RaceAtlas

Which Side Pays?

RaceAtlas is a tidal-current simulator built for understanding the actual conditions and helping sailors make good racing decisions. Set your marks, pick a scenario, simulate real races and see which side pays.

Open the map → SF Bay tides today Sign in
Two boats split tacks over the SF Bay current field on the Berkeley Circle, with the boat-length gap between them labelled.
One beat to windward showing the different boat-on-boat results based on the changing current conditions over time.

The current layer

In San Francisco Bay, current is the big factor, and knowing how to play the current is usually the most important strategic decision a sailor can make.

Historical snapshots

A library of modelled current fields for the Bay, catalogued across the whole tidal cycle — every phase, from max flood through the ebb.

Indexed to the cycle

Each moment shows the snapshot whose phase & strength match the tide you’re on, set by NOAA’s Golden Gate schedule.

Depth Contours and Relief Areas

Bathymetric contours from 2 to 100 m, with a depth read-out under the cursor — so you can see the shallow flats where the shore boat gets out of the ebb.

Tactics scenarios

Each one runs two (or more) boats over the real current field and tells you, in boat lengths, which choice won — and why.

  1. Split Tack Two boats leave the line on opposite tacks, sail an equal split, tack, and converge. The ladder-rung gap at the cross is the side advantage.
  2. Same Tack, Opposite Ends Boat-end vs pin-end on the same tack. Splits the result into what the line bias gave you and what the current gave you.
  3. Tack on Intervals Both boats short-tack up the beat. The rungs show the gap every time they converge — hold your side, or cross over.
  4. Shore Relief vs Open One boat short-tacks the shore for current relief, the other beats the open side. Counts the tacks each one paid for.
  5. Bay Tour Options Alternative land-avoiding routes to a mark, each committed to a different corridor, timed honestly against the current. Shore vs the deep channel.
  6. Manual Set each boat’s start, heading and tack angle yourself and run it over the live current — build any matchup the presets don’t cover.

Race playback

Every scenario replays. Scrub the clock, watch the boats sail their tracks over the current, and see the ladder rungs open and close in real time. Each boat carries live boat speed / SOG / VMG — so the gap between boat speed and SOG is the current, right there on the screen. Turn the wind dial mid-race and only the future re-solves.

On the water

Install it to your home screen and it runs full-screen like an app, with your boat's position on the chart.

iPhone / iPad

Open in Safari, tap Share, then Add to Home Screen.

Android

Open in Chrome, tap the ⋮ menu, then Install app.

Your position

Tap the locate button on the map for a live position, heading and accuracy ring, tracking as you sail.

Open the map →

Not for navigation. The current is a historical modelled snapshot matched to the tidal phase & strength — not a live measurement or a forecast. Scenarios assume a steady wind. Use it for strategy, not to keep off the rocks.