Posted: June 1, 2014
Yamaha’s new F115B means you can use the words lightweight and four-stroke in the same sentence.For many boats, 115 is the magic horsepower number that allows owners to participate in the full spectrum of activities, including most watersports. It’s often the engine size that’s paired with boat manufacturers’ compact “sport” boat packages, which are typically gateway models designed to bring budget-conscious buyers into the brand’s fold. It’s also one of the few engines that’s on nearly every boat type from 16-foot aluminum fishing boats to pontoons to fiberglass runabouts all the way to houseboats. Yamaha updated its F115 in 2012, but this year its engineers made significant improvements in many areas, including weight, to create the new F115B.
Lightest in its Class
For Yamaha outboard fans, choosing an F115 over the next largest outboard — the F150 — is a big decision, given the difference in power. But fortunately, Yamaha’s new F115B makes the decision easier by providing snappy performance to go along with it being the lightest 115 four-stroke on the market, a whopping 101 pounds lighter than the Honda BF115. At 377 pounds, the Yamaha F115B comes within a scant two pounds (dry weight) of the Evinrude E-TEC and Mercury OptiMax two-strokes of the same horsepower. Yamaha put its F115A on a weight-loss program to create the F115B by concentrating on items that didn’t compromise performance. Components such as the cowling and oil pan are made from a lightweight composite material, and engineers went to a single-ram power trim and tilt and employed a new mounting bracket. Inside the engine, dimpled cylinder sleeves, like those in the Yamaha F350, reduce weight, add strength and aid in heat transfer to keep the engine cooler, which is always a good thing. All this adds up to an engine that is ideal even for weight-sensitive models like flats boats, which can’t tolerate excess load.
The F115B has new valves and a cylinder head with a new 60mm single-throttle body with Yamaha’s long-intake track system and a new four-into-one exhaust manifold. It features an all-new powerhead with increased bore and stroke that measures slightly more than 1.8L to help it make more power with less effort. It has a dual-overhead cam (DOHC) design and a larger intake and exhaust for easier breathing, which leads to a better holeshot and throttle response in its midrange. The compression ratio has been increased to 10.0:1, and the top rpm has risen by 300, giving it a wide-open throttle range of 5300-6300 rpm. Unlike automobile engines, the F115B is designed to run wide open for hours if you’re in a hurry.
Numbers Don’t Lie
I had a chance to test the new outboard at the Miami Boat Show aboard a Scout 195 Sportfish, a stout 19-foot, 5-inch center console that weighs 2,150 pounds and sports a deep-V hull with 19 degrees of deadrise. It’s rated for a 150, but Scout recommends the new F115B instead. One thing is for certain: Running a 115 on a boat rated for a 150 means owners will be pushing it hard, and Yamaha builds the high-revving outboard knowing full well it will be flogged, which is the way we tested it.
Early four-stroke outboards were characterized as being tepid performers, but those days are over as evidenced by the Scout’s time to plane of 3 seconds. The Yamaha pulled strong in the midrange, and 30 mph was reached in 7.5 seconds. The best cruise speed for fuel economy was at 3500 rpm, which netted 6 mpg at 20 mph. Most Yamahas I’ve tested in the last few years seem to like being run at 4500 rpm, and the F115B is no different, producing a happy speed of 30 mph and reducing its fuel economy by less than 1 mpg (5.26). Sound levels were pretty typical for a four-stroke of this size, topping out at 94 decibels at WOT and a more moderate 85 at 3500 rpm. Although the F115B is rated to rev up to 6300 rpm, during our test it reached peak rpm at 5900 at the Scout’s top speed of 41.8 mph.
Charged and Ready
One of the major upgrades Yamaha made was to the outboard’s ability to keep batteries charged even when they’re powering the growing suite of electronics even small boats tend to carry these days. The alternator output has been increased to 35 amps at WOT, compared to 24 amps with the previous F115. At 1000 rpm, it produces a full 28 amps, so while you are trolling, you are charging. It also features the Variable Trolling RPM Switch (VTS), which allows a driver to tweak trolling speeds in increments of only 50 rpm, allowing the perfect presentation of lures or dialing in the maximum no-wake speed. For people who like to go old school, Yamaha has a Multi-Function Tiller handle option. New for this year is Yamaha’s Talon aluminum prop series F115B featuring the Shift Dampening System (SDS), which reduces the clunking sound when the engine is put in gear thanks to the specially designed splined rubber hub and spacer that absorb much of the force. F115B models can even be rigged to interface with any NMEA 2000–compatible display using a gateway device. In addition, the new outboard is Y-COP compatible, which is an exclusive Yamaha security feature that allows the owner to immobilize the engine using a key fob–like control to prevent unauthorized usage.
SpecsType: In-line four-cylinder DOHC four-stroke
Full throttle range: 5300-6300 rpm
Weight: 377 lbs. (20-in. shaft)
386 lbs. (25-in. shaft)
Gear ratio: 2.15:1
PerformanceTested with: Scout 195 Sportfish
Time to plane: 3.0 secs.
0-30 mph 7.5 secs.
Top speed: 41.8 mph
Decibels at idle: 58
Cruise: 30.0 mph/4500 rpm/85 dB-A
Peak: 41.8 mph/5900 rpm/94 dB-A