High or Low Tide?

[av8er23]

I always have trouble remembering the most favorable time to dive Jetties. Is it low or high tide. I was thinking about diving St. Andrew Bay Jetties in Panama City, FL on May 12th SA.


Tides for St. Andrew Bay Channel entrance starting with May 11, 2007.
Day High Tide Height Sunrise Moon Time % Moon
/Low Time Feet Sunset Visible

F 11 Low 1:44 AM 0.0 5:52 AM Rise 2:19 AM 42
11 High 5:08 PM 1.0 7:27 PM Set 1:59 PM

Sa 12 Low 1:36 AM 0.4 5:51 AM Rise 2:51 AM 31
12 High 8:47 AM 0.8 7:27 PM Set 3:04 PM
12 Low 2:58 PM 0.5
12 High 8:55 PM 0.7

Su 13 Low 12:20 AM 0.6 5:51 AM Rise 3:24 AM 20
13 High 7:41 AM 1.1 7:28 PM Set 4:11 PM
13 Low 4:08 PM 0.1

M 14 High 7:28 AM 1.4 5:50 AM Rise 3:58 AM 11
14 Low 5:06 PM -0.2 7:29 PM Set 5:21 PM

 

[rawls]

I would say slack tide.

 

[serambin]

No, No, go on the end of ebb tide. Then you go by the bridge pylons at 3 knots and when the tide changes, you go back by them at . . . yes, 3 knots. The greatest advantage in this is that if you see a pampano, there is no way you can shoot him, at 3 knots, you can hit him with a 105mm cannon.

Stan

 

[mike_s]

You want "High Slack Tide"

For the saturday you've chosen 8:47am.

Check to see when the gates open. I can't remember at St Andrews if they open at 8am or 9am.


Why High slack instead of Low slack?

At high slack tide all the water in the channel is fresh pulled in from the ocean.

At low slack tide all the water is a mix of freshwater and salt (or brackish) from the bay and also may contain silt stirred up from the bay. Your vis will be greatly reduced.

 

[rawls]

You want "High Slack Tide"

I agree with you 100% Mike...

 

[String]

Diving at low tide generally can mean lower visibility as sediment from inland is being sucked out to sea (high tide meaning clearer water pushed in).

Look up "Rule of 12ths" for tide - that'll tell you when the movement is highest, depth and so on. Its useful to know.

Must be said though, thats a fairly small tide.

 

[av8er23]

Diving at low tide generally can mean lower visibility as sediment from inland is being sucked out to sea (high tide meaning clearer water pushed in).

Look up "Rule of 12ths" for tide - that'll tell you when the movement is highest, depth and so on. Its useful to know.

Must be said though, thats a fairly small tide.

What do you mean by rule 12ths? What kind of change takes place on a strong tide?

 

[String]

12s mean firstly you can predict the depth of the site for a specific time, also you can estimate the water movement (ie current flow) for a given time as you know the rate of raise.

Its useful for working out what period a site will be diveable and how deep it'll be when you actually arrive. (especially with 7m/21ft range).

rule of 3rds also useful for tidal flow.

 

[av8er23]

String, that makes some sense but would you mind explaining a little more in depth?

 

[Charlie99]

Just google on "rule of 12ths". It is simply a way of estimating the water level for intermediate times between high and low tide.

It assumes that the water level has the normal sinusoidal height vs. time curve.

To understand it, just look at a normal clock, imagine that high water is at noon and low water is at 6PM. The change in the height of the tip of the hour hand is also sinusoidal and is a pretty good approximation of the water level. Ignore the side to side horizontal movement of the tip of the hour hand and look only at the vertical motion, and you can easily see that the height of the hour hand changes more rapidly around the 3PM point and has very little vertical movement around the Noon and 6PM points.

A reasonable estimate of change in height of the water is that during the first hour after high tide, it falls 1/12th of the distance to low water. 2/12ths in the 2nd hour. 3/12th in both the 3rd and 4th hours, 2/12th in the 5th hour, and only 1/12th drop in the last hour before low tide.