Rainbow's End Marine
Arc
A camera sextant, for the fun of it.
Your phone becomes a camera sextant. Photograph the sun and the sea horizon in one frame; the picture and the clock do the rest — a line of position in seconds, a latitude-and-longitude fix from two sights, and a deck log that keeps honest dead reckoning between them.
Why it stands out
Different by design. Honest by doctrine.
One photo is the sight.
Sun and horizon together in the frame. The horizon is the level reference, so the boat's roll and your grip don't matter — hold the phone any way that works.
The whole reduction, worked for you.
Dip, refraction, semidiameter, parallax — the same corrections a paper sight reduction works, shown line by line, against a built-in almanac good through 2050.
Marking you can mean.
Draggable handles with a magnifier loupe, then one-pixel nudge arrows — because on a sun sight, a pixel is roughly a nautical mile.
Fixes that own their error.
Cross any two sights into a running fix with a stated radius — and see the gap between where the log said you'd be and where the sky says you are. That gap is the current talking.
What it does
Built for the questions you actually ask at sea.
A real deck log.
Start from a known position, log course-and-speed legs, tap Stopped whenever she isn't moving. Every sight reduces against the DR for its own moment; every fix can restart the reckoning.
Noon, predicted.
Local apparent noon computed for your longitude with a countdown. A sight near the meridian reads directly as latitude — the classic noon sight, kept classic.
Honest about its limits.
When a sight isn't trustworthy — sun too low, camera angle too uncertain, a line falling absurdly far from your reckoning — the app says so in plain language instead of pretending.
Entirely offline.
Built-in almanac good through 2050. No network request is ever made.
What it won't do
What the app won't do is a feature.
Arc is not a chartplotter, and it never claims to be.
A camera sight is typically good to a few nautical miles. Arc states the accuracy of every result. Do not use it where GPS-level precision is required.
Arc will not take a sight for you. Every sight can be taken with the screen doing the looking — but the framing, the timing, and the judgment are yours.
Never look directly at the sun. The app is built around that rule.
Every boat carries GPS these days. Arc is not a contingency plan for the day they all fail at once, though it would serve. It is a fun alternative to try — and if you own a sextant, a genuinely useful one.
Available now
Arc is live on the App Store.
Available for iPhone and iPad. No account, no tracking.
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