Yamaha F8C

In the past five years or so, 8hp outboards have been overshadowed by their 15hp counterparts, which provide much better performance on the ubiquitous 12ft tinnie - especially on more recent hulls sporting beams of around 1.7m compared to 1.5m for older hulls.

But if you're planning to re-power an older hull with a four-stroke 15, most simply won't have the buoyancy aft to cope with the weight of it as most outboards are around 25 per cent heavier than their two-stroke counterparts. Carrying 45kg on the shortshaft transom of one of these narrow hulls is just asking for trouble in messy conditions.

This is where Yamaha's F8C scores with its reasonably light weight for output and brilliant trolling efficiency that no two-stroke 15hp can match. According to owner reports, the F8C has proven a much better performing engine than its two-stroke 8C counterpart.

The F8C has comprehensive engine protection features such as a rev limiter that activates at 6200rpm, and automatic rev reduction to 2000 should the oil pressure drop. The long multifunction tiller handle folds back alongside the upper cowl to reduce overall engine bulk when stowed in the boot of a small car and has adjustable throttle friction, an effective cable-operated gearshift, a stop button and the emergency ignition cut-off lanyard.

Cold and hot starting of the loan F8C required the same one-hand effort as Yamaha's 246cc two-stroke 15F. The motor warmed quickly from cold and remained hot during extended trolling periods - but perhaps due to an automotive SAE20W50 oil being used instead of Yamaha's own oil, the engine always blew some oil when cold for the first five hours.

Compared to a 15F (36kg) under identical conditions on a 3.6m Sea Al Super Skua aluminium dinghy - which had a beam of only 1.4m - the F8C was a lot slower but a lot more fuel efficient. Both engines had the same gear ratio and pushed a total of 285kg including two adults and fishing tackle, but a bigger 8.5in pitch prop was needed for the F8C whereas the standard 10.5in prop was perfect for the 15F on this hull.

Across the rev range, vibration levels of the F8C were lower than those of the loopcharged 15F, and it was quieter despite having the same dry exhaust relief system. The F8C trolled at 4.1kmh on 1030 revs using 0.3lt/h compared to 4.5 on 850 using 0.6lt/h. But whereas the 15F planed us at half throttle, the F8C needed two thirds.

At Wide Open Throttle the F8C averaged 32.6kmh on 5910 revs using 3.6lt/h compared to 46.2 on 6010 using 7.2lt/h.

But across a "loop" including 10 per cent WOT operation and averaging 15kmh, the F8C used 1.8lt/h compared to 2.7 for the 15F - and on completion of testing with a total of 6.25 per cent of WOT operation and averaging 1.04lt/h over the 9.6-hour evaluation period, the fuel/oil ratio was a low 1250:1 compared to the fixed 100:1 ratio for the 15F.

After a total of 48 hours of saltwater leg/lower unit immersion, no corrosion was apparent anywhere on the engine.

Powerhead access is good with an easily-reached oil dipstick and filler cap, and recommended servicing intervals are every 50 hours or six months after the first 10 hours. Straight from the 15F, the waterpump impeller should be replaced every 100 hours or once a year.

The F8C complies with US EPA 2006 and California Air Resources Board (CARB) 2004 exhaust emission regulations, and the warranty coverage is two years for recreational usage.