Quick Answer The Mercury 115 HP FourStroke weighs 359 lbs, making it the lightest 115 HP outboard available. It runs on the same 2.1L inline-4 block as the 75 and 90, tuned to 6,000 RPM. It's the right motor for 17, 20 ft aluminum fishing boats and mid-to-large pontoons (with...
Quick Answer
The Mercury 115 HP FourStroke weighs 359 lbs, making it the lightest 115 HP outboard available. It runs on the same 2.1L inline-4 block as the 75 and 90, tuned to 6,000 RPM. It's the right motor for 17, 20 ft aluminum fishing boats and mid-to-large pontoons (with Command Thrust), and it's the default choice for Ontario boaters who want real headroom without crossing into V6 territory and the price jump that comes with it.
Mercury 115 HP FourStroke Review
"Lightest 115 HP available" isn't a marketing line, it's a spec that changes how a boat behaves. An 80, 100 lb weight difference over the older two-stroke motors this motor commonly replaces affects how the hull sits in the water, how early it gets on plane, what the fuel economy looks like, and what happens at the trailer hitch.
Harris Boat Works has been selling and servicing Mercury outboards on Rice Lake since 1947. We're a third-generation family marina and a Mercury Marine Platinum dealer. The 115 FourStroke is one of the motors we sell and service most. Here's an honest look at where it makes sense, and where it doesn't.
Why "Lightest 115 HP Available" Actually Matters
The Mercury 115 ELPT FourStroke weighs 359 lbs. An older Mercury 115 OptiMax, the motor it commonly replaces, weighs around 425 lbs. That's 80, 100 lbs of difference. On a 17, 20 ft aluminum fishing boat, that weight change does real things:
- The hull sits higher at rest, improving fuel economy before you even turn the key.
- The boat planes earlier with the same load.
- The transom takes less stress over the long term.
- Trailer tongue weight drops, which matters if you're hauling with a half-ton truck.
Those aren't abstract benefits. They're what customers notice after a season.
What the 2.1L Family Shares
The 115 HP FourStroke belongs to Mercury's 75, 115 HP family: five motors (75, 80, 90, 100, 115) built on the same 2.1L inline-4 block with an 8-valve SOHC, maintenance-free valve train, and 17,000 hours of factory testing on this generation before shipping.
What they all share:
- Same 2.1L inline-4 block
- Maintenance-free valve train (no cam service, no valve lash adjustments)
- 35-amp / 441-watt alternator
- SmartCraft compatibility
- 3-year factory standard warranty (plus available promotional bonus years)
The 115 is the highest tuning of this family. It runs to 6,000 RPM and makes peak HP later in the power curve. Compared to the 90, the step from 90 to 115 is tuning, not a different motor. There is no weight penalty. The only real cost is price and fuel burn at full throttle.
What "ELPT" and "CT" Mean
- E, Electric start
- L, Long shaft (20"), fits the most common transom
- PT, Power trim and tilt from the helm
- CT, Command Thrust gearcase (larger lower unit, bigger prop swing, typically 14 or 14.5" instead of 13")
This post covers the 115 ELPT FourStroke and the 115 ELPT Command Thrust. There's also a 115 Pro XS (performance-tuned, sport gearcase) and a counter-rotation 115 (for twin setups). Different SKUs, different prices, different applications. Use the quote builder at mercuryrepower.ca to compare.
When to Take the Command Thrust Upgrade
| Boat Type |
Take CT? |
| Pontoon (any size) |
Almost always |
| Aluminum fishing boat |
Rarely |
| Fibreglass runabout |
Case by case |
CT gives you more low-end pulling power and hole-shot at the cost of some top-end speed. On a flat-bottom pontoon hull, that trade-off is worth it every time. On an aluminum fishing boat that runs at speed, the standard gearcase's lower drag profile is the better fit.
Where the 115 HP FourStroke Is the Right Answer
17, 20 ft aluminum fishing boats with heavier loads
A 16 ft boat with two anglers is the 90's job. When the hull is a 17, 20 ft Lund, Princecraft, Crestliner, or Legend with four people, full gear, a livewell, two batteries, and a trolling motor up front, the 115 is the right call. Cruise around 30, 35 mph, top out around 42, 48 mph depending on prop and load.
Mid-to-large pontoons, 20, 24 ft
This is where the 115 CT earns its keep. A 22 ft pontoon with a full family load and a cooler deserves at least 90 CT. The 115 CT is the right answer if the pontoon is a tritoon, if you tow tubes, or if the boat simply sits heavy.
Family runabouts that do a bit of everything
Cruise, fish, tow a tube, watersports occasionally, the 115 handles all of it without working hard, and does it fuel-efficiently.
Repowers from older two-strokes
The most common repower candidates for the 115 ELPT are older 115 OptiMax, 115, 150 OMC, and 90, 115 Yamaha two-strokes. Occasionally a boat that had a 150 V6 but found it was more motor than needed steps down to the 115.
You can build a live CAD quote for your repower online at Mercury Repower Centre.
The outcome on most of these repowers: the boat feels lighter, runs quieter, and uses 25, 35% less fuel for the same day on the water. After a season, some customers don't miss the V6 feel at all.
Where the 115 HP FourStroke Is the Wrong Call
Bass-boat hole-shot. The 115 ELPT FourStroke is tuned for fuel economy, smooth cruising, and reliability, not snapping off the dock. If you want strong acceleration on a 19 ft fishing rig, the 115 Pro XS is the different motor you're looking for.
Heavy tritoons, 24+ ft pontoons with full loads, or houseboats. These applications need 150 V6 or higher. The 115 will push them, but it'll work harder than it should over its service life.
Hulls rated under 90 HP. Capacity plate is the ceiling. If the plate says 90 HP max, a 115 is illegal. We won't put it on your boat.
When you actually need the 150. If you've already been thinking about the 150 because the boat needs it, don't compromise. Buying the 115 to save money on a hull that genuinely wants a V6 just means you'll be doing this again in a few years.
How the 115 Compares to the 90 and the 150
|
90 ELPT |
115 ELPT |
150 ELPT (V6) |
| Block |
2.1L inline-4 |
2.1L inline-4 |
3.0L V4 / different family |
| Dry weight |
359 lbs |
359 lbs (363 CT) |
~455 lbs |
| Full-throttle RPM |
5,000, 6,000 |
5,000, 6,000 |
5,000, 5,800 |
| Best hull range |
16, 18 ft aluminum, mid pontoons |
17, 20 ft aluminum, mid-large pontoons |
19, 22 ft, larger platforms |
| Price vs. 115 |
Less |
, |
More (~$5,000+ more) |
90 vs. 115: Tuning, not a different motor. No weight change. Price difference is real but modest. If the boat regularly carries four people and full gear, the 115 is worth it.
115 vs. 150: Completely different family. The 150 is a V6, heavier by about 100 lbs, in a different price bracket. Don't let someone talk you into a 150 for a hull that fits the 115, and don't settle for the 115 on a hull that genuinely needs the 150.
What We'd Actually Recommend
17, 20 ft aluminum fishing boat, Ontario buyer wanting real headroom without going V6: 115 ELPT FourStroke. Standard gearcase.
Mid-to-large pontoon, 20, 24 ft, normal cottage loads: 115 ELPT Command Thrust.
Same boat but you want hole-shot and run a tournament or performance fishing platform: 115 Pro XS. Different motor, different price, worth asking about specifically.
If you buy from us, we service it. For engine repairs, we only work on Mercury and Mercruiser.
Related guides
Prices shown reflect HBW's current Mercury dealer pricing. For live updates as Mercury issues new dealer pricing, see our Mercury pricing reference.
Frequently Asked Questions
Is the 115 FourStroke really the lightest 115 HP available?
Yes, at 359 lbs, it's lighter than equivalent outboards in the same horsepower class. The older Mercury 115 OptiMax it commonly replaces weighed around 425 lbs.
Is the 115 FourStroke the same motor as the 90?
Same 2.1L block. Different tuning, different RPM ceiling. No weight difference. The step from 90 to 115 is software and tuning, not a different motor.
Is the 150 comparable to the 115?
No. Different family, different block, different cylinder architecture, different weight class (~100 lbs heavier), different price point. Don't compare them as if they're close relatives.
When does the 115 CT make sense over the 90 CT?
When the pontoon is 20, 24 ft, when you regularly carry 5, 6 people, when it's a tritoon, or when you tow tubes. If the pontoon is 18, 20 ft and loads are light, the 90 CT is fine.
What fuel savings can I expect repowering from an old two-stroke?
Typically 25, 35% less fuel for the same day on the water. The exact number depends on the old motor's condition and how hard you used it.
Does the 115 Pro XS come in Command Thrust?
No, the Pro XS uses a sport gearcase designed for performance applications, not the CT gearcase. If you're shopping between Pro XS and standard FourStroke, use the quote builder to compare both.
Build a Quote
See the 115 ELPT, 115 CT, and 115 Pro XS side by side at mercuryrepower.ca. Real CAD prices, real configurations, no "call for quote" games.
Questions about which version fits your boat? Call 905-342-2153 or submit a service request at hbw.wiki/service.
Harris Boat Works, 5369 Harris Boat Works Rd, Gores Landing, ON K0K 2E0.
Related guides: Mercury 90 HP FourStroke review | Mercury 75 HP FourStroke, why we don't stock it | Mercury 40 vs 60 HP | Ontario Mercury Outboard Price Guide
Ready to price it out? Build a live CAD quote for your repower online at the Mercury Repower Centre.
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