Four Of A Kind
Sydney Morning Herald
Saturday February 27, 1999
IF YOU believe the spin merchants, a four-stroke outboard motor will change your life for good.
No more killer fuel bills, rancid smoke or deafening noise, a four-stroke outboard delivers crew comfort, environmental friendliness and even, some suggest, more fish in your boat.
But spend time messing about with four-stroke outboard motors and you may discover the benefits aren't always unconditional. With a flatter torque curve than a two-stroke, and more weight, the four-stroke can be the root cause of acceleration lag.
Believe Yamaha's spin merchants, however, and you'll find that's no longer the case. Yamaha says its new 100hp four-stroke outboard motor is a clear winner in the power-to-weight stakes.
Indeed, it is lighter, faster, and quicker off the mark than its rivals.
According to Yamaha, the F100 outperforms Honda's 90hp four-stroke - a favourite among anglers - with 8 per cent more speed at top speed, 1.3 per cent better acceleration to 50 metres, and 2.3 per cent better acceleration to 100 metres.
At idle, which is just 850rpm, the 100hp Yamaha is 8.7 per cent quieter and at wide-open throttle it is 4.5 per cent more fuel efficient than the Honda 90, yet it remains no more noisy when both are running flat out.
These might seem like paltry claims on paper till you realise Yamaha achieves this from a 100hp outboard that is seven kilograms (4 per cent) lighter than Honda's 90hp. And herein lies the material for the spin merchant's spiel.
Yamaha's F100 is being promoted as great leap forward in four-stroke outboard technology. From a technical viewpoint, it is hard to argue the case.
Based on an in-line four-cylinder, four-carburettor, 1.59 litre engine, the outboard has 16 valves and a double-overhead camshaft in a motor similar to that within small cars. It also has both microcomputer-controlled igni- tion and fuel injection, plus a 20-amp charging system which delivers a useful 12 amps at just 1,000rpm, trolling speed, so you can power onboard electronics.
In short, Yamaha believes its F100 is perfectly matched to the modern trailer boat. To prove as much, it fitted the outboard to two quite different test boats: the SR565 Southwind, a low-profile fibreglass family boat built for comfort on the water, and a new aluminium 560 Quintrex Spirit cuddy which is better suited to fishing.
Naturally, these very different hulls provided disparate performance results. While most marine hacks leant towards the fibreglass boat with hydraulic steering and lots of comforts, the flatter-bottomed, aluminium Quintrex hull per- formed markedly better at low-speed.
This performance of the Quintrex was encouraging considering that low-speed planing is not the forte of four-stroke outboards. While the Yamaha Southwind, a deep-veed family boat, was a little tardy off the mark, the Quintrex exhibited a willingness to cruise efficiently down to 2,500rpm.
But if outright speed is your priority then the sexy Southwind was a clear winner. The smoother hull gave 44 knots compared with the 38 knots registered on the Quintrex. Or let's put it another way: the performance of Yamaha's four-stroke motor remains governed entirely by the design of its host boat. While the new outboard will reward with less of a drain at the petrol pump and greater onboard comfort than a traditional two-stroke outboard, the burning question is whether the motor will work satisfactorily on your boat. The answer is a resounding maybe. Which leads me to conclude that perhaps the four-stroke outboard manufacturers should offer boat/ motor packages. The new Yamaha F100 costs about $2,000 more than an equivalent two-stroke motor ($10,000-$11,000). At that price a boat/motor package may be a useful performance guarantee. Details: Yamaha Motor Australia, (02) 9757 0011.
© 1999 Sydney Morning Herald
Share This