If you want to know exactly which data sits under a navigation app, this page lists it. Helm's coastal and Great Lakes charts are built from NOAA electronic navigational charts, reprocessed by Helm into its own chart packs. The soundings, contours, buoys, beacons, obstructions and channel limits you see there come from what NOAA publishes. The result is not an official NOAA product and does not replace official charts. The inland rivers come from the US Army Corps of Engineers Inland ENC instead.
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.
The chart is the source of the depth. Helm adds one thing to it, the predicted tide, and reads the result against your draft.
| Source | What it contributes |
|---|---|
| NOAA ENC | The electronic navigational chart for the coast and the Great Lakes: soundings, depth areas, contours, aids to navigation, obstructions and channel limits. |
| USACE Inland ENC | The Army Corps chart for the inland commercial rivers, with depth areas and contours. |
| NOAA CO-OPS | The tide prediction against the MLLW datum from a station within 25 nautical miles, added to the sounding so you see depth now rather than depth at chart datum. |
The state lake packs draw lake shorelines from the USGS National Hydrography Dataset, and Minnesota adds state contour lines on its lakes. When a route follows a dredged channel, the route explanation says the channel depth comes from the chart.
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.
In Helm, the depth card tells you what kind of figure you are reading: a charted sounding, a depth band from the chart, or water the chart has no soundings for, where it says so instead of printing a number.
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 chart 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. Trips you run with Go on a route are recorded to the logbook. Once your devices are signed in to the same account, routes, saved spots and recorded trips sync between them, so a spot you save on the phone at the ramp is on the iPad at the helm.
Yes. Helm's charts are built from NOAA electronic navigational chart data, reprocessed into Helm's own packs, and it adds the NOAA CO-OPS predicted tide to the charted depth where a station is close enough.
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.
The Great Lakes are on NOAA charts and carry charted depth. The Minnesota lake pack adds Minnesota DNR contour lines drawn on its lakes. The other state lake packs draw lake shorelines and names from the USGS National Hydrography Dataset.
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, so two soundings that read the same depth can sit in completely different confidence zones.
Yes. Download the chart pack for your area and the charts, depth where the chart carries it, routing in the coastal and Great Lakes packs that carry it, the measure tool and the anchor alarm run from the device.
Whether it is a charted sounding, a depth band from the chart, or water the chart has no soundings for. Where a NOAA tide station is within 25 nautical miles, the station's published tide prediction is added, and the depth card reads the result against your draft.
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