Outboard motors have seen considerable
development in recent years. In fact, such has been the pace and
scope of progress, that it could be argued that they bear little
resemblance to their early predecessors.
The first outboard was developed by
Ole Evinrude in 1909 in Milwaukee, United States. Almost a century
later, approximately 10 million outboards are in use globally.
The growth in sales and use goes hand-in-hand with the pace of
development, resulting in engines becoming more compact, light,
efficient, powerful and affordable.
With developments in computer chip
technology and advancements in engineering, the modern outboard
is a very sophisticated piece of electro-mechanical engineering.
This article discusses some of these developments and how they
have enhanced the experience of owning and operating a modern outboard
Many of the more recent developments
have been driven by the need to meet new environmental regulations
that are coming into force around the world within the next year
or two. The leading regulators are Europe and the United States,
which are enforcing stringent new environmental regulations in
2007 and 2006, respectively.
One of the biggest developments in
engine technology that has found its way into the outboard motor
is electronic fuel injection, commonly referred to as EFI. EFI
originated from the automotive industry and began to be incorporated
into outboard motors in the mid-1980s. Early versions of EFI were
sometimes troublesome, however later developments have seen dramatic
improvements in engine reliability and fuel economy. In more recent
years, EFI was further enhanced to incorporate multi-point fuel
injection; this provides more fuel and air directly into the combustion
chamber and results in more power through more complete combustion.
Digital engine management is now common,
especially on the medium-to-larger capacity four-strokes. The incorporation
of microcomputer-controlled sensors throughout the engine provides
precise control of ignition timing, fuel injection and other adjustments,
offering more performance gains. This level of control of engine
functions also guards against engine damage, including knocking,
over-revving, stalling, over-heating and insufficient lubrication.
Advances in intake and exhaust design
have made the modern outboard significantly quieter in all modes
of operation, in sharp contrast to its early cousins. Larger capacity
air intake silencers have reduced high frequency inlet noise, while
improved through-propeller exhaust systems have reduced
the mid to low frequency
New cowling materials and seals, along
with improved fastening systems, have further reduced noise as
well as resisting the ingress of unwanted water into the engine
The inclusion of larger alternators
within the modern outboard provides the opportunity for dual batteries,
reducing the possibility of flat batteries and associated dramas
out on the water. With more alternator output allowing dual batteries,
one battery can be dedicated to engine starting and the other for
all other on-board services such as navigation equipment, navigation
lights, house lights, etc.
Outboard manufacturers are now including
multi-function digital gauges as standard equipment to keep track
of a multitude of engine functions and provide diagnostic information.
These gauges provide sophisticated information such as running
time, water contamination warning, engine check warnings, trim
position, overheating warning and fuel consumption, along with
the usual information such as rpm and voltage. At least one outboard
manufacturer has also integrated its systems with a leading marine
electronics company to provide a wide array of information about
the status of the boat, fuel and the engine.
Problems associated with engine vibration
have been addressed with some lateral thinking. The flywheel has
been redesigned and repositioned under the engine, instead of the
traditional location above the powerhead. This lowers the centre
of gravity of the outboard and significantly reduces vibration.
One area that receives little thought
from the average outboard owner is the layers of paint that protect
their investment. The modern outboard utilises some of the most
advanced paint and coatings technologies available today. Typically,
the raw metal is etched with a special preparation then coated
with two layers of epoxy-based undercoat, before receiving two
further layers of two-pot finish. Finally, it is coated with a
clear acrylic urethane to give a depth and shine to the final colour.
The end result, while pleasing to the
eye, also helps protect engines from the ravages of salt water
DIFFERENT STROKES FOR DIFFERENT FOLKS
Until very recently, four-stroke outboards
have always been considerably larger and heavier than their simpler
two-stroke counterparts. This has been because of the relatively
complex design of the cylinder heads and overhead valve actuation
assemblies and drives used on four-stroke engines. But with clever
use of advanced alloys and improved designs, there is now very
little difference between the two. Casting and machining techniques
have also contributed to the weight reduction, as has the introduction of high-tech,
lightweight, non-metallic composites for some engine components.
The difference is typically now in the order of around ten per
cent between two- and four-strokes.
The vast amount of research and development
in recent years has gone into four-stroke engines of all capacities.
This has been driven by the increasingly strict exhaust emissions
legislation in big markets, such as the USA and Europe. Two-strokes,
by their very nature, tend to produce more hydro-carbons than four-strokes
of equal capacity.
Modern four-strokes in typical medium-sized
trailer boat applications tend to be three- four- or six-cylinder
engines, either in vee or in-line layouts. Overhead camshafts are
universal, while advanced counter-balancing provides smoother running
and significantly reduces engine vibration, especially at idle
or low rpm.
One of the most recent developments
has been in the recycling of exhaust gasses to extract further
energy from the partially burnt air/fuel mix. This has been achieved
by some very detailed analysis and clever design changes to the
combustion chamber. Significant developments in fuel injection
technology have further improved efficiencies. These features not
only make for cleaner running and more power; they also improve
fuel efficiency. And these advances also reduce the impact on the
The introduction of mechanical supercharging
is a more recent development, resulting in much higher power and
torque outputs, especially in the smaller capacity classes. Superchargers
are basically air pumps that force-feed the engine with more air
and fuel, thus resulting in a bigger ‘bang’ inside the combustion chamber. The
end result is more power and throttle response for a given capacity
of engine, with up to a 50 per cent boost over naturally-aspirated
In just about every area, four-strokes
have been refined to the point where the modern four-stroke outboard
engine is a very sophisticated piece of engineering.
Most two-strokes now have separate
tanks for oil and petrol, instead of the pre-mix arrangement of
earlier times, in which the oil and fuel were mixed together prior
to being fed into the engine. Most modern powerplants now employ
oil injection, with precise amounts of oil being injected directly
into the intake manifold to provide engine lubrication. One of
the advantages of this arrangement is that the engine management
system can vary the mixture in accordance with the requirements
of the engine, which minimises oil consumption.
Some modern two-stroke engines use
high pressure direct injection to drive the fuel into the cylinder.
Extremely high pressure results in a finer atomisation of the fuel,
making for more complete combustion. This is further enhanced by
improved flow of the air/fuel mix through the cylinder, from intake
to exhaust port.
|The world’s first 100-horsepower
introduced in 1962 was cause for celebration.
Many of the latest outboards also have
independently controlled air intakes to each piston for more precise
control of the air/fuel mixture.
Two-strokes tend to be considerably
cheaper than four-strokes of equivalent capacity because of much
lower manufacturing costs and less moving parts. They are simpler
engines to build, but cost benefits can be offset by higher fuel
consumption, especially when run at higher revs. And despite improved
fuel systems and more efficient combustion, it is becoming a real
challenge for manufacturers to meet harsher emissions limits now
coming into force.
It’s generally accepted that two-strokes are close to their
development limits in today’s environmentally conscious marine
industry. They still have their place as legitimate trailer boat
powerplants, but the focus has well and truly shifted towards the
more complex four-stroke engines.
Unless there are major breakthroughs
in the near future, it seems certain that four-stroke engines will
become the norm on most new boats. And it’s equally likely that we’ll see more
power and torque being produced by smaller and lighter engines
as engineers continue to find ways to give us a bigger bang for
our outboard buck.
Next issue we’ll look at what owners need to do to keep their
hardworking outboards purring reliably away to make the most of
our time on the water.