Maneuvers

Maneuver analysis can be a useful tool to determine To successfully analyse a maneuver, the criteria for maneuver detection and maneuver analysis must be met as described below.

Maneuver Detection

When you upload or re-process uploaded data, maneuver detection is performed automatically. All detected maneuvers show up as annotations in the Table or Line Chart visualization types. If a maneuver doesn't show up where you expect it, see Troubleshooting Maneuver Detection below.

Requirements For a Maneuver to be Successfully Detected:

  • The TWA (true wind angle) metric must be present in your data, which can either be included in your log files directly from your instrument system, or it can be automatically calculated by Njord from either apparent wind and boat speed, or true wind direction and boat Heading/COG.

The following parameters are used in maneuver detection. They can be configured under the respective boat's Settings - Filters. After changing these settings, you need to re-upload data or re-process uploaded data (re-process by going to the Process tab in your uploaded data, add a Derived Metrics step, and Apply).

  • Upwind TWA Range: the true wind angle range that would be considered upwind sailing for your boat (by default: 30 - 60 deg)
  • Downwind TWA Range: the true wind angle range that would be considered downwind sailing for your boat (by default: 120 - 170 deg)
  • Exclude Time Before Maneuvers: the maximum reasonable amount of time your boat requires from the first rudder inputs or trim changes in preparation for the maneuver, until the time of the maneuver
  • Exclude Time After Maneuvers: the maximum reasonable amount of time your boat requires from the time of the maneuver until target wind angle and boat speed have been re-established

Maneuvers are automatically detected when the following conditions are met. The time of the maneuver is the exact time when TWA hits the respective number (0/180/90).

  • Tack: any time where TWA is 0, Time Before Maneuvers seconds earlier TWA lies in the Upwind TWA Range, and Time After Maneuvers later TWA also lies in the Upwind TWA Range
  • Gybe: any time where TWA is 180, Time Before Maneuvers seconds earlier TWA lies in the Downwind TWA Range, and Time After Maneuvers later TWA also lies in the Downwind TWA Range
  • Turn Up: any time where TWA is 90, Time Before Maneuvers seconds earlier TWA lies in the Downwind TWA Range, and Time After Maneuvers later TWA lies in the Upwind TWA Range
  • Bear Away: any time where TWA is 90, Time Before Maneuvers seconds earlier TWA lies in the Upwind TWA Range, and Time After Maneuvers later TWA lies in the Downwind TWA Range

Troubleshooting Maneuver Detection

If a maneuver is not being detected as expected, check the following, starting at the time of the maneuver. Use the Table or Line Chart visualization types to inspect TWA data at and around the time of the maneuver.

  1. Verify TWA data availability. Confirm that TWA (true wind angle) data is present in your data at the time of the maneuver. If no TWA is available, add TWA for example by adding wind data.
  2. Verify TWA at the time of the maneuver. TWA must cross 0 / 180 / 90 degrees for tacks / gybes / turn ups and bear aways, respectively. If it doesn't do that, TWA data may suffer from miscalibration or other errors that need to be corrected.
  3. Verify TWA at Time Before Maneuvers before the maneuver time. It must fall in the Upwind TWA Range or Downwind TWA Range configured for the respective boat. If it doesn't, consider expanding the valid TWA range, or increasing Time Before Maneuvers.
  4. Verify TWA at Time After Maneuvers after the maneuver. It must fall in the Upwind TWA Range or Downwind TWA Range configured for the respective boat. If it doesn't, consider expanding the valid TWA range, or increasing Time After Maneuvers.

Maneuver Analysis

The Maneuvers Visualization Type will perform an analysis of all detected maneuvers (see above).

The following parameters are used in maneuver analysis:

  • Exclude Time Before & After Maneuvers: see above
  • Average Time Before & After Maneuvers: set to 20 seconds each. Contact us to have it changed for your boat.

Maneuver analysis starts at Average Time Before Maneuvers seconds + Exclude Time Before Maneuvers seconds before the maneuver time. Starting at this time, boat data is averaged for a period of Average Time Before Maneuvers seconds, to establish the "Before" baseline of the boat's course, speed, etc. which is used to perform the maneuver analysis (incl. maneuver loss calculation).

Maneuver analysis ends at Exclude Time After Maneuvers seconds + Average Time After Maneuvers seconds after the maneuver time. Starting at Exclude Time After Maneuvers seconds after the maneuver time, data is again averaged for Average Time After Maneuvers seconds to establish the "After" comparison.

The maneuver analysis table shows various relevant metrics as averaged before and after the maneuver, as well two different maneuver loss calculation approaches. Click the "i" symbol near the maneuver loss values to learn more about how those are calculated.

Troubleshooting Maneuver Analysis

If a maneuver is not being analyzed, check the following conditions:

  1. If a maneuver hasn't been detected, it cannot be analyzed. Verify that the maneuver you've looking for has been detected (see above).
  2. Not all detected maneuvers can be fully analyzed. To learn why a detected maneuver has not been fully analyzed, select the options Include maneuvers without full analysis and Extended data from the Maneuvers Visualization Type configuration menu. The Reason Not Analyzed column will show why a detected maneuver has not been analyzed.