BoatNavi app icon
⚓ Navi and Boat, one chart · San Francisco Bay & the Delta · iPhone and iPad · Works with no signal

Water under the keel, offline.
Then everything else the boat knows.

Navi answers one question at every point of the chart: how much water is under your keel, now and for the next 48 hours. Boat puts your instruments, your batteries and tanks, the autopilot and an anchor watch that actually wakes you on the same chart, one switch away — and none of it needs a signal.

clearance=charted depth+water level−your draft−your margin

In TestFlight, App Store to follow

iPhone iPad Offline Charts Signal K NMEA 0183 Raymarine SeaTalk1 Anchor Watch Autopilot Remote Apple Pencil
Navi

Will you float?

A chart coloured by clearance for your boat, a tide scrubber, the next shoal ahead, and a planner that only routes where the chart says you float. Seven regions from Dumbarton to West Sacramento, built from NOAA's own charts.

Boat

What is the boat telling you?

Connect the boat's Wi‑Fi and the chart runs on its GPS and sounder. The Boat screen shows the house battery, charger, engine, tanks and cabin, each with how fresh the reading is. Drop the anchor and the watch takes over.

Underway

One screen: a chart where the water is coloured by clearance for your boat, with a scrubber under it. Drag the scrubber, the whole map recolours. Red means you go aground.

🗺️

The Chart

Clearance-coloured water with a 48-hour scrubber that snaps to high and low water. Tap anywhere for the charted depth, the water level, the clearance, and the year the survey was done. Unsurveyed water says so, and old surveys are hatched.

🎛️

The Console

Water under the keel, the water level and its trend, your speed, and whether the tide is with you or against you — the four numbers you glance at, at the top of the chart at any text size.

⛰️

Next Shoal Ahead

The next shallow point on your track, with the clearance you will have when you get there — evaluated at arrival, not at departure.

📉

Track Profile

Depth against distance along your route with the water line at the scrubbed time. The controlling depth is named, and any hazard within 150 ft of the track is listed beside it.

🕓

Window Finder

When can I go? Sweeps the next 48 hours and returns the passable windows. Tap one and the scrubber and chart jump to the controlling point.

💬

Plan in Your Own Words

“Rio Vista to Benicia after lunch.” Parsed on the phone — deterministic rules first, Apple's on-device language model only for what the rules can't read — and the planner routes only where the chart says your boat floats. It tells you which brain understood you.

⚠️

Hazards and the Marks You Steer By

Wrecks, obstructions, rocks, pilings and foul ground from the ENC in three classes; one without a known depth is a zone the solver refuses to route through. The red and green lateral marks are drawn as charted, red right returning.

⛽

Marinas, Fuel and Anchorages

Marinas, fuel docks, ramps, restaurants and anchorages from OpenStreetMap on the chart, plus your own labelled marks — each one remembering what the chart claimed the day you dropped it.

At Anchor

Every anchor alarm is judged on three things: it keeps watching with the screen off, it wakes you, and it fails loud rather than silent. BoatNavi does all three on the phone's own GPS — and one thing the others can't. Next: the watch on the boat's Signal K server, with the chain counter marking the drop.

1

Drop

One large button marks the anchor where the bow is now. The swing circle is the rode's reach along the bottom plus your boat's length plus GPS scatter, with the working shown; the depth comes from the boat's sounder when it is talking, else the chart plus the tide now — and the screen says which.

2

It Wakes You

Dragging, a lost fix or a bad fix takes the screen and sounds until you acknowledge it — through the silent switch and with the screen off. A low battery, muted volume or a quiet server are each an alarm of their own, because the failure that sinks boats is the one that goes quiet.

3

It Fails Loud

The watch checks its own health while armed: a battery under 15% and not charging, volume off, notifications refused, the boat's server gone quiet — each listed with its remedy. It survives a relaunch, and a relaunch with no fix is itself an alarm.

4

Raise

Clears the anchor, stops the watch, and keeps the night's track for the trip log — a wind shift and a drag look different on a track, and identical on a distance readout.

“The circle reaches 4.1 ft at 03:12.”
BoatNavi's own line: the shallowest charted point inside your swing circle at tonight's low water, from the chart and the tide model. No other anchor alarm can say what the boat swings over.

Your Boat's Own Instruments

Monitoring the boat is a different task from navigating it, so it gets its own screen — one tap from the chart — and only its alarms come back.

📡

Connect

A Signal K server — a Raspberry Pi, OpenPlotter or a Victron GX — or an NMEA 0183 gateway on the boat's own Wi‑Fi, and the chart runs on the boat's GPS and sounder. Raymarine SeaTalk1 instruments — depth, speed through water, wind, heading and the autopilot — reach the app through the server with a single read-only tap on the SeaTalk wire; the wiring note is written and the first tap is going onto the partner boat. Bluetooth GNSS pucks work with no setup at all.

🔋

The Boat Screen

House battery, charger, engine, tanks, cabin and autopilot, each with how fresh the reading is. A stale number is marked stale; a sender that isn't there says so instead of showing a zero.

🧭

The Helm

Reading the pilot's mode, heading and rudder needs nothing switched on — Raymarine SeaTalk1 pilots through the tap, NMEA 2000 pilots directly. Steering is behind a switch, off by default, with a sign-in to the boat's server: then the sheet over the chart has the keys a Raymarine remote has, sized for a gloved thumb, a confirmation before the pilot takes the helm — never before it gives it back — and every reason a key can't work written next to it.

🔁

Sounder Loop

Once a sounder is on the bus: predicted depth beside the depth the transducer sees, divergence called out loudly — the chart is wrong here — and every comparison logged, the seed of a correction layer for your own water. Built and unit-tested; waiting on a boat that reports depth.

🌤️

Conditions

One Conditions chip on the chart. Tides: a 48-hour curve from the pack's own harmonics, offline, with the station's live gauge drawn over it when there is signal. Weather: the National Weather Service forecast for where you are, in knots — online only, and it says so.

📍

Trips and Marks

Record where you actually went with the depth you actually saw, reuse it as a known-good route, and share marks or private hazards boat-to-boat as a file. No server, no account.

✏️

Built for iPad Too

Chart and profile side by side on one scrubber, routes drawn with Apple Pencil, keyboard shortcuts for the nav station, and the chart on an external display with the controls on the iPad.

🔒

Yours Alone

No account, no ads, no tracking. Your position, your tracks and your boat's data stay on your device. Sharing is an explicit file export, nothing else.

San Francisco Bay and the Delta: Seven Regions, Dumbarton to West Sacramento

Every region is real charted data from NOAA's ENC — soundings, depth areas, hazards and aids to navigation, already in MLLW, each validated against its own source before it is written. The app opens the region you are floating in and carries on as you cross into the next.

RegionCoversSoundings
South BayBay Bridge to Dumbarton, San Mateo Bridge, Redwood City1,434
Central Bay & Golden GateThe Gate, the SF waterfront, Angel Island, the Oakland Estuary4,694
San Pablo Bay & Napa RiverRichmond–San Rafael Bridge, Pinole Shoal, Mare Island, Napa4,524
Carquinez Strait & Suisun BayBenicia, Martinez, Port Chicago, the Reserve Fleet13,924
West DeltaNew York Slough, Pittsburg, Antioch, Sherman Island4,545
North DeltaRio Vista, Steamboat, Miner and Cache Slough1,560
Sacramento RiverCourtland and Freeport up to West Sacramento572

Harbour-band data with median survey years from 1999 to 2005 — and the app says so on every callout.

Does it need a signal? No.

Offline is the operating assumption, not a feature — there is no cell service in most of the Delta. Download the regions you sail once, over Wi‑Fi. After that, exactly one thing needs a network.

WhatNeeds a Network?
Charted depthNo — it's in the region you downloaded
Tide predictionNo — computed on the device from harmonic constituents, indefinitely
Your positionNo — GPS is satellite, or the boat's gateway over the boat's own Wi‑Fi
Clearance, profile, windows, anchor watchNo — all of it runs on the two above
Live tide correction and the NOAA forecastYes — and the chart says “predicted tide only” until the correction arrives
0.030 ftRMS error of the tide engine against NOAA's own predictions across 10 Bay–Delta stations, over the full 18.6-year nodal cycle
31,253Charted soundings across the seven regions, every region past its survey gate at 0.030–0.095 ft median error
17Tide zones from the Golden Gate to Sacramento, each anchored to the CO-OPS station that governs it
330+Tests on the clearance, tide, hazard and anchor logic — no simulator, seconds to run — and dozens more driven through the UI on iPhone and iPad

A Planning Aid, Not a Navigation System

Public bathymetry outside dredged channels is old and Delta shoals move. The SFBOFS model is guidance, not measurement. Proximity alerts are advisory and are not a replacement for your boat's own depth alarm.

The right mental model: BoatNavi tells you which windows are worth attempting. The depth sounder tells you what is actually under the keel.

We are testing live on a boat with Signal K — reading its GPS, house battery, charger, engine, tanks and cabin sensors. The NMEA 0183 gateway path and the depth-sounder loop have not yet met hardware; the page will say so until they have.