Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 12-08-2011, 20:35   #1
Registered User

Join Date: Jul 2011
Location: WA
Boat: Small and simple, under 30'
Posts: 70
Current Station Calculation Errors

I'm doing a comparison of open CPN and some other navigation software to check current and tide station accuracy. One problem I found is that the current station reading does not seem correct.
The area I am checking is the mouth of the Columbia River in Oregon. The Tongue Point current station. Here are my preliminary readings:

Open CPN 2.5 = .90 kt
Polar View = 1.5 kt
Chart Navigator Pro = 1.55 kt

These were all taken at the exact time and date.

From this data it would seem that open CPN is calculating a lower current speed. Its not much, but any error could be dangerous, especially in this waterway. I will re-check these readings when there is a dangerous bar condition on an outer current station and see if the diferences are the same. I will do more testing and also compare with real time NOAA data.

Maybe I am doing something incorrectly with open CPN or possibly the tide and current formulas need to be updated.

Any ideas?
__________________

__________________
A little boat will go a long way...
Piney is offline   Reply With Quote
Old 12-08-2011, 20:53   #2
Registered User

Join Date: Jul 2011
Location: WA
Boat: Small and simple, under 30'
Posts: 70
Re: Current station calculation errors ??

Iím also getting huge inconsistencies with tide data in the same area. In fact, Tongue Point shows two tide stations right next to each other one with 1.8ft and the other with 4.1ft. Something is definitely wrong here.

Actual NOAA tide data show 1.8 feet, so the 4.1ft is not right..
__________________

__________________
A little boat will go a long way...
Piney is offline   Reply With Quote
Old 13-08-2011, 03:27   #3
Registered User

Join Date: Dec 2005
Location: WNA
Boat: Dufour 35
Posts: 3,247
Re: Current station calculation errors ??

A general overhaul of the tidal data, format and code is on the board for one the next development series. OpenCPN is not using the latest Harmonics from NOAA, and updates are far from trivial the way things are presently.
Looking at the max and min currents at a given day I cannot find any big differences, but it is possible that intermediary values shows bigger discrepancies. It is difficult to check what you are saying as you don't give any time for your data. It would also be interesting with a reality check, even though this is not so easy to check.

Looking at the Tongue Point tides I have a better idea of what' going on
During a cleanup of the tidal data it showed up that Tongue Point had two sets of data on top of each other, one probably "official" and one locally contributed. Which one do I choose, as an "outside" observer with no experience of Columbia River? My solution was to slightly separate the two sets of data for the same station, so both could be seen in OpenCPN, and then wait for local input. Someone had to react, both values can't be correct(both could be wrong, though).

The question is which is correct? "Oregon" or "Oregon (3)" ?

Generally, I'm surprised how little local US tidal input there has been from users, considering similar cases to Columbia River. How many users are actually using the tidal predictions in OpenCPN?

Thomas
__________________
cagney is offline   Reply With Quote
Old 13-08-2011, 10:29   #4
Registered User

Join Date: Jul 2011
Location: WA
Boat: Small and simple, under 30'
Posts: 70
Re: Current Station Calculation Errors ?

Thanks for looking into this Thomas. I am glad you are aware of this issue.

If there is anything I can do to help with this stuff please let me know. I am not a coder, but I have lots of access different navigational software and data. I can also help test and verify local tidal and current data. (OR, WA and the Puget Sound area)

Thanks again for your hard work with Open CPN.
__________________
A little boat will go a long way...
Piney is offline   Reply With Quote
Old 14-08-2011, 07:42   #5
Registered User

Join Date: Mar 2010
Location: Wandering around North America
Boat: Defever 43 - Gray Hawk
Posts: 602
Re: Current Station Calculation Errors ?

I've noticed the same thing along the BC coast - sometimes 2 tide stations close to each other with significantly different predictions, sometimes conflicting current predictions. Personally I'm inclined to trust nothing - when I run into this situation I consult Ports & Passes and then I assume that even if they all agree all of the information might be wrong. We saw a situation at Hole in the Wall this spring where Fugawi, OpenCPN and Ports & Passes all agreed on the current change and all were out by at least an hour.
__________________
bobofthenorth is offline   Reply With Quote
Old 14-08-2011, 08:42   #6
Registered User
 
HappySeagull's Avatar

Join Date: Dec 2010
Location: B.C.,Canada
Boat: 29'
Posts: 2,395
Re: Current Station Calculation Errors ?

Quote:
Originally Posted by bobofthenorth View Post
I've noticed the same thing along the BC coast - sometimes 2 tide stations close to each other with significantly different predictions, sometimes conflicting current predictions. Personally I'm inclined to trust nothing - when I run into this situation I consult Ports & Passes and then I assume that even if they all agree all of the information might be wrong. We saw a situation at Hole in the Wall this spring where Fugawi, OpenCPN and Ports & Passes all agreed on the current change and all were out by at least an hour.
Good oh!
when you spot these,please take a note and post em..particularly as you have in the last,of stations conflicting with whatever data you are using and the date.
The current and tide stations in this area are rooted from two sources(into xtide)...
One is from the Americans,the NOAA,the other is from a Canadian.The Canadian current stations are few (as in the CHS tidebook).I would like to have these IN CAPITALS...the American NOAA ones pop up in many places-in some cases they duplicate Canadian stations but with a different source harmonic ...
You are likely aware that publications describing themselves as Canada Tide Tables may also be using NOAA data ...personally,I'm a fan of CHS tidebooks but I like the extra stations too,if they can be shown to be accurate.
If you find that "hour" as a consistent error,it could be a time zone problem in the harmonics or your computer.
and then there's the fact that big runoffs and rains WILL throw out any current tables,particularly in the area you mentioned this spring might be an excellent example,increasing as to ebb,reducing and delaying the flood...at least on the surface depths

the Canadian tides are a bit odd alright,because there are metric and foot calculations...the bars have often been placed atop each other so only one may show.I mean to separate these to keep visiting Americans and Euro's happy .
again,anomalies you see will be interesting in the detail.
__________________
HappySeagull is offline   Reply With Quote
Old 14-08-2011, 10:42   #7
Registered User
 
HappySeagull's Avatar

Join Date: Dec 2010
Location: B.C.,Canada
Boat: 29'
Posts: 2,395
Re: Current Station Calculation Errors ?

PS..
The traditional Canadian tide book can be downloaded as a pdf nowadays for free.

CHS - PDF Files
Note that these are not corrected for Daylight savings...."Z+8"
I just quickly checked O's Hole-in-the Wall for Today versus CHS tide book.It seems to be right on within minutes...which is only as good as an armchair can be....Note those anomalies!I wonder if anybody passes them on to CHS or the NOAA.They might like em too..!
__________________
HappySeagull is offline   Reply With Quote
Old 16-08-2011, 10:02   #8
Registered User

Join Date: Jul 2011
Location: WA
Boat: Small and simple, under 30'
Posts: 70
Re: Current Station Calculation Errors ?

It would be great if somehow this information could be incorporated and updated within Open CPN.

Advanced Hydrologic Prediction Service: Portland: Columbia River at Tongue Pt near Astoria

or

http://www.ndbc.noaa.gov/station_page.php?station=46029


In Astoria, knowing the exact tide and current data is essential to safely crossing the bar in a small, slow boat. Especially in the winter months.

Maybe a plug-in that would allow a user to set up custom real time bouy, tide, current station data for thier area? This would be excellent for planning. Of course they would need an internet connection.

I sometimes go through my cellphone to check real time data once leaving the wi-fi of the marina.
__________________
A little boat will go a long way...
Piney is offline   Reply With Quote
Old 16-08-2011, 10:34   #9
Registered User

Join Date: Jul 2011
Location: WA
Boat: Small and simple, under 30'
Posts: 70
Re: Current Station Calculation Errors ?

I was just thinking... This info can already be incorporated through the "links" portion for marks..

The more I learn open Cpn, the better it gets..
__________________
A little boat will go a long way...
Piney is offline   Reply With Quote
Old 16-08-2011, 11:06   #10
Registered User

Join Date: Oct 2006
Location: Parry Sound Ontario
Boat: Irwin citation 40 "Southern Toy"
Posts: 169
Re: Current Station Calculation Errors ?

well well electronics cannot predict currents,other than average .Current is dependent on tides(fairly predictable)Not predictable is wind and precipitation and they can make a huge difference so the best predicter is the captains eyeballs wawes show current and depht enough to tell you wether or not to cross the bar,sea boys and channel markers show even light currents and directions so i use the electronics for rough guide in planning only Ole
__________________
olepedersen is offline   Reply With Quote
Old 16-08-2011, 11:43   #11
Registered User

Join Date: Jul 2011
Location: WA
Boat: Small and simple, under 30'
Posts: 70
Re: Current Station Calculation Errors ?

I agree.. the captians eyeballs are the best predicter, but knowing the timing of the tide cycles is also very helpful.
Timing is everything on the river, both when crossing the bar and using the flood and ebb to save time and fuel when heading up or downstream. In a 6kt boat, a few knots either direction make a huge difference..
__________________
A little boat will go a long way...
Piney is offline   Reply With Quote
Old 16-08-2011, 12:42   #12
Registered User
 
HappySeagull's Avatar

Join Date: Dec 2010
Location: B.C.,Canada
Boat: 29'
Posts: 2,395
Re: Current Station Calculation Errors ?

Quote:
Originally Posted by Piney View Post
I was just thinking... This info can already be incorporated through the "links" portion for marks..

The more I learn open Cpn, the better it gets..
good thinking,Piney!I wish that were a little better implemented...
__________________

__________________
HappySeagull is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale: Davis Vantage Pro2 Wireless Weather Station capval Classifieds Archive 0 08-08-2011 16:05
Current and Tides dockgoody Our Community 3 11-07-2011 21:41



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 17:19.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.