On a coast you can usually go around the thing that worries you. On the Upper Mississippi you cannot. The channel is the navigable water, the tows are in it, and a loaded one coming down with the current needs the whole of it, so what is left to you is timing and position. The current works on your margins as well. An approach you misjudge does not sit still while you sort it out, and there is no slack hour waiting later in the day. Then the passage stops at a lock, and how long you sit there is not yours to decide. Somewhere in all of that you also have to watch what is over your head, which is the part people coming off salt water forget first.
Helm builds a chart pack for this river covering the band from 45.14 north down to 36.95, a little over eight degrees of latitude, and it downloads at 26 MB. In it are 501 bridges and 114 overhead cables, 1,527 charted lights, 671 charted depth areas and 1,345 depth contours. The hazards are charted at 208 obstructions, 135 underwater rocks, 89 wrecks and 76 restricted areas. There are also 126 charted lock features, meaning the chambers, gates and dams drawn as the separate structures they are.
Helm builds chart packs for fifteen US rivers. On most of the figures that describe how closely a piece of water has been measured and marked, the Upper Mississippi sits at or near the top of that set.
First place in depth contours, with 1,345 of them, is the figure worth stopping on. A contour is a line rather than a point. Water that gets drawn in lines has been surveyed as a shape, which is what happens to a channel somebody is responsible for keeping open and goes back to measure again. The 671 charted depth areas underneath them, second of the fifteen, say the same thing a different way. Where those numbers come from is its own subject and Helm has a page for it.
The counts below describe what the chart pack carries. They do not describe the river this morning.
| In the chart pack | Count |
|---|---|
| Bridges | 501 |
| Overhead cables | 114 |
| Charted lights | 1,527 |
| Lock features | 126 |
| Charted depth areas | 671 |
| Depth contours | 1,345 |
| Charted obstructions | 208 |
| Charted wrecks | 89 |
| Restricted areas | 76 |
| Underwater rocks | 135 |
Counted from the Helm chart pack for the Upper Mississippi River, built from the official inland electronic navigational charts published for it. The pack downloads at about 26 MB. Lock features are counted as the chart draws them, with chambers, gates and dams as separate objects.
501 bridges, second of the fifteen rivers. 114 overhead cables, fourth. Put the two together and there are 615 charted crossings between the top of this pack and the bottom. On a river that is the count that decides which boats can make the trip at all, and it is a count you can do something about before you leave rather than one you discover at the eleventh crossing.
A bridge at least has a chart entry you can read and, where it opens, somebody to talk to. A cable has neither. There are 114 of them on this water, no tender, no schedule, and the only warning you get is the one you gave yourself at the dock.
This is the argument for setting your air draft in Helm once and leaving it set. The charted vertical clearance is then checked against your figure on every one of those crossings. If you run with a mast stepped, or with a flybridge carrying a radar arch and an antenna you stopped thinking about years ago, the number that matters here is the one measured from the waterline to the highest thing on the boat. Measure it. Do not remember it.
The pack carries 126 charted lock features, second among the thirteen rivers Helm packs that have any. That count is of structure rather than of stops. A chamber is drawn as one feature, a gate as another, the dam as another again, so the number tells you how much built work is on the chart and not how many times you will tie up against a wall.
They sit on the chart under the names you would use on the radio. Lower St. Anthony Falls, Chain of Rocks, Mel Price Main and Jerry F. Costello are in there, and those are examples rather than the whole list.
What a chart can do about a lock is put it in front of you while you are still planning, at the point in the passage where it actually falls, so the day comes out as a set of legs with the stops already sitting in it instead of as a distance divided by a cruising speed. The approach deserves as much thought as the chamber. You will be holding position in moving water, close to structure, with commercial traffic that was in line before you arrived.
1,527 charted lights, second of the fifteen rivers. That is a great deal of light for water this narrow, and very little of it was installed with pleasure boats in mind. A river that is worked through the night gets marked so it can be run through the night. The lights are how the channel describes itself when the bank behind them is a black wall that tells you nothing about where the water goes.
The same traffic shows up again as 76 restricted areas, third among the fourteen rivers that have any. Restricted water on a working river sits where the work is, which is often the exact water you would ease into while giving a tow the channel it needs.
Giving way costs you nothing, provided you remember what you are giving way into. Outside the channel line the bottom becomes the chart's business, and the 671 depth areas and 1,345 contours are what tell you how much room is really out there.
208 charted obstructions, first among the twelve rivers Helm packs with any charted. 135 underwater rocks, first among the six that have any at all. 89 charted wrecks, second of the fifteen.
The rocks are the entry worth noticing. Most of the rivers in this set carry no charted rock whatsoever, because most of them run over ground that moves with the season and gets surveyed rather than charted as hard bottom. A charted rock is a different kind of problem. It was there last year, it will be there next year, and it takes no interest in what the stage is doing.
The obstructions and the wrecks read the other way around. Something put them there. On water that has been worked this long, a charted obstruction is usually something that arrived rather than something that grew, and 89 wrecks along one river says that arriving is not rare.
None of these three counts describes anything you would pick out by eye from the helm. That is what the shading on the chart is for, and it is worth reading on the way into a bend rather than partway through one. Charted data ages, a river moves its own bottom around, and the lookout is still the thing that settles it.
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.
The pack carries 126 charted lock features, which is second among the thirteen rivers Helm builds packs for that have any. The count is of structure rather than of stops, since a chamber, a gate and a dam are each drawn as their own feature on the chart. They appear under the names you would use on the radio, with Lower St. Anthony Falls, Chain of Rocks, Mel Price Main and Jerry F. Costello among the entries, and those are examples rather than the whole list.
The pack holds 501 bridges, second of the fifteen US rivers Helm charts, with 114 overhead cables on top of that, so 615 charted crossings over the length of it. Set your air draft in Helm once and the charted vertical clearance on each crossing is checked against that figure. The cables are the ones to plan around first, because a cable does not open and there is nobody to call about it.
One pack at 26 MB, covering the band from 45.14 north down to 36.95, a little over eight degrees of latitude. Inside it are the 501 bridges, 1,527 charted lights, 1,345 depth contours and 126 charted lock features, and all of it works with no signal once it is on the phone. The Ohio and the Illinois have packs of their own.
Helm Boating