Deep water and a ledge that dries at low tide can sit a boat length apart on this coast. The bottom is granite, so what stops a boat here is not a bar that moved over the winter. It has been in the same place for a very long time and on the chart for most of it. The hazards are known and nearly all of them are drawn. The problem is their number, how close together they sit, and the fog that can take them away from you for days at a stretch.
Helm builds the Maine pack from 151 official NOAA ENC cells. That comes to 121,067 individual soundings, 40,522 depth contours and 38,341 charted depth areas, plus 14,185 charted underwater rocks. The pack downloads at 25 MB and works after that with no signal.
Helm builds chart packs for 18 US regions. Maine comes first in both of the counts that describe the shape of the seabed rather than the depth at a single point: 38,341 charted depth areas and 40,522 depth contours. Nowhere else in the country is the bottom divided into that many separately bounded pieces.
The soundings, 121,067 of them, rank fifth. The proportion between those figures is the part worth knowing. On a sandy coast a depth contour is a long line running more or less parallel to the shore, and one of them can describe miles of beach. Here a contour goes around a single ledge, closes on itself, and then does the same thing again a short way on. Forty thousand of them is what that looks like when somebody counts.
| In the chart pack | Count |
|---|---|
| NOAA ENC cells | 151 |
| Charted soundings | 121,067 |
| Depth areas | 38,341 |
| Depth contours | 40,522 |
| Lateral buoys | 1,793 |
| Lateral beacons | 231 |
| Charted lights | 675 |
| Anchorage areas | 67 |
| Bridges | 565 |
| Overhead cables | 242 |
| Dredged areas | 139 |
| Charted wrecks | 202 |
| Charted obstructions | 1,937 |
| Underwater rocks | 14,185 |
| Restricted areas | 218 |
| NOAA tide prediction stations | 118 |
Counted from the Helm chart pack for Maine Coast, built from official NOAA electronic navigational charts. The pack downloads at about 25 MB.
Maine carries 14,185 charted underwater rocks, second of the eighteen regions, and 202 charted wrecks, which is the fewest of all eighteen. Read together, those two numbers tell you what to be careful of. The thing that will catch your keel here was not lost in a storm and found by a survey afterward. It has always been there. On top of the rock the pack carries another 1,937 charted obstructions.
There are only 139 dredged areas in the whole region. Their median charted depth is 2.1 meters and the deepest is 10.6 meters, while one of them charts at minus 0.5 meters, which is to say it dries. Almost none of this coast has a maintained channel at all. The deep water is where the bottom put it, and it stays there.
That changes the order you do things in. On a coast with dredged channels you find the channel and follow it. Here you find the mark, then the next mark, and you hold what the chart gives you between them instead of cutting the corner, because the corner is where the rock is. Helm carries the rocks and the obstructions as the ENC has them, so they appear as themselves at the zoom you are actually navigating at, and water your boat cannot cross is shaded once you have entered your draft. How the depth under the hull is worked out, and where the survey date and the live water level come into it, is covered on the depth pages of this site.
The mark count that says the most about Maine is the small one. There are 62 safe water marks in this pack, first among all eighteen regions. A safe water mark is the one with navigable water all round it, set at the seaward end of an approach so that you have somewhere unambiguous to start from. A coast that needs more of them than anywhere else in the country is a coast where you do not steer for the harbor. You steer for the fairway mark and pick up the buoyage there.
There are 1,793 lateral buoys to pick up, fifth of the eighteen, against 231 lateral beacons and 675 charted lights. Most of what marks this water floats, and most of it is unlit, so in fog or after dark you are working from the chart and from buoy positions rather than from a light you can raise at a distance.
The Maine box contains 118 NOAA tide prediction stations. That is dense enough that the figure you get comes from a station in your own water rather than from a correction applied to some distant reference port.
The stations are not interchangeable. Bar Harbor and Bass Harbor sit out among the islands, as does Burnt Coat Harbor on Swans Island. Go up a river and the character of the prediction changes: Castine, then Bucksport, then Bangor, each one taking the flood later than the one below it. In the middle of the coast there is Boothbay Harbor, with Back River and Bath inshore of it. Down to the west sit Cape Porpoise, Cape Neddick, and Camp Ellis at the entrance of the Saco.
The range on this coast is big enough that a cove you sounded on the way in is a different cove on the way out. Helm reads the nearest station and labels the height with where it came from, whether that is a NOAA prediction corrected by a live gauge or a curve computed on the device when you have no signal. What the tide never does is decide whether a passage is possible. That reasoning belongs to the routing and depth pages.
Eighty three areas of this coast are charted as marine farming. Those are leases with gear in them, and the gear is the part that concerns you: floats, lines and cages sitting somewhere inside a boundary the chart draws once. The chart tells you the area is leased. It does not tell you where this season's gear went in, which makes a charted block a reason to slow down and look rather than an edge you can run along in poor visibility.
The rest of what the pack carries for this region:
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.
Both. The Maine pack carries 14,185 charted underwater rocks and 1,937 charted obstructions alongside its 121,067 soundings, all of it out of the 151 official NOAA ENC cells the pack is built from. Only one US region Helm packs has more charted rock than Maine, so the rocks are kept as individual charted objects rather than folded into a depth shade.
The nearest one. There are 118 NOAA tide prediction stations inside the Maine pack, and Castine, Bucksport and Bangor are three separate stations on the same river, so a height read up the river is not the height at the mouth. Bar Harbor, Bass Harbor, Boothbay Harbor, Blue Hill Harbor, Cape Porpoise and Camp Ellis at the Saco entrance are all stations of their own as well.
Yes. 83 marine farming areas are charted in the pack, including the salmon and shellfish leases down east and in the river reaches. The chart gives you the leased boundary rather than the position of this year's gear, so treat one as a place to come off the throttle and look, particularly in fog.
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