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Outboard Innovation

We check out the most sophisticated and powerful 4-stroke outboard available - the supercharged Mercury/Mariner Verado!

By Michael Knowling

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At a glance...

  • World's first range of supercharged and intercooled outboards
  • Highly efficient Lysholm twin-screw blower
  • 275hp version the most powerful 4-stroke outboard in production
  • Latest in electronic control systems
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If you ever needed proof that marine outboard technology is progressing in leaps and bounds, this is it – the supercharged and intercooled Mercury/Mariner Verado 4-stroke outboard!

Released during 2004, the Verado is the result of Mercury Marine’s monumental US$100m and 5 year engineering effort. It’s the world’s first range of supercharged outboards and the top-line 275hp version is currently the most powerful 4-stroke in production.

So why go for a supercharger on an outboard engine, you ask?

Well, it’s all about achieving similar power to a 2-stroke with the smoothness, fuel efficiency and emissions of a 4-stroke. Mercury claims a supercharger provides the best possible combination of packaging, throttle response and thermodynamics management.

Engine and Supercharger

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The Verado is not merely an existing engine design with a supercharger bolted to the side – it’s all-new from the skeg up. With input from companies such as Lotus and Cosworth, the 4-stroke in-line 6 cylinder engine displaces 2.6 litres and breathes through a sophisticated DOHC, 24 valve cylinder head. Mercury claims the in-line engine configuration was chosen for its balance, lack of vibration, narrow width and suitability to a screw-type supercharger.

The engine’s block and cylinder head are cast aluminium and the bores are equipped with 1.5mm grey iron liners. A series of ‘long bolts’ sandwich together the head, block and bedplate to provide even distribution of heat and operational stress. The camshafts are hollow to reduce dynamic mass, each cylinder is oil cooled, a dry sump is used and oil temperature is thermostatically controlled. The engine is designed to rev between 5800 and 6400 rpm depending on propeller selection.

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Blowing into the 2.6 litre in-line six is a highly efficient Teflon-coated twin-screw Lysholm supercharger, which was jointly developed by Mercury Marine and IHI Turbo America. The blower is driven by a V-belt from the flywheel end of the engine. Boost pressure is controlled using an ECU-controlled supercharger bypass valve and reaches up to 15 psi (depending on model). Charge-air temperature is reduced by a water-to-air intercooler that draws on a fresh supply of water.

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The intake manifold is an elegant 1-piece unit moulded from glass reinforced nylon. This provides a 50 percent weight saving over aluminium, and has smoother internal surfaces as well as better corrosion resistance. Note that the blower is built from anti-corrosion parts and oiled foam filters help reduce the amount of moisture that reaches the powerhead.

The engine’s fuel, ignition timing and boost pressure are controlled by a Motorola-based PCM03 computer system incorporating Mercury Marine’s SmartCraft Engine Guardian – a ‘whatever happens’ engine protection strategy. Fuel is delivered to the combustion chambers through a sequential multi-point injection system that eliminates the need for a primer bulb.

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The Verado is currently available in four versions – 200, 225, 250 and 275hp (149, 168, 186 and 205kW respectively). All four engines are virtually identical – the power difference can be attributed to variations in boost pressure, fuel and ignition mapping. Note that each engine can be run on normal unleaded fuel but the top-line 275hp version requires high octane to generate full power. At 275hp, this is the most powerful 4-stroke outboard engine in production – it offers superior performance to other 4-strokes displacing up to 3.6 litres... It is also credited with a 3 star CARB (California Air Resources Board) rating and long-term emission compliance.

To cope with the grunt of the supercharged in-line six, the Verado employs a bigger gearcase than is used in the Mercury 3.0 litre 4-stoke. The gears are reputedly 50 percent stronger and the drive ratio is 1.85:1.

A Total Drive System

To further improve the motorboat operator’s experience, all Verado outboards employ an integrated ‘total drive’ system.

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The Verado features Mercury’s ‘SmartCraft Digital Throttle and Shift’ – an electronic-controlled throttle and gear selection arrangement. Just like the system used on today’s cars, electronic throttle control provides better response, less vibration and is easily adapted to ECU control strategies. Its smooth operation makes docking easier and the age-old practice of throttle cable adjustment becomes a thing of the past. The electronic gear selection system also eliminates crude cable operating systems and provides smoother gear engagement.

In a category first, the Verado comes standard with an electro-hydraulic power steering system – something that’s only now starting to appear in cars. The system uses a brushless DC motor that operates a gear pump and a ‘slave’ piston is mounted the engine. This system eliminates steering wheel torque and vibration while maintaining feel. The aim is to provide car-like steering feel.

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Stylistically, the Verado employs an award-winning 2-piece ‘swept forward’ cowling that looks at home on the transom of a variety of boats. The cowl is reportedly the largest injection-moulded, glass reinforced nylon component ever made. It weighs about 5kg – considerably lighter than a thermoset plastic part. It’s also strong; able to withstand hitting a floating log while travelling 40 mph (72 km/h).

The Verado outboard weighs between 288 and 302kg. That makes it one of the heaviest on the market – but, then, it is the most powerful.

Feedback from the Boating Press

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The Verado is widely claimed to give excellent throttle response and torque throughout the rev range. Its “hole shot” acceleration is apparently excellent. Many testers are also amazed by its level of refinement – it’s wonderfully noise and vibration-free. It is said that the only way to tell if the engine is idling is by the stream of cooling water exiting the motor... At high speed the Verado can barely be heard over water slapping the hull and aerodynamic noise.

And this refinement is no fluke.

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The Verado’s supercharger initially caused an objectionable induction howl which was eliminated with a sophisticated tuned resonator. The resonator is a 2 chamber design and incorporates an internal air filter. This resonator is claimed to reduce intake noise by up to 14 decibels (average) from mid to wide-open throttle. A generous amount of sound-deadening foam is also applied inside the engine cowl as part of Mercury’s noise reduction strategy.

Vibration is reduced thanks to a 4-point progressive rate cradle mounting arrangement, which is set around the engine’s centre of gravity. This cradle absorbs vibration and high frequency chatter and stiffens under load and water speed to enhance steering and handling. Mercury claims a 50 percent vibration reduction.

Cost and Suitability

The Verado can be mounted in single, twin or triple configurations to suit everything from ski-boats to large offshore fishing boats. Each model is available is available with a 20 or 25 inch shaft - a 30 inch shaft is also available for the 225, 250 and 275hp versions. Counter-rotating propeller configurations can also be specified on 25 and 30 inch shaft models.

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At present, the base Mercury/Mariner 200hp Verado outboard retails for AUD$28,524 while the top-line 275hp version checks in at AUD$33,832 – plus fitment. Note that the Mariner version (which is aimed squarely at the fishing market) is available only outside of North America.

Footnote – It the time of writing, it appears likely that the range of Mercury/Mariner supercharged outboards is likely to expand with smaller and cheaper 135, 150 and 175hp versions.

Contact:

www.mercurymarine.com

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