It plans the passage. You still decide.

Plotting a passage by hand is the part of trip planning that everybody says they enjoy and almost nobody does properly. It takes twenty minutes, it needs the chart open, and the honest version of what most people do is draw a line and hope the bit in the middle is deep enough.

Tell it where you are going

Give theONE a start and a finish and it will lay out a route between them — a real chain of waypoints that stays in navigable water, keeps clear of what should be kept clear of, and holds to the depth your boat needs rather than a generic one.

Including the long ones

This is the part we are quietly proud of. Auto-routing on the water is a hard problem at any distance, and it gets dramatically harder the further you go — which is why the marine apps that offer it at all tend to offer it for a harbour hop and quietly decline the passage you actually wanted planned.

theONE will take a leg up to 400 nautical miles point to point. We have measured a 464 nm route over 87 waypoints come back from a single request.

Not a harbour entrance. Not the last two miles into a marina. The overnight run — the one you were going to spend an evening plotting by hand with the chart open and a cold dinner going colder.

Two honest things about that. It takes minutes, not seconds — a long passage is real work and the app does not pretend otherwise. And on the densest stretches of coast, a corridor can pack more charted depth and hazard data than one pass can carry, and the app will say so and ask you to drop one waypoint in the middle and take it as two legs. That is a real limit on a real coastline, it is stated on the screen rather than discovered by you, and two auto-routed halves is still an evening you get back.

Getting this far took a long time and a genuinely different approach, and we are not going to explain how it works. What matters to a captain is what comes out the other end, and what comes out is a route you can look at, understand, and disagree with.

On the chart, with the numbers that matter

However the route was made, it lives on the chart with the leg, and under way it carries the three numbers you actually steer by.

It will not guess your draft

Ask it to route before the boat's draft is on file and it stops and asks for it, in one small card, and then carries straight on. It does not assume, and it does not fall back to something typical for the size.

A wrong guess could mark a six-foot sounding “safe” for a nine-foot keel. There is no version of that we are willing to ship.

From the draft it derives the boat’s minimum operating depth: one and a half times the draft, plus two feet. A boat drawing 5.4 ft needs 10.1 ft of charted water, and that is the figure the router holds to on every leg it plans. It sits on the chip before you ask for a route — not quoted back at you afterwards as the reason one was refused.

The depth on the chip is the depth the planner requires. One boat, one number.

Set your own minimum instead and yours wins, because it is your boat and your bottom. Some captains want more on an unfamiliar lee shore at night; some want less at slack water in a creek they have run for twenty years. What theONE will not do is let the two figures disagree behind your back.

The per-leg under-keel margin is a second, separate knob doing a separate job: it is what the app checks soundings against when you plot a leg by hand and want the pins that are too shallow for you flagged red. Presets for the three answers most captains actually give (conservative, default, and skinny water for when you know exactly what you are doing), or step it yourself a tenth of a foot at a time. Both are adjustable before you leave and while you are running — the same chip is on Mission Control under way.

You review it before it exists

A proposed route is not a committed route. theONE shows you the proposal on the chart with your own straight-line plot underneath it in faint red — the passage you would have drawn without it — because the difference between the two lines is the whole point and you should be the one who judges whether it was worth it.

With it comes the arithmetic in one line, a plain-language list of what it kept you away from, and three buttons: accept it, accept it and keep editing, or reject it and keep what you had. Every waypoint stays draggable afterwards. It is a first draft written by something that has read the chart, not an instruction.

Look at what the Why this route block is doing there. It is not a progress log and it is not a disclaimer — it is the route arguing its own case, in the order a captain would ask: what water did you use, what did you prefer, what did you cross, and where are you least sure. The yellow-segment line is the one to notice: the app tells you which parts of its own answer it has not verified, before you accept it, rather than after something goes wrong.

And when it can’t

Sometimes there is no route to give you. The margin is tighter than the water, the passage is closed, or the chart data will not come down. theONE says so.

It does not hand you a route that ignores the constraint you set and leave you to notice. The screen turns from teal to red, it tells you what stopped it, and it draws what it was looking at — the restricted areas, the shallow ground — so you can see the problem rather than take its word for it.

Read what those screens actually say. Not “routing failed” — we found no water charted at 10.1 ft or deeper within 1.5 nm of the destination pin. Nudging the pin a few yards won't help; it needs to move to charted navigable water. A number, a distance, and the thing that would fix it. The second one goes further and tells you not to bother retrying, which is the opposite of what software normally does with a failure it does not want to explain.

Then it offers the ways forward that actually apply. Where the margin is what stopped it, you can tighten it or loosen it and try again. Where it is not — a pin in the wrong place, a chart service that could not be reached — those two buttons are greyed out, because adjusting a constraint that was never the problem is theatre. Plotting it yourself by hand is always available, in every case, and always will be.

We are not going to tell you it always finds a route. It does not, and any marine app that claims otherwise is either lying or has not been taken anywhere interesting. What we will tell you is that it never invents one.

Then it goes to the plotter

However the route was made — auto-routed, hand-plotted, or auto-routed and then argued with — it leaves as a GPX file, the universal chartplotter format. Garmin, Simrad, Lowrance, B&G, Raymarine, Furuno, by card or companion app. No proprietary format, no subscription, no re-typing waypoints at the helm with the engines running.

Why it is built to be argued with

Because a route is the one output of this app that gets steered. Everything else is a record somebody reads later; this becomes a line on a plotter with a boat following it at fifteen knots in the dark. Software that hands you that with confidence and no explanation has misunderstood the job. The best thing it can do is a good first draft, the reasoning behind it, and an honest answer when there is not one.