Depth tells you whether you fit. Weather and tide tell you whether you should go at all. Helm puts both on the same chart you are navigating with, rather than in a separate app you check and then forget.
Predictions come from NOAA CO-OPS against the MLLW datum — the same reference the charts use. The predicted level from a station within 25 nautical miles feeds straight into the depth reading, so a number that looks fine at high water does not quietly mislead you three hours later.
Current arrows are drawn on the chart and rotate as you scrub through the day. You can see whether a pass will push you or hold you back before you commit to it, which matters more than wind for a slow boat in a narrow cut.
Animated wind, wave and current overlays sit on top of the chart rather than beside it, so you are reading conditions in the place you are actually planning.
A multi-day forecast in three-hour columns: wind and gusts, air temperature, rain, and water temperature where the data exists. Gusts are shown separately from sustained wind, because the difference is what decides whether the day is pleasant.
Outside US waters the forecast comes from a global model, so weather works there too. Tides and currents come from NOAA's US stations.
Helm watches the National Weather Service alert feed for the water you are on. A Special Marine Warning, a Small Craft Advisory, a Marine Weather Statement, a Gale or Storm Warning: if one is in force, a bell appears on the chart and the alert sits at the top of the shelf with its full text.
The lookup runs two ways, by your position and by the marine zone you are in, because a point sitting just inside a land zone would otherwise miss the offshore warning that actually applies to you. Unread alerts are counted, so one you have already read stops competing for your attention.
| What you see | Source |
|---|---|
| Tide heights and times | NOAA CO-OPS, against the MLLW datum the charts use |
| Tidal current arrows | NOAA CO-OPS current predictions |
| Wind, gusts, temperature, rain, waves | Open-Meteo, served from the ECMWF and GFS model runs |
| Warnings and advisories | National Weather Service active alerts |
The forecast can be read from ECMWF, from GFS, or from a best-match blend, and you switch between them in the weather sheet. All three are included. When two models disagree about Saturday afternoon, that disagreement is itself the forecast, and seeing it is more useful than being handed one number and told to trust it.
Forecast fetches are cached by a grid cell of 0.05 degrees, roughly five and a half kilometres. Two taps in the same bay share one fetch; the next town over gets its own.
Wave height and period get their own view. Height alone is a poor guide; a two-foot swell at a long period is a different day from two feet of short, steep chop.
The departure planner reads all of this and reduces it to one bar: when the passage is calm and when it is not. That is usually the only question you actually have.
Every hour of every leg gets one of four verdicts: calm, caution, rough, or unknown. Unknown is a real answer and it is used. Where there is no forecast data for that water at that hour, Helm says so rather than filling the gap with a guess and colouring it green.
Two rules then push an hour one step worse than the raw wind alone would make it:
Current running against wind gets its own line, because that combination builds short breaking water out of conditions that look mild in a wind forecast.
The numbers behind those rules live in a written spec that the code points back at, so the thresholds on screen and the thresholds on paper cannot drift apart.
NOAA CO-OPS, against the MLLW datum, the same reference used by the charts.
Yes, as long as Helm downloaded the prediction while you had signal. It keeps the last NOAA curve for the station nearest the boat on the device, running about a week ahead.
Partly. Helm is built for US waters, and it also has 60 packs outside the US, built from each country's public data: 42 German rivers and canals, 12 Irish coastal bays with depth shading and contours, and 6 Dutch waterway areas. Tides and currents come from NOAA and cover US stations only. Weather works anywhere.
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