On most water the first question is what sits under the keel. On the Monongahela it is usually what sits over the arch or the mast, and the crossing that ends a trip is the one you could not have judged from the water. The river runs inside a corridor narrow enough that there is no outside route and no standing off to think it over. The traffic with the first claim on the channel is commercial, working the useful width through the bends, so the room you give a tow comes out of the water you were holding. Then there are the dams, which turn a passage into a series of stretches with a wait between them. A day here gets planned against a clock more than against a fuel gauge.
Helm's Monongahela pack covers a box running from 39.435 N up to 40.442 N, a little over sixty nautical miles of latitude and under twenty of longitude at that height. Inside it the pack carries 207 charted bridges and 87 overhead cables, 484 charted lights, 283 charted depth areas and 412 depth contours, 72 charted obstructions, 10 charted wrecks, 14 restricted areas and 39 charted lock features. The whole thing downloads at 2 MB.
Helm builds chart packs for fifteen US rivers. On most of the counts that describe how much charted furniture a piece of water carries, the Monongahela sits in the upper middle. On one count it is second.
72 charted obstructions puts this river second among the twelve rivers that have any charted at all. That is a great deal of charted obstruction for a corridor under twenty nautical miles wide. The overhead counts come next, with 87 cables placing fifth of the fifteen and 207 bridges seventh, and the lock features place fifth among the thirteen rivers that carry any. Nothing about this river is remarkable for how deep it is. What is remarkable is how much hardware has been built across it and into it.
| In the chart pack | Count |
|---|---|
| Bridges | 207 |
| Overhead cables | 87 |
| Charted lights | 484 |
| Lock features | 39 |
| Charted depth areas | 283 |
| Depth contours | 412 |
| Charted obstructions | 72 |
| Charted wrecks | 10 |
| Restricted areas | 14 |
Counted from the Helm chart pack for the Monongahela River, built from the official inland electronic navigational charts published for it. The pack downloads at about 2 MB. Lock features are counted as the chart draws them, with chambers, gates and dams as separate objects.
Add the two counts and the pack holds 294 charted crossings. The cable figure alone is the fifth highest of the fifteen rivers Helm builds packs for. A cable has no tender and no opening schedule, and from the water it gives you very little to judge height by, so the charted vertical clearance is the figure that settles the question before you are underneath it.
Set your air draft in Helm once and the charted clearance on each crossing gets checked against it. That check carries more weight on a river than it does on a coast. A bridge on open water is something you go around. Here the crossing spans the whole navigable width, and the alternative to passing under it is running back to the last place you could turn.
The practical reading of 294 is that air draft here is not a number you take once at the dock and forget. A flybridge with the arch still up, or an antenna nobody thought to fold down, gets asked the same question 294 times between the ends of this pack.
The pack carries 39 charted lock features, fifth among the thirteen rivers Helm packs that have any. Read the figure for what it is. A chamber is charted as one feature, the gates at its ends are charted in their own right, and the dam beside it is another again. So 39 is a count of structures drawn on the chart, not a count of stops on a trip, and it should not be quoted as anything else.
Names you will see along this river on the chart include Braddock, Charleroi, Grays Landing and Opekiska. What each one does to a passage is the same. Distance stops setting your arrival time and the chamber ahead of you starts setting it, and a tow already inside will hold a recreational boat for as long as the lockage takes. Lockage time is the part of a river day that no amount of speed buys back, which is why a run here gets planned around where the chambers fall.
There are 283 charted depth areas and 412 depth contours in the pack, eighth and sixth of the fifteen. On open water numbers like that describe a surface you can cross in any direction you please. On a river held by dams they describe an edge. Almost everything the chart has to say about depth here is a statement about how far off the line you are, and the line is narrow enough that leaving it is a decision rather than a drift.
That matters most in the moment you are giving way. A tow needs the working width through a bend, and the water you hand over is the water you were using, so the useful thing to know is which side of the bend has something in it before you are committed to the bend. Helm plans against the draft you enter and reports the thinnest water on the leg up front. That is the number to have in your head when you are deciding how far over you are prepared to go.
484 charted lights against 207 bridges works out to better than two charted lights for every bridge on the river, sixth of the fifteen. What a count like that says is that after dark this water gets read mark by mark. There is no horizon to work a light against and no open water to lose one in, so a light you cannot account for is a question to answer before you pass it.
The pack also carries 14 charted restricted areas, tenth of the fourteen rivers that have any. A modest count, and each one is drawn on the chart so the edge of it is visible while you still have room to stay outside it.
The hazard figures are where the character of this river shows up clearly. 72 charted obstructions against 10 charted wrecks is better than seven to one. The wreck count is eleventh of the fifteen, which makes sense, since a wreck is an event and ten events across a whole corridor is not many. An obstruction is generally something that was put into the water or left in it, and it stays where it was put rather than moving with the season the way a bar does. On this river the things that will hurt you mostly sit where the chart says they sit, and there are seventy two of them charted in a box you could cross in an afternoon.
These counts describe what the chart pack carries, not the state of the river today. Charted data ages, pools change with the dams, and a lock can be out of service. Keep a lookout, listen to the traffic, and verify locally.
Helm's Monongahela pack charts 39 lock features, which is fifth among the thirteen rivers Helm builds packs for that carry any. That figure counts chambers, gates and dams as separate charted structures, so it is not the number of places you lock through and should not be read as one. Names you will see on the chart along this river include Braddock, Charleroi, Grays Landing and Opekiska.
The pack carries 207 charted bridges, seventh of the fifteen US rivers Helm packs, and 87 overhead cables, fifth of the fifteen. Together that is 294 charted crossings inside a corridor a little over sixty nautical miles of latitude tall. Set your air draft in Helm once and the charted vertical clearance on each of the 294 is checked against it, which is the check that matters most on a river, because a crossing here spans the whole navigable width and there is nothing to go around it by.
Yes. 72 of them, which puts the Monongahela second among the twelve rivers Helm packs that have any charted obstructions at all, and that is a high count for a corridor this narrow. Set against 10 charted wrecks, eleventh of the fifteen, the ratio says the thing to watch for here is fixed rather than accidental. Fixed hazards have the advantage of staying put between seasons, so the 72 are worth looking at on the chart before the trip rather than on the way past.
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