The new Mercury 115 FourStroke is smaller, lighter, more powerful and perhaps more versatile than any motor in this key segment of the outboard market, and it was introduced at an event in Wisconsin lately that also noted the 75th anniversary of the founding of Kiekhaefer Mercury in the state. The new 2.1-liter, four-cylinder outboard will also be offered with a 75- and 90-hp ratings.
While the motors in this category may not offer the glamour and technical flash of those at the top of the line, the segment does represent 30 percent of annual sales, according to Mercury. These motors wind up on a wide variety of boats, in water from the Florida flats to the Lake of the Woods, and in some applications may prove a viable alternative to much heavier 150-hp models.
In concept, the new 2.1-liter motors are related to the Mercury 150 FourStroke that has been a smashing sales success since it debuted in 2011. Displacement is generous so power is generated without stress. At the 115 rating, only the 2.4-liter Honda BF115 offers more cubic inches, but the Honda is also 120 pounds heavier than the new Merc. There has been a major effort to boost efficiency through weight reduction and gearcase design – at 359 pounds, the new Mercury 115 is the lightest model at this rating, an amazing 40 pounds lighter than the 1.7-liter model it replaces and 20 pounds lighter than the new Yamaha F115. There’s a careful balance between technology and simplicity – a single over-head camshaft controlling eight valves is more compact and requires fewer parts than the 16-valve, double over-head cam designs featured on Yamaha and Suzuki 115 HP models, but Mercury employs low-friction roller finger followers in the valve train that boost efficiency and never require maintenance. Design features borrowed from the 150 FourStroke include a light-weight cowl that provides outstanding sound reduction, the Focused Mount System that reduces vibration, and a large muffler. All of the easy-maintenance features introduced on the FourStroke 150 are here, too – a drip tray under the oil filter and quarter-turn oil drain fitting that accepts a hose, a quick-change fuel filter with snap-fit connectors, a flush fitting that can be reached from inside or outside the boat, and a label on the powerhead with all maintenance specs and a QR code you can scan with a smart phone to watch service demonstration videos.
An all-new standard gearcase was designed for the FourStroke 75 HP, 90 HP, and 115 HP models. Intended to optimize performance on light, fast boats, it produces 15 percent less drag than the gearcase it replaces, according to Mercury. This 4.2-inch diameter gearcase has a 2.07:1 gear ratio. The FourStroke 90 and FourStroke 115 models will also be offered with a 4.9-inch Command Thrust gearcase (a term that’s replacing the previous and unfortunate Big Foot tag) with a 2.38:1 ratio and available counter-rotation. This is the same gearcase used on the 150 FourStroke. On some boats the Command Thrust gearcase provides a significant performance gain because the case provides more hydrodynamic lift aft to reduce drag, and because it can swing a prop with more pitch. As a demonstration, Mercury rigged a 2,685-lb. 17'11" Four Winns H180 RS with the standard FourStroke 115 and with the Command Thrust version.
The Command Thrust case delivered a modest gain in hole shot (10.8 seconds versus 11.0) and top speed (44.9 MPH and 43.5), but there’s a huge difference in cruising speed – 13 percent faster at 4500 rpm, with the Command Thrust. And, the Command Thrust model posted a 35 percent gain in fuel economy at cruising speed. Both are bonuses provided by the 22-pitch Enertia prop that the motor can handle, thanks to the low gear ratio. I was also told on the side at the intro that the new FourStroke 115 is “strong” in the category, meaning it’s producing more than 115 HP. That same source told me the previous, 1.7-liter model actually made less than 115 HP.
The Command Thrust case and a prop with lots of blade area will also be a good match for pontoons. But according to Merc, the Command Thrust models are not the right choice for lighter boats with pad-hull designs because the gearcase delivers too much lift. One of my favorite boats at the demo was a Tracker Pro Team 190 TX, an aluminum bass boat rated for 115 HP but rigged with a Mercury 90 FourStroke with the standard gearcase. Running a 20-pitch Laser II prop, this boat planed smartly, ran over a flat-calm Lake Winnebago at 45 mph and aired out well with modest trim. Fuel economy was outstanding at a peak 8.1 mpg at 3500 rpm, and 6.3 mpg at a more stimulating speed of 39 mph at 5000 rpm. While this boat was lightly loaded (no fishing gear) I would be very satisfied with this performance, and I couldn’t see spending an extra $1,000 for a 115 on this boat.
All of the new 2.1-liter models I ran were sewing-machine smooth and incredibly quiet. On the Tracker I could have a conversation at cruising speed without raising my voice. Here’s an example of the attention to detail Merc has lavished on these motors: while we looked over the powerhead, Jeff Broman, the project leader for the 2.1, pointed to the crankshaft position sensor that collects impulses from teeth on top of the flywheel. The clearance between each tooth and the sensor is thinner than a sheet of paper. During development of the engine, Broman’s team was puzzled by a high-pitched whistle coming from the engine, and traced it to the air whizzing between the two parts.
“We never noticed this before because previous motors were never this quiet,” said Broman. “So to fix it we beveled off the edges of the pick-up, and the sound went away.”
The 75 HP, 90 HP and 115 HP FourStroke models are in production and being shipped to dealers and boat builders. Pricing (MSRP) ranges from $9,235 for the 75 FourStroke (offered only with a 20-inch shaft) to $10,975 for the 115 Command Thrust model. The Command Thrust gearcase adds $330 to the price of any 90 or 115 HP model. All 2.1-liter models are available with the optional Big Tiller control, and there are 65 and 80 HP jet-drive versions as well.
Mercury says it has more than 17,000 testing hours behind the new 2.1-liter models, more time than it has ever invested in a new outboard. Seasons on the water is the only way to truly measure durability, but it appear Mercury has really raised the bar for outboards in this segment.
For information, visit Mercury Marine.