Chart inaccuracies

[Steve Laume]

While cruising in Maine for a month this summer I hit a rock ledge.

It was almost dead low and they were only predicting 0.3' below normal low tide. So there was no exceptional tidal conditions at play. We were motoring along at less than 3 knots and I was watching the chart plotter and the surroundings very carefully. The plotter was zoomed in to show a maximum amount of detail and it called for a shelf of water 10' deep where we were crossing. I didn't expect any problems and was not watching the depth sounder. My son was aboard for a couple of days and he mentioned that it seemed shallow. I cut power and we hit almost immediately. We hit hard enough to raise up the bow and then rolled off, all in a matter of seconds. I had my hand on the wheel and did not feel the rudder react so no problems there. We looked around and slowly motored into deeper water.

I checked my chart plotter and the paper charts for that spot and they all showed 10'. It was easy to identify where we were from the surrounding features and there was no indication of water less than 10' or any boulders where we were. I am always amazed at the accuracy of charts. In this instance that was not the case.

I spoke to a fisherman's wife later in the trip and she asked if I had reported it. I told her I had not and then thought she had a valid point. If I had hit there due to my reliance on inaccurate chart data then this posed a hazard to navigation that should be noted or the charts corrected. I have no idea who should be contacted to be made aware of this situation. Any idea who to call?

I do know that if this had been a wooden boat, or Raven had a bolted on, fin keel, things might have ended differently. After diving to check the damage, I found a good scrape and to gouges about the size of the palm of your hand. These were over the lead ballast and more than just lost gel coat but not all the way through the glass. It was a good hit and a rather sickening feeling when it happened.

I do now know that Cape Dories make a rather ineffective battering ram for granite ledge. They to do nothing to the granite and it does very little to the boat. So there is no point in pursuing this endeavor.

I lost a bit of faith in charts that day, Steve.

[Neil Gordon]

>> I have no idea who should be contacted to be made aware of this situation. Any idea who to call?<<

I suspect your local Coast Guard station might be a shortcut to an answer.

[Jim Walsh]

https://nauticalcharts.noaa.gov/charts/ ... dates.html

You can use this link to ask questions or report an error.

[Mbigos]

I'm curious, where was the ledge?

[Paul D.]

Yes, by all means call the USCG and/or go to that link and let them know. Electronic charts are updated much more frequently and easily than their paper counterparts. I would also mark it on your own paper chart. If you have the precise lat & long, they would love you!

[Steve Laume]

I need to get back down to the boat where I can take a picture of my track on the plotter. This will also give me a precise Latitude and longitude for the spot where we hit. We didn't do any investigation of the area other than one pass with the keel so I am not sure of the extent of the shallow area but I am sure it exists and is uncharted, Steve.

[wikakaru]

Steve,

It's good of you to remind us all that charts are, as the Pirate Barbossa would say, "more what you'd call 'guidelines'" than actual depths.

Here are a couple of things to keep in mind:

* There are few areas where charted depths are "guaranteed". These are areas that have been tested by wire drag. We have a few of those here in Maine, most notably around Casco Bay. Here is an example from chart 13290:

Guaranteed depths.jpg

Despite the depth soundings, the green area is only "guaranteed" to be as deep as the underlined number (42 feet). Handy to know if you happen to be in a submarine.

* Actual tidal heights often vary from predictions. Check out the NOAA Tides/Water Levels page (https://tidesandcurrents.noaa.gov/water ... id=8729840) for side-by-side graphs of actual vs. predicted heights. For example, in Pensacola, Florida where our tidal range is usually around 2 feet, it is not uncommon for the government tidal predictions to be off by a foot or more. (Often these differences are caused by prolonged winds that blow water out of or into the area.)

Observed vs Predicted.jpg

* In addition to reporting the problem to the US Coast Guard, consider entering a "Hazard" on ActiveCaptain.com so other mariners know immediately where the spot is. The Coast Guard may take months or years to get your report onto the charts, but if you put it on ActiveCaptain, everyone knows immediately about the problem.

* Finally, I'd also like to see you post the exact lat/lon of the spot on this board so I don't run into it too!

Smooth sailing,

Jim

[Neil Gordon]

>>Actual tidal heights often vary from predictions... For example, in Pensacola, Florida where our tidal range is usually around 2 feet, it is not uncommon for the government tidal predictions to be off by a foot or more.<<

What's on the chart for depth is generally "mean lower low," basically the average of the lower of the two daily tide cycles. What's predicted is astronomical, i.e., tides based on the relative position of the earth, moon and sun, but in the tide tables, obviously weather isn't taken into consideration.

We tend to focus on tidal surges when there are storms driving high tides higher, and especially over the land; not so much the reverse.

Note also that shoaling is common in many areas. In Boston harbor, the bottom is slowly filling... much of the sand that's used to treat the streets in the winter ends up in storm drains and then into the harbor. (At least the bottom is soft and generally at a gentle slope.)

[Bill Goldsmith]

Pivoting slightly, this story reminds me of some nicks and gouges I inflicted on Loonsong's keel over the years. The confidence that a Cape Dory inspires is not just in deep water with a sea running, but also in thin water with rock ledges. Sounds like the "damage" is a fairly trivial fix for a fiberglass professional or in the alternative a fairly easy job for a DIY repair. Sorry to hear about the grounding.

[Markst95]

I think you can leave nav alerts on the Waterwayguide website.

[kerrydeare]

... I checked my chart plotter and the paper charts for that spot and they all showed 10'. It was easy to identify where we were from the surrounding features and there was no indication of water less than 10' or any boulders where we were. I am always amazed at the accuracy of charts. In this instance that was not the case ...

Steve, I know you're well aware that areas with no particular commercial or military interest are not physically surveyed as often as we might like. This is the nature of things and is only one part of the drive to reduce services. I can recall quite clearly when this started in earnest: the closure of lighthouses and other USCG facilities, the elimination of electronic services (RDF beacons, LORAN, etc.). Frankly things will get much worse before they get any better.

All that aside, Steve, as you're further well aware in Maine waters it's difficult if not impossible the determine exactly what you hit. Most likely it was a natural obstruction, but it could easily be something left over from a mid-winter accident, an intentional dumping, etc. We have had this issue on Barnegat where, after a winter of ice boating, someone forgot to mention (and mark) that old pickup truck that went through the ice and was never recovered. Yes, I made that discovery myself. I also recall when author Steve Pavlidis named two previously unknown rocks near Long Island Bahamas after Kerry Deare. He told me he did it in my honor, but I never swallowed that story.

Sometimes stuff just happens.

[tartansailor]

Coordinates?