Near-shore tide what to expect. "Need some Guidance" - Page 2 - 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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  #11  
Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Quote:
Originally Posted by jmallett View Post
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.
I have 3
1) brand new for christmas a Garmin echo50s
2) Working Garmin 215 backup unit
3) Garmin 72 hand held.
I have been studing the charts for



Thanks for the great advise
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  #12  
Old 01-06-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

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Originally Posted by jimrafford View Post
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.
Jim
Hey and thanks Jim, We live with 10 miles of each other we should sail sometime. I have been sailing the Morgan river Beaufort River, and the Port Royal sound for a couple of years now. Light air most of the time. a lot of Shoaling. Great place to sail.

My question, Where the Port Royal Sound dumps into the Atlantic Ocean is in a south easterly direction. How far north or south would I have to run north or south of that current on a out going tide for the effects to calm down?
Thanks Curtis
S/V East Coast Lady
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  #13  
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Re: Near-shore tide what to expect. "Need some Guidance"

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Originally Posted by marianclaire View Post
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
Yes I have and I have thought something was wrong with where I get the tide information from?
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  #14  
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Re: Near-shore tide what to expect. "Need some Guidance"

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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.
Its a 1981 C&C30 MK1 with a newly installed Yanmar 2gm20D
S/V East Coast Lady
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Old 01-07-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Have you been out with 15-20 kts on the bow? What's your speed with the engine then? My boat has a fair bit of freeboard and other "windage" so we're probably not a good comparison, but our first day out of our "migration" north we had a headwind of 15-20, and we only saw 3.5-4 kts with the engine at essentially full throttle. When the wind wasn't on our nose, we were able to reach a little over 6 with the engine alone, and a little over 7 with the sails and engine employed at the same time. Of course, your boat is more performance-oriented than mine, so you will probably do better, but still...if it were me, my luck would be that the winds would be on my head on the way out, and then change to be on my head on the way in, too.
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Re: Near-shore tide what to expect. "Need some Guidance"

You may also want to read the following article
www dot ritchienavigation dot com/docs/ESRitchieLR dot pdf

It illustrates well the problem with GPS units when your speed over the ground is low (resulting from sailing at a speed close to the speed of the current). A GPS unit determines direction from position measurements. The GPS also determines the direction of movement of the boat, not it's heading, so if the current is carrying you sideways then the difference becomes obvious.

Keep a good compass on board ($50 - $80 is quite enough), cross check your heading taken from the GPS against the compass from time to time, and plot your GPS position on the chart. Any difference between compass heading and GPS will show up.

Are you single handing ? Do you have some sort of self-steering gear rigged up ? There will be times when you need, want, to take a break from helming.
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Re: Near-shore tide what to expect. "Need some Guidance"

Here is another article which may help. It explains how GPS finds direction. Because sail boats move at a slow speed (unless you are on an America's Cup team!) and because the current can be significant compared with boat speed then your movement over the ground (which is what GPS measures) can be low enough to confuse a GPS.
www dot gpsreview dot net/electronic-compass/
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Old 01-07-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Maybe you could find a local shrimp boat captain at the dock and hitch a ride with him/her for a day and document the trip with your gps? Or just ask him about the tide generated currents around the inlet.
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  #19  
Old 01-07-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Quote:
Originally Posted by jmallett View Post
You may also want to read the following article
www dot ritchienavigation dot com/docs/ESRitchieLR dot pdf

It illustrates well the problem with GPS units when your speed over the ground is low (resulting from sailing at a speed close to the speed of the current). A GPS unit determines direction from position measurements. The GPS also determines the direction of movement of the boat, not it's heading, so if the current is carrying you sideways then the difference becomes obvious.

Keep a good compass on board ($50 - $80 is quite enough), cross check your heading taken from the GPS against the compass from time to time, and plot your GPS position on the chart. Any difference between compass heading and GPS will show up.

Are you single handing ? Do you have some sort of self-steering gear rigged up ? There will be times when you need, want, to take a break from helming.
I have 3 GPs's and a binnacle compas.
I also have a auto-helm 4000 self steering that works from my GPS or from the the ST50 wind vane.
I will be single handed, however there will be a experienced sailor on board in case I need support.
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Old 01-07-2014
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Re: Near-shore tide what to expect. "Need some Guidance"

Start of Route 32.391848 -80.677071 0
Waypoint 32.377352 -80.672951 0.9
Waypoint 32.36434 -80.677199 0.81
Waypoint 32.34324 -80.661364 1.5
Waypoint 32.315354 -80.650635 1.76
Waypoint 32.260826 -80.656857 3.29
Waypoint 32.169001 -80.592828 6.41
End of Route 32.097991 -80.584931 4.29

One way =18.96 nautical miles
Total Distance: 37.92 nautical miles
37.92 / 4.5 = 8.42 hours.
do-able yes?
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