PNW conflicting current & Tide data - SailNet Community
Reply
 
LinkBack Thread Tools
post #1 of 12 Old 06-17-2011 Thread Starter
Hmmm
 
Bilgewater's Avatar
 
Join Date: Jul 2008
Location: Campbell River, British Columbia
Posts: 514
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
PNW conflicting current & Tide data

I've known this for quite a while but I thought I would post the data I have come up with for tomorrows currents at Sechelt Rapids and all the conflicting data. It happens that I have to take my work boat through there at full ebb and it's running pretty good at that time so I went through all my normal tides and current sources and here is what I come up with.

Sechelt Rapids - Current data - Saturday June 18th 2011

Nobeltec Tides and Currents Pro (laptop software)
Max 12:48 - 8.1 Kt ebb
Slack 16:24

CHS - Canadian Hydrographic Service (publication)
Max 12:53 - 11.6 Kt ebb
Slack 16:43

Aye Tides App (iPhone app)
Max 13:10 - 12.19 Kt ebb
Slack 16:41

Tide App (iPhone app)
Max 13:11 - 12.19 Kt ebb
Slack 16:41

Ports & Passes (publication)
Max 12:54 - 11.6 Kt ebb
Slack 16:43

Navionics (iPhone chartplotter app - embedded tides and currents data)
Max 12:50 8.12 Kt ebb
Slack 16:27

OpenCPN built in tide & current tables (Is not corrected for DST)
Max 12:11 + 1hr - 12.19 Kt ebb
Slack 15:39 + 1 hr

It's not just these rapids I get these wide variations, sometimes they're pretty close but in this case we have a variation of 4.09 kts. and I've seen a greater variation but this is quite substantial. Obviously if it's a critical crossing, I trust CHS or Ports and Passes but I use the others quite regularly for convenience purposes. In any case, on a large tide the numbers can be quite misleading in some cases.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Impulse III
Truant Pilothouse

Last edited by Bilgewater; 01-15-2012 at 10:14 PM. Reason: Added OpenCPN data
Bilgewater is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 12 Old 06-17-2011
the pointy end is the bow
 
erps's Avatar
 
Join Date: Aug 2006
Location: La Conner, Washington
Posts: 6,261
Thanks: 2
Thanked 27 Times in 26 Posts
Rep Power: 11
   
Wow. There is nearly twenty minutes difference in the listed times for slack and a 50% difference between 8 knts and 12 knts for the predicted ebbs. Must be the new fuzzy math they're teaching in schools?

Ray
S.V. Nikko
1983 Fraser 41
La Conner, WA


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Boating for over 25 years, some of them successfully.
erps is offline  
Quote Quick Reply Share with Facebook
post #3 of 12 Old 06-17-2011
Courtney the Dancer
 
jrd22's Avatar
 
Join Date: Nov 2000
Location: San Juan Islands., WA, USA
Posts: 3,917
Thanks: 4
Thanked 26 Times in 25 Posts
Rep Power: 16
 
Well at least now I can blame bad data if I forget that all the Canadian tide books are listed in standard time, not daylight saving time:-))
Thanks for the heads up Steve!

John
SV Laurie Anne

1988 Brewer 40 Pilothouse

jrd22 is offline  
Quote Quick Reply Share with Facebook
post #4 of 12 Old 06-18-2011 Thread Starter
Hmmm
 
Bilgewater's Avatar
 
Join Date: Jul 2008
Location: Campbell River, British Columbia
Posts: 514
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
Ya, this is pretty crazy data for sure. I never really knew why CHS publishes the listings in Standard Time but Ports & Passes (a Canadian publication and my personal favorite) are corrected for DST and I also think they might get their data through CHS.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Impulse III
Truant Pilothouse
Bilgewater is offline  
Quote Quick Reply Share with Facebook
post #5 of 12 Old 06-18-2011
Senior Member
 
blt2ski's Avatar
 
Join Date: May 2005
Posts: 7,122
Thanks: 1
Thanked 40 Times in 39 Posts
Rep Power: 13
   
I wonder if some are going by old ave data, or some might be going be past years what they think will happen based on ave data. OR maybe they got together and had a beer and some one said "here hold my beer while I throw a dart at the target for an answer!"

I am sure some of this is a best guess estimate, but some has to be based on some kind of know science as to what has or is happening in the universe. I am sure some variations will occur due to larger than normal spring runoffs as we are having right now too. One would hope that those variations would not get into the future swags as to what is going to happen. South where I am, there are some pass's that one end will vary max wise vs the other by 15-20 min, and be greater on one end than the other, slack will be sooner vs later.

marty

She drives me boat,
I drives me dinghy!
blt2ski is offline  
Quote Quick Reply Share with Facebook
post #6 of 12 Old 01-15-2012 Thread Starter
Hmmm
 
Bilgewater's Avatar
 
Join Date: Jul 2008
Location: Campbell River, British Columbia
Posts: 514
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
I updated the OP to include the OpenCPN PC & Mac chartplotting application's built in tide & current table data. OpenCPN was updated July 27 to V2.50 along with the tide/current data.

Steve


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Impulse III
Truant Pilothouse
Bilgewater is offline  
Quote Quick Reply Share with Facebook
post #7 of 12 Old 01-16-2012
Senior Member
 
jackdale's Avatar
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 9,145
Thanks: 29
Thanked 68 Times in 63 Posts
Rep Power: 8
 
Quote:
Originally Posted by seayalatermoonglow View Post
Ya, this is pretty crazy data for sure. I never really knew why CHS publishes the listings in Standard Time but Ports & Passes (a Canadian publication and my personal favorite) are corrected for DST and I also think they might get their data through CHS.
An oldy but goody.

Standard time is used with the Z difference noted because ocean going vessels use UTC.

The first time I used Ports and Passages there was a discrepancy between it and CHS numbers. I use CHS tables. I also have OpenCPN on the netbook and Navionics on the Android phone.

I also use a form to make calculations for secondary ports and stations. As I head for the Yucultas or Beazley Pass / Upper Rapids (or any other pass) these are posted on the walls near the nav station. I also use one for tides.

They are posted here

Swiftsure Sailing Academy

__________________
ISPA Yachtmaster Ocean Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)

Last edited by jackdale; 01-16-2012 at 12:46 AM.
jackdale is offline  
Quote Quick Reply Share with Facebook
post #8 of 12 Old 01-16-2012 Thread Starter
Hmmm
 
Bilgewater's Avatar
 
Join Date: Jul 2008
Location: Campbell River, British Columbia
Posts: 514
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
Quote:
Originally Posted by jackdale View Post
An oldy but goody.

Standard time is used with the Z difference noted because ocean going vessels use UTC.

The first time I used Ports and Passages there was a discrepancy between it and CHS numbers. I use CHS tables. I also have OpenCPN on the netbook and Navionics on the Android phone.

I also use a form to make calculations for secondary ports and stations. As I head for the Yucultas or Beazley Pass / Upper Rapids (or any other pass) these are posted on the walls near the nav station. I also use one for tides.

They are posted here

Swiftsure Sailing Academy
Good work sheets Jack...Thanks

Speaking of secondaries, for those using "Ports and Passes" there are links/downloads for extra tables on their website which are not included in the printed publication: Downloads from Ports and Passes
They have some secondary tide and current tables, including Malibu Rapids "tides (not current)", Hole in the Wall "current", Nahwitti Bar "current", Second Narrows "current" and numerous others up and down the coast.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Impulse III
Truant Pilothouse

Last edited by Bilgewater; 01-16-2012 at 12:18 PM.
Bilgewater is offline  
Quote Quick Reply Share with Facebook
post #9 of 12 Old 01-16-2012
I don't discuss my member
 
zz4gta's Avatar
 
Join Date: Aug 2007
Location: Chesapeake Bay
Posts: 2,550
Thanks: 0
Thanked 33 Times in 33 Posts
Rep Power: 9
 
On the Ches Bay tides and current can vary from dead on to 2-4 hours off. I've been in an overnight race where the flood never showed up. Tides are from the moon, Currents are what you see on the water. They don't always match up.

Merit 25 # 764 "Audrey"
zz4gta is offline  
Quote Quick Reply Share with Facebook
post #10 of 12 Old 01-16-2012
Over Hill Sailing Club
 
smurphny's Avatar
 
Join Date: Feb 2009
Location: Adirondacks NY
Posts: 3,645
Thanks: 90
Thanked 108 Times in 105 Posts
Rep Power: 8
 
Seems to be a pretty common problem that published data is not what happens with tides and currents. I contacted Eldridge last summer about a discrepancy around Fishers Island here in the NE. I wasn't even cutting it close and wound up bucking 2 knots for 2 hours. They were interested in the info but indicated that a lot of the current data was compiled a long time ago and that the coastal survey was due to be reassessed soon. So I guess there is no good way to predict with any accuracy unless you've been nearby for a few days and become tuned to the tides. This is too bad because we sailors really depend on going with the current. I don't know about anyone else but I base most of my departure times on current information. The sunset picture in my page is close to where the discrepancy occurred:-)

Alberg 35: With a philosophical flourish Cato throws himself upon his sword; I quietly take to the ship.

Last edited by smurphny; 01-16-2012 at 04:51 PM.
smurphny is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Online Tide and Current charts paris General Discussion (sailing related) 6 08-10-2010 05:20 AM
Canadian tide/current tables Faster General Discussion (sailing related) 4 03-24-2010 05:45 PM
How to find tide current direction? eamnesia Seamanship & Navigation 19 08-28-2007 08:23 PM
Wind vs Tide/Current Hyperion Learning to Sail 7 07-07-2007 08:20 PM
Need help, please with tide/current issue FrankLanger Seamanship & Navigation 9 06-28-2006 06:23 PM

Posting Rules  
You may post new threads
You may 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome