Marine Grade — SF Bay Current Atlas

The current layer

The Bay's current is the whole game, so it's the foundation everything else sits on.

A phase-indexed nowcast

Five days of a high-resolution circulation model (~88 m, every 30 min) indexed by tidal phase — hours from max flood, and how strong that cycle ran.

Matched to today's tide

Today's NOAA flood/ebb schedule at the Golden Gate sets the phase and strength; the atlas shows the historical snapshot that actually matches it.

Depth, where relief lives

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.

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.
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.
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.
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.
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.

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 atlas →

Not for navigation. The current shown is a tidal analog — a past modelled snapshot matched to today's predicted phase and strength, not a live measurement or a forecast. Scenarios assume a steady wind and an idealised polar. Use it to think about strategy, not to keep off the rocks. Carry proper charts.