Tested: Yamaha F70 Four-Stroke
YAMAHA’s newly released F70 four-stroke marks a further continuation in the evolution of light, powerful and fuel-efficient outboards. According to Yammie, the inline four cylinder F70 is an enhancement of the Japanese engine maker’s popular F60. It shares the same displacement (996cc) and is only marginally heavier (10kg) than the F60. But the F70 differs from the F60 via its a unique engine design. Unlike other 16 valve engines, the F70 operates via by a single, not dual, overhead camshaft. This gives it a weight advantage over its competitors in the 70-75hp class and also increases performance.
I first checked out the F70 at Yamaha’s HQ in Brisbane at its official launch last year. Initial impressions were that it was a zippy yet refined performer. While four-strokes are generally quiet, clean and extremely fuel efficient, I’ve found they can be a bit sluggish, especially in a boat laden with gear and a couple of hefty fishos. But the new generation of four-strokes, like the F70, and comparable mid-range products from Suzuki, Honda and Mercury, are starting to match the out-of-the-hole performance of DI two-strokes. That really interested me because at the time I was looking at a new project boat for estuary and inshore sportfishing. I had my eye on a Sea Jay 4.65 Discovery Sports and discussions with Yamaha’s Brett Hampson and Glenn Gibson revealed that the new F70 would be an ideal powerplant.
The reason the F70 performs so well is again due to its innovative engine design. According to Yamaha, the four valves per cylinder used in the F70 “have dramatically increased this engine’s volumetric efficiency – the efficiency with which the engine can draw fuel and air in and push exhaust out of the cylinders”.
The net result of this increased efficiency means the F70 is able to run at higher RPMs (up to 6300RPM, in fact). And higher RPMs mean higher speeds, an important consideration for competition anglers and those, like me, who don’t have time to waste puttering along.
With a stock standard alloy prop, the F70 pushes the Sea Jay to a GPS-recorded top speed of 30 knots (55.56kph), which is plenty fast in a modest sized tinny. Of course, it’s not in the same league as the supersonic velocities being achieved by the flash bass boats favoured by serious comp anglers. But these boats are often powered by engines in the 150-250hp class, not 70s.
And the go-fast boys are using upwards of 100 litres of fuel an hour. With my Yammie flat stick at 6000RPM, I’m using just under 23 litres an hour.
I can zoom 10 miles up the Shoalhaven River to my fave bass locations, fish all afternoon and use less than 20 litres for the entire trip. The Sea Jay’s 65 litre underfloor tank means that I can enjoy at least three major fishing trips without having to refuel.
In this day and age, that sort of fuel efficiency is pretty important. And the great thing is that the F70 provides plenty of performance while minimising pain at the fuel bowser. It’s the best of both worlds, in my book.
I’ve now got just under 30 hours on the F70. It got its first service at 20 hours ($220) and isn’t due for another service until 100 hours or 12 months.
In terms of overall ease or use and reliability, I can honestly say that the motor has started first turn of the key since day one and hasn’t missed a beat. I don’t recall ever smelling or seeing any exhaust fumes. The engine is whisper quiet at low and middle revs and has a nice muted howl at WOT. On the downside, it vibrates more than expected at low revs, which is annoying when slow trolling. Yamaha advises that upgrading to a stainless steel prop would eliminate this, and also improve overall efficiency and speed.
Like most modern outboards, the F70 is fully rigged up for digital control via its dual LAN gauges. These gauges provide all the info you need to monitor engine performance and provide far more detail than you’d get in even the most upmarket motor vehicle.
With fuel at upwards of $1.50 a litre these days, keeping an eye on fuel use is of prime importance. The Yammie’s LAN gauges give you 100 per cent accurate fuel use at any given RPM, thus allowing you to adjust trim and throttle settings to achieve maximum performance with minimum fuel use.
I like to cruise at about 20 knots (37kph) at just under 4500RPM. This uses 13 litres of fuel per hour (which equates to just under $20 worth of fuel, based on it costing $1.50 a litre) and gives me a total range of 100 nautical miles (185kms). That’s a long way in a 4.65m boat …
You can see from the stats opposite that the engine is particularly efficient in the 3500-5000 RPM range, which is where most work will be done in regards to travelling to and from fishing locations. It’s also very efficient in the lower revs, especially the 2000 RPM troll speed range range. You can troll for flatties, cod, barra or trout at 3-4 knots all day and use less than 20 litres of juice. That makes for a fairly affordable day out fishing …
All up, I’m pretty impressed with my Yammie F70. It’s very pleasant to operate, is cheap to run and when it’s up and boogieing it’s a heap of fun to drive.
For more info, go to www.yamaha-motor.com.au. For a video showing the F70 in action on the back of the Fisho Sea Jay, check out www.fishingworld.com.au.
By Jim Harnwell