Mercury made its already hot and fast 115 four-stroke hotter and faster.
When Mercury Marine came out with a new version of its 115 FourStroke on its 75th anniversary, in 2014, I got to check it out in Wisconsin. At this year’s Miami Boat Show in February, Mercury one-upped itself, unveiling the 115 Pro XS FourStroke, a high-output version of that already hot outboard. I got a chance to test it at the show on a Mako Pro Skiff 19 CC, which sports Mako’s Advanced Inverted V (AIV) hull, which is a modified catamaran design. And it’s a good thing it wasn’t the usual flat-bottomed skiff, because the wind was starching out the flags at the docks on Virginia Key, but Mercury had something up its sleeve to help cope with choppy conditions on Biscayne Bay.
Mercury based the 115 Pro XS on the same 2.1L, four-cylinder platform the 115 FourStroke uses. Only Honda has more displacement in its class, with the 2.4L BF115, but that’s a detuned BF150 that weighs 122 pounds more than the Mercury, which is the lightest in its class at 363 pounds with the Command Thrust gearcase ours had. (The regular gearcase model weighs 359 pounds.) The engine itself is a blend of new technology and a simple single overhead cam (SOHC) design that has two valves per cylinder. Suzuki, Yamaha and Honda all employ dual overhead cam (DOHC) engines with four valves per cylinder on their four-stroke 115 outboards. The cam design is one of the reasons the Merc is 18 pounds lighter than anything else in its class — and 16 pounds lighter than the two-stroke it replaces.
Firing up the 115 Pro XS and shoving off from the dock, we idled away with the Merc at a preternaturally quiet 58 decibels. Vibration was nearly nil, thanks to the Focused Mount System, which positions upper motor mounts at 45-degree angles to the engine centerline. The rubber mounts are located away from the heat-producing powerhead, which can shorten the life of rubber. Once we got under the Rickenbacker Causeway Bridge and out of the no-wake zone, we could finally romp, but first we pushed a magic button.
Hands Off The Trim Switch
On the dash of our Mako test boat was a compact panel labeled Active Trim, a Mercury system also introduced at the show. Unlike Volvo Penta’s Boat Trim System (BTS), which bases its trim level on engine rpm, Mercury’s patented system is speed-based and even has a built-in GPS receiver for accuracy. Mercury performed many tests on boats of all kinds and analyzed which trim positions helped them achieve their best performance at varying speeds and then created five general profiles that a boat builder or dealer can assign to the system for a particular boat. Even for expert boaters, it’s well worth the $500 cost.
Active Trim engaged with the press of one button and worked remarkably well when we hit the throttle for our time-to-plane test. The 115 Pro XS was properly trimmed down and allowed the Mako Pro Skiff 19 to reach plane in just 2.9 seconds. Zero to 30 mph times are always a bit tricky, because you’re not sure how to trim during the event to “unstick” the hull from the water. Usually it’s trial and error, requiring multiple attempts, but with Active Trim, I jammed it and felt the power of the 115 Pro XS accelerate hard. After the boat planed, the engine trimmed itself out, and we reached 30 mph in just 8.2 seconds. Where the newfound power is really noticeable is during acceleration from cruise speed. Midrange throttle response is phenomenal, and the Active Trim keeps up no matter how the captain jockeys the throttle. The only time we adjusted the trim manually — using the up and down buttons — was to squeak out the last mph in our top-speed run, which hit 45.8 mph. The system disengages at 50 mph, to allow the driver to take over on other, faster boats.
One new feature is Idle-Charge, which boosts battery charging at idle speeds by up to 48 percent when it senses the batteries could use some extra juice. It will be especially appreciated by fishermen, who are packing big-screen fishfinders and trolling motors.
We tested the 115 Pro XS with the Command Thrust gearcase, which has a lower 2.38:1 gear ratio than the standard 2.07 lower unit. The lower ratio allowed it to swing a bigger 13.8-inch diameter Enertia prop on our test. And because the Pro XS is a higher-revving engine than the 115 FourStroke (300 rpm more), owners can run reduced pitch on the props for better performance, such as the 20-inch pitch prop we used.
It comes in a 20- and 25-inch shaft version, and it comes in a counter-rotating model, which would be perfect for powering smaller, dual-engine catamarans. Because of its two available shaft lengths and the choice of lower units, the 115 Pro XS is a great match on a wide range of boats, including flats and bay boats, pontoons, and sub-20-foot runabouts.