AC38 Race Analytics

Plot Guide

This page explains what each chart and table means, how to interpret it, and where the numbers come from.

Data and Source

  • Repository: ac38 (GitLab)
  • Generator script: scripts/generate_race_site.py
  • Frontend chart logic: static/js/race-chart.js
  • Race pages are generated from telemetry .jsonl files and rendered by Hugo templates.

Across All Races (Homepage)

Across All Races table

  • Mean Upwind VMG (% of race-best): For each race, each boat’s upwind VMG is normalized to that race’s best. The table shows the mean across races.
  • Avg Tack/Gybe Loss: Mean VMG loss during tacks and gybes.
  • Tacks/Gybes: Event counts observed in telemetry.

Across All Races Polar Speed

  • Shows mean boat speed against true wind angle across all races.
  • Uses post-start samples only.
  • Ignores telemetry points where boat speed is below 10 knots.
  • Aggregates each boat’s performance into angle bins, then averages across races.
  • Includes a wind-range selector with prebuilt bands plus an all-wind view.
  • Useful for comparing broad sailing-mode efficiency rather than one specific race.

Maneuver VMG States

  • Shows before / during / after VMG states around maneuvers for the selected boat.
  • Useful to compare execution quality and recovery.

Per-Race Page

Boat Summary

  • Boat-level aggregate stats for that race: speed, VMG, distance, and computed start/finish/race times.
  • Boats with no detected finish are shown as DNF.

Start, Roundings & Finish

  • Each row is a milestone event (start line crossing, each rounding, finish).
  • Cell line 1: elapsed race time at that milestone.
  • Cell line 2: gap to milestone leader.

Speed Over Time

  • Raw speed time series in knots.
  • Best for spotting acceleration/deceleration phases and disturbance periods.

VMG - Upwind vs Downwind

  • Compares directional VMG efficiency.
  • Highlights whether a boat gains more in upwind or downwind legs.

Tack & Gybe - Average VMG Loss

  • Average VMG loss during maneuver windows relative to nearby steady sailing.
  • Lower is better. Negative can occur in powered-up conditions.

Gap To Leader (Estimated)

  • Time gap to race leader as race evolves.
  • Sudden rises can indicate mistakes, traffic, incidents, or tactical losses.

Maneuver Quality Scatter

  • Each point is one maneuver.
  • X-axis: VMG loss. Y-axis: recovery time.
  • Better points cluster toward bottom-left.

Leg-By-Leg Gain/Loss

  • Leg split matrix with loss relative to leg-best boat.
  • Fast way to identify where each boat wins or loses time.

Start Diagnostics

  • Measures around the gun: time-to-line, speed at gun, distance to line, and first-90s distance performance.

Boundary Pressure

  • Time spent near boundary edges and VMG near boundary vs center.
  • Helps evaluate whether edge usage was tactical or costly.

Race Story

  • Auto-generated event timeline from lead changes, wind context, and maneuver events.

Boat Mini Charts

  • Compact per-boat traces for speed, VMG, and gap.
  • Designed for quick side-by-side scanning.

Race Track & Maneuvers map

  • Replay of boat positions with start/gate/boundary overlays.
  • Includes maneuver markers and wind widget at replay time.

Replay VMG Subplot

  • Static VMG-versus-time chart placed with the replay slider.
  • One line per boat, with the same race-time axis as the map replay.
  • The vertical marker follows the current replay time when you scrub or play the map.
  • Useful for seeing when boats were fast or slow without turning the subplot itself into a second replay.

Notes on Robustness

  • All charts include telemetry-derived estimates and may be sensitive to missing or noisy points.
  • Gap and mini-chart y-scales are now robust-capped so a retirement does not flatten all other traces.