Offshore - Lake Ontario 300

Page 98 Lake Ontario Offshore Racing Guide Lake Ontario Offshore Racing Guide Page 99
wind and upwind legs. In that case the concern is that you may not be sailing
the optimum angles. Too high for the down-wind leg and too low for the beat.
So why not simply use VMG? You can and the AVIA system also shows VMG
but I find it tricky to use as an instant indicator of sailing efficiency. It provides
a good indication of progress over a longer period of time but small heading
changes initially give an impression of improved progress until the speed bleeds
off resulting in an unstable hunting for the magic combination of speed and
heading. Target speeds are a more direct indication of how you’re doing.
To help with this concept we put in 2 versions of the polar charts. The normal
version that gives the VPP for any combination of true wind angle and wind
speed and a special version for windward/leeward situations that forces a
“fixed” target speed for a given wind speed regardless of the actual wind angle
whenever the boat is close to beating or running angles. For instance, if the true
wind angle is less than 52 degrees, the programme gives the best beating target
speed and “coaches” the helmsman to the best target for beating at that particular
wind speed. A simple click of the mouse selects between polar charts while
the programme is operational.
The polars are easy to install from a spreadsheet and the system logs all the
data on the computer for later review and fine tuning the polar data.
So what about instrument sensors? That question eventually led me to the
NMEA 2000 network and the “intelligent” sensors that put information directly
on the network. One of the most interesting developments since I last looked
at the state-of-the-art is the ultrasonic wind sensors. These have no moving
parts and use ultrasonic sensors and
receivers to detect wind flow across
the sensing area.
I found two manufacturers that build
sensors suitable for a sailboat, Maretron
and Airmar. The published specifications
on accuracy did not look too
promising but I wanted to see how
well they worked. The answer was
to build a small wind tunnel in the
sailloft that could generate up to 12
knots of breeze and test these sensors
as well as a conventional masthead
wind sensor.
The results were pretty good, much
better than the published specifications.
The average absolute error for
both ultrasonic sensors was about
3/4 of one degree with a few readings
2 degrees out. The conventional
Furuno masthead sensor we tested was dead on with no measurable error with
our setup.
What finally swayed my choice to the Airmar PB200 was that it also has a GPS,
a fluxgate compass, barometric pressure, air temperature and heel and pitch
angle all built into one device the size of small coffee cup. We built a mount
that elevates the sensor about 4 feet above the masthead and it seems to benefit
from being in clear air away from the sails and mast.
The system worked well during the 2010 season with 2 exceptions. During the
second thunderstorm in the LO300, the wind sensor shut down completely, no
reading at all. It resumed normally after the lightening had moved away. The
other time was the LOSHRS 100 mile race during the heaviest downpour. The
wind angle shifted 20 degrees to port but returned to normal when the rain
diminished to “moderate” levels. One remarkable feature of the ultrasonic wind
sensor is how well it works in very light winds. In the last LOSHRS race from
Dalhousie we were able to use this feature to get across the quiet spot in the
middle of the lake.
For displays, we experimented
with a number of options
through the 2010 season. For
the computer I initially used
an IBM laptop that I could see
from the helm. We also had a
Maretron DSM 250 that was
useful for the longer races
because it didn’t take as much
battery power. At the end of
the season we installed the
software on an HP netbook
that provided enough computing
power, a handy size and doesn’t take too much battery power to operate.
For the 2011 season I added an Argonaut Proteus 10”, daylight viewable, waterproof
VGA display to make all the features including chart plotter available in
the cockpit.
So for the 2011 season we will start with the Airmar ultrasonic wind sensor
mounted on a 4’ tall custom-carbon wand on top of the mast, an Airmar boat
speed, water temperature and depth transducer, both communicating over a
an NMEA 2000 network through an Actisense USB interface to the netbook.
The netbook at the navigation station has the AVIA Pro software and Fugawi
ENC chart plotter software and the display in the cockpit will be the Argonaut
10” monitor. If we decide we need additional repeaters in the cockpit we can
always add individual repeaters or the Maretron display to the NMEA 2000
network, at any time.
Now, the question is, will we get 25 years out of the system?