At 01:20 PM 4/02/2010, Terry wrote:
>James
>
>What are your thoughts on Hybrid?
>
>I have a cruiser with twin v8's, would be nice to convert to Genset maybe I
>v8 two electric. Big advantage would be more RPM maybe? 1 V8 Less fuel.
>
>Still a bit grey on this petrol ver electric torque HP equivalent thing.
G'day Terry, All
First a little about torque:
1) torque is the twisting force available out of the shaft of any motor.
2) electric torque comes from amps in the motor, and the controller
current limit sets the torque, so until the motor is fast enough to
come out of current limit, the graph is flat.
3) a typical graph (view with fixed-width font) you can see that the
electric provides full torque at low RPMs.
= represents electric,
* represents internal combustion engine
Torque
| ***
|===========
| * === *
| * ==== *
| * ===== *
| * ===*==
|* =*===
____________
4) horsepower is torque x RPMs, so with electric the horsepower has a
nice straight climb to the point where full volts is on the motor
(this is also seen by the battery amps climbing) then a gentle fade.
internal combustion can be all over the place, depending on the
torque produced (carburettor/
Hybrid power has some potential advantages - I am no means an expert
on this, just what I've picked up along the way. I was a speaker at a
national symposium on hybrid power a couple of years ago, (my talk
was technology transfer from industrial and automotive-electric power
into the marine environment)
mostly picked up working with the AMC-VPL group.
1) a drive system is most efficient when the power/rpm curve of the
propellor is closely matched to the power/rpm curve of the motor. I
saw this when the Greenliner was optimised the year before last, the
original 'get it going' build had the performance curves almost at
right angles, the optimised version had a much 'taller' impeller,
plus a 2:1 reduction between the motor and jet, letting the motor rev
more. This almost doubled the range.
2) Electric drives can be brilliant for manoevering, depending on the
control system, so may provide this benefit anyway.
3) V8 engines have efficiency plots that are all over the show, there
are 'sweet' RPMs and bad RPMs for efficiency, but without proper fuel
flow meters, you'll have no idea. When I say 'proper' I mean the
$2500 McNaught (ones that properly measure) not the $1200 Navman
(typical of type, but many others) that take forever to set up
because they rely on guesswork to calibrate.
4) A good hybrid/electric boat may get significant efficiency gains
by having multiple smaller gensets feeding a common power buss, the
buss controller starts just enough gen sets to keep up with demand.
This allows the gensets to operate at peak efficiency. The system
that I have seen discussed includes a large solar array to charge a
battery bank as well, but even without that there is potential.
So, specific to your boat: Depending on the shaft speeds required, it
may be possible to use standard industrial 3-phase motors, direct
coupled to the shafts, doing away with gearboxes (reversed
electrically)
typically 1500RPM max (but there are ways to get up to 3600RPM from a
4-pole motor designed for 50Hz 'mains'). A standard industrial
variable-frequency drive (called a VFD or VSD) could be used to
interface between a standard 3-phase gen set and the motor. However,
you need to keep the VSD pretty dry - my fathers' steel boat has dry
bilges, a friends Riviera is always a little wet. Dads' boat would be
an OK environment, the Riviera would not be so good. 3-Phase VSDs
have 600 volts inside, it doesn't take much water to cause problems,
but 'Solar sailor' uses standard VSDs, (but at 300V if I remember
correctly) so it has been done.
On the genset side, if you have big V8 motors then you'll be ...
300hp per motor? if so then a couple of 250kW gensets to give maximum
power... not looking like a good system choice due to weight. If you
already have a genset system it may be possible to use a couple of
20kW or so motors belt drive after the gearboxes, with a generator
change to 50kW and use the genset/electric for great manoevering and
slow speed cruising with good efficiency, then the V8s for power and
freewheel the electrics.
It is one of those situations that is very dependant on the specifics
- the weight of the genset/s, the weight of the motors, the weight of
the engines and gearboxes, available space, etc. A boat can be
designed to be a successful hybrid, a conversion would need careful
research before commiting to it, unless you have plenty of cash to play with.
Hope this helps
Regards
[Techik] James
No comments:
Post a Comment