Data Collection

The data collector captures all NMEA 0183 data transmitted and then uses selected elements to produce a picture of a boat’s performance. Data is aggregated as it is received; creating summary data that combines new information with existing values.

Data points are related to a central time period making it possible to combine and compare a large number of variables at a given point.  Its possible to compare the way the sails are set of the sails with the true or apparent wind speed and the weight of the crew. The same figures can be compared on different days to determine the effects of relatively small changes to the boat’s configuration.

architecture_data

The table below summarizes the data points collected:

Data Description
Session Information Information about the recording session; date, time period size, boat name
Time Period The technology collects and summarises for a specified time interval in the range of 1-60 minutes
NMEA Data All the NMEA data received during a session irrespective of whether the data is used in calculations
GPS Position GPS Latitude and Longitude
Speed through water Speed of the boat through the water
Speed over ground Speed of the boat over the ground
Apparent Wind Apparent wind speed and direction
True Wind True wind speed and direction
Time Period Summary A summary of the averages for the data listed above for a given Time Period
Session Polar Data Calculates Polar data for given true wind speeds and angles based on the data collected during a session
Boat Polar Data Calculates Boat Polar data for given true wind speeds and angles based on the data collected during the sessions for that boat
Boat Configuration Boat configuration items are customisable, for instance: current sail area can be recorded. The level of detail collected will depend on the information recorded about a boat
Route Information Distance and heading to a defined waypoint are calculated and recorded.

The following summary data points are held for each predefined time interval:

Summary Data Point Description
Average true wind speed in knots The average true wind speed in knots during the sample period. For instance if there are 5 MVW relative wind speed sentences in a given time slot the program will average them out and convert the value to a true wind speed
Average speed through the water in knots The average water speed, expressed in knots, in the time period based on the NMEA VHW sentence. Where the NMEA data is only being supplied in KPH or metres per second the software will convert the data
Average apparent wind speed in knots The average apparent wind speed in knots based on the MVW Relative wind sentence
Average speed over the ground in knots The average speed over the ground, rather than through the water, derived from the NMEA VTG sentence
Average true wind direction relative to the bow The average true wind relative to the bow. Figures are 0-180 and should be read in conjunction with the Tack data point taken from either the NMEA MWV Relative converted figure or the NMEA MWV True figure where present
Average true wind direction degrees relative to magnetic north This average combines the NMEA VTG Heading data with the NMEA MWV data to derive actual magnetic wind direction averaged during the time period.
Average apparent wind direction degrees relative to the bow The average apparent wind speed relative to the bow taken, as above, from the NMEA MWV Relative or True sentence and converted as required. Data is in the range 0-180 degrees and should be read in conjunction with the Tack
Average ground speed heading degrees magnetic The average heading of the boat over the ground, as opposed to the direction the boat is actually pointing, in degrees magnetic taken from the NMEA VTG Sentence
Apparent wind tack Tacking the boat will generate the start of a new sample period either Port or Starboard, calculated from the NMEA MWV Sentence
True wind tack Calculated as the apparent wind tack and should normally be the same
Ratio of true wind speed to water speed Indicates how efficient a boat is, ie if there is a 10 knot True Wind and the boat generates a speed through the water of 5 knots this will have a ratio of 2. A lower ratio implies less efficiency, hence a boat travelling 10 knots through the water in 10 knots of wind will have a ratio of 1,  20 knots in 10 knots of wind a ratio of .5 and so on
Ratio of apparent wind speed to water speed Applies a similar logic as the ratio of true wind speed to water speed but analyses the apparent wind speed compared to water speed.
Latitude degrees minutes seconds The latitude at the end of the sample period taken from the NMEA GLL Sentence.
Longitude degrees minutes seconds The longitude at the end of the sample period taken from the NMEA GLL Sentence.
Latitude as a decimal The latitude at the end of the sample period taken from the NMEA GLL Sentence expressed as a decimal.
Longitude as a decimal The longitude at the end of the sample period taken from the NMEA GLL Sentence expressed as a decimal.
Depth below transducer The depth in metres of the water below the boat.
Boat heading in degrees magnetic Where a fluxgate compass sensor is present on the boats network the current boat heading (as opposed to course over the ground is recorded in degrees.
Estimated/calculated values indicator Where data is missing for a time period the system will estimate a reasonable number based on the last known data values. ‘ESTIMATED’ will appear for this data point while the record will show ‘CALCULATED’ when the figures are fully calculated.

In addition to the predefined values collected from the NMEA data an unlimited number of boat configuration variables can be recorded via the boat configuration screens. This makes it possible to record everything from the current sail area to the number of tea bags left in the galley!

After setting the variables the data collector reads the active variables at the start of each time period and records them against the other variables defined in the table above.

As an example, if a boat starts sailing with a large No 1 Genoa and Main Sail these would be recorded as ‘active’. If the wind then gets up and the decision is made to reduce the sail area, this can be recorded by amending the data on the screen and the data collector will record the updated configuration at the start of the next sample.

Given this information its possible to determine the expected boat speed given sail plan A and wind speed B.