Yamaha 425hp outboard: Most powerful V8 set-up tested

Alex Smith heads for the French Riviera to sea trial Yamaha’s most powerful outboard to date

While Yamaha is not a company to shout about power, most of us already know how extraordinary the specs for the new XTO are. Taking the mantle as Yamaha’s flagship motor from the established F350, this naturally aspirated direct injection 5.6-litre V8 generates an output of 425hp, making it the world’s most potent mainstream outboard engine.

However, given the streamlined size and weight of Mercury’s 303kg, 2.6-litre inline-6 Verado 400R, there needs to be a good reason why the average leisure boater would choose to add another 130kg to the transom for the sake of what, on the face of it, appears to be a relatively modest gain in power.

The answer of course is that there is much more to the XTO than just numbers. Buoyed by a pronounced global market shift in favour of outboard propulsion, the point of the XTO is to cater for that demand by making outboards relevant not just to RIBs and sportsboats but to much larger, heavier, cabin-equipped platforms with bigger payloads and more generous dimensions. We’re talking about fast offshore cruisers and pilothouse craft well in excess of 40 feet, as well as cruising RIBs and superyacht tenders approaching 50 feet in length.

Plainly then, while it’s exciting to see the back end of the XTO’s cowling decorated with emotive figures like ‘425’, ‘5.6L’ and ‘V8’, what matters more than anything here is torque – the kind of prodigious torque that can turn a 17-inch prop and bring outboard propulsion to an altogether new scale and weight of boat.


Yamaha’s new 425hp outboard is not just suitable for sporty RIBs, but offshore cruisers and pilothouse craft as well

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The on-water experience

While Yamaha hasn’t given us the official torque figures, the nature of the XTO’s performance profile is unmistakable. Despite carrying ten people and 1,500 litres of fuel, Capelli’s quadruple-rig Tempest 50 exhibits a satisfying visceral surge that doesn’t ease off at any point between initial hole-shot and 5,500rpm.

In fact, this nine-tonne express cruiser is every bit as rapid from 40 to 50 knots as it is from 20 to 30 or from 30 to 40. Certainly, when you reach 5,500 to 5,700rpm, the revs flatten right off and you have to wait 20 or 30 seconds while a fistful of trim enables those big props to spin up the last 300 to 500 rpm.

But almost wherever you happen to be in the rev band, the unrelenting urgency of the pick-up is astonishingly linear – and that is precisely what Yamaha’s torque-rich XTO was designed to achieve.

Just as this very distinctive performance profile is much the same on every one of our test boats (whether 40 or 50 feet in length and whether double, triple or quad), so the fuel flow figures also exhibit stark similarities. As you would expect, wide-open throttle sees the efficiency tail right off, more than doubling the fuel flow of each engine from 60 litres per hour at 32 to 34 knots to around 139 litres per hour at 50 to 53.

But with fuel flow of between 40 and 45 litres per engine at 25 to 26 knots, the XTO’s real-world cruising stats come far closer than you might expect to those of a well-regarded inboard engine, like Volvo Penta’s 5.5-litre D6 400.

The XTO’s integrated electric steering system also feels very singular. Designed to eradicate the pumps, hoses and rigging complexities of hydraulic lines and linkages, it makes the helming experience very easy and accurate – and while there’s no physical feedback from the wheel, neither is there any pulling or instability.

You can simply tweak the wheel with your fingers, take your hand away and leave it set, while the boat executes a long, unaltering arc across the chop. There’s no deviation or straightening of the line and, with its short handles, fat base and thumb-friendly rocker switch, the ergonomics of the throttle are equally slick.


Helming is aided by an electric steering system

The joystick control of Yamaha’s Helm Master system is also a highlight. It comes with a ‘HIGH’ setting to increase the revs from 1,000 to 1,100rpm and, with the big props, the generous 62° steerage angle and the exhaust venting above the waterline to improve ‘bite’ at the prop, the results are impressive.

However, notwithstanding the potency of the performance, the sophistication of the interface and the economy of the cruising figures, the XTO’s refinement feels unusually ‘traditional’.

In addition to the pronounced clunking of the gears during low speed manoeuvres and the relative prominence of the engine note right from idle to the top end, the low-speed fumes smell unusually intrusive for a four-stroke engine.

Yamaha’s method of diverting the exhaust away from the prop at less than 2,500rpm in pursuit of greater manoeuvrability is certainly effective, but the fact that the exhaust emerges above the waterline when you’re sitting still can become quite unpleasant for those in the aft part of the cockpit, if you’re compelled to potter around there for any length of time.


The 425hp 5.6-litre V8 is Yamaha’s most powerful outboard yet but it weighs 442kg

The practical implications

While the XTO’s low-rev refinement might be questioned, its performance feels entirely unique. With its extraordinary ‘zero-to-top-end’ grunt, its free-running revs and its exquisite user interface, it feels like a fiercely sporting hybrid of an inboard diesel and a cutting-edge outboard.

True, our test boats were not the best means of showcasing what this big, weight-shifting outboard was designed to achieve, but its performance on Capelli’s cabin RIBs leaves me in no doubt that, on a well-matched family cruiser or fisher of between 35 and 45 feet, it could form a formidable partnership.

Whether the XTO’s big transom weight (or the premium of its final package price) might yet put it on a collision course with multiple rigs of lower-powered engines has yet to be seen. But for now, its refreshing clarity of purpose puts the XTO in prime position to bring far greater relevance and practicality to big outboard-powered cruisers than ever before.


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