Depth readings on NOAA charts

I was recently motor-sailing down the ICW from Houston, Tx to Corpus Christi, Tx. In several of the bays we crossed it would have been nice to be able to cross out of the channel at various times. Although the charts indicated plenty of water depth in the bay, they showed “discontinued spoil” areas between the channel and the deeper water we wanted to travel in. The “discontinued spoil” area was shown in the color of shallower water, but there were no depths shown. We chose to stay in the channel to be safe.

Is there some other reference (other chart, pilots guide, etc) where I could find out the depths of these “discontinued spoil” areas.

Thanks for any help you can give.


wouldn’t stop me

– Last Updated: Feb-13-09 10:41 AM EST –

If there is any sort of wave motion on the surface, you would be able to read the water to tell if it is too shallow for most any paddle vessel. So it sure wouldn't stop me from paddling there (and actually, I would probably tend to use this area over a channel, as there would be less other boats).

Oh, don't have an answer to our question about finding the depths on charts.

EDIT - sorry about not reading that you wrote motor sailing (not paddling) in your message. My goof.

Chart #1 is key

chart #1 doesn’t show depths
that’s what the individual charts do

or not, as the case may be

(someone must have deemed it unfit for ships over there)

don’t know but
I don’t know the answer to your question but I, too, was wondering why it would matter in a paddlecraft - were you in a some other kind of boat?

If it’s a recreational motor boat or sailboat, you may be interested in buying a “fish finder” for it. They call them fish finders but they also can serve as depth finders, since they always show bottom depth and also spot suspended structure, like an underwater log, that might be navigation hazards. Like all electronic gizmos, they’ve gotten extremely cheap and powerful in the last decade. There are many basic models under $100, and fancier ones running up to $500 or more.

His first sentence said MOTOR-Sailing.

It was late at night and I thought the definition of the term may aid the poster’s understanding.

My sense from charts in that if there is no depth given then there is no measurable depth.

The Coast Pilot might be of help for the particular locale.

So, what, now I’m supposed to READ questions before answering them? This place gets more difficult every day. :slight_smile:

Oh, well, at least I guessed correclty what I had failed to read.

Depth finder use
We had a depth finder on the sailboat. We did use it in Galveston Bay to figure out that we could run over the “discontinued spoil” outside the Houston Ship Channel. We wanted to run just outside the channel so we slowly eased over and were able to run outside the channel and in almost full bay depth (13-15 ft). However in the other bays we had 2 problems with using the depth finder. First the wind conditions were such that it would have been very difficult to ease over slowly into the shallow area. We might have been blown aground before we had time to turn around. Second, even if we did manage to cross using the depth finder, we needed to be sure that we could re-enter the channel some 10 miles further down across more of the spoil. We did not want to exit and then find that the spoil farther down the channel was shallower and would not allow us to get back in.

Maybe if we go back in calmer conditions we can use the depth finder to check out some of the depths in those spoil areas. Wind was gusting 35-40 one day and was gusting 25-30 the other day.


I reckon you wanna
know what a spoil area is an why there ain’t a depth ? Spoil area’s are usually dredged materials dumped from clearin a channel . So when this stuff is dumped there it takes time to settle an react with tides,currents an such , so they ain’t gonna put a depth there . Alot of the charts in use haven’t been updated in 20 yrs. more/less , depends on area . Loads o times I’ve been asked where a channel was that someone is lookin for and have told em yer 25 yrs. late for that hole , closed up that long ago .

You made a good move not to try yer luck in those conditions when it’s just fer fun .

Get the #1 book or use the link to copy it . And that will tell ya what all them funny lil things on the chart are . Like what are those arrows there for ? why are they pointin that way , how come the otherr one has a vane on it ? an such…good information .


they change too often and frequently
to make an long term depth measurements. One spoil area might have a depth of a few inches in some areas and very close to those areas the depth might be a few feet. All of that could change in a week or two, especially if a big storm rolls through.

another blind answer
I didn’t bother to read your answer but it looks long so it’s probably some whiny crap about how the problem with depth finders is that you have to get right on top of what you’re measuring, and for sharply rising areas like spoil banks and reefs you could be aground before you get a reading saying it’s shallow. :slight_smile:

Well, they have a new gizmo which I bought, which has a small transponder that you can cast ahead of your boat. It’s a roughly 1-inch by 2-inch green thing with a nice weight for casting, and which floats. Again, it’s designed for fishing, so you can see conditions in the area you are casting to rather than just where the boat is. But it seems to me it would also work as a look-ahead for navigation purposes. If you were to set it up solely for navigation purposes (add weight and put it on a long pole with a good reel), you would be able to throw the thing a good ways in advance of where you lay at anchor, and then slowly reel it back in as you watch for obstacles.

There are some problems (of course). For one, you have to maintain direct line-of-sight for the receiver to work. Since the transponder broadcasts from about 1/2 inch above water level, even small waves can get in the way when the receiver is at canoe height – up on the deck of a sailboat should be better. Second, it won’t work in rough, turbulent waters. Small, regular waves are okay, but any action that prevents the transponder from settling down and pinging the bottom prevents it from working. Also, there may be an absolute range limit –I’ve never tested it that way. But still, it will give you some of the info you don’t already have, and the cost is under $100.