Jet Blast

Jet boats are white hot. The National Marine Manufacturers Association (NMMA) revealed that jet-boat sales were up an astonishing 36.4 percent in 2012. Ironically, in September 2012, Bombardier Recreational Products announced it was pulling out of the jet-boat business to concentrate on its more-profitable core products such as its state-of-the-art personal watercraft. That void has sparked a resurgence in the number of manufacturers jumping into the jet-boat business, such as Sea Ray, Chaparral, Scarab and Glastron. Coincidence, perhaps. The last three will be using Rotax 4-TEC 1503 engines that BRP is making available to other companies now that it is out of the boat business. The Sea Ray Jet models are using a German-built Weber 850cc engine, while Yamaha, the undisputed jet-boat leader, is using its own FX HO/SHO 1.8L engine on most of its boats. Let’s take a look under the hood and see what’s happening down there.

Weber MPE 850

Engine details
Weber is the “new” kid on the jet-boat engine block, but it has been building marine engines since 2003 and is powering Sea Ray’s Jet 21 and Jet 24. It is a well-established name in the automotive world, having built components for companies such as BMW, VW, Audi, Ford and Chrysler since 1969. The new MPE 850 being used on the new Sea Rays is a modified version of the venerable 750, building on the reliability it has shown over the past decade.

There are two huge differences between this engine and the others: its small 850cc displacement (0.85 liters) and its light weight (198 pounds for the 120 hp version). Plus, it is turbocharged rather than supercharged like the high-performance versions of the Sea-Doo Rotax and Yamaha engines. Weber uses a twin parallel-cylinder design similar to certain high-performance motorcycles such as the Kawasaki Ninja 250. For cooling, it uses a closed-loop system and is lubricated using a dry-sump oil system. Turbochargers power a compressor from its exhaust gases, which historically produces throttle “lag,” because the engine has to spool up first before producing enough exhaust pressure to spin the compressor fan. But by using performance features such as an intercooler along with Map-based (software-controlled) multipoint fuel injection, which also automatically compensates for altitude, the Weber has no discernible lag when you jam the throttle, although its power is slower to build than on supercharged models.

We tested the 120 hp version of the Weber 850 in a twin-engine configuration on Sea Ray’s new Jet 21, a 21-foot, 6-inch, 2,883-pound bowrider-style boat with a deep-V hull that sports 21 degrees of deadrise. When you jam the single-lever throttle, the power comes on very smoothly, which is a good thing for pulling skiers, and it reached plane in 3.3 seconds. Its time to 30 mph was 6.5 seconds, and the Jet 21 reached a top speed of 47 mph. There’s also a 155 hp version of the Weber, which Sea Ray uses on its 24-footer, also in a twin-engine configuration, that’s even faster.

Rotax 4-TEC 1503

Engine details
The 1.5L Rotax 4-TEC 1503 is the momma bear of this trio in displacement. It’s an in-line, three-cylinder engine that uses 12 valves and a drive-by-wire system. It comes in two configurations: 215 hp and 260 hp. Both are supercharged and intercooled; the main differences in the higher horsepower incarnation are the more potent supercharger and the external intercooler. Superchargers make power more quickly than their turbocharger brethren because the turbine is powered by a direct-drive system, so as soon as you jam the throttle, it’s producing boost. Like all charged-air systems, the idea is to jam more air into the combustion chamber, so a corresponding increase of fuel can be added. The 260 hp version prefers premium fuel, but its ECU computer brain will adjust if regular gas is the only kind available, while regular is the preferred fuel for the 215 hp model.

Boating World has tested both variants of this engine on many different platforms, including the Sea-Doo GTR 215 personal watercraft, whose review can be found on page 32 of this issue. Since Glastron, Scarab and Chaparral haven’t yet given the media boats to test, our performance comparison is based on one of the most recent models before BRP discontinued building boats. The 210 Challenger SE is a 3,100-pound boat that sports twin 215 hp Rotax 1503 engines, which give it tremendous performance. On plane in just 2.3 seconds, it streaked to 30 mph in 4.3 seconds with a top speed of 54 mph.


Engine details
Yamaha’s newest engine features the largest displacement in the jet-boat and PWC industry. The goal of this engine is to make power as effortlessly as possible for the greatest possible reliability. It’s an in-line four-cylinder engine that features a dual overhead cam design and 16 valves. One of its unique features is the coil-in-plug design that delivers a hotter spark for more complete combustion. While Yamaha doesn’t officially release its horsepower ratings on these engines, the supercharged SHO model is guesstimated to produce around 210 hp, while the normally aspirated (nonsupercharged) HO version cranks out around 180 hp. In other words, they aren’t even breaking a sweat. It also uses a drive-by-wire throttle, which allows it to include features such as Cruise Assist and No-Wake mode. Both run on regular gas.

Our most recent test was on the SX192, a single-engine, 19-foot, 2-inch sportboat with 19 degrees of deadrise that weighs 2,150 pounds. It was powered by a single SHO Yamaha that proved to be more than enough power. It reached plane in 2.4 seconds and hit 30 mph in 5.3 seconds, with a top speed of 49 mph. The larger 212 model — 21 feet, 3 inches long and 3,060 pounds — powered by a pair of the lower-horsepower HO engines, reached plane in 2.5 seconds, hit 30 mph in only 4 seconds and topped out at 56 mph.


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