Low tide
- Thread starter All U Get
- Start date
https://en.wikipedia.org/wiki/Slack_water
I got in a lot of trouble a while back by suggesting a Google search, so I did this one for you.
Any reputable marine book will discuss this phenomenon.
It's one of the first things those of us who sail in tidal waters learns.
I got in a lot of trouble a while back by suggesting a Google search, so I did this one for you.
Any reputable marine book will discuss this phenomenon.
It's one of the first things those of us who sail in tidal waters learns.
Thanks Stu, but wouldn't an area go lower if the current was running away? We're in a bit of a pickle tied to a dock that is exposed to swift currents. If we wait for slack to leave the dock, we risk losing the most room under a fixed bridge because the tide is no longer low. The AICW has many rivers connected with cuts and traveling up and down this waterway doesn't necessarily mean against the current. Some days you just can't find the current in your direction. There have been times when we were in a marina aground waiting for water to flood in. So disappointing to see it ebb away. I guess you just have to see it.
All U Get
All U Get
Your description is quite clear. I sailed in San Francisco Bay and The California Delta for 35 years. One recognizes the differences between tidal heights and currents, and their times. Of course, they are listed in the great tide¤t books available in The Bay Area. Here on Vancouver Island, things are a lot more complicated, but the concept's the same.
A simple example: you use tide heights to anchor, you use currents to sail.
And they're out of whack with each other for about an hour in San Francisco. Now that spring has finally sprung up here (and I didn't sail since November) I'm learning what "The Deal" is up here by learning the HUGE book and tables that come with it.The fact that you have a bridge to deal with certainly complicates your particular issue, one which may be almost unique to your location and mast height.
The good news is that almost every place we boat has predictable tables to tell you all this. Of course, everywhere is subject to variations due to heavy rains and outflow.
Good luck.
Tides are a VERY complex interaction between the forces that create them (sun and moon) and the water and geography that they effect. While a look at an areas tidal almanac will give you and idea what the curve will look like, remember that as you say 'the water has to go somewhere'. That 'somewhere' is of course nearby, with a slightly different tidal reality.
In general, the rate of change is fastest mid tide and much less at high and low water. This creates a 'sloshing' effect that will differ based on geography.
In general, the rate of change is fastest mid tide and much less at high and low water. This creates a 'sloshing' effect that will differ based on geography.
Damage done while being towed to the dock recently. Current and wind pushing us on the dock as two center console tow boats tried to move us to a slip. That post didn't stand up to our Manson Supreme.
All U Get
Today high tide is 1:45pm , max flood is 12:20pm at the turning basin here in Beaufort, NC just for example. I have been through here a few times a
All U Get
All U Get
I started laughing when this thread started reminding me of North Carolina until you reminded me you are still in Beaufort, NC. One word of caution, do not transit the Alligator River portion of the ICW or locals call the Ditch at night. There is a Marina to the left just right past the swing bridge of the US 64 roadway. Make sure you know your wind conditions before leaving the ICW into the Albermarle Sound. Can be rough there being shallow if a lot of wind. Once on a Catalina 38 all us chummed off the stern rail. Ugh. Gusting up to 65 knots when that happened
I started laughing when this thread started reminding me of North Carolina until you reminded me you are still in Beaufort, NC. One word of caution, do not transit the Alligator River portion of the ICW or locals call the Ditch at night. There is a Marina to the left just right past the swing bridge of the US 64 roadway. Make sure you know your wind conditions before leaving the ICW into the Albermarle Sound. Can be rough there being shallow if a lot of wind. Once on a Catalina 38 all us chummed off the stern rail. Ugh. Gusting up to 65 knots when that happened
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,867
AUG,
Try DeepZoom (http://www.deepzoom.com) on a PC using InternetExplorer as a browser.
It is a bit crude (no search feature to locate map). It opens in our PacificNW. You will need to shrink the map, physically move the map to find NC then enlarge it around Beaufort. But once there you can see the tide heights and currents change graphically. It is a pretty cool software package developed by some Microsoft folks. There is an automate function, and you can move it through the year to see the info on a specific date and time (like when you are next thinking about leaving the dock).
Try DeepZoom (http://www.deepzoom.com) on a PC using InternetExplorer as a browser.
It is a bit crude (no search feature to locate map). It opens in our PacificNW. You will need to shrink the map, physically move the map to find NC then enlarge it around Beaufort. But once there you can see the tide heights and currents change graphically. It is a pretty cool software package developed by some Microsoft folks. There is an automate function, and you can move it through the year to see the info on a specific date and time (like when you are next thinking about leaving the dock).
We actually get about an hour of slack. Stuck at the dock waiting for the tide to come back in on a gorgeous day for sailing can be a real bummer.
On one of the last overnight cruises our local sailing club did, I checked the tide times, but forgot to check tide levels the night before. We got to the dock at 10:30am, expecting low tide at noon. not only were we stuck at the dock, but we did not get off until 3:00pm due to the stronger than normal tides. My boat which normally floats at our dock at low tide was listing at 10° to 15° at dead low that day. We made it to the anchorage by about 8:00pm, but had already missed entering our dish in the annual Chili Cook off. Plan ahead!
On one of the last overnight cruises our local sailing club did, I checked the tide times, but forgot to check tide levels the night before. We got to the dock at 10:30am, expecting low tide at noon. not only were we stuck at the dock, but we did not get off until 3:00pm due to the stronger than normal tides. My boat which normally floats at our dock at low tide was listing at 10° to 15° at dead low that day. We made it to the anchorage by about 8:00pm, but had already missed entering our dish in the annual Chili Cook off. Plan ahead!
I think the main reason you see this is because the tide datum is for a particular exact point. If you are several hundred yards away things will be slightly different. A mile could make a huge difference depending on the depth, narrowness of a channel or wind.
If you are exactly where the datum point is at low tide, it should be slack water. However wind, barometric pressure and rainfall can also affect these things, so it may never be exact.
If you are exactly where the datum point is at low tide, it should be slack water. However wind, barometric pressure and rainfall can also affect these things, so it may never be exact.
The tide¤t tables, for exampleThe Golden Gate, make it quite clear that this not not so.
Take a trip to the Bay model in Sausalito sometime. It's fascinating. If I remember right, they had good correlation between the two because there were no external factors.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,867
But Stu, I think that is because there are back currents (i.e deep ocean flow that starts prior to the slack of the tide leaving the bay.) that flow while the main current is reaching zero. This occurs up her in the PacNW all the time. Slack in the middle stream while reverse currents are flowing on the edgies or in eddies near bay/river entrances. Certainly the Columbia entrance exhibits this during spring river flow. In some instances the slack may be only a minute or two.
There are two reasons why there may be a difference in time between the tide height and slack water.
The first is because the water has momentum. It will continue to flow out of (for example) an estuary even after the sea level has begun to rise. (Just like a car would continue to coast up a hill)
The second reason could arise from for example a narrow waterway connecting the sea to a inland lake. The lake level would be at about the average of the sea height, so water would flow in any time until the sea was below lake level and vice versa.
To simplify thingsthe above two phenomena combine.
The first is because the water has momentum. It will continue to flow out of (for example) an estuary even after the sea level has begun to rise. (Just like a car would continue to coast up a hill)
The second reason could arise from for example a narrow waterway connecting the sea to a inland lake. The lake level would be at about the average of the sea height, so water would flow in any time until the sea was below lake level and vice versa.
To simplify things
the above two phenomena combine.
In Beaufort water is flowing through narrow canals and channels. So even when the tide peaks the water is still forcing its way up the Newport river, north river, core creek, and into bogue sound. I never see really slack water it seems like the current changes instantly but changes in strength. Also there is a rule that no matter where you are going the current will work against you :>)
High tide WHERE? If that's not calculated in the table you are looking at for the turning basin, it for sure is going to be different. That was my point.