Stroke of Genius

Never before has competition in the top-end outboard market been so fierce. The major engine manufacturers are spending big on R&D to bring so-called "new technology" outboards to market to meet American and European emission regulations. The upside for us in Australia - where this sort of legislation is yet to make traditional two-strokes obsolete - is that we're not starved for choice when it comes to selecting a clean and miserly outboard, whether it be a 4hp portable or a 225hp offshore engine.

The performance and power-to-weight gulf between carburetted and fuel injected two-stroke engines and four-strokes is rapidly closing, especially now that fuel injection is being introduced across most manufacturers' four-stroke model ranges. These days it's difficult to decide which is the best technology for yourself. But rest assured, whether you opt for two-stroke DFI or four-stroke, there's no longer any need to compromise on weight or power to enjoy the benefits of next-generation "clean and lean" technology.

According to Australian market research company ERG, the market share of what is termed "new technology" outboards has grown from a mere four per cent a few years ago to about 17 per cent today. True, carburetted and EFI two-strokes still command the lion's share of the market, but the rapid growth in DFI and four-stroke technology suggests those figures could be closer to 50:50 within the next five years.

FOUR ON THE FLOOR
When evaluating the new Yamaha 150hp four-stroke, it's easy to see just why this is. The new inline four-cylinder, electronic fuel injected outboard weighs just a handful of kilos more than its two-stroke cousin (22kg to be precise), is only slightly slower at Wide Open Throttle and is only a little sluggish in the sub-3000rpm torque curve compared to two-strokes of the same horsepower. And the advantages? Try compliance with EPA 2006 emission regulations, substantial savings on fuel, very quiet operation and a complete lack of oil smoke and vibration right through the rev range. And compared with some of the early model four-strokes, Yamaha's engineers have done a fine job creating an incredibly compact powerhead.

NUTS & BOLTS
The 2.6lt engine has 16 valves (four per cylinder) with double overhead cams. Electronic fuel injection and transistor-controlled ignition with a powerful engine management computer deliver the optimum fuel/air mix throughout the rev range, promoting better economy and crisp acceleration. The electric start also has a neat feature built in that won't allow the operator to attempt to start the engine when it's already running, causing damage. These engines are so silent at idle it's an easy thing to do! While on handy features, the oil filter on this engine is mounted down so that when it comes time to change it, oil doesn't pour all over everything, but drains into the sump.

The alternator pumps out a healthy 35amp, while acoustic resonators and special sound-damping equipment is used to keep this engine running as quietly as possible.

Size-wise, the F150 measures 51.1cm wide by 171.4cm long (long-shaft) and is available in long and extra-long shaft.

Let's take a closer look at how the engine performed on three different hulls. All results published here were taken from the boat instruments only, but serve as a basic guide to performance.

Mustang Bluewater 2000
New from Mustang Pleasure Boats this year is a swish 6.2m sportsfisher. Boasting clean, flowing lines and slick hull shape, the Bluewater seemed a little narrower than some comparable boats.

However, its roomy cabin and top-notch finish will please families. The hull weighed about 1000kg plus 120lt of fuel and three adults for an estimated all-up weight of 1650kg. Mustang states the recommended maximum horsepower at 225, so the results with a 150hp four-stroke were pleasantly surprising. Prop was a standard 19in stainless steel.

Seafarer Victory 6.0m
The F150/Seafarer Victory was without doubt the pick of the bunch - an incredibly sweet, surefooted and well-balanced hull ideally suited to an outboard of this type. Seafarer recommends outboards between 115 and 225hp for the Victory, which has a bare-hull weight of 1000kg and an estimated total testing weight of 1800kg. Sporting a deep-vee hull with a fat beam, the Victory loved plenty of positive trim for brilliant acceleration and top-end speed. The F150 delivered a particularly punchy holeshot.

Freedom Mirage 6.0m Bowrider
This locally-made fibreglass bowrider had an incredible amount of internal room due to its maximum beam of 2.5m.

With a moderate vee and planing plank, this hull also liked plenty of positive trim and responded eagerly to the throttle with snappy holeshots and quick acceleration to WOT. The lightest boat of the bunch at 800kg, we estimated the total weight to be about 1400kg with three adults and a full load of fuel. Standard 19in prop fitted.

THE VERDICT
As stated, these figures represent a rough guide as to engine performance on different hulls. Things like trim, load distribution, headwinds, water conditions and the different hull shapes all took their toll on the results.

The two most similar hulls - the 6m Seafarer and the 6.2m Mustang - show that you can expect to burn between 20-30lt/h for a comfortable, brisk cruising speed of 50-55kmh.

Wide Open Throttle for both returned a fuel burn of about 58lt/h for speeds just shy of the magic 80kmh mark.

In all cases, however, the new F150 packed a pretty powerful punch below 3000rpm and delivered comparable top-end speeds to an equivalent two-stroke, using less fuel doing so.

This engine is also unbelievably quiet and smooth. Normal conversation at high speeds is possible, and that can only contribute to a more pleasant day out on the water.