TWo-STroke CoMBUSTioN CYCle
Far left: Four steps
are required for
(firing of the spark
(near left) the
spark plug fires
on every upstroke
in a two-stroke
engine. You can
see how the gas
(green arrows) can
pass right over the
the right-hand side
of the cylinder and
out the exhaust on
the left side during
and more juice to satisfy gadget-loving boaters, forcing outboard
engine makers to find innovative ways to provide all that power.
First and foremost, outboards have become more energy efficient
themselves. Using less electricity for internal operations means there’s
more left over to charge the battery and run your chartplotter, sounder,
radar, stereo, iPod, VHF, AIS, night-vision camera, and so on. But even
so, more powerful alternators are needed. Honda has created a system
they call Amp+, which senses the electrical load on the battery and
bumps up the idle speed of the engine if necessary. Yamaha started
using those aforementioned rare-earth magnets that make 13-percent
more power, but reduce the weight of the alternator by 10 percent. But
perhaps the most far-reaching development, not directly related to the
engine, is the rise of electronic engine controls, also called “fly-by-wire.”
No More CaBleS
No matter what you call it, using electrons rather than a metal cable
to change throttle positions, steer, and shift your outboard has numerous benefits. Chief among these is that it eliminates the burden of
routing through the bowels of your boat one or more stiff, unforgiving
mechanical controls that will eventually freeze up due to rust.
“You can tie 12 granny knots in a digital throttle and shift cable, and
it will still work,” says Mercury’s Miller. But digital control means more
than simpler rigging. All sorts of useful benefits, including automatic
dual-engine synchronization, single-lever control options, steady-speed
presets for towing skiers, and perhaps the most popular, joystick con-
trol, all derive from letting the computers talk to the outboards.
The CoMiNg DeCaDe
As outboard manufacturers further refine their offerings, we’ll continue to see improvements in performance, efficiency, and power
output. Many in the industry expect the EPA to apply the same emissions standards to outboards in 2018 as they recently did to inboard
engines, which would make a catalytic converter necessary. To
accomplish this, manufacturers would have to switch to closed-loop
cooling, like on an inboard engine. An engineering challenge to be
sure, but Seven Marine, a newcomer to the outboard market which
marinized a GM 8-cylinder engine, already offers closed-loop cooling
on their 557-hp outboard and a horizontal engine orientation, both
of which are unique in today’s market. Given the remarkable changes
in the past 10 years, those may not be unique attributes for long.
THE REPOWER PREDICAMENT
So which outboard is right for you?
Repowering right means sorting through the many options now available to find the one that best matches your boat, the way you use it, and
your brand preferences. You’ll want to consider the following:
■ Boat design. Your engine choices will be limited by the weight your boat can carry, the horsepower it can handle, the space you have on the
transom, the fiberglass work necessary to mount the new engines, and the structure at the stern.
■ Duty cycle. Stratified combustion will save fuel if you spend most of your time trolling; mid-range punch will be better to get you through a
choppy inlet or out to your offshore fishing grounds.
■ Maintenance schedules. In general, DI two-strokes will have longer intervals between scheduled services because they lack mechanically
controlled drive trains that need adjustment every 500 to 1,000 hours.
■ Electrical demand. If you want to keep those fancy electronics running all the time, make sure to check not only the rated amperage output,
but also output at lower rpm, where it could be half of what it is at cruising speeds.