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Old 30-04-2021, 16:35   #1
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Looking for an Explanation

I wanted to find out if the tide had turned. Currents in our harbor can be tricky and strong. My eyes told me it was at or near low by looking at the piling. I turned on our trusty Garmin which told me it would be high in 15 minutes. I internet searched and found we were 20 minutes past low.

If I can't trust the tide information I'm being shown why should I trust anything else?

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Old 30-04-2021, 16:55   #2
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Re: Looking for an Explanation

There are high and low tides and there are slack times. The slack times don't match the tide times unless there's no current. Current can impact water level and must be convolved with the tide.
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Old 30-04-2021, 17:05   #3
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Re: Looking for an Explanation

Thanks for your input. But surely it would be off by a percentage and not almost exactly opposite reality. The report is generated by data. For example, I can look up tides for tomorrow, etc which could not be affected by slack because it hasn't happened yet.

Not trying to argue, but this has me questioning position information which is of great importance.

I'll ask Garmin, and see what they have to say.
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Old 30-04-2021, 17:15   #4
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Re: Looking for an Explanation

redhead, it will always vary. However, if your Garmin is 6 hrs. or so off, maybe it has to do with its settings.

We use a very old tide program, that has served us very well: Wxtide. These are all computer rather than smart phone based. [even though smart phones are computers, sigh!] There's also Tides & Currents, and Open CPN has a tide program that works quite well.

As mentioned above, high water occurs later at places further upstream, and the timing seems to be different at neaps than springs. Out here in Oz, there are many entrances with sand bars to seaward of them, with impounded waters to landward, and the timing is affected by the water having to go through a restricted opening in both directions, so high water upstream has little to do with high water at the bar (when you might want the greatest depth to get over the bar, and also to have a nice incoming tide to ride up to your destination.) Cruising guides will often divulge the offset. It will depend on the weather, place of tide cycle and sea conditions, too. It doesn't work to think about it as if it is one thing, because so many things affect it, including local geography.

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Old 30-04-2021, 17:50   #5
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Re: Looking for an Explanation

Thanks Ann. I agree with all you say.

But since our harbor is the last (or first) in US waters, the tidal information comes from less than a mile from where I sit. I've been watching the tide from this very harbor for the last 5 years and haven't observed anything near as dramatic as this. I've seen a 20 minute discrepancy, maybe as much as an hour, but not 12 hours.

It's very like Twilight Zone - knowing it's noon and your watch is telling you it's midnight.

I've sent the info to Garmin and will share any reply they send.
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Old 30-04-2021, 18:31   #6
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Re: Looking for an Explanation

Greetings, Redhead,

The Twilight Zone in your Garmin may be due to a gremlin. They're good at bending time and enjoy a good joke. I had one aboard my boat for a while. After it left l bought a tide clock, and am no longer confounded by anything to do with tides that is electronic. It's two clocks in one, so it even shows me what time of the day or night it is, and it's very accurate. Simple and trustworthy.

I hope Garmin sleuths out the glitch for you. Sounds like a potentially dangerous scenario you have there, but tons of fun if you can view it as a problem-solving situation. Enjoy the ride. Everything changes.

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Old 30-04-2021, 18:51   #7
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Re: Looking for an Explanation

Tide predictions are PREDICTIONS, not a schedule.....many factors can influence them, particularly persistent abnormal winds- a strong wind for a period of time can back water up in an enclosed body - water there stays high, held in by the wind, or stays low, held out, depending on which way it’s blowing. I’ve seen tides off by hours at montauk.

Your particular gap is excessive, however. What did the printed tide tables say?
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Old 30-04-2021, 21:02   #8
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Re: Looking for an Explanation

Have you cross checked it with DeepZoom Nautical Charts Tides and Currents
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Old 30-04-2021, 21:34   #9
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Re: Looking for an Explanation

Is the time zone set properly on your on your Garmin?
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Old 30-04-2021, 21:43   #10
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Re: Looking for an Explanation

The OP posted pictures of the tide predictions from his Garmin and another picture of the predictions from an Internet source. They are diametrically opposite, and the Internet source appears in concert with real-world observations. Id be concerned too. Took a look at NOAA, their predictions agree with the OPs Internet source.

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I would expect Garmin gets their harmonics from NOAA, but Id sure like to confirm that. Otherwise the Garmin harmonics file is corrupt and it is pulling and displaying data from some other station - IOW it is displaying the wrong station name for the data presented.
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Old 30-04-2021, 22:50   #11
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Re: Looking for an Explanation

Looks to me as though the Garmin is showing the tide at 05:00 with no indication if that is 12 or 24 hour tiime. Are you sure it's not 12 hours out? ( IMNSHO, using as 12 hour clock display with no indication of am/pm is a very bad idea)



The internet is showing the tide at 16:17.


Looking at the internet graph, the tide at 05:00 on that day matches what the Gramin is showing.
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Old 01-05-2021, 02:12   #12
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Re: Looking for an Explanation

I thought not 12 hrs. out, after thinking about it a bit, but more likely 6....?

Ann
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Old 01-05-2021, 04:57   #13
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Re: Looking for an Explanation

Redhead,

Im interested in hearing what Garmin says. In the meantime, can you check what sw update you have installed? They periodically issue updates on their support site.
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Old 01-05-2021, 08:49   #14
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Re: Looking for an Explanation

Quote:
Originally Posted by JPA Cate View Post
I thought not 12 hrs. out, after thinking about it a bit, but more likely 6....?

Ann
You're right 6 hours. I was so addled it didn't register. With 10 feet of draught under us I rely on this pretty heavily. I'll be using another source from now on unless Garmin gets back to me. 20 years in the air traffic control business makes me pretty adamant about having my facts straight before I leave the dock.
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Old 01-05-2021, 08:53   #15
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Re: Looking for an Explanation

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Originally Posted by StuM View Post
Looks to me as though the Garmin is showing the tide at 05:00 with no indication if that is 12 or 24 hour tiime. Are you sure it's not 12 hours out? ( IMNSHO, using as 12 hour clock display with no indication of am/pm is a very bad idea)



The internet is showing the tide at 16:17.


Looking at the internet graph, the tide at 05:00 on that day matches what the Gramin is showing.
Stu, the text screen is showing how many hours until the next low and high tides, is that what you're referencing?
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