The Tennessee does not behave like a coast. It is a run of pools held up by dams, and the level in the pool you are sitting on answers to an operator rather than to the moon. The water under the boat is rarely what stops you here. What stops you is the height of the next crossing, or a tow coming around a bend that needs the whole channel and has nothing to give back. Behind both of those sits the chamber ahead of you, which sets the clock for the rest of the day whatever the distance on the chart says. Skippers who came off salt water usually spend their first day watching the wrong number.
The Tennessee River pack in Helm downloads at 15 MB. It carries 357 charted overhead cables, which is the highest count of any of the fifteen US rivers Helm builds packs for, together with 397 bridges, third of the same fifteen. Under the keel there are 618 charted depth areas and 749 depth contours, third and fourth, and 879 charted lights to show where the channel goes. The pack holds 41 charted lock features and 22 restricted areas. The charted point hazards come to 5 obstructions, 5 wrecks and 6 underwater rocks, which is a short inventory for a river of this length and says something about the water rather than about the survey.
Helm builds chart packs for fifteen US rivers. The Tennessee is at or near the top of most of the counts that describe how thoroughly a piece of water has been marked and measured, and on one of them it is first outright.
That first place is overhead rather than under the keel, which tells you most of what you need to know about running here. The depth figures back it up from the other side. 618 charted depth areas and 749 depth contours in a 15 MB pack is a well described bottom, and 879 charted lights is a well marked channel. The number that changes how you plan a trip is still the 357.
| In the chart pack | Count |
|---|---|
| Bridges | 397 |
| Overhead cables | 357 |
| Charted lights | 879 |
| Lock features | 41 |
| Charted depth areas | 618 |
| Depth contours | 749 |
| Charted obstructions | 5 |
| Charted wrecks | 5 |
| Restricted areas | 22 |
| Underwater rocks | 6 |
Counted from the Helm chart pack for the Tennessee River, built from the official inland electronic navigational charts published for it. The pack downloads at about 15 MB. Lock features are counted as the chart draws them, with chambers, gates and dams as separate objects.
357 charted overhead cables is the highest count of the fifteen rivers, and the reason is geometry. A river is narrow enough that a crossing is cheap to build, so power and telephone go over the water wherever the banks suit, including plenty of places where nobody ever bothered with a bridge. Add the 397 bridges, third of the fifteen, and there are 754 charted things above this water that a boat has to pass under.
For a boat with the mast stepped, that count is the trip. Set your air draft in Helm once and the charted vertical clearance on every one of those crossings gets checked against it. That is a job worth doing before the first pool rather than at the first crossing that looks low, and a flybridge or a radar arch runs the same arithmetic with less to spare than most owners assume. Clearance on an impounded river also moves with the pool. A pool held high takes that difference straight out of the gap over your masthead.
The cables deserve the larger share of the planning. A bridge is a structure you see coming from a long way off and can identify while you still have room to change your mind. A cable is a line that disappears against a gray sky until you are close to it, and the only place its clearance is written down is the chart.
The pack carries 41 charted lock features, fourth among the thirteen rivers in Helm that have any. Read the figure for what it is. The source data counts chambers, gates and dams as separate items, so 41 measures how much structure the chart draws where this river steps down. It is not a count of the stops on your itinerary, and nothing on this page should be read as one.
Among the names the chart carries here are Fort Loudoun, Watts Bar, Chickamauga and Guntersville. What is useful on approach is that the chamber and the gates are drawn where they actually sit, because the approach is the part of a lockage that goes wrong. You are holding position in current, off a wall, waiting on a chamber that a tow may already be inside or already committed to, and commercial traffic goes first. Call ahead on the radio as you come up on it. The distance between two pools tells you very little about how long the day is going to take.
618 charted depth areas and 749 depth contours put the Tennessee third and fourth among the fifteen rivers. The point hazards are a different story. There are 5 charted obstructions, seventh among the twelve rivers whose packs carry any, 5 charted wrecks, twelfth of the fifteen, and 6 underwater rocks, which is last among the six rivers with any underwater rock charted at all.
Taken together those two sets of numbers describe an impounded river honestly. Very little here is going to hurt you by sitting at a fixed point that somebody surveyed and drew a symbol on. What catches boats is the edge: the shelf where the old bank still is, and the flat that the pool covers at one level and not at another. Depth areas and contours are what you read for that, which is why having 618 and 749 of them matters more on this water than a long list of wrecks would.
The pack also carries 22 restricted areas, eighth among the fourteen rivers that have any. On a river organized around structures, a restricted boundary is not something you can see from the water at all, so it is drawn on the chart in Helm and sits there before you need it.
879 charted lights puts the Tennessee fourth of the fifteen rivers. On this water the lights are the channel. You are not holding a course across open water, you are working bend to bend, and which side of the bend the good water is on is a thing the marks tell you rather than a thing the surface shows you.
After dark that stops being a convenience. A tow coming the other way is a set of lights on a hull whose length you cannot judge, and the searchlight takes your night vision for as long as it is pointed at you. What you have left during those minutes is the chart and the marks drawn on it, which is a fair reason to know how many of them there are before deciding to run one more pool instead of stopping for the night.
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.
Air draft, for most boats. The pack carries 357 charted overhead cables, the highest count of any of the fifteen US rivers Helm builds packs for, plus 397 bridges, which is third. That is 754 charted crossings to pass under. The bottom is described in the same pack by 618 charted depth areas and 749 depth contours, third and fourth of the fifteen, so the water itself is well covered. Set your air draft in Helm once and the charted vertical clearance on each of those 754 crossings is checked against the figure you entered.
The pack carries 41 charted lock features, fourth among the thirteen rivers in Helm whose packs carry any. Chambers, gates and dams are separate items in the source data, so 41 describes how much structure is drawn rather than how many places you stop. Names on the chart here include Watts Bar and Chickamauga. On approach the useful part is the chamber and the gates being drawn where they actually are, since the approach is where the current and the commercial traffic are.
No. It is one pack at 15 MB. The area runs from about 34.31 N up to 37.07 N and from 88.56 W east to 83.83 W, so the pools come down together rather than one at a time, and once the pack is on the phone the chart works with no signal. Boats carrying on past the ends of it will want the Ohio River pack or the Black Warrior-Tombigbee pack, which Helm builds separately.
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