If you want to know exactly which data sits under a navigation app, this page lists it. Helm reads NOAA electronic navigational charts directly. The soundings, contours, buoys, beacons, obstructions and channel limits you see in Helm are the ones NOAA publishes, and they carry NOAA's own scale and quality information with them.
An electronic navigational chart is a vector database in the international S-57 format, published by NOAA's Office of Coast Survey for United States waters. Each sounding, contour, aid to navigation and wreck is a separate object with its own attributes: a position, a value, a datum, and metadata describing how the underlying survey was made.
That structure is the reason a chart app can do more than draw. The shoal at the mouth of an inlet is an object with a depth value, so software can compare it to your boat's draft and answer the question directly.
NOAA maintains ENC cells on a rolling basis and issues updates as surveys, Notices to Mariners and aid changes come in. A buoy moved off a shifting bar, a newly charted obstruction, a revised channel limit: these arrive as chart updates rather than as a new edition of a book. Helm's chart packs are built from that published NOAA data, so the beacons, obstructions and channel limits in the app are the ones NOAA publishes.
Official charts are the foundation. On top of them Helm adds three more sources of truth about water level, and reports the combined answer with the date the measurement was taken.
| Source | What it contributes |
|---|---|
| NOAA ENC | The official electronic navigational chart: soundings, contours, aids to navigation, obstructions, channel limits and the chart's own quality metadata. |
| USACE eHydro | Hydrographic and dredging surveys from the Army Corps of Engineers, covering the federally maintained channels the Corps keeps open. |
| State lake elevation data | Surveyed depth for inland reservoirs and lakes, which is why a Texas or Tennessee lake is charted water in Helm rather than a blank shape. |
| NOAA CO-OPS | The live water level and tide prediction against the MLLW datum, applied to the sounding so you see depth now rather than depth at chart datum. |
The Army Corps surveys the channels it dredges, often on a much tighter cycle than a chart edition. Run the Atlantic Intracoastal Waterway through a cut that was dredged last spring and the eHydro survey is the number that describes today's bottom. Helm layers that survey over the ENC, so a maintained channel reads with its most recent measurement and the date behind it.
A charted sounding is referenced to mean lower low water, the chart datum. Helm pulls the NOAA CO-OPS prediction for the nearest station and applies it to that sounding, so the depth on screen is the depth at the hour you are reading it. Scrub the time forward and the number moves with the tide. Current arrows rotate with the same scrub, so a cut that runs hard on the ebb shows the direction it will set you at the hour you plan to run it.
Every ENC carries a field called CATZOC, the category of zone of confidence. It records how the area was surveyed, from a modern full-coverage multibeam survey down to a lead line pass made generations ago. Two soundings that read the same depth can sit in completely different confidence zones.
Helm surfaces CATZOC on the chart. A high-confidence surveyed channel and a zone charted from older reconnaissance work read differently from each other instead of both rendering as plain blue. Picking a line across an unfamiliar bay at dusk, you can see which class of survey each depth came from.
Enter your boat's draft once. Helm shades the water your boat cannot cross and plans routes around it, so a passage from a marina out to an inlet bends around a shoal instead of drawing a straight line over it. The measure tool draws a line anywhere on the chart and returns the distance and bearing along it, from the chart data already on the device.
All of it comes down to the device in 161 downloadable chart packs. Anchored behind a barrier island with no bars showing, the charts, the depth, the routing, the measure tool and the anchor alarm keep running from the pack on the phone.
Underway, the same official data feeds the strip along the bottom of the chart: depth, speed over ground and course over ground in one place, with the anchor alarm a tap away and satellite and night chart styles on hand. Every trip is recorded to a logbook you can replay later. Routes, markers, tracks and the logbook sync across your own devices, so a spot you save on the phone at the ramp is on the iPad at the helm.
Yes. Helm reads official NOAA electronic navigational charts directly, and adds USACE eHydro dredging surveys, state lake elevation data and the live NOAA CO-OPS tide on top of them.
A raster chart is a scanned image of a paper chart. An ENC is vector data in S-57 format where each sounding, contour and aid to navigation is a separate object with attributes. Helm uses ENC data, which is what lets it compare charted depth to your draft.
From state lake elevation surveys. Inland reservoirs and lakes are charted water in Helm with real contours you can read.
CATZOC is the zone of confidence attribute inside an ENC. It records how a survey was made and what class of survey produced its depths. Helm displays it so a well surveyed channel is visibly distinct from an area charted long ago.
Yes. Download the chart pack for your area and the charts, depth, routing, the measure tool and the anchor alarm run from the device.
Yes. Every depth reading comes with the date of the survey behind it, so you know whether you are looking at a recent dredging survey or an older chart sounding.
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