Mercury EFI F115

Since its local release a couple of years ago, Yamaha's EFI F115A has had no real competition apart from Honda's much bulkier and heavier BF115.

Mercury Marine's EFI F115A changes all that.

Although it utilises the same basic powerhead as the Yamaha, it differs in cylinder head and manifold, leg and lower unit design and EFI componentry. Unfortunately, Mercury's approach to over-engineering its four-strokes does make the EFI F115 incur a 2% weight penalty over the F115A, but then the Merc develops 2% more propshaft horsepower at the same revs. Even with its massive weight the EFI F115 is 15% lighter than Hondas' BF115. This is very important when the motor is mounted on an aluminium hull in the 5.5-6.0m range.

A drawback at this stage is the non-availability of counter rotation.

While the Merc does boast engine protection features that automatically reduce revs should the engine overheat or suffer low oil pressure, the electronic control unit is 'first generation' and misses out on the brilliant Motorola PCM 555 micro-processor. This prevents interfacing with the 'SmartCraft' system available with Mercury's 30-60hp EFI four-strokes, which allows for the connection of a digital fuelflow meter.

The Merc's multipoint EFI injects fuel at the intake valves like a standard automotive system, while the ECU maintains the correct air/fuel ratio regardless of barometric pressure. This enables the EFI F115 to perform as well on high altitude dams as it does at sea level.

Tested on two very different hulls, the EFI F115 performed brilliantly on both. Mounted on a 5.6m Bermuda Sea Scape bowrider, the EFI F115 tested at the 2001 Mercury Expo performed brillia ntly across its entire rev range. It started instantly hot or cold, with no oil smoke appearing at any time, and warmed quickly from cold. Vibration levels were very low at trolling speeds and power astern was good. No cooling water starvation occurred providing the anti ventilation plate was kept immersed.

Pushing a total of 960kg including two adults and spinning a 16in pitch stainless steel Quicksilver Vengeance prop, the demo motor trolled quietly at 4.1km/h on 750rpm consuming 1.3lt/hr. The revs were 150 higher than the F115A trolls at, but the ECU can be re-mapped to reduce revs to 600-650, according to Rick Davis from Mercury Marine.

The EFI F115 achieved a clean plane at 24.1km/h on 3100rpm and the best cruising revs were 4000 where the average was 38.9km/h. At these revs through tight figures-of-eight no prop ventilation occurred.

Though very tricky to achieve in the confines of the lagoon at Novotel Twin Waters, we managed to record Wide Open Throttle figures before literally 'hitting the wall'. The WOT average was 63.9km/h on 5900rpm, and the motor was so quiet a normal conversation could be held at the helm.

Mounted on a 5.5m Seafarer Ventura and spinning a 16in Vengeance, the demo EFI F115 provided comparable performance to an Evinrude Ficht 115 tested some time ago on this hull. Pushing a total of 1380kg including two adults, the Merc planed us at 26.9km/h on 3100rpm and cruised quietly at 42.2 km/h on 4000rpm consuming 15.5lt/hr. Through tight figures-of-eight at 4000rpm there was no prop ventilation. The WOT average was 69.2km/h on 6000rpm consuming 38.5lt/hr with the motor under-propped for handling up to five adults and fishing tackle without overloading.

Servicing the Merc appears straightforward. Mercury Marine recommends intervals of every 100 hours or once a year (also for waterpump impeller replacement) after the first 20 and 50 hours.

However I would change the engine oil and filter every 50 hours or six months, whichever comes first.

During the ten-hour break-in period there should be no extended WOT operation, and because it's a four-stroke, remember that this motor will probably not develop its full output until at least 50 hours have been accumulated.

Being relatively new, the EFI F115's corrosion resistance is unknown but it should survive saltwater usage as well as its proven F75 and F90 counterparts.