Huron and Superior are joined through the St. Marys, and most people who run one of them end up on the other. The bottom under both was cut by ice rather than laid down by a river, and that single fact governs how you read a chart here. Rock does not migrate over a winter the way a sand bar does, so a hazard the survey found decades ago is still sitting exactly where it was found. The water beside it can be deep enough that nothing underfoot warns you on the way in.
The Helm pack for these two lakes is built from 372 official NOAA ENC cells, which is the largest cell count of the eighteen US regions Helm covers. Inside them are 130,063 individual soundings, 20,394 depth contours and 19,436 charted depth areas, plus 7,617 charted obstructions and 7,227 underwater rocks. It downloads as one pack covering both lakes and keeps working with no signal, which is the normal state of things once you are an hour off a north shore.
An ENC cell is one chart file covering one area at one scale band. Coverage of Huron and Superior is cut into more of them than any other US region Helm ships, and Helm builds the pack from all 372 rather than from the small scale sheets alone. The practical result is that the file which gets you across open water and the file which shows you the last half mile into a harbor are both in your pocket, and you do not lose the fine one when the signal goes.
The sounding count follows from that. 130,063 soundings, fourth of the eighteen regions, spread across 19,436 charted depth areas and 20,394 contours. That works out to roughly seven soundings for every depth area, which is another way of saying the shape of this bottom is drawn rather than implied.
| In the chart pack | Count |
|---|---|
| NOAA ENC cells | 372 |
| Charted soundings | 130,063 |
| Depth areas | 19,436 |
| Depth contours | 20,394 |
| Lateral buoys | 1,887 |
| Lateral beacons | 540 |
| Charted lights | 2,604 |
| Anchorage areas | 33 |
| Bridges | 1,031 |
| Overhead cables | 638 |
| Dredged areas | 724 |
| Charted wrecks | 579 |
| Charted obstructions | 7,617 |
| Underwater rocks | 7,227 |
| Restricted areas | 897 |
Counted from the Helm chart pack for Lakes Huron & Superior, built from official NOAA electronic navigational charts.
These lakes are known for what is on the bottom, so the figure people expect to be large is the wreck count. It is 579, tenth of the eighteen regions. The two numbers that should actually change how you drive are the ones nobody quotes: 7,617 charted obstructions, second only to one other US region in Helm, and 7,227 underwater rocks, fifth. That is 14,844 charted things down there that are not wrecks.
A rock in fresh water is a permanent feature. It does not scour out or fill in between seasons, so an old sounding over rock is worth considerably more than an old sounding over a shifting bottom. What the old survey cannot tell you is what was never sounded beside it, and that is what the chart's own confidence rating is for. Helm prints that grade next to the depth instead of rendering every blue area the same.
The habit this rewards is looking at a line before you take it, particularly when you are cutting inside an island or closing an unfamiliar shore. Drawing the line and reading the shallowest point along it takes a few seconds and answers the only question that matters on a rock bottom, which is whether the worst spot on that line clears you.
The pack carries 724 dredged areas. Taken as a group they cover almost the entire useful range of draft: the shallowest carries a charted depth of 0.1 m, about four inches, the deepest carries 18.2 m, about 60 feet, and the median sits at 6.4 m, close to 21 feet. A dredged area on Huron or Superior can be a deep draft commercial cut, and it can be a small basin with a few inches on the chart. The label is the same across all 724. The number attached to it is not.
There are also 897 restricted areas in these lakes, third of the eighteen regions. That is a great many edges to stay outside of, and edges are what quietly lengthen a passage on a big lake. When a planned leg steers around one, Helm tells you how much of it the straight line would have crossed, so the extra distance is a decision you can look at and overrule rather than a bend you either trust or ignore.
Navigation aids here run heavily to lights. The pack holds 2,604 charted lights, fourth of the eighteen regions, alongside 1,887 lateral buoys, also fourth. Fixed lateral beacons number 540, thirteenth. Safe water marks come to six across both lakes combined.
The ratio is worth sitting with before a night run. Most of what marks the water for you here carries a light, which is the good half. Most of it is also floating, and a floating aid reports where it was set rather than where the hazard is, so a buoy dragged off station is still a buoy on your screen. With six safe water marks between two lakes you will rarely have a mid channel mark to steer at, so the laterals and the charted depth underneath them do the work.
Air draft turns into real planning work in this region because of the connecting waters. The pack carries 1,031 bridges, ninth of the eighteen regions, and 638 overhead cables, seventh of the eighteen. That is 1,669 charted objects above the water, and the cables are the half people forget, because a cable is not a structure you see coming the way a span is.
Helm checks the charted vertical clearance against the air draft you entered, reading fixed bridges and the closed position of an opening bridge both. Where a bridge carries no clearance figure at all, it is reported as unknown rather than as zero, which with this many crossings in one pack saves a fair number of long ways around.
These counts describe what the chart pack carries, not the state of the water today. Charted data ages, channels shoal and marks move. Keep a lookout and verify locally.
Yes. Both lakes come as a single pack built from 372 official NOAA ENC cells, which is the largest cell count of the eighteen US regions Helm covers. Once it is on the phone, the chart, the depth and route planning all run with no signal, so crossing out of coverage on the way up a shore changes nothing.
579 in this pack, which is tenth of the eighteen US regions Helm covers. The hazard counts that sit above it are the ones to plan around: 7,617 charted obstructions, second of the eighteen, and 7,227 underwater rocks, fifth. The wrecks are the reason people come here with a camera. The rock is the reason they come back with the hull intact.
Only 33 formal anchorage areas are charted across both lakes, thirteenth of the eighteen regions, and nearly all of the places boats actually lie here are not among them. That makes it a depth and shelter question rather than a symbol question. Helm reports the depth against your draft and lets you drop and name your own spots, which then sync to your other devices, so a pocket you found last August is on the chart next season.
Helm Boating