VMG isn't a logged instrument value — it's derived on the fly from boat speed and true wind angle: VMG = Bsp × cos(TWA). This chart bins |TWA| every 5° and plots the average VMG in each bin, which turns the tradeoff between speed and angle into a curve with a visible peak — the boatspeed polar alone doesn't make that peak obvious.
Downwind (default) covers TWA 90–180° and flips the sign so running deeper reads as a rising curve — the peak is the best angle for making progress away from the wind.
Upwind covers TWA 0–90° unflipped — the peak there is the best angle for pointing toward the wind.
Dot size scales with sample count (n) in that bin. Where a curve fades to a dashed line, sample count has dropped thin for that band — the shape may still be suggestive, but don't trust a "better" angle out there without more data. The starred point is the single best-sampled-enough peak across all active TWS bands.
Compares every angle bin to whichever bin has the most samples (usually the angle actually sailed most often) — showing the % change in boat speed and in VMG relative to that baseline. A deeper angle typically costs boat speed but can still gain VMG; this table shows whether that tradeoff is actually paying off in the data currently on screen.
Curves — connects each TWS band's binned VMG into a line.
Smooth — 3-point weighted average across adjacent angle bins, to cut through bin-to-bin noise.
Scatter — every individual raw point's VMG, not summarized.
A gybe is detected as a Twa sign-flip while sailing broader than 100° on both sides; a tack is the mirror image — a sign-flip while sailing narrower than 80° on both sides. Either way the flip must complete within 3 minutes, so two unrelated same-side periods hours apart aren't mistaken for one continuous maneuver. "Omit" excludes every point within ±2 minutes of each detected event — gybes when viewing Downwind, tacks when viewing Upwind.
Why it might matter: during the maneuver itself, boat speed stalls then surges as the sails re-fill — readings that aren't representative of steady-state sailing at that angle. Those transient points land right in the thinnest-sampled part of whichever curve you're peak-finding, so a handful of contaminated points can move the answer more than they should.
Three theoretical/VPP reference polars can be overlaid: MM reference (the same table used on the Polars page's "MM Reference Polar" view), WCE (Main+A5O, 308m² downwind sail), and WCN (Main+VMG Spin, 344m² downwind sail) — WCE and WCN are two different downwind sail configurations from the same VPP revision, sharing identical upwind numbers but diverging past TWA 130° or so. Each overlay runs its target boat speed through the identical VMG formula (target Bsp × cos(TWA)) so it's a fair, apples-to-apples comparison against the empirical curve, not a different metric.
Each active TWS band gets one dashed target line, matched to the nearest discrete wind speed that target's table actually has data for (each is a sparse grid at fixed TWS values like 6, 8, 10, 12… — not every 2kt band has an exact match). The line color always matches its TWS band; the marker shape tells the three targets apart when more than one is switched on — diamond (MM), triangle (WCE), square (WCN). Where the empirical curve sits below a target line, that's a real speed gap at that angle — worth asking whether it's a boat-handling issue or the target itself being optimistic.