Ran Aground Using Navionics.

[rwidman]

My alarm is 3 feet below my draft

You are the daredevil. When the alarm sounds you had better not be heading for the beach. Seriously, you will not have time to react if ahead is less than 3 feet.

It really depends on how fast you are travelling. In my seven knot boat, I set the alarm to 1 1/2 feet deeper than my boat's draft and can stop before I hit bottom.

Of course, I would not be heading towards the beach, but if I was, I would take that into consideration and adjust my speed.

 

[rwidman]

All good if you stay on the path well travelled.
Much of the world is wildly inaccurate

I don't know how you got that from my post1

The depth sounder doesn't know or care about "well travelled", it reports the actual depth of the water, right now and right where you are.

 

[OldDan1943]

The depth sounder indicates the depth below the sounder soooooo, if your sounder is placed wrong in the boat or the speed is not slow and if the helmsman is not paying attention, the sounder will explain why you ran aground.
"Look ahead" depth sounder is supposed to give you a better 'chance' but, some people rely too much on this feature, outrun their sonar and run aground anyway.

I am told, with enough electronics, the boat will sense the impending danger, slow or shift to reverse. Of course is the boat is traveling at a speed, it is still possible to run aground or spill the contents of the lockers and catch the crew unaware as the boat shifts to reverse and increases speed in an attempt to prevent running aground.

 

[rslifkin]

I keep my depth alarm set to go off when I've got 3 feet below the props. That's basically the "hey dummy, pay attention and don't take your eyes off the depth" reminder. Most of the times it goes off, I know I'm squeezing into somewhere a bit tight and I'm expecting it. If it goes off unexpectedly, it's time to figure out really quickly whether it's going to keep getting shallower or not.

Honestly, I'd probably like it set to 4 or 5 feet of clearance, but then I'd have to deal with it going off every single time we come in and out of our slip. As-is I was dealing with that this spring until the water came up a bit on Lake Ontario (marina is due for dredging this winter), as we only had about 6 feet in our slip at the beginning of the year (alarm is at 6.7 feet).

 

[bligh]

A good example of good charts made using methods pre GPS technology.

 

[backinblue]

I keep my depth alarm set to go off when I've got 3 feet below the props. That's basically the "hey dummy, pay attention and don't take your eyes off the depth" reminder. Most of the times it goes off, I know I'm squeezing into somewhere a bit tight and I'm expecting it. If it goes off unexpectedly, it's time to figure out really quickly whether it's going to keep getting shallower or not.

Honestly, I'd probably like it set to 4 or 5 feet of clearance, but then I'd have to deal with it going off every single time we come in and out of our slip. As-is I was dealing with that this spring until the water came up a bit on Lake Ontario (marina is due for dredging this winter), as we only had about 6 feet in our slip at the beginning of the year (alarm is at 6.7 feet).

Exact same situation with me. At low tide, there is about 6' of water in my slip. The alarm is to grab my attention if I wander into mopre shallow water than expected.

 

[backinblue]

I don't know how you got that from my post1

The depth sounder doesn't know or care about "well travelled", it reports the actual depth of the water, right now and right where you are.

And Lindsey's law never fails....

Lindsey’s Law has it that “when your draft exceeds the water’s depth you are most assuredly aground.”

In 1772, the captain and crew of the H.M.S. Gaspee, on patrol in Narragansett Bay to enforce a restrictive British trade policy, learned that the hard way. Lured into shallow water by Benjamin Lindsey aboard a small trading vessel, the Hannah, the Gaspee promptly ran aground, was overrun by Rhode Island colonists, and set ablaze in an incident that would prove a precursor to the Revolutionary War.

 

[Simi 60]

I don't know how you got that from my post1

I got that from the first part of your post

A chart (paper or electronic) tells you how deep the water is supposed to be.

Well travelled, therefore well charted areas you can probably rely on chart depths
In "tiger country" all bets are off

The depth sounder doesn't know or care about "well travelled", it reports the actual depth of the water, right now and right where you are.

Yep and I have seen it go from 100ft to 5ft in a boat length so in suspect areas I always set 20ft under keel
If that alarm goes off and it's apparent that it's staying shallow, it's back to idle with 10ft under, then 5ft (with track running for a way out)

A good example of tiger country in the pic below

 

[rwidman]

The depth sounder indicates the depth below the sounder soooooo, if your sounder is placed wrong in the boat .........

Most depth sounders have a "keel offset" adjustment (with mine, it is part of the MFD) so you can adjust the reading to either display the actual water depth (my preference) or the depth under the deepest part of the boat.

 

[rslifkin]

Most depth sounders have a "keel offset" adjustment (with mine, it is part of the MFD) so you can adjust the reading to either display the actual water depth (my preference) or the depth under the deepest part of the boat.

Yup, knowing where the offset is set matters. And I agree with surface depth. Makes it easy to know if you're in the right spot when working off local knowledge.

 

[Alaskan Sea-Duction]

A chart will help you, but the depth finder will save you....sometimes.

Cruising Frederick Sound in SEAK and all of a suddered my depth sounder dropped to 36 ft, then 12 ft. WTF! FULL REVERSE!

Then I realized I was actually in 2600ft. The sonor beam didn't have enough time to return to the boat at the speed I was going.

 

[rwidman]

Yup, knowing where the offset is set matters. And I agree with surface depth. Makes it easy to know if you're in the right spot when working off local knowledge.

I calibrated mine while docked at low tide using a boat pole to measure the actual water depth.

The water depth was eight feet at the time so I just set the keel offset to show eight feet.

 

[rslifkin]

I calibrated mine while docked at low tide using a boat pole to measure the actual water depth.

The water depth was eight feet at the time so I just set the keel offset to show eight feet.

I did pretty much the same. I measured transducer to waterline while on land one winter, then confirmed by physically sounding my slip as close to the transducer as I could and comparing the reading after we launched in the spring.

 

[Vandeusen]

LOL me too I love telling her stop telling me what to do LOL

 

[slowgoesit]

Late to the party here, but last Summer in Neets Bay in Alaska, we tucked in behind a small island to anchor. Chart showed ONE small rock near the middle of the bay, with an area about 350' in diameter totally clear of obstructions further up the bay. Tide was incoming, about 3' from high. Smack in the middle of that 350' area, showing 40' of water, just as we were about to anchor, my anchor ho (a friend who was visiting and helping out on the bow) yelled "ROCK!" and pointed just off the Port bow, about 20' or so. The rock was about 3' under the water, and absolutely MASSIVE! Probably 30' across, and roughly flat on top . . . .
Had the water been turbid, or milky, as is often the case up there, or the waters surface been ruffled by wind, we would never have suspected it was there. Double and triple checked our location, Navionics said nothing there. Paper chart didn't show very good info in the area either.

Needless to say, we left that bay (dead slow, and with three spotters on the bow now) and found another spot to anchor for the night . . . .
Except for this an a few other small variations, Navionics has been spot on for us. Now to see if it is spot on in the Sea of Cortez . . .

 

[FWT]

Late to the party here, but last Summer in Neets Bay in Alaska, we tucked in behind a small island to anchor. Chart showed ONE small rock near the middle of the bay, with an area about 350' in diameter totally clear of obstructions further up the bay. Tide was incoming, about 3' from high. Smack in the middle of that 350' area, showing 40' of water, just as we were about to anchor, my anchor ho (a friend who was visiting and helping out on the bow) yelled "ROCK!" and pointed just off the Port bow, about 20' or so. The rock was about 3' under the water, and absolutely MASSIVE! Probably 30' across, and roughly flat on top . . . .
Had the water been turbid, or milky, as is often the case up there, or the waters surface been ruffled by wind, we would never have suspected it was there. Double and triple checked our location, Navionics said nothing there. Paper chart didn't show very good info in the area either.

Needless to say, we left that bay (dead slow, and with three spotters on the bow now) and found another spot to anchor for the night . . . .
Except for this an a few other small variations, Navionics has been spot on for us. Now to see if it is spot on in the Sea of Cortez . . .

That is where forward looking sonar would come in handy

 

[DDW]

Forward looking sonar would be great if it worked. According to all of the tests I have read, it doesn't work well, not well enough to navigate an unknown passage.

 

[ksanders]

Late to the party here, but last Summer in Neets Bay in Alaska, we tucked in behind a small island to anchor. Chart showed ONE small rock near the middle of the bay, with an area about 350' in diameter totally clear of obstructions further up the bay. Tide was incoming, about 3' from high. Smack in the middle of that 350' area, showing 40' of water, just as we were about to anchor, my anchor ho (a friend who was visiting and helping out on the bow) yelled "ROCK!" and pointed just off the Port bow, about 20' or so. The rock was about 3' under the water, and absolutely MASSIVE! Probably 30' across, and roughly flat on top . . . .
Had the water been turbid, or milky, as is often the case up there, or the waters surface been ruffled by wind, we would never have suspected it was there. Double and triple checked our location, Navionics said nothing there. Paper chart didn't show very good info in the area either.

Needless to say, we left that bay (dead slow, and with three spotters on the bow now) and found another spot to anchor for the night . . . .
Except for this an a few other small variations, Navionics has been spot on for us. Now to see if it is spot on in the Sea of Cortez . . .

Nothing is accurate in Mexico.

But... You are a mariner. You understand that off of a point you get rocks.

Also the water here is pretty clear, the sand is white, and with the sun shining it's easy to see shadows in the water.

 

[twistedtree]

Forward looking sonar would be great if it worked. According to all of the tests I have read, it doesn't work well, not well enough to navigate an unknown passage.

But distinguish that from a Search Light Sonar that does work in such a situation, or an Omni that works even better. But each is a significant step up in cost.

 

[Simi 60]

Navionics , in fact all chart packages are wildly inaccurate once you travel off of well travelled shipping routes.

OpenCPN and georeferenced satellite imagery overlays pick up the slack and are our #1 nav source on board.

 

[Simi 60]

Forward looking sonar would be great if it worked. According to all of the tests I have read, it doesn't work well, not well enough to navigate an unknown passage.

Our vessel had interphase
Didn't last long before failure says the previous owner.
But while it was working it was still a failure
Didn't work at over 3 knot speeds - vessel does 5+ knots at idle.

 

[OldDan1943]

It was never designed to much over 2 or 3 knots.
If you are in skinny water or trying to searching for a private channel, just fast enough to maintain steerage.
I have never heard of anyone who was proud that they bought it.

 

[Hippocampus]

We’re now heading north in the ICW. Between Hilton head and now a bit south of Oriental there have been numerous occasions navionics has been way off. But also a few so has C-map. First ascribe it to the aids to navigation having been moved. But that doesn’t explain the more frequent occasions navionics has been off. Have concluded you still need to look at the water, pay attention to depth and slow down when necessary. Bob, waterway guide and ICW planning guide at least have you a clue where to be cautious but that’s it. Given you can get both types of charts and update them nearly daily. Don’t understand these inaccuracies. Just don’t get it.

 

[Portage_Bay]

The inaccuracies of Navionics and C-map have been noted and discussed other previous threads. I've experinced a few. The proprietary charts are getting better all the time but in my mind do not and cannot replace official hydrographic agency charts. NOAA charts in the US. CHS charts in Canada.

I realize that most people are using MFDs and other kinds of electronic plotters. So they will want to continue to use Navionics, C-map or other proprietary charts. Well understood.

My advice to all cruising the US and Canada is to find a way to at least view official charts that are kept up to date. NOAA charts are updated every friday. For free. My main chart plotter is a laptop running OpenCPN with official charts. I realize many don't like OpenCPN, there is a learning curve involved. But to simply use it to view charts is dirt simple. It's free, runs on laptops, tablets and phones.

There will still be surprises for those crusing out of the way areas. Or places where every weather event moves sand bars and sometimes even channels.

We’re now heading north in the ICW. Between Hilton head and now a bit south of Oriental there have been numerous occasions navionics has been way off. But also a few so has C-map. First ascribe it to the aids to navigation having been moved. But that doesn’t explain the more frequent occasions navionics has been off. Have concluded you still need to look at the water, pay attention to depth and slow down when necessary. Bob, waterway guide and ICW planning guide at least have you a clue where to be cautious but that’s it. Given you can get both types of charts and update them nearly daily. Don’t understand these inaccuracies. Just don’t get it.

 

[mvweebles]

........
There will still be surprises for those crusing out of the way areas. Or places where every weather event moves sand bars and sometimes even channels.

I have a friend who's [new] wife is new to boating. For some reason, she cannot accept that electronic chart data may not be accurate which is odd to me as she is very knowledgeable in her technical field. I would think she'd be more suspect of data especially here in Florida with it's skinny waters where she thinks we can thread a needle into a shallow anchorage. My questions to her are always "we're in the middle of nowhere - no channel. Where does the base data come from? How does it get assimilated into a chart?" The answer is it doesn't - depths in many areas are interpolated with a Zone of Confidence (ZoC) factor underpinning the accuracy.

In my part of Florida, "Johns Pass" is the main access to the Gulf. 150-years ago it didn't exist but a hurricane blew through and voila - Johns Pass. The approach still hasn't made up its mind where it wants to be, or even if it wants to silt-over and revert to barrier island. The only reliable aid to navigation is the USCG temporary buoys that get moved pretty frequently.

Charts have come a long way, but every one of them have a caveat that they are not to be relied upon. It's the lawyers talking, but still, they are an aid, not gospel.

Peter

 

[Hippocampus]

NOAA charts are updated every friday.

We use them as well. Guess our troubles must occur on Thursdays. . Will keep track.

Becoming convinced near the inlets shoaling shifts nearly daily but ATONs don’t. Also see a lot of pilings where the sun has removed the color or the triangle or square has simply fallen off. Our infrastructure is falling apart. Bridge falling down or unable to open and close, roads falling apart. Just a shame.

 

[Simi 60]

NOAA charts are updated every friday.

We use them as well. Guess our troubles must occur on Thursdays. . Will keep track.

Becoming convinced near the inlets shoaling shifts nearly daily but ATONs don’t. Also see a lot of pilings where the sun has removed the color or the triangle or square has simply fallen off. Our infrastructure is falling apart. Bridge falling down or unable to open and close, roads falling apart. Just a shame.

Just because they get updated every Friday does not mean they are correct
Perhaps for easy visual or reported stuff, but not bottom.
You actually need hydrographic vessels checking the area and how often does that happen?

 

[SteveK]

Just because they get updated every Friday does not mean they are correct
Perhaps for easy visual or reported stuff, but not bottom.
You actually need hydrographic vessels checking the area and how often does that happen?

Agree. I cannot imagine every square foot of seafloor has been or will be mapped.

 

[FWT]

Just because they get updated every Friday does not mean they are correct
Perhaps for easy visual or reported stuff, but not bottom.
You actually need hydrographic vessels checking the area and how often does that happen?

And just because they are updated, doesn't mean the spot you are interested in has been checked at all recently.

 

[Northern Spy]

Agree. I cannot imagine every square foot of seafloor has been or will be mapped.

Or will have the security clearance to access it, if it has been. [emoji846]