Most of the Bay is shallower than people who have not run it expect, and the parts that are not shallow are dredged channels with ship traffic in them. The work here is mostly the work of knowing which side of a mark you are on, on water where the channel edge and the flats sit very close together. Then there are the rivers, where the bottom answers to the season's runoff and the crossings overhead start getting low. None of that rewards a casual look at the chart.
Helm's Chesapeake pack is built from 237 official NOAA ENC cells and carries 141,077 individual charted soundings, more than any US region Helm covers except one. With them come 23,447 charted depth areas and 24,211 depth contours, and the marks that organize all of it: 2,083 lateral buoys, 2,837 lateral beacons, 28 safe water marks and 3,473 charted lights. The pack also holds 1,045 dredged areas, 1,519 bridges, 85 charted anchorage areas and 217 NOAA tide prediction stations. The whole thing downloads at 30 MB.
Helm builds chart packs for eighteen US regions. On the figures that describe how thoroughly a piece of water has been measured and marked, the Chesapeake sits at or near the top of nearly all of them.
Second place in soundings, with 141,077 of them, says more about the water than about the app. The Bay has been surveyed this densely because it is shallow enough and busy enough to be worth surveying again and again. The marks tell the same story. Put the 2,083 lateral buoys together with the 2,837 lateral beacons and you get 4,920 pieces of lateral aid on one bay, which is the signature of water where the channel is something you follow rather than a direction you point.
| In the chart pack | Count |
|---|---|
| NOAA ENC cells | 237 |
| Charted soundings | 141,077 |
| Depth areas | 23,447 |
| Depth contours | 24,211 |
| Lateral buoys | 2,083 |
| Lateral beacons | 2,837 |
| Charted lights | 3,473 |
| Anchorage areas | 85 |
| Bridges | 1,519 |
| Overhead cables | 1,160 |
| Dredged areas | 1,045 |
| Charted wrecks | 1,673 |
| Charted obstructions | 5,870 |
| Underwater rocks | 591 |
| Restricted areas | 624 |
| NOAA tide prediction stations | 217 |
Counted from the Helm chart pack for Chesapeake Bay, built from official NOAA electronic navigational charts. The pack downloads at about 30 MB.
1,160 charted overhead cables, first of the eighteen. 1,519 bridges, fourth. Very little of that is out on the main stem. It is up the creeks and the rivers, where the banks come together and a crossing gets cheap to build, which is exactly where a skipper is watching the depth and the bank and not the sky.
A cable has no tender and no opening schedule. If you carry a mast, the thing that ends a trip up a Chesapeake tributary is usually overhead rather than under the keel, and it is worth setting your air draft in Helm before you go up one. The vertical clearance in the chart gets checked against that figure on every one of the 1,160.
There are 1,045 dredged areas in the pack. Their charted minimum depths run from 16.9 m at the deepest down to a shade under datum at the shallowest, with a median of 7.4 m, a little over 24 feet.
The median is the useful figure. Twenty four feet of maintained channel is more water than most boats on this bay will ever ask for, so the channel itself is rarely what stops you. What stops you is the ground immediately outside it, and the moment you decide to cut a corner because the channel was taking you the long way around.
The shallow end of the range deserves its own look. One of those areas carries a charted value of -0.1 m, which puts it a hair above datum and means it dries. Spread across 1,045 areas, the word dredged is a statement about history rather than a promise about this afternoon.
Count the charted hazards and the character of the Bay shows up in the ratio. There are 5,870 charted obstructions and 1,673 charted wrecks, fifth and fourth among the eighteen regions. There are 591 underwater rocks, which puts the Chesapeake thirteenth. The bottom is mud and sand, so almost nothing here that will hurt you got there by geology. Pilings, stumps, sunken hulls, the remains of old structures. That is the inventory.
It changes how you read shaded water. In a rocky region a charted hazard sits where the rock has always sat and will sit next season. Here, a large share of those 5,870 are things that arrived, and they arrived in water shallow enough that you would otherwise cross it without a second thought. 1,673 wrecks on a bay whose maintained channels run a median of 7.4 m are not all comfortably beneath you.
The pack also carries 624 restricted areas, fifth of the eighteen, which is what this much military and commercial water produces. And 292 marine farming areas, second among the sixteen regions that have any at all. Oyster and clam ground gets charted here because it is worked ground with gear in the water on it. Running across a lease in a chop or after dark is an ordinary way to lose a lower unit.
NOAA publishes 217 tide prediction stations inside the area this pack covers. That is not redundancy. The tide arrives at the mouth and works its way up, and every river then runs its own version of it, so the water at Cape Charles Harbor and the water at Alexandria, Va. are not doing the same thing at the same hour.
The list runs from the Chesapeake Channel at the Bay Bridge Tunnel up through Annapolis at the Naval Academy and Baltimore at Fort McHenry, out to Cambridge, Broomes Island, Benedict, Brewer Point, Bishops Head over in Hooper Strait and Ape Hole Creek up in Pocomoke Sound. Helm quotes the station nearest to where you actually are. On a bay this long that is the difference between a number you can use and a number that is decorative.
Water level here also answers to the wind as much as to the moon. A few days of hard northerly moves the Bay in a way no harmonic prediction accounted for, and the station closest to you is the one that shows it first.
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.
The rivers are in the same pack. The area runs from the Chesapeake Bay Bridge Tunnel at the mouth north past Baltimore, and the NOAA tide stations inside it include Alexandria, Va., Bladensburg, Md., Aquia Creek, Benedict and Ape Hole Creek up in Pocomoke Sound, so the tributaries are charted at the same time as the open Bay. All 237 NOAA ENC cells come down in one 30 MB download.
Yes, 1,160 of them, which is the highest count of any of the eighteen US regions Helm builds packs for, along with 1,519 bridges. Set your air draft once and the charted vertical clearance on each crossing is checked against it. On this bay that matters more than in most places, because the cables are concentrated up the creeks and rivers rather than out on the main stem.
Yes. The pack carries 292 charted marine farming areas, second among the sixteen regions that have any, which is a fair picture of how much worked bottom there is on this bay. They are drawn on the chart in Helm so you can see a lease before you are in it, which is the point of charting ground that has gear sitting in the water on it.
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