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Introduced last fall as part of an exciting lightweight family of powerful 2.1 liter four-stroke outboards, Merc's new 115 is the largest of three siblings that is sure to find its way onto the transoms of many coastal sport fishing craft.
By Capt. John N. Raguso
Like a top middleweight boxer or MMA fighter, the new Merc 115-horsepower FourStroke offers a lot of power and performance for its relatively diminutive size. At 359 pounds for the 20-inch shaft "L" version, the Merc 115 is 20 pounds lighter than its closest four-stroke competitor - it's even 16 pounds lighter than a Mercury OptiMax two-stroke that features a smaller 1.5-liter block. That added displacement creates more low-end torque to pop your boat up on plane faster, accelerate with authority and provide optimal fuel efficiency at cruising speeds. The single overhead cam (SOHC) valve train never needs maintenance, which is a nice cost-saving feature for extended ownership.

The new 115 FourStroke and its 75- and 90-horsepower 2.1-liter siblings are designed using the same internal architecture as Merc's very successful 150 FourStroke. The benefit is that they are some of the easiest four-strokes to maintain and keep running with a minimum of tools and special knowledge. When routine service is needed, it's nice to have the step-by-step instructions posted where you can find them right away - like right under the cowling on the front engine cover.

Everything you need to do at the 100-hour and 300-hour intervals is clearly spelled out on a large waterproof decal. You can even use your smart phone to scan the QR code on the maintenance label and it will link you to a Mercury mobile site with handy "how to" online videos. When it's time to change the oil or the fuel filter, everything is out in the open with easy access. No tools are required to change the fuel filter, which takes less than a minute to swap out for a fresh one. The convenient drip tray positioned under the automotive-style, spin-on oil filter catches and residual oil left in the system after the sump is drained. This brings outboard ownership and maintenance to a new level of simplicity, insuring that you will stay on top of it.

The Merc 115 FourStroke's ability to allow each operator to tailor optimum performance for his/her ride is a unique selling proposition that puts this outboard at the top of her competitive class. The standard 2.07:1 ratio gearcase possesses significantly higher hydrodynamic efficiency than last year's 1.7-liter version, which equates to less drag and better fuel efficiency when underway. The added 0.4 liters of cylinder displacement also adds more power and torque. This standard streamlined gearcase delivers the best performance on lighter coastal fishing boat hulls, like aluminum or fiberglass skiffs, flats boats and small bay boats with modified-vee running bottoms. The new optional Command Thrust gearcase on the new Mercs replaces the older "BigFoot" models and features a lower 2.38:1 gear ratio with a larger bullet that allows the use of "big boy" propellers used on 150- to 350-horsepwer Mercs. The larger props grab more water, providing increased lift and acceleration and the CT gearcase is the perfect match for heavier fiberglass skiffs, commercial boats, walk-arounds and center consoles that sport deep-vee hull designs and transit coastal and open ocean waters.

To demonstrate how each gearcase maximizes on the water performance, two recent factory tests tell the story. A 115 Merc FourStroke was hitched to the transom of a Carolina Skiff 218 DLV, producing a top speed of 43.2 mph at 6,000 rpm and 5.4 mpg at optimum cruising speed, getting 27.1 mph at 4 grand, spinning a 21-inch pitch laser II S/S prop. A similar Merc 115 FourStroke was installed on a Scout 195 Sportfish CC, but this one was equipped with a Command Thrust gearcase and 21-inch pitch Enertia prop, due to this vessel's deep-vee hull design, larger fuel tank and more substantial displacement. The combination of the lower gear ratio and larger blade diameter of the Enertia's three-blade stainless steel wheel enabled the Scout to hit a top speed of 43.6 mph at 5,800 rpm, with superb 5.4-mpg fuel efficiency at 4,000 revs, hitting 25.9 mph at 4.8 gph. Point proven, as each lower unit was the right choice for these two disparate applications.

The new 2.1L Merc 115 FourStroke, along with her two smaller 75- and 90-horsepower sisters, are next-gen outboards that are as light (or lighter) than a two-stroke, are equally as fuel efficient, plus offer more years of useful service due to the inherent longevity of the four-stroke design for marine applications.