Near-shore tide what to expect. "Need some Guidance" - SailNet Community

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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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Old 01-06-2014
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Near-shore tide what to expect. "Need some Guidance"

So I'm as some of you know in the process of moving to the next step in my training. I'm in the planing stages of my first over-night near shore passage. I will leave early am: 4:00 with a full moon to help and head out to the "R 4" F1 R4s @ 32-05,901"N 080-35,099W this is the channel into Port Royal sound Beaufort SC.
I intend to sail out with the tide its a 19 mile ride I figure 5.5 knots of speed? That will put me there at Day break or just after 3.45 hrs.
Then run straight east for 5nm to 32-029'899N 080-29'988 W That will take a nother 90 min,
Here, I will turn south to 32-03,997W 080-29'167W 1.92 miles = 34min
Here i will turn back west to 32-03'984W 080-34'965w this 4.92 leg take .89 min
Then I will turn North to will bring me the 4.92 nm back to to the "R 4" F1 R4s @ 32-05,901"N 080-35,099W the bell marker at the mouth of the channel. Then my hope will be to take the the Tide back in.
So here is the question." If I do this near shore how much will the tide effect my timing in the course: I plugged in the 5.5 based off motor speed.
All together time from the dock and back to the dock. 10.956 hours to cover 60.26nm
How much time will the tide cost me off shore? I know a bought the tide in and out of the river. Just need help with the offshore expectation?
Thanks again. let me know if you need more information.
Cheers, LT
Near-shore tide what to expect. "Need some Guidance"
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Simple rule for tides when offshore: the tides go 'up' and 6 hours later (on the East Coast w/ diurnal tides) the tides go 'down'. When offshore you dont get the FLOW (current) of tides as you do in shallow estuaries / onshore .... and their 'hydraulic anomalies' due to land 'differences'. Once youre in more than 50-100 ft. deep water and well offshore, tides are 'inconsequential'.
The only place you need to be concerned with tides and their resultant generated CURRENTS is in Rivers, Bays, Inlets, etc. as in the 'ocean' the tide only go 'up' and they go 'down'.
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Maybe try to get a Tidal Current chart book showing tide current direction and speeds at different times. We use them all the time racing in the PONW. Very useful.
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Quote:
The only place you need to be concerned with tides and their resultant generated CURRENTS is in Rivers, Bays, Inlets, etc. as in the 'ocean' the tide only go 'up' and they go 'down'.

Except for thing called "The Gulf Stream"

I bought a place on Ladies Island and haven't had the chance to explore much beyond Port Royal Sound. The currents in the rivers and sound are significant. The distances you are talking about are pretty close to shore. I'm sure currents would be effected by the volume of water going in and out of the sound. Looking for some charting.
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

I like the detail you are taking in your cruise planning.
The best way I know of in answering your question is to refer you to the Maritime "PILOT CHARTS" here:

https://www.google.com/search?q=pilo...ih=713&dpr=0.9
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Itgoshen. Have you spent time at the inlet around posted high and low tide and observed the current? The current often lags behind the posted time for high and low. If for example you plan to be back at the inlet at posted low hoping to catch the slack and then flood up river to Beaufort you will probable be way to early and will be running against the current. I have no notes on Port Royal but that is what I have seen at other east coast inlets.
FWIW. Dan S/V Marian Claire
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Itgoshen
Be flexible, research the inlet tidal current and near shore currents, but be ready for the wind and near shore breeze to not cooperate. Have an alternate plan ready if needed.
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Something else to be aware of is that tide tables are based on algorithms (not direct observations), and are frequently off. The current will vary significantly on where you are (shallow vs deeper water) throwing another big variable in your calculations. Add to that, the surface water doesn't really start going back the other way after a tidal change for more than 1/2 an hour (in Charleston harbor, at least). Offshore, I would be willing to bet that current is downright unpredictable once you get away from a channel entrance. Sorry-- I hate to rain on your parade, but this stuff is full of all kinds of pitfalls...

Man, I hope you're not going anytime in the next few days... brrrrrr!

Last edited by Irunbird; 01-06-2014 at 08:31 PM.
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Consult Eldridge's Tide and Pilot book
www dot landfallnavigation dot com/-bp002 dot html

I am not familliar with that section of the coast (mostly I sail in New England) but Eldridge covers the entire East coast.

Also learn how to add the current vector to your course vector and plot it on a chart.

From your use of Lat Long coordinates it appears that you may be planning on relying on a GPS. That's OK, but use the marine chart, course vector and current correction as well so you have a back up. Don't rely entirely on GPS, it can go wrong for many reasons.
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Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

I also see a bigger issue. Maybe I'm just dead wrong, but if you've got a good headwind on any leg, you can expect to NOT make the 5.5 kts you're using as your rule of thumb. Sure, you might get ahead of schedule on some of the legs because of the strong wind, but once you're pushing hull speed... What kind of boat, and what kind of engine do you have again? Also, since you're assuming day break is 7:30 AM, that sounds to me like you're expecting to do this some time in the next several weeks. What time will the sun set? Are you OK getting back in the dark if something happens? If you wait a month, you might have more daylight to play with as a safety factor.
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