Anyone who runs this water already knows the middle is deep. What makes a passage here its own problem is that the depth in the middle tells you very little about the edge of it. The thing that stops a boat in Puget Sound is usually a single charted object rather than a broad shoal, and the chart says as much about itself: 7,845 charted underwater rocks and 6,484 charted obstructions, both of which put this region fourth out of the eighteen US regions Helm builds packs for.
The pack is built from 219 official NOAA ENC cells and carries 103,658 individual soundings, 23,387 charted depth areas and 25,604 depth contours, along with 2,193 charted lights. Its box holds 178 NOAA tide prediction stations, from Astoria and Aberdeen at the south end up to Blaine at Semiahmoo Bay. The whole thing downloads at 32 MB and works with no signal once it is on the device.
A depth contour is what a chart draws when the bottom changes grade. This pack carries 25,604 of them, the second highest count of the eighteen regions, and 23,387 charted depth areas, fourth highest. Flat bottom does not produce numbers like that. The contours are packed tight because the bottom is doing something almost everywhere, and the practical effect on screen is that the shading changes under you inside a very short run in places the chart still reads as open water.
Where this region sits among the eighteen Helm builds:
None of that is about how big the water is. The pack comes from 219 ENC cells, which ranks eighth, and 103,658 soundings, which ranks ninth. Puget Sound is middling by how much chart there is and near the top by how complicated the bottom is inside it. That gap is the whole character of navigating here.
| In the chart pack | Count |
|---|---|
| NOAA ENC cells | 219 |
| Charted soundings | 103,658 |
| Depth areas | 23,387 |
| Depth contours | 25,604 |
| Lateral buoys | 500 |
| Lateral beacons | 861 |
| Charted lights | 2,193 |
| Anchorage areas | 99 |
| Bridges | 827 |
| Overhead cables | 437 |
| Dredged areas | 539 |
| Charted wrecks | 457 |
| Charted obstructions | 6,484 |
| Underwater rocks | 7,845 |
| Restricted areas | 507 |
| NOAA tide prediction stations | 178 |
Counted from the Helm chart pack for Puget Sound & PNW, built from official NOAA electronic navigational charts. The pack downloads at about 32 MB.
7,845 rocks and 6,484 obstructions is more individual objects than anyone carries in their head, and 457 charted wrecks sit on top of that. The count matters less than the pattern it forces. In this region a leg can be clear on depth the entire way and still be wrong, because what catches you is an object the chart marks as a point rather than a shallow patch you would notice as a change of color.
So the order you check things in changes. Enter your draft and Helm shades the water you cannot cross and the router treats it as blocked rather than as a suggestion, which settles the depth question. For a rock the useful move before an unfamiliar cut is to draw the line first. The measure tool gives distance, bearing and the shallowest point along that line rather than the average, and the average is exactly the number one charted rock ruins.
When a route does steer around something, the explanation for that leg names what it avoided and what the detour cost in distance. In water carrying 6,484 obstructions, a line that bends quietly is a line you stop trusting. The chart's own confidence grade for each area is on screen as well, which counts for more here than it does over open sand, since a sparse old survey in rocky ground is not missing a foot of depth, it is missing objects.
NOAA publishes tide predictions for 178 stations inside this pack's box. That figure is worth sitting with. It is not generosity. It is that a prediction from one station does not travel far in this water, and NOAA maintains separate ones because the height and the timing genuinely differ from inlet to inlet.
At the south end there are published stations at Budd Inlet by Olympia Shoal, at Arcadia in Totten Inlet, at Barron Point by the entrance to Little Skookum Inlet and at Allyn in Case Inlet. Up north the same thing happens again with Anacortes in Guemes Channel, Bellingham, and Blaine at Semiahmoo Bay. Armitage Island in Thatcher Pass, Aleck Bay on Lopez Island and Ala Spit on Whidbey Island are all separately published too.
Helm reads the nearest station to where you are and tells you which kind of figure you have, whether that is a NOAA prediction corrected by the residual from a live gauge or the published prediction on its own. With no signal it computes the curve on the device from the station's harmonic constants. Routing still runs at chart datum with no tide added, so a station you happened to pick wrong never makes a passage look legal when it is not.
There are 539 charted dredged areas in the pack. The median charted depth across them is 11.0 m, roughly 36 feet, and the deepest is 17.6 m. By the standard of most US regions that is a great deal of water inside a maintained channel, and it is why a passage here is rarely organized around finding the channel the way it is on a coast where the channel is the only water there is.
The figure that earns attention is the other end of the range. The shallowest charted dredged area in this pack carries 0.1 m. A dredged area is a polygon and the depth attached to it applies across the whole shape, so a number that low is the chart saying the maintained depth there is close to nothing at datum. Helm reports the figure it holds rather than smoothing it, and where a leg follows a dredged channel whose depth came from the chart instead of a recent channel survey, the route explanation adds that of its own accord.
827 bridges and 437 overhead cables are charted in this region. Air draft goes in once, and Helm checks the charted vertical clearance against it, reading the down position of an opening span as well as fixed spans, so a bascule you would have to wait for does not render as open sky.
The aids are a different picture. 2,193 charted lights, 861 lateral beacons and 500 lateral buoys, against 4 safe-water marks in the entire region. Almost every mark out here is telling you which side of something to pass, not that you are in clear water. Fifteenth of eighteen for buoys and sixteenth for safe-water marks, in water with the fourth highest rock count of any region in the app, is a plain statement of how much of the work the chart is doing between marks.
There are also 196 charted marine farming areas, fourth among the sixteen regions that have any. Shellfish ground and net pens carry anchors and lines, and they are places you route around and do not spend a night in. They draw alongside the 507 restricted areas and the 99 charted anchorage areas, which is the set you want visible together when you are picking somewhere to stop.
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 box runs from 46.0 N to 49.1 N and from 122.0 W out to 124.9 W, so it takes in the Sound, the islands, the outer coast, and the water down at Aberdeen and Astoria. It is built from 219 official NOAA ENC cells, holds 103,658 charted soundings, and downloads at 32 MB for use with no signal.
The nearest published one, and at that end it is a real choice rather than a formality, because NOAA runs separate stations at Budd Inlet by Olympia Shoal, Arcadia in Totten Inlet, Barron Point by the entrance to Little Skookum Inlet and Allyn in Case Inlet. There are 178 stations inside the pack's box altogether. Helm names the station it used and says whether the height is a prediction corrected by a live gauge or the prediction on its own.
Yes. This pack carries 196 charted marine farming areas, which is fourth among the sixteen US regions that have any at all. They draw as areas on the chart, so you can see the ones lying across a line you were about to run and keep a route or an overnight stop clear of them.
Helm Boating