Because of the popularity of our comparison articles, I thought it would be fun to do one for the best 115 HP outboards. An incredibly versatile power option for fishing boats of all kinds, small runabouts, small pontoons and almost any boat under 19’ really. There are 2 serious contenders here, maybe 3 if you include Suzuki but the Mercury 115 and Yamaha 115 are the leaders by far when it comes to specifications. For our purposes I want to look at the Mercury 115 Pro XS and the Yamaha 115 Vmax SHO version, the semi performance versions of these diminutive 4 cylinder four strokes.

When it comes to comparing the Yamaha and the Merc it is no surprise that they are so close in almost every detail. Where Mercury leads is in options, you can get an optional “Command Thrust” gearcase with the Merc; a larger diameter case with lower gears for pushing bigger boats. Both engines come in 20” or 25” mid sections. The Yamaha utilizes a double overhead cam with 4 valves per cylinder, whereas Mercury uses a more traditional 2 valve SOHC setup.

Both of these 4 cylinder engines will have great low end torque, the Mercury having a slight displacement edge, 2.1L to 1.8L and Yamaha having a slight edge with the DOHC 4 valve design making more power up top. Of course, both probably make very similar HP, definitely more than 115 HP technically, and both are allowed to rev 300 more RPM than the regular versions. Standard gearcases are similar, with the 115 ProXS offering the taller 2.07:1 ratio over the Yamaha’s 2.15:1. I would give the advantage to Mercury here, potentially more torque with taller gears is going to equate to more speed when everything else is equal. The Mercury command thrust has 2.33:1 gears which are housed in the larger 4.9” case from the 150 HP.

Let’s take a look at some tests knowing that this is about as close as it gets in an incredibly competitive engine class. Both are light, with the Pro XS being slightly lighter, 360 Lbs. vs 377 Lbs for the Vmax SHO. This is why I love this category, if you’re repowering an older lightweight performance boat, these are truly light engines.

Bass boats are always good tests to look at because they are semi performance hulls and many in this size are very similar, so we can get some good head to head type comparisons even if it’s not the exact same hull. Unfortunately, it was difficult to find proper bass boat tests with the Yamaha. We will look at a Nitro bass boat vs a Hell’s Bay flats boat and a Crestliner aluminum bass boat vs an Xpress aluminum bass boat. These boats will be slow compared to performance boats like an old Hydrostream, Action, any Allison or any other light V pad performance hulls. Fishing boats tend to be a heavier and going fast isn’t the focus.

Yamaha 115 Vmax SHO, Hell’s Bay Marquesa

The Hell’s Bay Marquesa is a really cool technical skiff / flats boat. At 18’1” and a 6’7” beam, the boat was tested at 1,100 lbs. These are light but basically flat hulls, 12 degree deadrise, with very little lift, so they aren’t as fast as you would think. However, they are fishing machines and very well built. The focus is shallow water capability and being able to get to fishing areas other boats can’t. Amazingly, the Hell’s Bay only drafts 7” of water.

With a 115 SHO, from the Yamaha bulletins, the little Hell’s Bay runs 51.2 MPH at 6,000 RPM, turning a 20” 13-⅛” Talon SS prop. Test weight includes Power Pole, 2 Lithium Ion batteries, 2 people, 5 gallons of fuel, safety and test gear. If you were going for a top speed, removing the trolling motor, power pole and some gear you could see a little better. The Yamaha can turn 6,300 RPM. That’s not bad though for this boat.

I couldn’t find actual tests but anecdotally owners of Marquesa’s the with the Mercury 115 ProXS report 52 MPH, which is where you could get this Yamaha to run with a few adjustments, showing how close these two match up. For cruising, the Yamaha ran best at 3,500 RPM at 30 MPH, getting 8.87 MPG, which is great.

Mercury 115 ProXS, Nitro Z17

How does the Nitro compare to the Hell’s Bay from purely a design perspective? It’s very different, here are the details; a 17' 4'' length, beam of 8' 4'' and a dry weight of 1,450 lbs. Although heavier and tested at 2,317 lbs, the Nitro has a more sophisticated hull, 16 degree deadrise and gets more lift from it’s design, with a pad bottom.

With the standard 2.07 gearcase, the 115 ProXS turning a small diameter, 12.7”, Spitfire 19” at 6,000 RPM, the Z17 went 51.3. At 3,500 RPM it ran 26 MPH getting 7.5 MPG. As you can see, completely different boats, similar engines with slightly different gearing and they achieve almost the exact same speed. The Nitro is very heavy for its size and like the Marquesa is loaded with extra stuff, trolling motor, extra battery etc.

The Nitro has a faster hull design, the Hell’s Bay uses more advanced construction to be lighter but doesn’t get the same lift, so viola, you get similar performance, illustrating the importance of the hull design. The Hell’s Bay outperforms it at cruising RPM, because of the weight and the small Spitfire prop maybe a little too small, slipping quite a bit. Either way, the engines swapped out would probably achieve about the same overall performance. Both should strive for running closer to the 6,300 range. Now imagine these engines on a small and light Hydrostream or little Checkmate Predictor. You could get them to run really well.

A closer comparison might be these two aluminum bass boats. A Crestliner TC 18, measures 18’3” and has a 1,220 Lbs dry weight. With a Mercury 115 ProXS and standard case it’s running 50.3 MPH at 6,150 RPM. And, the cruise is 3,500 RPM at 27 MPH. This is from the Mercury Bulletin. These numbers are pretty good for a basic aluminum boat that isn’t light and doesn’t have much of a hull design. The Spitfire 19” was also used on this boat.

For a good comparison, the Xpress H18 measures in at 17' 10", a 7' 9" beam and a dry weight of 1,215 lbs. This is about as head to head as it gets for two different hulls. Spinning a Talon SS, 20” pitch, the Xpress hits 50 MPH at 6,300 RPM. Keep in mind the Yamaha 115 SHO has 2.15 gears, which is a slight disadvantage for top speed in most cases. Cruise was also 27 MPH at 3,500 RPM and just under 7 MPG. Also, these are different drivers, conditions and tests all together so there is no telling how they were driven and other factors. This is really close. With some tinkering and some weight reduction, there is probably 1 or 2 MPH in each boat.

One takeaway is the heaviest boat is tied for the fastest with the lightest boat. This is strictly because it has a better hull design than the others but the Nitro is still a bit of a pig. If you strapped one of these engines on an Allison Grand Sport or XB it would run 75+ MPH. Any of the small Hydrostreams would rip with one of these setup right. These four stokes, because of the torque and RPM range will most likely outperform many older 115 HPs. That’s why I really like them, great affordable repower engines for small boats and these engines are light. If you don’t need to go really fast, then these can be great options, never mind the incredible fuel mileage they would get. You can find lightly used ones for good deals too.

I really like both of these outboards, you can’t go wrong with either one. The Mercury has the gear case option, plus the command thrust is the same as the 150 HP case, so you could slide in the 1.92 gears from that engine if you were inclined. Both engines are excellent here and you can see why they lead the 115 HP class. I would want to run them myself before declaring a winner.

Mercury and Yamaha own this market. The Suzuki 115 SS has gearing that is way too low for anything performance oriented. That might change as Suzuki is slowly adding gear ratio options to their SS lineup, the larger 150 and 200 SS now have 2:1 gears, so hopefully that trickles down to the 115 HP because competition is good.