Page 69 - Misconduct a Reference for Race Officials

Note than when a GPS track is being compared with the charted position of a mark, a major
uncertainty is the actual position of the mark. Strong wind and/or tide, may move a mark
significantly from its charted position. Waypoints, however, are, by definition, fixed points.
Penalty turns. Depending on the frequency of logging, a GPS track may not contain
sufficient data to show that a penalty turn (or turns) has been made or completed correctly.

Checklist of GPS Related Information that may be required

(Required for each boat if using data or tracks from boats’ own instruments)
 Accuracy specification of the GPS unit(s) (note 1) .
 Where on the boat the GPS Antenna is located (distance from bow/stern and
centreline).
 Logging interval of the tack data (note 2) .

 Geographic datum used (e.g. WGS 84).

Notes
(1) GPS accuracy may be quoted using a number of statistical measures; typically:

 Horizontal 95% (the most common, the radius of the circle of 95% probability)
 CEP (circular error probable, the radius of the circle of 50% probability), multiply by
2.08 to convert to horizontal 95%.
(2) The logging interval must not be confused with the ‘fix frequency’ of the GPS unit.

The logging interval is the rate at which calculated position data is stored or transmitted
for the purposes of generating a track.

The fix frequency is the rate at which the GPS calculates position information. For many
existing GPS units this is one fix per second, however it is becoming increasingly
common for marine GPS units and dedicated sports trackers to operate at 10 or more
fixes per second.

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