Massachusetts is a rock coast. From Annisquam and Beverly at the top, down through Boston Harbor to Cohasset and Brant Rock, the thing that decides your line is rarely the depth of the bay itself. It is what stands up out of it. The chart carries that as a scatter of individual objects rather than a clean edge between water you can use and water you cannot, and reading it is a different job from reading a coast where the shoal is a shape you can watch coming.
The Massachusetts and Boston pack is built from 179 official NOAA ENC cells and carries 115,953 individual soundings, close to 650 per cell, with 17,597 depth areas and 18,607 depth contours behind them. The point hazards come across whole: 17,175 charted underwater rocks, 1,918 obstructions and 707 wrecks. So do 1,910 lateral buoys, 1,109 lights, 780 bridges and 100 NOAA tide prediction stations. All of it is an 18 MB download that sits on the phone.
Underwater rocks are where this region separates itself from every other one. 17,175 of them are charted inside the box, first of the 18 US regions Helm builds packs for, and nothing else in this pack sits that high. Wrecks come in at 707 and obstructions at 1,918, both of them mid table. Rock outnumbers wreck here by about twenty four to one.
The other standouts follow the same coast. Anchorage areas are second of the 18 at 214, which is what a hard shore with deep pockets behind it produces. Lateral buoys are third at 1,910 and safe water marks are third at 35. Restricted areas are fourth at 821. The soundings themselves are sixth at 115,953, denser than the 179 cells would suggest, which is what a long surveyed and heavily worked piece of coast looks like on the chart.
| In the chart pack | Count |
|---|---|
| NOAA ENC cells | 179 |
| Charted soundings | 115,953 |
| Depth areas | 17,597 |
| Depth contours | 18,607 |
| Lateral buoys | 1,910 |
| Lateral beacons | 197 |
| Charted lights | 1,109 |
| Anchorage areas | 214 |
| Bridges | 780 |
| Overhead cables | 135 |
| Dredged areas | 639 |
| Charted wrecks | 707 |
| Charted obstructions | 1,918 |
| Underwater rocks | 17,175 |
| Restricted areas | 821 |
| NOAA tide prediction stations | 100 |
Counted from the Helm chart pack for Massachusetts & Boston, built from official NOAA electronic navigational charts. The pack downloads at about 18 MB.
Rocks, obstructions and wrecks together come to 19,800 discrete objects, set against 17,597 charted depth areas. There is more than one point hazard for every depth area on this chart. That ratio is the practical difference between here and a coast where the danger is an area you can shade and stay outside of. The color of the water you are crossing can be perfectly honest and still not describe the thing that stops the boat.
It makes the shallowest point along a line worth more than the depth at any one spot on it. Helm reports the minimum along a measured line rather than the average, and with objects packed this closely the average of a dredged cut and one rock sitting beside it is not a number anybody can steer by. The same figure comes up on a planned leg before you leave rather than after.
The 639 dredged areas show how wide the span is here. Median charted depth across them is 7.6 m, about 25 feet, the deepest is 17.0 m, and the shallowest is charted at 0.1 m. Half the maintained water in this region is deeper than 25 feet, which is why a deep draft boat works in and out of Boston without much thought while some of the charted cuts hold almost nothing at all.
The pack carries 1,910 lateral buoys against 197 lateral beacons, close to ten to one in favor of the mark that floats. Add 35 safe water marks and 1,109 charted lights and you have most of what tells you which side of the rock you are on.
A buoy is a mark on a chain and a rock is not. When the two disagree, the rock is the one that is where the chart says it is. That is an argument for working off the charted object and the charted depth first and reading the mark as confirmation, which is easier when the objects are all on the screen at the scale you are actually running.
There are 100 NOAA tide prediction stations inside the region's box, close enough together that the nearest one to you is usually worth reading. The Cape Cod Canal alone holds four: Sagamore, Bournedale, the railroad bridge and Bourne Bridge. A transit that starts at one end and finishes at the other is a transit where the nearest station changes under you, and the pack keeps all four rather than electing one to stand for the whole cut.
The stations also run well up the rivers and around into the harbors, so the one nearest your slip is often not the one named for the nearest city.
Anchorage areas are second of the 18 regions at 214. Restricted areas are fourth at 821. Those two figures sitting side by side describe old, busy, working water, where a lot of what reads as open bay on a small scale chart has something written on it. Helm draws both, and a planned route steers around restricted water with the reason attached to the leg rather than bending quietly.
The region is stitched with fixed structure as well. 780 bridges and 135 overhead cables are in the pack, and they matter most on the rivers above Boston and along the Canal, where the number you care about on a rising tide is air draft rather than depth.
Coverage runs from Annisquam and Beverly at the north end to Cotuit, Chatham and Cedar Tree Neck at the south, with Boston roughly in the middle of it. Water past either end belongs to the Maine Coast pack or the Long Island Sound pack.
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. The Canal sits inside the pack's box and carries four separate NOAA tide prediction stations along its length, at Sagamore, Bournedale, the railroad bridge and Bourne Bridge, so the prediction at one end is not the prediction at the other. The Canal's bridges are part of the 780 bridges in the pack, and their charted vertical clearance is read against the air draft you enter.
The nearest one to where you are, and inside the harbor there are several. BOSTON and Boston Light cover the harbor and its entrance, Charlestown sits at the Charles River entrance, the Chelsea St. Bridge station is on the Chelsea River and the Amelia Earhart Dam station is up the Mystic River. They are part of the 100 NOAA prediction stations inside the region. The figure on screen says whether you are reading a published prediction or one corrected by a live gauge.
The pack carries 214 charted anchorage areas, second of the 18 US regions Helm builds. They are drawn on the chart alongside the 821 restricted areas, so before you go looking for a spot in water like Hingham Harbor or Cohasset Harbor you can see which ground is designated for anchoring and which has a rule on it.
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