Tech Talk...
Who wants a hybrid?
Wouldn’t it be nice if you could slip the yacht out of her berth and glide silently out to
sea without the need to start the diesel? Well, if your propulsion system incorporates an
electric motor it’s perfectly possible. James Turner takes a look at some of the hybrid
diesel-electric engines currently available to see if they could be viable alternatives.
M
ost of us have a what are the options for using many. You can install the heavy the system. A typical DC system
straightforward diesel electricity to drive a yacht? engine in the middle of the boat comprises a 48V DC generator
engine installation in for better weight distribution, – again housed in an acoustic
which the engine provides the Simple diesel/electric it will run more quietly due to box and mounted wherever you
motive power for the propeller its acoustically insulated jacket want – and a DC drive motor.
to turn, either through a straight Instead of the diesel engine and it can be set to run at the This time, because it’s DC, you
shaft or a Saildrive. The only driving a propeller mechanically, engine’s optimum revs for fuel can add banks of batteries,
electricity on board (aside from this system uses an AC economy and efficiency. so if you only want to motor a
shore power) is the DC circuit, generator to run an electric short distance, you can do so
charged by the alternator, though motor. The generator is housed DC for flexibility on battery power. You still retain
these days a growing number in an acoustic box and mounted the advantages of electric drive
of boats have inverters that take anywhere in the boat. The drive Using DC electrics, it’s possible – quiet running, greater thrust,
the battery’s 12V DC and convert unit can be mounted on a short to bring even more flexibility to improved manoeuvring – but
it into 240V AC mains power. propeller shaft just inboard of the
Such devices in yachts tend to stern gland or the equivalent of a
be limited in power, due to the Saildrive. A steerable AC motor
need for large battery banks, so that protrudes under the hull
and gives you the ability to
deliver power in any direction is
also available. The linkage from
The key benefits of generator to motor is just wire.
diesel electric drive With this system you need the
1. Very quiet running.
generator running continuously
in order to have propulsion, just
2. Greater thrust throughout
as with ‘normal’ diesel power.
the rev range. A petrol or
For sailing yachts around 2.5kW
diesel engine only delivers
of electrical power is needed per
top power with high revs,
ton of displacement in order to
whereas the electric motor
delivers maximum torque at
reach hull speed, but for normal
any revs.
cruising (70 per cent of hull
speed), only 20 per cent of this
3. Improved manoeuvring
is needed.
– directional thrust and more
power from bow thrusters
(if fitted).
Why isn’t it standard?
4. One generator for several
So, why doesn’t everyone
drives – motor(s), thrusters,
have diesel-electric drive?
air conditioning.
Probably because, while the
5. Generator can be
science isn’t new, it has not
positioned amidships. been commercially available.
6. Plenty of AC power for
Now it is and, although it costs
domestic use.
around 25 per cent more than
a straightforward diesel engine
Some of the alternatives from Fischer Panda. As well as Whisper Prop diesel
installation, the benefits are
electric power, they also offer swivelling props with built-in electric motors.
56 Sailing Today July 09
ST147
TechTalk_HybridrRTG.indd 52 15/5/09 12:26:22
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