The Green River gives you a narrow piece of water with a good deal going on above it. The channel is the river rather than a dredged lane inside something wider, so there is no outside to step into when a tow comes around a bend needing all of it. The water under the boat sits where the dams hold it, which means the clearance over your mast and the depth under your keel are set by the same thing on the same day. A day here does not run as a straight count of hours either. It runs as a sequence of pools, and the passage between them happens on somebody else's schedule.
Helm builds the Green its own pack. It carries 33 charted bridges and 30 overhead cables, 107 charted lights, 201 depth contours, 12 charted depth areas, 12 charted wrecks, 4 restricted areas and 9 charted lock features. The whole thing downloads at 1 MB, which is small enough that the entire charted river is on the phone before you have the boat off the trailer.
The pack runs from 87.5118 west to 86.87783 west and from 37.20481 north to 37.91489 north. At this latitude that is a box of about 35 miles east to west and about 49 miles north to south. Those are the dimensions of the box, not of the river inside it, and the river inside it is a good deal longer than any straight line across the box. Everything counted below sits in there, and it comes down as a single 1 MB download.
Helm builds a pack for fifteen US rivers, and where the Green places on each count says more about this river than about the packs. Its 201 depth contours put it tenth of the fifteen, which is higher than a river with 33 bridges on it would suggest. Its 12 charted depth areas put it fifteenth, and that is the clearest single statement in the whole inventory about what sort of water this is. A chart fills big depth polygons where there is a wide bottom to describe. Here there is not, so the description arrives as lines instead.
| In the chart pack | Count |
|---|---|
| Bridges | 33 |
| Overhead cables | 30 |
| Charted lights | 107 |
| Lock features | 9 |
| Charted depth areas | 12 |
| Depth contours | 201 |
| Charted wrecks | 12 |
| Restricted areas | 4 |
Counted from the Helm chart pack for the Green River, built from the official inland electronic navigational charts published for it. The pack downloads at about 1 MB. Lock features are counted as the chart draws them, with chambers, gates and dams as separate objects.
Put those two counts together and the Green carries 63 charted crossings over the water, with very nearly as many cables as bridges. That ratio is the thing to look at before anything else on this page. A bridge announces itself from a long way off and its clearance is charted. A cable is a line you may not pick out of the trees until you are close under it, it opens for nobody, and there is no tender on the far end of a radio call.
If you run with a mast up, or with a flybridge and an antenna above that, this count is what decides whether the trip happens rather than how pleasant it is. Set your air draft in Helm once and the charted vertical clearance gets checked against that figure on every one of the 63. Treat the charted number as the place you start from. The pool moves with the dams, so the clearance printed on the chart and the clearance you have this afternoon are two different figures, and the second one is the one that finds the antenna.
The pack carries 9 charted lock features and draws each one where it sits. That figure counts objects on the chart rather than facilities on the river. A chamber, a gate and a dam are drawn as separate objects in the source data, so 9 is not a count of lock and dam sites and nothing on this page should be read that way. Among the thirteen river packs that carry any lock features at all, the Green sits twelfth.
What the locks do to a Green River day resists a number altogether. The passage is broken. You run a pool, you arrive, and from that point you are on the lock's clock and behind whatever commercial traffic is already working through. Distance divided by speed will be wrong every time you plan a day that way, and it will be wrong by an amount nobody can hand you at the ramp. Having the features drawn in the right order in front of you before you leave is worth more here than an estimated arrival time would be.
The bottom of this river is carried in lines rather than in areas. 201 depth contours against 12 charted depth areas is a shape of data you do not get on open water, where a chart can fill a large polygon with a depth range and be done. Read the Green the way its chart was drawn. A contour tells you where a depth runs, and on a river a depth runs along the bend, so the question is which side of the line you come around on. Where those numbers come from in the first place is covered on the depth page.
The pack also holds 12 charted wrecks, ninth of the fifteen rivers. On a coast a charted wreck is a thing you route around by going outside it. On a river whose entire pack contains 12 depth areas, outside is not being offered on the same terms, and a wreck charted inside the navigable width is something you pass close to rather than something you avoid. Twelve is a small enough number to look at all of them before you go.
There are 4 restricted areas in the Green pack, which places it fourteenth of the fourteen river packs that carry any at all. A list that short is easy to file away as noise. It is worth taking the other way around. When a river carries only 4, every one of them was drawn for something particular to the water you are about to be in, and the chance that the one ahead of you is the one that matters today is far higher than it would be on water with hundreds of them.
The 107 charted lights in the same box work on a similar logic. On a river you are not holding a course across open water so much as working from the mark you can see to the next one around the bend, and 107 of them inside a box this size is roughly what that kind of running requires. They are all in the 1 MB pack, which means they are still there when the signal is not.
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.
That is a clearance question before it is a depth question. The pack carries 33 charted bridges and 30 overhead cables, so there are 63 charted crossings over this river and very nearly half of them are cable, with no tender and no opening schedule. Set your air draft in Helm and the charted vertical clearance on each of the 63 is checked against that figure. Take the charted number as the starting point, because the pool moves with the dams, and read the crossing in front of you as well.
The pack carries 9 charted lock features and draws them where they sit on the river. That figure counts objects on the chart rather than facilities on the water, since a chamber, a gate and a dam are separate objects in the source data, so 9 is not a number of lock and dam sites and should not be used as one. Among the thirteen river packs that carry any lock features at all, the Green is twelfth.
The pack runs from 87.5118 west to 86.87783 west and from 37.20481 north to 37.91489 north, a box of about 35 miles east to west and about 49 miles north to south, and it downloads at 1 MB. Inside it are 33 bridges, 30 overhead cables, 107 charted lights, 201 depth contours, 12 charted depth areas and 12 charted wrecks. Once the pack is on the phone it keeps working without a signal.
Helm Boating