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Old 08-12-2014, 09:50 AM   #1
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Tidal Current Prediction

On my recent trip from the Chesapeake Bay to Ocracoke, NC I needed to know the tidal current prediction for a route for planning purposes. More often than not, the current predicted by my Garmin BlueChart App running on the iPad bears no resemblance to the observed current. Instead of favoring the run, it would roar against me. The Hampton Roads Approach have currents of two plus knots, and for a boat that moves at only 6.5 knots, it is important to time it right. The Garmin BlueChart was totally useless on that count. I love it for the charting, premium weather forecast, and Active Captain.

What has been your experience with this app? Is there a better way to predicting tidal currents? Any solution that does not involve being connected to the Internet?

NDM
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Old 08-12-2014, 10:31 AM   #2
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Is there a better way to predicting tidal currents? Any solution that does not involve being connected to the Internet?
I use Aye Tides XL on my Ipad and have found it to be very accurate here in the Pacific Northwest and along the west coast. We have large tides and currents that can exceed the speed of the boat, so it is an important planning tool.
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Old 08-12-2014, 10:37 AM   #3
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Originally Posted by NDM View Post
On my recent trip from the Chesapeake Bay to Ocracoke, NC I needed to know the tidal current prediction for a route for planning purposes. More often than not, the current predicted by my Garmin BlueChart App running on the iPad bears no resemblance to the observed current. Instead of favoring the run, it would roar against me. The Hampton Roads Approach have currents of two plus knots, and for a boat that moves at only 6.5 knots, it is important to time it right. The Garmin BlueChart was totally useless on that count. I love it for the charting, premium weather forecast, and Active Captain.

What has been your experience with this app? Is there a better way to predicting tidal currents? Any solution that does not involve being connected to the Internet?

NDM
Potomac River
Why don't you call Garmin and tell them about your problem. They may have a solution or they may be glad to know about the problem so they can work on a solution.

Remember though, these are only predictions, not actual measurements so other sources may be just as inaccurate.
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Old 08-12-2014, 11:28 AM   #4
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I use OpenCPN and find it reasonably accurate...it's a free download though a pain for planning as I haven't figured out how to jump ahead easily...seems like you have to scroll through the days, not jump to a date.

Remember though that both tides and tidal currents an vary (usually only speed and rarely direction) quite a bit.

Also just being a few hundred yards from a tidal current station can change the speed quite a bit.

Running Delaware Bay is my real challenge to/from Florida. Wrong day and wrong times can double the length of the trip for my 6.3 knot boat.

Here's a link to real time current as well as other data. It gives you an idea of the predicted data accuracy and you can adjust.
http://tidesandcurrents.noaa.gov/cda...&filter=active

I sometimes take divers out that work on these current meters...pretty cool stuff.
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Old 08-12-2014, 12:00 PM   #5
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Been using tidal currents for years here in Southern California for Predicted Log contests and they are rarely correct. That's why we run the measured mile on the day of the event.
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Old 08-12-2014, 12:16 PM   #6
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Been using tidal currents for years here in Southern California for Predicted Log contests and they are rarely correct. That's why we run the measured mile on the day of the event.
In a days cruise in either the Delaware Bay/River or the Chesapeake... predicted (modified by actual) is all you really have as you may be cruising through a tidal current shift and through many areas of varying speed. Running a measured mile wouldn't tell you much in these areas.

Up and down much of the AICW...you hit a reversing current with every inlet you pass and there's usually no "real time current data"...so that is all guesswork anyhow.
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Old 08-12-2014, 12:37 PM   #7
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Originally Posted by NDM View Post
On my recent trip from the Chesapeake Bay to Ocracoke, NC I needed to know the tidal current prediction for a route for planning purposes. More often than not, the current predicted by my Garmin BlueChart App running on the iPad bears no resemblance to the observed current. Instead of favoring the run, it would roar against me. The Hampton Roads Approach have currents of two plus knots, and for a boat that moves at only 6.5 knots, it is important to time it right. The Garmin BlueChart was totally useless on that count. I love it for the charting, premium weather forecast, and Active Captain.

What has been your experience with this app? Is there a better way to predicting tidal currents? Any solution that does not involve being connected to the Internet?

NDM
Potomac River
Let's do a little test. Give us what your Garmin told you or tells you for a specific day and time, and we can match it up against another source. For instance, I show it to be slack before ebb at Hampton Roads Entrance, mid channel. right now. Max ebb this afternoon is at 3:35pm, 2.72 knots.
It may be you are not allowing for the difference between where you are and a particular station, or not interpreting the direction (set) the current will be going. In the case of the ebb, it flows 059 degrees northwest. Or the clock in your Garmin app is not set right, such as being on GMT.
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Old 08-12-2014, 12:44 PM   #8
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We keep WXTide32 on the lap top in the pilot house. It seems to be as accurate as any plus it's free.

WXTide32 - Tides and Currents for Win9x/NT
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Old 08-12-2014, 03:41 PM   #9
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I tried your test on wxtides 32. There doesn't seem to be a Hampton Roads current station. The closest was the Chesapeake Bay Entrance (Virginia) which showed the slack before ebb at about 1:00 PM today and the max ebb at 4:32 PM this afternoon at -1.8 kts.

Since your post was at 12.37 PM (all times are EDT) that was within a half hour of your reported slack. The max ebb was off about an hour and the current was about a knot less.

I have used the tide and current facility on the Raymarine chartplotters. When I can find a close current station the results seem pretty close to actual.

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Old 08-12-2014, 04:14 PM   #10
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Predictions

Tide predictions can't account for rain runoff or storm driven current.
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Old 08-12-2014, 04:17 PM   #11
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I tried your test on wxtides 32. There doesn't seem to be a Hampton Roads current station
Yes there is!

Tidal Current Predictions - NOAA Tides & Currents

All tide apps and programs use the same NOAA data base.
The OP sent me a PM, and I asked him to bring the conversation back up here. I think he may have a timing issue, or not reading set correctly. I have boated the area he is speaking of pretty extensively and have found the predictions to be spot on. As has the Navy and the large commercial shipping and marine services trade around there.
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Old 08-12-2014, 04:19 PM   #12
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Tide predictions can't account for rain runoff or storm driven current.

yep...that's why I posted the link to the real time current data..

I asked the Woods Hole guy who was there on one of the current meter maintenance dives and he said the project is partially funded by major shipping because they WANT real time current info when brining the big boys up/down these major estuaries and bays/rivers.
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Old 08-12-2014, 04:22 PM   #13
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Tide predictions can't account for rain runoff or storm driven current.
Up in the Delta, true, but in the location under discussion they won't counter the huge movement of water taking place due to the natural tide. Wind can also have an effect, maybe; I am not sure what the OP's windage and wind conditions are or were.
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Old 08-12-2014, 04:30 PM   #14
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yep...that's why I posted the link to the real time current data..

I asked the Woods Hole guy who was there on one of the current meter maintenance dives and he said the project is partially funded by major shipping because they WANT real time current info when brining the big boys up/down these major estuaries and bays/rivers.
Yeah, take a look at the Thimble Shoals station on that link. Very close to the prediction station being discussed; variances are slight.

Woods Hole? Now THERE'S some current:





Quote:
Been using tidal currents for years here in Southern California for Predicted Log contests and they are rarely correct.
That's out in the ocean, the area under discussion is more confined, and akin to say, the Golden Gate and adjacent currents in the Bay.
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Old 08-14-2014, 11:37 AM   #15
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The only time we saw a buoy leanin' like that was when the Fukashima tsunami came into San Diego bay. We rarely get any current over 1.8 knots.
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Old 08-14-2014, 11:50 AM   #16
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I should point out for those not familiar with WH, that is not a river there!

Nothing back from the OP yet. But as I think the PORTS links show, there is not an issue with timing in the predictions vs reality. And very little at all in current speed.
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Old 08-14-2014, 06:42 PM   #17
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We run 8 Predicted Log contests in San Diego Bay, and 4 off-shore. The off-shore contests have consistently better scores than the contests held in the bay as the off-shore currents are more predictable than the harbor currents. The harbor currents are effected by the configuration of the different parts of the harbor while the off-shore currents are not.
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Old 08-15-2014, 09:20 AM   #18
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There are areas on the AICW where there are no current stations or predictions because with all the inlets and rivers it's impossible to accurately predict the current.

Also, if you're just looking at your device and selecting the closest current station, the current there may be irrelevant where you actually are (or plan to be).
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Old 08-15-2014, 10:42 AM   #19
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There are areas on the AICW where there are no current stations or predictions because with all the inlets and rivers it's impossible to accurately predict the current.
I'm trying to think of some place that is applicable. In our several trips the length of the ICW, can't recall off hand a place like that. Example?
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Old 08-15-2014, 10:58 AM   #20
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I find Jeppesen Plan2Nav tide predictions more or less correct for the upper bay.
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