Can You Trust Your Charts?

[Cmdr Pete]

Navigation charts are only as good as the survey they are based on. The last survey could have been done a very long time ago.

In my local waters, the paper and electronic charts can be way off. The currents tend to reshape the bottom--even the whole coastline.

In one spot, the Garmin Bluechart has me on dry land when I'm in 30 feet of water. Makes me anxious every time. In another spot, I was bumping over a sandbar when the GPS is assuring me I'm in 8 feet of water. I can think of quite a few spots like that.

My paper chart shows the same thing. But, since its a few years old,  I went to West Marine to see if there was something better. I lined them all up--the regular paper chart, Maptech chart, Richardson's chart, the large scale waterproof chart. All the same, and all wrong.

Makes exploring new waters a bit nerve-wracking. I wonder what might help. Cruising Guides usually don't say much. Mostly I just hug the buoys, watch the water and the depthsounder, and be ready to bail out.

Where do you get this local knowledge everybody talks about? West Marine didn't carry it.

[Captain Smollett]

Mostly I just hug the buoys, watch the water and the depthsounder, and be ready to bail out.

Sounds like the right plan to me.

Of course, what do I know?  I run aground even where the chart indicates I SHOULD run agroun.   ::)

[CharlieJ]

Laura and have in the last two years, done the ICW from here to Florida and return. In portions of the ICW there aren't ANY, and in portions few, decent places to anchor. We've figured ways to get ourselves far enough off the channel to not be in danger of being run down by a tow on our two trips. And we've spent some time aground too.

When we are searching for deep enough water (where we THINK there will be some) She runs the boat at bare steerage way speeds, while I stand on the bow and heave the sounding lead. I have my lead line marked with a bright red yarn tied in at a "go/no go" point. In our case that's our draft plus 6 inches or 4 feet.

If I heave it and the red goes under, we keep crawling in further- if the red stays in sight, we bail out. We always come in at an angle so Laura knows exactly which way to bail.

Another trick is a cheapie fishing rod and push button reel. Use fairly heavy line, tie on a goodly sinker, like an oounce and up at the "no go" mark tie in a small float. You can cast the sinker out in front or to either side and get the same feed back- if the float sinks you're ok- if it floats it's too shallow for you. Using this trick, you can feel out water far ahead of the boat- OR from a dinghy searching for a narrow channel.

Over on the east coast, there are many cruising guides available that give you numerous safe anchorages- here on the Gulf Coast, we aren't so lucky. There is one available for Texas waters and one that covers western Florida, Ala, Miss and eastern La TO New Orleans- In between the Texas line and the Mississippi River, you are on your own.

[Captain Smollett]

I have my lead line marked with a bright red yarn tied in at a "go/no go" point. In our case that's our draft plus 6 inches or 4 feet.

If I heave it and the red goes under, we keep crawling in further- if the red stays in sight, we bail out.

Tha's a really good idea.  I have my sounding lead marked at 1 fathom intervals ( with knots ); since the current boat draws 4 ft (board down), I always figured if the first knot went under I was gettin close.  I like the idea of adding a bright mark at the absolute "don't go" depth.

:)  Grog for CharlieJ!

[AdriftAtSea]

Charts, especially in close coastal charts in areas that aren't of great commercial or military importance are likely to be less well updated than those of commercially/miltarily important areas.   Also, it depends on the type of bottom.  On Cape Cod, a lot of charts are known to be inaccurate, and local knowledge is a requisite for sailing in those areas...

[Lynx]

No, don't trust the charts  and I do not trust maps when driving either.

A $ 1000 forward sonar(fish finder) would help. Requires a through hull.

I was doing some GPS research on the web and, from what I recall, there are people who report wrong chart data and GPS problems. Some of the problems may be fixed before the next chart updates and before the next major storm.