 rpm. Acceleration improved slightly with the Stern Jack going from 7.6 seconds to 7.4 seconds. The 21-inch prop was much less prone to ventilate and a better performing prop overall but with its tendency to let the engine over rev, it is still not a suitable prop for this outfit.

Back to the 144-126 Torque Shift prop which was still adjusted for approximately 23 inches in pitch. Top speed went to 51.8 mph at 4650 rpm. With the 12-inch initial pitch, we expected some of the same ventilation problem we experienced the first time around. It is amazing what an additional inch of depth and 8 more inches of setback will do. There was a trace of ventilation on initial acceleration, but it was considerably less than first experienced and 0-to-30 acceleration times dropped to 6.7 seconds.

The 144-132 prop, adjusted to 23 inches of maximum pitch, produced a top speed of 52.0 mph at 4700 rpm at its minimum setting. With the initial pitch of 14 inches, acceleration from 0 to 30 mph fell off slightly to 6.8 seconds. Again there were no ventilation problems with this prop on initial acceleration; at top speed, we could use just a tad more positive trim.

There is little doubt that the Torque Shift prop and Stern Jack are effective performance enhancing devices. With the two units, we were able to raise top speed from 47.7 mph to 52.0 mph. a 4.3 mph gain. At the same time we took our 0-to-30 mph time from a very sluggish 9.9 seconds to a snappy 6.8 seconds. We could have done slightly better, had we been willing to give up a bit in top speed. At these performance levels, it is a tradeoff not worth making.

From a performance gain per dollar spent, the Torque Shift prop is the hands-down winner. The prop alone was responsible for a top-speed gain of 2.3 mph and a reduction of 0-to-30-acceleration times of 2.9 seconds.

The Stern Jack added another 2 mph to the top speed and shaved an additional 0.2 of a second off of the 0-to-30 mph acceleration time. This is respectable performance for an add on, but the Stem Jack. being a more costly piece of equipment. was less cost-effective in the over-all project.

It is important to remember that not every boat will respond to these modifications in exactly the same way. Some will do better and some won't fare as well. I have yet to experience a boat where there were not at least some gains with the addition of a Stern Jack. Over the years, Land & Sea has compiled a large database on the performance gains of a wide variety of boats equipped with the Stern Jack. Any interested party should contact Land & Sea for recommendations.

Performance Results
  Stock* Torque Shift Prop**

Stern Jack w/ Torque Shift Prop**

Top Speed 47.7 50.0 52.0
Acceleration (0-30 mph) 9.9 sec 7.0 sec 6.8 sec
*23-inch MerCruiser 3-blade aluminum prop
**No. 144-132, adjusted to 23-inch pitch at maximum

Trailer Boats
March 1999



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