Nothing about the Lower Mississippi rewards treating it as a long lake. The channel sits where the current has put it, it crosses from one bank to the other through the bends, and the surface that looks wide and ordinary has a great deal of water moving under it. Traffic is the other half of the job. A loaded tow needs the channel, the whole of it, and it cannot hand the river back to you on short notice, so much of what a skipper does here is arranging not to be where that tow is going to be. Upbound and downbound are two different jobs on the same water.
Helm builds a chart pack for this river covering the ground from 36.95 N at the top down to 30.49 N, and from 91.69 W across to 89.07 W. It carries 447 charted lights, 430 depth contours and 339 charted depth areas, 69 bridges and 21 overhead cables, 263 restricted areas, 45 charted wrecks and 2 charted obstructions, along with 6 charted lock features. The whole pack downloads at 8 MB and keeps working once the signal goes.
Helm builds chart packs for fifteen US rivers. The Lower Mississippi does not lead the field on the counts that say how finely a piece of water has been measured. It leads, or comes close to leading, on the counts that say what gets done on it.
The pairing worth sitting with is 45 charted wrecks against 2 charted obstructions, third of fifteen on the first and eleventh of twelve on the second. A rocky coast comes with an inventory of hazards that were in place long before anyone charted them. This riverbed is made of the same sand the river is carrying, and it does not hold much of that kind. Nearly everything charted here as a hazard arrived under its own power and then stopped.
| In the chart pack | Count |
|---|---|
| Bridges | 69 |
| Overhead cables | 21 |
| Charted lights | 447 |
| Lock features | 6 |
| Charted depth areas | 339 |
| Depth contours | 430 |
| Charted obstructions | 2 |
| Charted wrecks | 45 |
| Restricted areas | 263 |
Counted from the Helm chart pack for the Lower Mississippi River, built from the official inland electronic navigational charts published for it. The pack downloads at about 8 MB. Lock features are counted as the chart draws them, with chambers, gates and dams as separate objects.
69 bridges and 21 overhead cables, which comes to 90 charted crossings. The cable figure is the lowest of the fifteen rivers Helm packs, and the bridge figure sits eleventh, so the overhead question on this water is mostly a bridge question. That is the better of the two positions to be in. A bridge is a structure somebody owns and posts a clearance for. A cable is simply there.
Air draft behaves differently on a river than it does on the coast. Under a fixed coastal bridge the number is close to the same number all year. Here it answers to how much water the river is carrying, so the same span gives you different room at high water than it gives you at low, and a crossing you cleared once is a crossing you look at again. Set your air draft in Helm once and the charted vertical clearance gets checked against it on every one of the 90. If you run a flybridge, or you are taking a sailboat through with the mast still up, those 90 are the list that decides the trip.
263 restricted areas in one river pack, second among the fourteen rivers Helm packs that carry any charted at all. The number is a description of what this river is for. Working water gets written on, and what gets written is the ground around terminals and structures, along with areas where something is moored or worked on and the through traffic is expected to stay outside the line.
For a small boat the count mostly shows up in planning. When a leg steers around a restricted area, Helm says so in the route explanation and gives the distance the straight line would have cut through it, so the detour is something you can look at and overrule instead of a bend you never find out about. On water carrying 263 of them, that is the difference between an explanation you read and one you learn to skip.
447 charted lights, seventh of the fifteen. On the coast a light usually marks a hazard or an entrance. A river worked this hard is lit so the channel can be run after dark by vessels that do not tie up at sundown, which is also a fair description of the traffic you are sharing it with.
Underneath is the shape of the bottom, 430 depth contours and 339 charted depth areas, fifth and sixth of the fifteen. Contours earn their keep on a river, because what they show is where the deep water has gone in a bend. It runs to the outside while the sand builds on the inside, and a set of lines bunched against one bank is telling you which of the two you are looking at.
What the pack holds is the charted picture rather than a report on what the river did last week. A channel that moves is a channel the survey is always a little behind, so what is drawn is a starting position. Keep a lookout and verify locally.
The pack holds 6 charted lock features. That count treats chambers, gates and dams as separate items, so it is a count of charted structure and not a count of places you lock through, and nothing on this page turns it into one. Montgomery Point is one of the names attached to those features.
Among the thirteen rivers Helm packs that carry any charted lock feature, this one comes last on the count. It fits the river. The passage here is organized by current and by traffic far more than by lockages, and the planning that goes with it looks different for that reason. What a chart is good for at a lock is the position and the shape of the structure, drawn where it actually sits. The rest is a radio call and somebody else's answer.
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 area runs from 36.95 N at the north end down to 30.49 N, and from 91.69 W across to 89.07 W, so it is the run of river between those corners rather than the whole Mississippi. Water above the top of that box belongs to the Upper Mississippi River pack, and the Atchafalaya has a pack of its own. This one downloads at 8 MB and works with no signal once it is on the phone.
69 bridges and 21 overhead cables, 90 crossings in all. The cable count is the lowest of the fifteen US rivers Helm builds packs for, so what is over your head on this river is nearly always a bridge. Set your air draft once and the charted vertical clearance on each of the 90 is checked against it, which is the check that decides the trip for a flybridge or a mast that is staying up.
The pack carries 6 charted lock features, and that figure counts chambers, gates and dams separately rather than counting facilities, so it is not a number of locks. Montgomery Point is one of the names in it. Among the thirteen rivers Helm packs with any charted lock feature, the Lower Mississippi has the fewest, which suits a river where the passage is set by current and traffic more than by lockages.
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