Yamaha's double act

Kevan Wolfe | VOLUME 29, ISSUE 3
Club Marine was recently given the opportunity to test two new Yamaha outboards. We came away impressed.
Club Marine was recently given the opportunity to test two new Yamaha outboards. We came away impressed.

It was no wonder the Yamaha team had big grins on their faces when they unveiled a new generation four-stroke 175hp engine designated the F175A and a brand new F115B four-stroke.

When the new outboards first arrived at the Murarrie office in Brisbane, the boys admitted they didn't know what to expect, especially with the new 115hp outboard. Yamaha has been marketing a class-leading 115hp outboard since 1999 and they were keen to see what the factory had done to this new model to make it even better.

The F175A was a different matter. This new outboard has been long-awaited to fill the gap between the F150A and the recently-released four-cylinder F200. The F175A shares the 2.8lt F200 platform, with the same displacement, four-cylinder, 16-valve dual overhead camshaft design.

When the boxes were opened, the first thing to stand out was the new styling of the composite top cowling. The Yamaha cowls are already distinctive. While the cowls on both new engines can be described as elegant they have a very practical purpose - incoming air is routed through a labyrinth of passages that help trap and drain water before it enters the engine's intake.

But it wasn't until they bolted the new engines on to a couple of locally built boats that they realised they had something special.
The F115B is a step up and replaces the F115A. Weighing in at 171kg, it is 15kg lighter than the old model and some 11kg lighter than its nearest competitor in the four-stroke class.

This has been achieved by combining a single ram power trim-and-tilt mechanism with a new lightweight mounting bracket. People who launch off the beach will find it handy as it works quicker than the previous - and heavier - two-cylinder ram.
The flywheel flange is cast from a single piece and fastened by six easy-to-get-at bolts.

Under the cowl the cubic capacity now measures 1.8lt and, coupled with a double overhead camshaft, four-cylinder block with larger intake and exhaust valves, the engine breathes easier and thus gives more power and better mid-range torque.

The bore has been taken out from 79mm to 81mm, allowing for larger intake and exhaust valves for the 16-valve DOHC system, which maximises combustion. The compression ratio has been increased to 10:1 and the throttle operating range from 5300 to 6300rpm.

Other features include a newly developed exhaust manifold, which is easily removed for service and is anodised to stop corrosion, a knock sensor that retards the engine should it detect abnormal combustion, and the ability to run on regular unleaded rather than premium fuel to produce its horsepower.

The charging power of the alternator is now 35 amps at WOT compared with 24 amps from the previous model and even as low as 1000rpm it produces 28 amps to keep the battery charged.

Another feature is the optional variable trolling speed that adjusts the engine speed between 600 and 1000rpm in 50rpm increments to give anglers the ability to fine-tune the presentation of their lures, even to the most fussy fish.

Yamaha bolted a F115B fitted with a 131/4x16in K-series polished stainless steel propeller to a CruiseCraft 530 Explorer, which weighs in at 1453kg wet and is rated for a 140hp outboard. They filled the 140lt fuel tank and recorded a maximum average speed of 34.29 knots (63.5km/h). At a cruising speed of 4000rpm the engine used a litre of fuel every 1.2nm (2.2km) giving it a range of approximately 8.2 hours from the 140lt tank or, at 95 per cent usage, about 168nm (310km).

The new 115 was also married up to a SeaJay 5.1 Striker, which normally runs a F115A and produced similar figures to the other single rigs.

The new F115B was impressive, but the big test came when the team bolted a twin-115hp rig to a NoosaCat 2400HT Sportsman (above) using the same configuration as the single rig.

According to Yamaha's testing, overall, the F115B in cruising rev range between 3000 and 5000 is quicker and 20 per cent more fuel efficient than the previous model and is 10 per cent faster out of the hole.

The 6.7m Cat ran at an average top speed of 33.64 knots (62.3km/h) and used a litre of fuel every 0.6nm (1.12km/lt) at 3500rpm. This gave it a range of some 213nm (394km) leaving a safety factor of five per cent fuel in the tank.

This gives a potential buyer something to think about. The vessel weighs in wet at around 2605kg and is rated for 300hp, but with the performance of the twin rig, why spend the extra for bigger and heavier engines?

All-new F175A

As mentioned earlier, the new F175A is a brand new engine that fills the gap between the F150A and the recently released F200A.

Although it is based on the 2.8lt, four-cylinder F200A platform, it's not a depowered version of the bigger outboard. It shares the same four-cylinder displacement and 16-valve dual overhead camshaft design and, at 219kg, is lighter than some of the less powerful outboards on the market. It has an exceptional power-to-weight ratio and, with 660mm mounting centres, it is ideal for a twin-rig configuration, especially on a narrow transom.

Another advantage is the offset crankshaft and gear-driven balance shafts, which makes it an ultra compact unit.
For those who like to run a suite of electronics, the alternator has been boosted 13 per cent to output a total of 50 amps. Even at a low 600rpm the alternator is charging the batteries at 22 amps. This allows for a house battery and a separate starting battery that can be charged individually, to be installed.

There are no more 'clunks' when the engine is shifted in and out of gear, either. First introduced in the V8 and V6 models, Yamaha's Shift Dampening System uses a splined rubber hub and aft washer to absorb noise and vibration, giving smoother and quieter gear-shifts. Variable trolling speeds are also available on this model.

Set up with an M Series polished 141/4x17in propeller, the 175 powered a CruiseCraft Explorer 625HT, which weighed in at approximately 2040kg wet, at a maximum average speed of 40.19 knots (74.4km/h). Best cruising speed was around 4000rpm where it used around a litre per nautical mile (1.85km/lt).

And from the 240lt fuel tank it had a range of 233nm (431km) leaving a safety margin of five per cent fuel in the tank.
The 175 was a little slower onto the plane than the 200, but doesn't drop off as quickly.

Both the F115B and the F175A are Three Star Ultra Low Emission rated.

(All test figures supplied by Yamaha. The outboards were tested under controlled conditions by certified Yamaha technicians.)