Jump to content

Current(ly) Confused - San Juans


Recommended Posts

Back in July, I spent a couple of weeks meandering around the Sound (what SHOULD have been a cruise to Desolation Sound got canned.  F'ing COVID).

But I digress.

On one of the days, I was going from Sucia, around the north-east side of Orcas to Obstruction pass.  Timed things so that I would have favorable current push (or, at the very least, not a counter-current)

The current atlas says that at 1pm on July 12th (page 38) the currents in the area should look like this:

1587207880_2020-07-121300.jpg.88d3ab9aeaf69e882a02101bc7cbda66.jpg

and should look like that for a couple of hours.  So I expected to find favorable current along the Orcas shoreline, and weak/variable counter-currents once around Lawrence point

Instead, what I got was at least a knot of counter-current along the Orcas shoreline.

Not a big deal, I mean... it's a half hour out of my life, but spent on the water on a gorgeous NW summer day.  Whatever. 

Except... nearly 2 months later it is still bugging me.  First time I can recall that - when I did my part with the tables and the current Atlas - I got something different than I expected.

What'd I do wrong?  I've double-checked that I got the right page from the tables for the right date.

Did I need to be closer to the beach to get that counter-current?  It seems like, even a half-mile off the beach, I should have been seeing (at worst) a slightly favorable push toward the beach.  Or something.  I was well inside a line from Echo to Clark the whole way. 

_/)_

Link to post
Share on other sites

I've found them to be a little either way of the chart timeline.  Especially when you have apposing in the same channel.  Depending on the size of the tide the push can be non-existent or slightly opposed.  Presidents is definitely that way as is the area around Jones to Deer Harbor.

Link to post
Share on other sites

I've found the atlases to be greatly affected by other factors like freshnet and wind. I don't have a great deal of experience in the San Juan's but in the Canadian portion of the Gulf Islands, the Georgia Strait, and English Bay I find the counter currents move around a lot and can be off by an hour or more due to wind but you can usually spot them from their anticipated location.

A lot of the time the counter currents wriggle around and you end up weaving around a bit to stay in them. In English Bay the Ebb flow is sometimes only a couple cables wide but it's going 1-3kts against the flood current the whole way out of the bay like a big snake.

 

 

Link to post
Share on other sites

If you're looking for a countercurrent, watching the tide lines can help a lot. Usually there is a pretty clear demarcation between flows, with flotsam and foam at the boundary. A couple of days ago, we went from a GPS speed of 6.3 knots to 5.2 knots in one boatlength as we went through the tide line. 

Link to post
Share on other sites

I've found the atlas to be off by as much as 2-2.5 hours in odd cases. I assume three things explain it:

Broadly, it's a guide primarily intended to show the large scale movement of the currents.

More specifically, the CHS predictions are based on modeling of only three magnitudes of tide - 3, 1.8, and 0.6 meters, if I recall. So tides that fall significantly between those ranges will have different characteristics, someone's by a significant margin. again, I assume this to be even more true for fine-grain predictions like a countercurrent along an island shore.

Last, they do not account for the seasonal pattern of the tides, such as whether a tide is a neap tide.

Additionally, the starts at the beginning and end of the tides are generally the least accurate, as CHS notes in their book. They note that the most accurate depiction of the currents just before or after the change is gained by looking comparing/combining the overlapping charts.

 

*By 'the current atlas' I'm assuming you mean current charts based on the CHS data/models (aka the classic ring bound book in English/french w a picture of a sailboat on the front and the time sequence map).

 

Link to post
Share on other sites
15 minutes ago, Breamerly said:

*By 'the current atlas' I'm assuming you mean current charts based on the CHS data/models (aka the classic ring bound book in English/french w a picture of a sailboat on the front and the time sequence map).

Yes.  This one.  With the appropriate (2020) tables.  I double-checked <lol>

496003631_currentatlas.jpg.40e255f39d9b2cfc1c85d7d0c76490a5.jpg

 

  • Like 1
Link to post
Share on other sites
1 hour ago, SASSAFRASS said:

I've found them to be a little either way of the chart timeline.  Especially when you have apposing in the same channel.  Depending on the size of the tide the push can be non-existent or slightly opposed.  Presidents is definitely that way as is the area around Jones to Deer Harbor.

Thx.  This is the first time in... decades... that I haven't found the current to match what the current-atlas indicates.  Maybe I've gotten lucky, but I've used it a lot (e.g., I love the little northeasterly-flowing counter-current along the west side of San Juan that pushes straight toward Sidney during an Ebb.)

Kinda have that "there is no Santa Claus" feeling, now.

  • Like 1
Link to post
Share on other sites
1 hour ago, climenuts said:

I've found the atlases to be greatly affected by other factors like freshnet and wind. 

Thanks.  On that day I had a 12-15k southeasterly breeze on the nose for that leg.  So there may have been more surface current than I would have otherwise expected, due to the amount of fetch from (maybe) as far away as Samish Bay.  Dunno.

And, @Ishmael, that breeze made it a little hard to see tide-lines, but you're right, they're always a good indicator.  Last weekend I came back from Ludlow and found a significant tide-line right at Possession Point.  couple hundred yards one way or the other meant the difference between 5.5k and 7.5k for the run home to Everett.

Link to post
Share on other sites
2 minutes ago, sledracr said:

Kinda have that "there is no Santa Claus" feeling, now.

Definitely felt this way myself the first couple times it happened.

another place I have found it is at the north entrance to the channel from Stuart down to Friday harbor, and along the west coast of orcas. Tide change was an hour and a half off predicted last time I was going north from Jones.

One thing you might try, if you don't already, is comparing what's in the atlas to the corrections listed in one of the better American tide books, which will typically have a list of time and current corrections for various spots including all over the islands. For fine scale predictions I find them to be more accurate.

Link to post
Share on other sites

Ho boy, the currents through that complex of islands and canyons + local weather is a complex creature.

Sometimes you'll be lucky enough to spot an eddy line. Occasionally a deadhead or floating bird will offer a clue.

I always assume a countercurrent near shore is in play. 

Link to post
Share on other sites
14 minutes ago, Breamerly said:

 comparing what's in the atlas to the corrections listed in one of the better American tide books,

yeah, I do that.  but (usually) the current atlas does a really good job of demystifying what the water is actually (likely to be) doing.

Like, figuring out, during a flood, which direction the water is actually going in Wasp or Obstruction.

  • Like 1
Link to post
Share on other sites

@sledracr In 12-15 kts of opposing wind you'd be able to see a couple knots of counter current. It would be pretty nasty chop. There's an App called PNW Current Atlas that takes the Pt. Atkinson Tide table and correlates it to the correct page on the Canadian Current Atlas automatically. I forget what it cost but it was cheap enough that I bought it. There's a free trial - my only disappointment is it doesn't show the Northern Strait of Georgia sections like the Current Atlas does.

My OpenCPN and Navionics Tides/Currents files seem to be littered with current stations all around the San Juans which I assume must be from the American predictions (no idea what the source on those are or their accuracy). It has one on the NE Orca's shoreline and one a bit further out which are showing current in two different directions (Raccoon Point and the on between Orcas and Clark Island) right around the turns but not when flow is fully developed.

 

 

Link to post
Share on other sites

I have found the same thing in the same area, like Sass noted President's channel is even worse. I end up spending 15 min looking at everything convinced I am reading something wrong, which is usually the case, but once in a while the tables are not accurate. I have never found the important areas like Cattle or Rosario to be off.

  • Like 1
Link to post
Share on other sites

Malaspina Strait is the worst, it's a total crap shoot sometimes. It seems to be somehow related to time of year, so if we're going to/from Desolation in the fall, we assume the atlas is dead wrong. It seems to be closer in summer, but not totally reliable.

  • Like 2
Link to post
Share on other sites

How big were the tides that week? This can bring surprises, with high water on one side of a pass still flooding through as the other side has started lowering. The usual countercurrents can be going the wrong way too.

Tug captains know! A great resource, if you happen to meet 'em.

Link to post
Share on other sites
On ‎9‎/‎5‎/‎2020 at 8:45 PM, blurocketsmate said:

How big were the tides that week?

I thought about that too, and the answer is.... "not that big"

Nearest station for where I was that day is Friday Harbor, and the tides were a +4.0' high at 10:45am, and a +2.63 low at 4pm.  For this area... a 1.4' swing is practically a non-event

  • Like 1
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...