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Method note

Tacks and gybes

How turns are found, which ones are clean, and how the metres lost are measured.

Finding a turn

A tack is where the aligned compass heading crosses the wind and a gybe where it crosses dead downwind, with each side held for 10 s. Without a compass, ground course stands in.

Clean turns

Only clean turns are measured: more than 30 s after the gun, more than 30 s from any other turn or rounding, a tack on a beat or a gybe on a run, and entered above 2.5 kn. Double tacks, a tack that close to a rounding and the first move off the line are left out.

Metres lost

The target is the boat’s own VMG: the mean of its pace 30 s before to 10 s before and 30 s after to 50 s after the turn, so a lift or header through the turn is not charged to the crew. The loss is the distance that pace would have made 10 s before to 30 s after the turn minus the distance actually made toward the wind. The boat’s figure is the median of its clean turns, compared with the median of the fleet’s clean turns in the same race.

The traces run from 20 s before to 40 s after the turn as a share of entry speed. Recovery is the time until speed holds 95% of entry for 3 s.

The figures, one by one

Tack and gybe loss

Distance toward (or away from) the wind given up against the boat’s own pace either side of the turn, measured 10 s before to 30 s after the turn. The target pace is the mean of the VMG 30 s before to 10 s before and 30 s after to 50 s after the turn, so a shift through the turn is not charged to it. Only clean turns count.

Unit
metres per turn (median clean turn); boat lengths on the charts
Reading it
Delta − is fewer metres lost than the fleet.
Scope
Per race median of clean turns; regatta value is the median over races.
Rules this figure depends on, read from the analysis code
RuleValueSource
Entry VMG baseline-30 to -10 s from the turnfleet-race.ts · DEFAULT_FLEET_RACE_POLICY.lossBaseline
Exit VMG baseline30 to 50 s from the turnfleet-race.ts · DEFAULT_FLEET_RACE_POLICY.lossExitBaseline
Measured span-10 to 30 s from the turnfleet-race.ts · DEFAULT_FLEET_RACE_POLICY.lossSpan
Clear of other turns and roundings30 sfleet-race.ts · DEFAULT_FLEET_RACE_POLICY.cleanSeconds
Earliest clean turn after the gun30 sfleet-race.ts · CLEAN_MANEUVER_RULES.afterGunSeconds
Lowest entry speed of a clean turn2.5 knfleet-race.ts · CLEAN_MANEUVER_RULES.minEntrySog
Each side of a turn must hold10 sfleet-race.ts · DEFAULT_FLEET_RACE_POLICY.maneuverHoldSeconds

Speed and heel through the turn

Each clean turn from 20 s before to 40 s after the moment the bow crosses the wind (or dead downwind). Recovery is the time until speed holds 95% of entry speed for 3 s, searched for up to 90 s.

Unit
% of entry speed; degrees of heel
Reading it
100% is entry speed.
Scope
Median trace per second over the boat’s clean turns, and the fleet’s.
Rules this figure depends on, read from the analysis code
RuleValueSource
Turn trace window-20 to 40 s from the turnfleet-regatta.ts · PROFILE_WINDOW
Recovered at this share of entry speed95%fleet-race.ts · CLEAN_MANEUVER_RULES.recoveryShare
Held for3 sfleet-race.ts · CLEAN_MANEUVER_RULES.recoveryHoldSeconds
Searched for up to90 sfleet-race.ts · CLEAN_MANEUVER_RULES.recoveryLimitSeconds

Analysis version: fleet-race-4 · fleet-regatta-1.The numbers in this note are read from the same code that computes the figures, so they change when it does.