PNW Current Charts Question

[TylerFromEverett]

Hello,

What are fellow PNW boaters using your track current speed and direction? I’ve been using https://www.deepzoom.com/ and I like that it shows the directional flow and speed of currents at certain times. It’s helpful as we’re in a 21. That said, I feel like it’s not always accurate. For example, it shows slack tide at Deception Pass at 12 noon this Thursday, but my tide book calls it at around 3 pm. Would love some other pro tips from some of the seasoned vets on here.

Thanks for your time,
Tyler

 

[Ken W]

Assuming that you have a Garmin chart plotter, you might consider the Garmin Active Captain app on an iPad or equivalent. You can download charts, pick a spot on the chart and it will display tides and currents.

 

[Brian98133]

Good to see you again, Tyler. I, too, have been wondering about something more accurate!

I was quite surprised that my Garmin's currents showed a northerly current pushing through Agage Passage last week (20th about 3pm) when I knew that we were in a flood stage, which would mean a southerly push through the passage. :shock:

My plotter showed a yellow arrow which indicated (when I hit info) 1.6Kts northerly. I knew differently, but wanted to go through Agate anyways. When I passed through (northbound), there was indeed a heavy southerly flow. I would estimate about a 2-2.5Kt southerly flow. Quite different from my Garmin's indication! :?

Maybe there's a setting of which I'm not aware? My time of day and tide chart were correct....

:?:

 

[oberrys]

Have you compared the Garmin data to the NOAA Tides and Currents Maps for your region?

https://tidesandcurrents.noaa.gov/noaac ... ions?g=698

You can create your own local charts and take a paper copy with you - useful if your Garmin gives out.

I also use the TideGraphPro app on my iPad.

https://www.tidegraph.com/page-home.php

Shaun

 

[Wee Venture]

The gold standard for tides and currents in the Northwest IMO is the Ports and Passes book published by Mark Bunzel and the Waggoner Cruising Guide people. We buy it every year and wouldn’t go cruising without it (at least not very far). I also use the Navionics app on my iPad, which has arrows right on the chart which give currents and tides for any given day and time. And I have to say, I also find the Garmin chartplotter to be pretty accurate. There have been times when I have thought each of those sources was wrong but in almost every case it was “operator error” (mine). For example one time I checked Ports and Passes for Dodd Narrows right after crossing the Georgia Straight and determined I had just enough time to make slack current through the pass, saving us an overnight in Nanaimo. Turned out I got a wilder ride than I expected...and then realized I was looking at the “AM” slack and not the “PM”!

I did just check all three sources regarding the previous posts on Agate Passage for August 20 at about 3:00 p.m. (southerly flood) and Deception Pass for August 27 at noon, and they all do agree. One confusing thing that has tripped me up in the past, though, is that on the Garmin screens for currents and tides, there are numbers at the top with labels such as “Slack” and “Max Flood.” These numbers look as if they represent “time of day” but actually they are hours and minutes from the current time (or the time that you have selected on the chart) to the event. So if you have selected “Current Date and Time” and Slack shows as “1:20”, it doesn’t mean that slack will be at 1:20 p.m.; it means that slack will occur one hour and twenty minutes from now. I wish they would make that more clear.

John

 

[Red Raven]

Like John I have found the Garmin chartplotter tides and currents to be pretty accurate. One thing to note is that in all these tools they are predictions only based on the sun and moon positions and under nominal weather conditions. Local weather effects like a storm surge, excessive rainfall from nearby rivers etc., will sometimes significantly effect the actual tides and currents and the time of flood, ebb, and slack.

Note also that not all are adjusted for daylight savings time. Navionics specifically notes that it does not adjust for daylight savings time. Regardless, in the case of Navionics I have found pretty good agreement with the Garmin info in the Salish Sea. Perhaps the note regarding lack of daylight savings time adjustment is old? In Alaska, our Garmin and Ports and Passes matched fairly well while Navionics was regularly off.

I have always assumed that they all draw data from the same sources NOAA, and Fisheries and Oceans Canada. Not sure why the different apps disagree and not all stations are available on each. The bottom line is that If critical I check multiple sources and trust Ports and Passes the most.

Curt

 

[Brian98133]

I did just check all three sources regarding the previous posts on Agate Passage for August 20 at about 3:00 p.m. (southerly flood) and Deception Pass for August 27 at noon, and they all do agree. One confusing thing that has tripped me up in the past, though, is that on the Garmin screens for currents and tides, there are numbers at the top with labels such as “Slack” and “Max Flood.” These numbers look as if they represent “time of day” but actually they are hours and minutes from the current time (or the time that you have selected on the chart) to the event. So if you have selected “Current Date and Time” and Slack shows as “1:20”, it doesn’t mean that slack will be at 1:20 p.m.; it means that slack will occur one hour and twenty minutes from now. I wish they would make that more clear.

John

Thank you all for your great input and links, etc.! I caught on to the 'time issue', where the chart shows time-from, and not time of day. It seems odd to do it that way, but once you know, it's easy to store that info in my little noggin. 😎

In my case, the discrepancy came in the form of the yellow and red arrows that show direction (and speed if you touch said arrow) because I have 'currents - animated' turned on in my plotter. TBH, I had not checked the current table, just referred to the arrows... which were pointing north when the flow was definitely southerly.

I'm not at the plotter now, so apologies if any of my references are off... but next time on the water, I'll be checking my plotter against the previously listed links and see which one is more accurate.

 

[Wee Venture]

In my case, the discrepancy came in the form of the yellow and red arrows that show direction (and speed if you touch said arrow) because I have 'currents - animated' turned on in my plotter. TBH, I had not checked the current table, just referred to the arrows... which were pointing north when the flow was definitely southerly.

Interesting. I see now that your previous post did refer to an arrow. I do not have currents-animated turned on in my chartplotter and actually have never used it. Maybe I should try it out sometime. I have noticed the words, “Current” and “Direction” listed together on my Garmin chart as I am cruising. It lists a “heading” for direction of current but always seems to say “0.00” for speed though so I have stopped paying attention to it.

One other addendum: while I have found the Garmin tides and currents window to be pretty accurate, there can be small discrepancies which at times can be significant. When traveling north from Desolation Sound through Dent Rapids, I found a discrepancy of 15 to 20 minutes for time of slack between Garmin and Ports and Passes. This particular rapids is one where you do not want to get the timing wrong. I went with Ports and Passes and it proved to be correct.

John

 

[johnbenj]

One confusing thing that has tripped me up in the past, though, is that on the Garmin screens for currents and tides, there are numbers at the top with labels such as “Slack” and “Max Flood.” These numbers look as if they represent “time of day” but actually they are hours and minutes from the current time (or the time that you have selected on the chart) to the event. So if you have selected “Current Date and Time” and Slack shows as “1:20”, it doesn’t mean that slack will be at 1:20 p.m.; it means that slack will occur one hour and twenty minutes from now. I wish they would make that more clear.

This is incredibly helpful to me!

John