Tide charts

[Cargile]

Just purchased a canal lot in Hudson Florida. Naturally tides are now of interest to me. I downloaded a couple of Apps from the App Store. There are negative numbers attached to many low tides. High tides are all positive numbers. What is the mean or zero around which these tides fluctuate? Thanks. Oh, also, what is your favorite tide app?

 

[Flatswing]

Reference 0 is Mean Low Water-i. e. What your charts show

 

[sjisailor]

On US charts, "0" is set by taking the lower tide on each day, over some historical period, and averaging them all. On any given day, the lowest tide may be higher than that or lower than that. See NOAA Tides & Currents for more.

In some areas the difference between chart 0 and actual low can be large. I had a marina offer me a covered slip once that had 6' depth via chart. But the area often sees -2' and -3' tides. So my 4' draft boat would rest on the rocky bottom at least 20 times a year, and I didn't want that. It is worth understanding!

As for apps, on iOS my strong personal favorite is AyeTides XL. On Android, it is eTide HDF, especially for the widgets. Most charting apps have tides, too.

 

[jleonard]

I use “ tides near me” app. I used it in new england and i use it in flory( New Port Richey).
The negative and positive numbers are feet below and above “ mean low tide” and “ mean high tide”. In other words a minus .5 low tide means it will be .5 feet lower than mean low tide plus numbers are the same for high tides.
To explain further, if you see just a tip of a sandbar normally, if the tide is minus .5 that day and time, the water eill be approximately 6 inches lower and you will see a lot of that sandbar.
Does that help explain it?

 

[Cargile]

On US charts, "0" is set by taking the lower tide on each day, over some historical period, and averaging them all. On any given day, the lowest tide may be higher than that or lower than that. See NOAA Tides & Currents for more.

In some areas the difference between chart 0 and actual low can be large. I had a marina offer me a covered slip once that had 6' depth via chart. But the area often sees -2' and -3' tides. So my 4' draft boat would rest on the rocky bottom at least 20 times a year, and I didn't want that. It is worth understanding!

As for apps, on iOS my strong personal favorite is AyeTides XL. On Android, it is eTide HDF, especially for the widgets. Most charting apps have tides, too.

Thanks. I suspected as much. Wanted to hear it from a salt.

 

[Cargile]

I use “ tides near me” app. I used it in new england and i use it in flory( New Port Richey).
The negative and positive numbers are feet below and above “ mean low tide” and “ mean high tide”. In other words a minus .5 low tide means it will be .5 feet lower than mean low tide plus numbers are the same for high tides.
To explain further, if you see just a tip of a sandbar normally, if the tide is minus .5 that day and time, the water eill be approximately 6 inches lower and you will see a lot of that sandbar.
Does that help explain it?

Thank you, That works. I have the "tides near me" app on the phone.

 

[Cargile]

On US charts, "0" is set by taking the lower tide on each day, over some historical period, and averaging them all. On any given day, the lowest tide may be higher than that or lower than that. See NOAA Tides & Currents for more........................................................As for apps, on iOS my strong personal favorite is AyeTides XL. On Android, it is eTide HDF, especially for the widgets. Most charting apps have tides, too.

Spot on! Thank you

 

[dhays]

Late response, but I believe the NOAA tide tables which provide the data for not only their tide tables but is what is used by all the typical apps show the tidal height based on Mean Lower Low Water, not Mean Low Water. This is likely not a significant difference for Florida, but can be very significant further North.

There are typically two low tides a day, a low tide and and lower low tide. NOAA uses the MLLW value for both charting and the tide tables. So the 0 tide datum is the average of all the lower low tides during the reference period. In my home port of Gig Harbor, the difference between MLLW and MLW is 2.8 feet. In Olympia at the southern end of Puget Sound, the difference is 3.1 feet.

On a related note, if you see bridge clearance heights on a chart, those heights are referenced to Mean High Water. In my area, MHW is typically around 10.5 feet. We don't have many low bridges, but if there is a bridge with a listed clearance of 20' and the tide height at the time is 8', it means that around here there will be around 22' of clearance. At a 0 tide there would be around 30' of clearance.