Mercury OptiMax 115 Outboard Engine Review

There are only three outboards in the 115hp range of direct fuel injection (DFI) two-strokes: the Evinrude E-TEC 115, Tohatsu TLDI 115 and Mercury OptiMax.

The E-TEC and TLDI enginees both have four cylinders and are relatively smooth across the entire rev range.

MERCURY OPTIMAX 115

The most powerful of a trio of DFI two-stroke outboards from 75hp, the three-star OEDA-rated Mercury 115 develops 113.3hp at 5375rpm from its 1526cc loopcharged powerhead and has a Wide Open Throttle range of 5000-5750rpm.

Developed by WA’s Orbital Engine Corporation, the Mercury OptiMax DFI is a two-stage system that mixes air with fuel before injecting the atomised mix directly into the combustion chambers. I don’t want to put anyone to sleep so I won’t go into operational details, but suffice it to say this DFI system gives incredibly low trolling fuel and oil consumption with traditional two-stroke outboard performance.

A belt-driven, voltage-regulated 60A alternator provides plenty of power for electronic toys and since the only other belt is for the air compressor, the 115 is relatively trouble free compared to 115hp four-strokes. The dry weight is 170kg for the longshaft version (175kg for extra-long) and the gear ratio 2.07:1, which is a little taller than its OptiMax 75 and 90 counterparts.

Powerhead access is good even though a 4.7L oil tank is fitted. Mercury recommends servicing every 100 hours or annually after the first 20 hours, and the engine has a five-year recreational use warranty.

PERFORMANCE

A hull that could handle 230kg was a good match for the demo Mercury 115 engine and the Stacer 565 Coral Master Sports Runabout planed at incredibly low speeds. It easily lifted out of the hole and the Mercury 115 planed cleanly from trolling revs in 2.5 seconds, despite swinging an 18in prop and pushing a total of around one tonne, including two adults.

The Merc 115 started instantly hot or cold with no oil smoke and, providing the anti-ventilation plate was kept at least three quarters immersed, it was great for backing off estuarine sandbars. However, the Mercury remote-control ’box was a tad notchy in its operation.

At less than 1000rpm we really appreciated that Mercury had opted for such a large-displacement three-cylinder engine and that we didn’t have to endure the same level of vibration through the hull at engine speeds of over 1000rpm. Maintaining a clean plane at only 2700rpm is something few four-stroke 115s could achieve, and the 115 was incredibly fuel efficient at the most economical cruise speed of 3000rpm. There was no prop ventilation through tight turns at 4000rpm and at WOT the 115 let us know it was working hard for our enjoyment.

THE VERDICT

The Mercury OptiMax 115 outboard motor is a compromise between the lower but wider profile of the V4 E-TEC 115 and the tall stature of the in-line TLDI 115. It’s cheap to run for a 115, and with Mercury’s proven saltwater corrosion protection and outstanding warranty coverage it’s a logical re-power choice for older hulls. Parts are easily available across Australia because the 115 uses the same pistons and other components as the V6 OptiMax 200-250 range.

Throw in the fact the Orbital Combustion Process has been the most trouble-free system of the three DFI options on the market, and the OptiMax 115 represents very good value. As of May 2013 the extra-long-shaft 115 including prop and installation was quoted at $13,140 (Melbourne dealer). A spare Vengeance prop retails for around $1000.

Thanks to Lifestyle Marine, Toronto (NSW) — call (02) 4959 1444 or visit www.lifestylemarine.com.au — for the use of the demo engine.

PERFORMANCE

2.5kts (4.7kmh) @ 650rpm (trolling) — 0.7L/h
4.3kts (7.9kmh) @ 1000rpm (fast troll) — 1.4L/h
6.8kts (12.6kmh) @ 2000rpm (offshore troll) — 4.5L/h
8.4kts (15.6kmh) @ 2300rpm (min. plane) — 6.4L/h
11.4kts (21.2kmh) @ 2700rpm (clean plane) — 7.2L/h
14.9kts (27.6kmh) @ 3000rpm (most economical cruise) — 9.6L/h
23.9kts (44.4kmh) @ 4000rpm (cruise) — 17.6L/h
31.3kts (58.1kmh) @ 5000rpm (max cruise) — 27.8L/h
35kts (64.9kmh) @ 5500rpm (WOT) — 37.6L/h

THE COMPETITION

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Originally published in TrailerBoat #298, August/September 2013.