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post #11 of 20 Old 09-09-2019
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Re: Caught in a squall

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The IFR analogy is appropriate. I'll add a couple of things to consider.

You should trust your instruments, because your imagination and seat of your pants will deceive you. However, you should have a way to confirm/crosscheck your instruments. Confirming that your depth gauge is reading something similar to what your chartplotter suggests is easy enough. If not, stop or slow to figure out what's going on. When in the fishbowl and seeing nothing, visibility always looks worse than it really is. Yes, we've all been in fog/rain that was hard to see the bow, but it's rare. Try to navigate within a hundred feet or so of an ATN, preferably one with safe water around, so that you confirm it visually when you should. I think I actually saw one off your bow at 1 o'clock in the vid. Finally, slow down. You obviously need response time, if your chartplotter is wrong. The saying goes, you should not be moving faster than you can think. Even in a slow sailboat, I find backing down just one knot makes a huge difference.

Good on ya for making it through safely.
Speaking electronic charts...and depth... The depth information can be confusing because they are given as low tide I believe...

So if I were to anchor where the chart read 12' and the depth sounder read 12' I should be at low tide and expect the depth to increase where I was 8' to 20'. But of course the given tide times are slightly different depending where you are or the distance you are from the tide station.

There are depths reported of say 8' which gives me 2 feet of clearance for 6' draft... but I am too paranoid to sail there thinking there are little hills and the occasional boulder which I could encounter.

Which got me thinking...in this day and age of digital data... why can the charts we have on our plotters show the ACTUAL depth taking the tide into account. I have current arrows with number representing knots (CRUDE). This data also should display WHERE you are... Granted mapping currents is a big projects. But it seems that there may be a way to build the data base from crowd sourcing by actually automatically upload data from the boat's electronics. Current speed would require calibrated speedos. But conceptually this is doable.

So I would sail over bottom that is now shown on the chart as 8' in mid tide which would be 12' in real time real world.

pay attention... someone's life depends on it
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post #12 of 20 Old 09-09-2019
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Re: Caught in a squall

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Speaking electronic charts...and depth... The depth information can be confusing because they are given as low tide I believe...
That's true, hence the saying, you shouldn't be moving faster than you can think. You need to be conscious of this math and tidal range. However, one can only be so scientific in this regard. I'm really looking for anything in the range and not off by more than the contour line on the chart. If everything around you is the same depth, it's of little value anyway.

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Which got me thinking...in this day and age of digital data... why can the charts we have on our plotters show the ACTUAL depth taking the tide into account..
No doubt that one could program our devices to show predicted depth on a specific date and time. However, if you look at te NOAA weather buoy data, actual depth is often different from even predicted depth. Most dramatically, when there is storm surge, during which I hope one isn't navigating. However, in some tidal basins, strong winds can affect the actual tide height, sometimes by feet. I think even the Chesapeake is impacted if there are strong prolonged northerly or southerly winds. I don't recall that being an issue in LIS.


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post #13 of 20 Old 09-09-2019
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Re: Caught in a squall

Minni.... I think in the future we will have charts will real time depth data wherever we are sailing!

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Re: Caught in a squall

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Minni.... I think in the future we will have charts will real time depth data wherever we are sailing!
How do you see them programming for unpredictable tidal impact, such as I described. Narragansett Bay is 6 inches higher than the predicted tide table, as I type. I just checked the buoy. Not much, of course, but this can be and sometimes is more significant.


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post #15 of 20 Old 09-09-2019
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Re: Caught in a squall

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How do you see them programming for unpredictable tidal impact, such as I described. Narragansett Bay is 6 inches higher than the predicted tide table, as I type. I just checked the buoy. Not much, of course, but this can be and sometimes is more significant.
I think they can use either designated buoy which report depth real time and an algorithm will adjust the charted depth which would be available for download online...

I have internet on board using a cellular hot spot. I presume I could conceivable down load depth data and input a plotter. I realize that we not have this technology today. But look what data we have online / on out smart devices with AIS sites like MarineTraffic!

We get all sorts of real time local weather data... collected by crowd source weather stations too.

Obviously we need smart buoys to report... Why can't some existing buoys be upgraded to report the depth at its location... and current too???

Just like a RACON when you come within range the buoy would send a "correction number" to your electronics to correct the baseline chart depth. Seems doable. It would perhaps apply for a small area until you come within range of another smart buoy.

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post #16 of 20 Old 09-09-2019
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Re: Caught in a squall

Got it. It's more of a comm issue than a programming one.


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post #17 of 20 Old 09-10-2019
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Re: Caught in a squall

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Originally Posted by SanderO View Post
Speaking electronic charts...and depth... The depth information can be confusing because they are given as low tide I believe...

So if I were to anchor where the chart read 12' and the depth sounder read 12' I should be at low tide and expect the depth to increase where I was 8' to 20'. But of course the given tide times are slightly different depending where you are or the distance you are from the tide station.

There are depths reported of say 8' which gives me 2 feet of clearance for 6' draft... but I am too paranoid to sail there thinking there are little hills and the occasional boulder which I could encounter.

Which got me thinking...in this day and age of digital data... why can the charts we have on our plotters show the ACTUAL depth taking the tide into account. I have current arrows with number representing knots (CRUDE). This data also should display WHERE you are... Granted mapping currents is a big projects. But it seems that there may be a way to build the data base from crowd sourcing by actually automatically upload data from the boat's electronics. Current speed would require calibrated speedos. But conceptually this is doable.

So I would sail over bottom that is now shown on the chart as 8' in mid tide which would be 12' in real time real world.
In principle, crowd sourcing could be very helpful with depth information, but only if the crowd sourced data came from calibrated depth sounders indexed to the vertical datum. Unfortunately, that is not likely to happen if the calibration is up to the individual boater. Adding to the resulting confusion is the fact that recreational boat sounders are not calibrated to tides, let alone actual instantaneous depth.

Speaking from experience, the actual hydrographic survey data available in our area does not agree very well with the “sonar” charts based on crowd sourcing. The “sonar” charts are qualitatively interesting in the additional detail provided (compared to NOAA charts), but they are quantitatively in error in ways that can get you aground in the Mystic River. For example, the error by my moorings is on the order of feet, but thankfully a lot of the bottom in the Mystic River is soft mud.
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post #18 of 20 Old 09-10-2019
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Re: Caught in a squall

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In principle, crowd sourcing could be very helpful with depth information, but only if the crowd sourced data came from calibrated depth sounders indexed to the vertical datum. Unfortunately, that is not likely to happen if the calibration is up to the individual boater. Adding to the resulting confusion is the fact that recreational boat sounders are not calibrated to tides, let alone actual instantaneous depth.

Speaking from experience, the actual hydrographic survey data available in our area does not agree very well with the “sonar” charts based on crowd sourcing. The “sonar” charts are qualitatively interesting in the additional detail provided (compared to NOAA charts), but they are quantitatively in error in ways that can get you aground in the Mystic River. For example, the error by my moorings is on the order of feet, but thankfully a lot of the bottom in the Mystic River is soft mud.
For sure... The data gathering would have to use calibrated and certified devices on "registered" boats." who participate in the program. The shallower areas where sail boats avoid need to be surveyed by shallow draft power boats obviously. Heck I don't know how to implement it. But the idea of using boats on the water to gather environmental data seems like it could be a good idea if the technical hurdles could be worked out.
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Re: Caught in a squall

Drove around this one a couple weeks ago
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Re: Caught in a squall

Drove around this one a couple weeks ago.
When you see this coming get the hell out of the way!
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