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
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.
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.
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.
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.
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
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.
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
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.
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
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.
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
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