WA State Nautical Charts in Flux

All paper charts across the country were discontinued at the end of last year, leaving electronic navigational charts (ENC) as the only official charts. The shapes and scales of ENC, however, have been fairly chaotic for many years, but it has been planned to change this also for many years. The change is called "rescheming," which will standardize the scales and shapes of the charts, and eventually will also standardize the depth contours. 

At present (end of Oct, 2025) most charts have been reschemed, but only a few have been “metrified” — a NOAA term meaning the depth contours have been converted to a set of standard metric values.  All ENC have heights and depths in meters already, but the all important depth contours are so far only rarely converted. 

Here is a list of references on this process:

US Nautical Charting Plan

NOAA ENC Design Handbook

Rescheming and Improving Electronic Navigational Charts

Rescheming Status

Most of the US has already been reschemed and it is finally reaching into the Pacific NW.

Here is the present state of affairs for WA state charts.

This shows all charts in all scale bands. The scales vary from 1:10,000 to 1:180,000. They include mostly legacy ENC, meaning not reschemed, and a few scale band 4 reschemed charts.

Reschemed bands are defined by

This official NOAA table uses outdated terminology in that "Usage Band" should be called "Scale Band," and "Navigational Purpose" should be called "Usage Band."  Not the end of the world; but not at all useful—a chart name USWA430M means it it is a US chart of the state of WA with a scale band of 4, a number. Usage bands was a term describing paper charts, using the same words as used now, but completely different scale ranges.

WA charts are all less than 49º Lat so new ones will all be made square with regard to distance, ie a scale 4 chart will be 0.3 x 60 = 18 nmi tall and 18 nmi wide, but it will still appear as a rectangle on a mercator chart, with the width to height ratio being the cosine of the latitude. At 47º, for example, width to height on a mercator will be cos(47º) = 0.68.

Here we can see how the legacy scales are being changed from a range of values to just 2 specific values for each band... which seems good progress, but it was not long after making that decision that NOAA decided to change these values to match the proposed new S-101 scales, which are now the new NOAA standard. 

This has meant that most of the earlier reschemed charts at 1:20,ooo and 1:10,000 (Scale Band 5) have to be redone to be 1:22,000 and 1:12,000. That is a transition now in process. The same is true for  Scale Band 4 (1:40,000 and 1:80,000 ) now getting changed to 1:90,000 and 1:45,000. This will not affect the WA charts, because that decision was made before they got to the WA charts in the first place.

The legacy column is a range of scales, but the reschemed options are just two.
See also note in above image above about Scale Bands.

Looking more closely at WA state charts by Scale Band at present:

These are Scale Band 5, which are all legacy except for along the Columbia River, which is covered by a series of 1:12,000 reschemed charts.

We have no Scale Band 6 (Berthing) charts in this region.

We have these three Legacy Scale Band 3 charts

And as of a couple months ago we now have several new Scale Band 4 charts at 1:45,000.

The four irregular shaped charts above (NW most) are the remaining legacy Band 4 we have.

_______________

Now we can get to the punch line: what will this look like sometime next year? Here is that plan for this area...

There are two chart sizes, the larger ones are 1:90,000 along the coast and west of Port Angeles, and 1:45,000 inside of PA. The smaller charts are all 1:12,000.

We see here obvious progress in chart organization, but with a potentially serious step backwards with regard to charting along the coast of Canada—implied by the gap below Vancouver Island. At present we have that coast all covered with ENC (see above) except for the area around Victoria, for which we need just one Canadian chart, CA470075. 

We are up against an IHO rule that a region of adjacent national waters can only be created by one nation, which is what left that gap in our ENC for Victoria, BC.  But US-Canadian hydrographic relations have been in question since 2020, when hydrographic data stopped being shared. So we do not know what is going to take place along that border in the future. At present, no one at NOAA answers emails presumably related to the government shut down. If we learn anything about this, we will post a note.

In the meantime, it seems valuable to download the existing ENC for all of the Strait of Juan de Fuca and San Juans that border on Canada so you have charts. Using qtVlm this is an easy task, just draw a box around the southern half of Vancouver Island and open the NOAA catalog to see what is there and to download the charts.

The charts we want to preserve for back up are: US4WA 30M, 31M, 34M (80k), and 36M (100k) plus US5WA 43M, 44M, 41M (25k)

qtVlm Training Mode — Available to all Schools

We designed the Training Mode supplement to qtVlm to be available to all schools that teach marine navigation or weather. The getting_started link explains how to install it for Mac, PC, or mobile devices — with the note that qtVlm is free for Mac or PC computers, but to run Training Mode on a mobile device requires the paid version of qtVlm mobile (iOS or Android), which as of Oct, 2025 is $49.

We recommend getting started with qtVlm on a computer, then when ready to use it underway you can wirelessly transfer all the set up information to a mobile device with its new Data Exchanger function.

In this note we will go over what is included in the Training Mode and explain how to get started using its contents. The Training Mode install does two things to your installed copy of qtVlm:

(1) Assigns several optional settings

(2) Installs several data sets for navigation and weather work

 

Assigned Optional Settings Examples

Any of which can be undone to meet user's preference.

• Changed the water color from dark blue to white. This makes a few of the weather data overlays or image overlays easier to view. 

• Minimized the toolbar icons to ones we need at first, knowing we will want to add others back later in the training.

• Choices have been assigned to dozens of other optional settings, such as extent of the COG predictor, set to start at 6 min; length of the heading line, set to start at half a mile (926m), colors and thicknesses of these two lines, depth contours that control alarms and water colors, instrument display options (size and location of selected meters, etc), and so on.  All easy to change as desired. 

Here is an example, showing optional instrument displays (qtVlm has many options for meters, dials, graphs, etc), but we start very simple for basic speed and course meters:

To see details: click it, open image in new tab, and zoom.

Install Environmental Data and Data Links

• qtVlm is an international product, so it does not come with US tidal harmonics installed. We have videos on how to do that, but we do this in advance for the  Training Mode.

• State of the art tides and currents, however, are not the NOAA harmonic values at a few selected locations, but rather the Operational Forecast System (OFS) that provides high res digital forecasts across the chart. We included two links to this live data, one for San Francisco Bay and one for Chesapeake Bay. These files provided by qtVlm also offer unique data on actual water depth at each location on the chart, which can be used for very realistic navigation simulation, plus the OFS forecasts are a way to demonstrate the limits of the harmonic predictions.

• We also include custom link to NCOM currents, which are typically better than the ubiquitous RTOFS global values for waters adjacent to the US.

• To get a quick start on weather work, we include three preloaded GRIB files: HRRR and GFS model wind and pressure data, plus the Salish Sea OFS tide and current data for the same region, so routing and simulations can be practiced.  Later users can, of course, display GRIB files from external sources or use their direct connections to XyGrib and to Saildocs from within qtVlm.

Pre Installed Charts

• qtVlm focuses on official electronic navigational charts (ENC). It has one of the best presentations of these charts of all navigation software, including the very expensive ECDIS units used on large commercial and governmental vessels. As it turns out,  qtVlm also has a state of the art built in system for selecting and downloading US charts, but to save some time several have been loaded.

• Several scales of charts in the Pacific NW are included, as well as several samples in other parts of the country to seed the NOAA catalog function for further download — of charts from your local waters, for example.

• Also included are two raster navigational charts (RNC) as samples, one for 18456TR that we use in the Starpath Inland and Coastal Nav Course and also 1210TR which is used in many of the ASA navigation courses.  The US no longer produces RNC, but other nations do, so it remains of interest to have a look at these, plus piloting exercises from nav courses can be solved with them.

• qtVlm lets users store 4 screen/chart layouts (F9, F10, F11, and F12). We have preset F9 = start up view and F10, which are sample NOAA charts on the East Coast.

Special IHO Resources Included

• The International Hydrographic Organization (IHO) creates several custom products that are useful for learning ENC. One is called ECDIS Chart No. 1. This is a set of ENC showing all ENC symbols. It is a good place to review and compare symbols. Just like paper chart symbols, some that are very similar have notably different meanings. The dozen or so ENC for this presentation is hidden in the desert near Timbuktu, Mali!  There is a mark assigned to the location so we can get there quickly from any place in the program.

Note: there are no marks in the Marks Management list in the initial Training Mode, but they are in the Archives. So open Archives and choose load into qtVlm.

• More interesting still, is the IHO has created a make-believe island group off the coast of Madagascar. The multiple ENC for this region, called Micklefirth, includes all the possible official ENC symbols, including, areas, lines, and point objects presented in a realistic setting. It is a great way to study the intended uses of the symbols. The IHO made these ENC as a way for navigation apps to check that they are presenting the symbols properly, but we can use it for whatever we like.

Owlswick Harbor in Micklefirth.

So that is most of what is included in the Training Mode. Schools can use these resources as they see best. Advanced instructors can also create their own Training Mode if they need something different.  

On the other hand, once the program is learned, which does not take long with instruction and the support resources available (Manual, Cheat Sheet, PlayList, English FaceBook), it is easy to change all the configurations, and to load all resources from built-in or primary sources.  The Training Mode is just intended to make the initial introduction a little bit easier.

Note that once the Training Mode has been loaded, the menu item shows these options:

Download and activate will take you back to the initial configuration of the Training Mode.

Deactivate closes the Training Mode but saves all the changes you have made.  You will then have the option to Reactivate Training Mode bringing back the configuration you you had, or you can then also choose to Uninstall Training Mode, which takes you back to the base configuration you had before installing the Training Mode.

Uninstall Training Mode does just that. All trainings settings will be lost and only option is to start over from scratch with a new Training Mode install from the getting_started page.

Later we will add sample videos on how we use these tools in our courses.

Here is a video illustration of the topics listed above:

qtVlm Training Mode: Overview and Content (22:10)

Shared Remote Simulation with qtVlm

A unique feature of qtVlm that is a powerful training tool is its ability to share AIS positions amongst simultaneous users. We can have, for example, three users in different parts of the world agree on a time and place to meet up for a practice sail. To do this we need to have the three (or ten!) users set up the program in the same way. Each will then drive their own boat, but see on the screen the other boats taking part.  We will turn on collision avoidance setting in AIS to see how that works as well.

We can do this with a canned environment by forcing a fixed wind and fixed current, or we can share the same model forecasts for wind and current. The Training Mode includes wind and current for a section of the Eastern Strait of Juan de Fuca, between WA state and Canada, so we will use those for the example.

These are text notes for the process, followed by a video demo of the operation. Here are the settings that need to be the same for all participants:

1) Same polar loaded. We can use the default classic 40 version.  These could be different but if we want to race it would be more interesting if all the same.

2) Same GRIBS loaded. In the Training Mode, you can load the HRRR wind in Slot 1 and the OFS current forecasts in Slot 2.

3) These environmental data overlap starting at 4/11/2025 at 15:00:00 UTC. So after loading the GRIBS, use the clock icon to set the Grib time to that value. (If needed, go to Config/General/Units, and choose UTC.) 

4) Since we are not using live data, we also need to tell qtVlm when we want to start the simulation. This is done under menu Boat/Boat Settings/Navigation Simulation Mode. Force the starting time to 4/11/2025 15:00:00 UTC.

5) It might be helpful, but not crucial, to display the Grib time slider in the Grib Config window. If it does not look like this, then something is wrong. Do cmd+I or ctrl+I to see what is loaded. 

Check in the Grib config/Corrections window to be sure you have no forced wind or current. That will override the Grib data.

6) For simulation and real sailing it is valuable to turn on the Microboard (this is not on in the initial Training Mode configuration). Menu/Config/Boat/Show microboard.

7) We might also share 3 marks to show where we should start our boats. If we are not mindful of this, we could run into each other quickly, which ends the simulation. Here is a sample. None of this has to be precise.

8) When you start the simulator, the boat will start head to wind, so it will not be moving. If you are moving, then the engine is on. Check Boat/Boat Settings/Engine and Tacks/Gybes.  Be sure both are set to 0.0.

9) We also need to set up the AIS configuration to make this work. Menu/qtVlm Config/AIS to see this:

And we need to turn on the AIS from the tool bar:

AIS icon must be green.

Then we should be ready to go, and each participant can start the simulation and it should look something like this, keeping in mind that it takes a minute or two for the actual AIS vessel name to show up.

Note in the Seattle screen above, he has a COG predictor cone turned on and we are sitting head to wind in a current, so he is drifting backwards.  All the boats are doing this, but only this one has that turned on.

In principle we could agree to a boat set up and a chart, etc. But once this is running there is much to learn and practice with.

Here is a look at the three computers running the simulation. 

Later we will discuss the various program controls we can use to optimize sailing routes.

Steering in a following current

There is a video of this article linked at the end. 

A few years ago we analyzed the grounding of the Ever Given in the Suez Canal just a few days after it happened. The results are presented in a 5-min video, followed by three support videos, one of which had to do with the effect of a following current on steerage, which was likely a factor in the event.  See discussion of tides and currents about 6 min into that video. There presented and discussed this diagram:

It shows what we mean when we say "steering is inhibited in a downbound vessel with following current."

When we turn left 30º relative to the water, we can see it on the  compass, but it is not apparent by looking at the water alone. Where we would see any change of course would be relative to, say, a rock ahead that we were turning away from. We will see that we have turned the heading away from the rock, but we will not be making good the full extent of our turn. The current causes us to lose some of the turn we made. In other words, the heading HDG (also called course through water, CTW) changes, but the course over ground (COG) changes less, which is the issue at hand. Conversely, when sailing into the current the maneuvers are enhanced relative to the ground.

Yesterday we got a call asking if this reckoning could be generalized into a formula which motivated some work on the topic.  The above diagram we got from qtVlm app using its simulator function plus a forces current function.

Here is the geometry

Vessel moving due west at 6 kts in a 3 kt following current. Then turns left 40º but only achieves a 27º turn in COG. 

Here is the trig and formula for the angle loss (beta) as a function of the turn (alpha) and the ratio of current to speed, r = C/S

We can also make a plot of the values:

For example, for r= 0.4, a 35º turn will lose 10º and you only make good 25º

Here are results as a table. Here speed over ground (SOG) is a ratio of the boat speed S.

Note in our figure above BA = SOG and we get SOG from:

Here are a couple examples from Excel:

Video presentation of the above discussion.

Symmedian point in a triangle

Some years ago we presented a procedure for finding the most likely position based on a plot of 3 lines of position (LOP).  We focused on finding that position when the random uncertainties in each of the LOPs was different, and we also added the crucial factor that there could be a fixed systematic error that applied to all triangles. We will return to that subject in the near future, with more details on the mathematics behind that solution.

In the meantime, we step back to the simpler case where the random uncertainties in all three of the lines are the same, and there is no systematic error to the set of sights—which could be cel nav sextant sights, or compass bearings, or any means of piloting that puts 3 LOPs on the chart. In this case, the most likely position is located at a very special point in the triangle called the symmedian point.

The concept of the symmedian was first reported in 1803, but  the name "symmedian" did not come about until 1883. It comes from an abbreviation of the original French name  "symétrique de la médiane," which was meant to convey "symmetrical counterpart of the median" — in that the symmedian line of a triangle is obtained by reflecting the median over the bisector. 

The discovery that this point reflects the minimum of the sum of the squares of the distances to the sides of a triangle, and thus could represent the most likely position from three LOPs, was presented in 1877 by another French mathematician, but the point had not been named at that time. 

Looking at the picture below, for any point P, there is a distance to each side of the triangle (dashed lines), and the argument is that the most likely position is where it is the closest it can be to all three sides, but since a distance can be negative outside of the triangle, the most likely position is the location where the sum of the squares of all the distances is minimum. 

One can solve for that location several ways, and always end up with the answer being the symmedian point K.

Here is an interactive online app that you can use to show that K is the minimum of the sums.

Least squares demo (to do it yourself)

Or watch this video on the process.

Navigating underway, we want to know how to find the point in any triangle of LOPs we run across. There are several ways to do this, maybe dozens! We go over here the basic method of reflecting the median over the bisector, which is all plotting, and then we combine a computation with plotting for a faster solution.

The traditional way reflecting the medians over the bisectors, but with some short cuts.

A hybrid approach of doing a couple computations first and then plot the results. 

Download the free online app that computes the distances needed.

Symmedian proportional distances computer

To get it on your phone, open that link in your phone and then share it to your home screen.

I will be back with more details on this topic as we proceed with our 3-LOPs rejuvenation program.

The app computations are based on this discovery from a German article in 1827:

Here is a form for solving the above rule by calculator:

Download a copy of the form.

Here we apply the plotting to a real cel nav sight session.

Role of qtVlm in the Starpath Coastal Nav Course

Starpath School of Navigation offers several online courses that use qtVlm for electronic chart work. 

In our Electronic Chart Navigation Course we cover qtVlm from the basics on up to advanced techniques of route planning and route safety evaluation, along with an introduction to optimum sailboat routing based on a boat's polar performance diagram and a wind forecast. We also take advantage of of its sophisticated simulation mode.  

In our Marine Weather Course we emphasize weather analysis using its sophisticated features (load multiple GRIBS, overlay images and maps, view near-live ship reports and ASCAT winds, meteograms, and more), and work on optimum sailboat routing using full environmental forecasts (wind, seas, and currents.) We also carry out simulated races where students in various locations can meet and compete in sailboat races using the same boat polars and wind, each seeing the others as AIS targets.

Our Inland and Coastal Navigation Course (ASA105), on the other hand, has a more basic, but still crucial, introduction to qtVlm, where we focus on the equivalent to paper chart plotting. The course is oriented toward paper chart navigation, as mariners would carry out using back up NOAA custom paper charts (NCC), but at the same time providing an introduction to a truly powerful electronic nav app, qtVlm. Below is a sequence of video tutorials that are limited to those applications we cover in that course, where we show that all of the traditional paper chart plotting and piloting we are accustomed to with paper charts, can be carried out more quickly and more accurately using qtVlm.  A broader range of qtVlm support can be found at starpath.com/qtVlm/#support.

If you are taking our Inland and Coastal Navigation Course, this would be the sequence to follow:

1) Install qtVlm and the Training Mode  Mac (9:09); PC (12:19)

2) Mac v. PC, chart types, 18465tr, menus, units, zooming, saved views. (13:59)

3) Compass set up, using marks, landmark searching (15:47)

4) Measure range and bearing between points (10:29)

5) Update a DR position from logbook entries (15:44) — WorkBook 5-24

6) Compass bearing fix (10:31) — WorkBook 4-9

7) Range and bearing fix (8:01) — WorkBook  4-15

8) Fix from two ranges (4:58) — WorkBook 7-5

9) Running fix (11:03) — WorkBook 6-3

10) Danger bearings (10:11) — WorkBook  6-2

11) Read Tides and Currents (past, present, and future) (23:39) — WorkBook 8-12, 8-13, 8-14

12) Find current from two fixes and DR between them (8:43) — WorkBook 9-1

13) Find CMG and SMG in a known current (7:59) — WorkBook 9-11 (A)

14) Course to steer (CTS) for desired course in known current (12:14) — WorkBook 9-2 (E)

15) Running fix with current and course changes (12:15) — WorkBook 9-14 (Errata)

          ________ How to load NOAA charts for your area ________

16) Loading NOAA Charts into qtVlm on iOS devices (5:03) 

17) Loading NOAA Charts into qtVlm on Mac or PC (7:06) 

If you are not taking our online course (sorry to hear that!), but you still want to practice with these methods, then you can work through the exercises in our Navigation WorkBook 18465Tr. This is a large set of plotting exercises that can be worked with qtVlm. The Workbook's support page provides an RNC of the needed 18465Tr.

Shapefiles for qtVlm

A powerful function of qtVlm is its ability to show shapefiles in a very convenient manner. They can even be configured to include links to live data. One example is the UK shipping forecasts that we made for qtVlm some time ago, which we put here at the top of the list.  But we need a list because there are many of these floating around that can be very useful for navigation, and I am beginning to loose as many as I find. Just found a couple neat ones for the Gulf Stream, which motivated setting up this index.

(1) UK Shipping forecasts
Note this is a special type of shapefile in that Starpath has made code that lets you get live forecasts at each zone. Normally shapefiles load static data. If we want overlays that update automatically we need to have links to images or KML files.

(2) Add elevation contours to an ENC

(3) Add north and south walls to the Gulf Stream plus Add eddies with ID 

The above Navy data were typically updated every 36 hrs, but at present (4/30/25) it is nearly a month old. So we need to keep an eye on this.  There is a lot of chaos in ocean and weather data delivery these days. A sample below:

These shape files (two are loaded here) are to be overlaid onto either the RUCOOL SST images or one of the model forecasts for the current, or overlay onto the Navy Gulf Stream Analysis to annotate what they show. These eddies will coincide exactly with what are on the Analysis maps.  Note too that these shapefiles have to be downloaded  each time they are new, which is typically every 36 hr. They are identified by day of the year, ODate, ie in 2025, 90 = Mar 31.... however, as of May 4, 2025 we are seeing only erratic updating on Navy GS products, so their fate is uncertain.

(4) Up dated US Forecast zones

Digital Soundings and Water Depths from OFS Forecasts

The Operational Forecast System (OFS) model forecasts tide height and tidal currents for 15 locations around the country — a true revolution in modern marine navigation.

What is probably less known, is that we can potentially get the actual water depths for any point on the chart from these same forecasts.  These values should match the charted soundings and depth contours—to the extent that they are right, and indeed the OFS model bathymetry data are right as well.

Plus, we have to assume that the logic presented here is valid for extracting this information. So a main reason for this post is to have a way to ask the experts if this is a sound process.

When we then add the tide heights to the digital depths we have the forecasted water depth at any point in space and time, which would be another revolution in marine navigation. The concept of digital water depth has been planned to be part of the future S-100 electronic navigational charts (ENC), but I would like to show here that this is essentially available now.

When one of the OFS forecasts in netCDF format is downloaded from the NOAA AWS server and then opened in Panoply, we see these parameters from the San Francisco Bay model (SFBOFS).

u_eastward and v_northward are the vector components of the tidal current.

zetatomllw is the tide height, which is always relative to (above) MLLW.

But we also have

h, which is the depth of the water below MSL and 

zeta, which is the depth of the water above MSL.

(The parameter called Depth is just the number of depth layers where data are provided, which is 21, from 0 to 100 m.)

The diagram below shows how these parameters are related.

There are stand alone programs such as CDO that lets users combine parameters in a netCDF file and make a new file with the new parameters. So we have experimented with the process.

It seems we can get the total water level by just adding h and zeta, since they are both relative to MSL, even though that is not a datum used for this purpose in charting.

To obtain digital values of the soundings at any point on the chart, we need the depth relative to MLLW, not the h values in the native files, which are relative to MSL. The actual charted depths will be deeper than h by the difference between MLLW and MSL. 

But we can compute that value, which varies across a chart, because it is just the difference between zetatomllw and zeta, as shown in the diagram. Since in the nautical chart world, MLLW is the sounding datum defining zero tide height, this difference is just the tide height equivalent to MSL, which is a datum that NOAA lists for each of their tidal stations.

It is presented at tidesandcurrents.noaa.gov on each tidal station's home page. Below is a sample from Redwood City, CA.

We can then make a plot of this difference in Panoply and check for what it thinks this value is at each of the locations where the value is known. That plot looks like this:

The places where MSL is known in this area are shown in this figure.

In Panoply you can interrogate a point in a plot to get location and value, which we did at each of these locations. Samples are below.

The results are summarized in this table:

The agreement is good over a fairly large range of values, so it appears that this is a valid way to extract the MSL depth from the OFS data that we can use to compute chart depth from h.

Below is an example of a custom GRIB file made in the manner described and viewed in qtVlm—a popular free nav app for Mac and PC. It shows digitized chart depths in the region of SFBOFS just outside of the Golden Gate Bridge.

This shows the depth in feet, with a color gradient background designed to match the standard depth contours on US ENC. We end up with a display that is similar to an ENC depth area object  (DEPARE), but now we have digital values of the soundings any place on the chart. The famous Four Fathom Bank (yellow patch) stands out very nicely.

It will take more testing to be sure this is a productive useful addition to our navigation. We can now display the digital soundings (chart depths) and the digital water depth, which is chart depth + tide height.

It is a promising development, and new use of the OFS forecasts, but it will take some work to test its value.

Predicting Tidal Currents in the Swinomish Channel

Historically there have been no NOAA predictions for the tidal current speed in the Swinomish Channel flowing past La Conner, WA, but local mariners know it can be strong—over 2 kts at times.

Years ago we noted that this current should be predictable from the tide difference at the north and south ends of the channel—a driving force called a hydraulic head. The current flows from the high-tide end toward the low-tide end, and the bigger that difference, the stronger the current.

There is a NOAA tide station at La Conner (#9448558), 1.4 nmi into the 6-nmi long channel from the south and another right at the north end of the channel (#9448682). Typical channel widths are 300 to 400 ft, but navigable waters are narrower—dredged to minimum of 12 ft over 100 ft width. I note that the only chart of the Channel (US5WA31M) apparently has the dredge depth wrong at 6 ft. We have reported this to NOAA.

Historically mariners did not have digital tides on board, so it was tedious to copy the tides from tidesandcurrents.noaa.gov and transfer them to a spread sheet to make the current forecasts. I am not sure that method ever caught on with local mariners; we originally worked on this for a specific Seattle to Bellingham kayak race.

Whether or not that procedure ever became popular does not matter, because we have now an all new way to get presumably good forecasts for the channel current with the click of a button, thanks to the newly available results of the Operational Forecast System (OFS) model along with also new developments in how to read that data.

The driving force of the current and the way to forecast it remains true, but we have much better data now on the actual tide heights. The Salish Sea and Columbia River OFS model (SSCOFS) forecasts the current in the channel every hour out 3 days, and the model is recomputed every 6 hr to take into account changes in local environmental factors that can have major effects on tides and currents. The big advantage of the model forecasts is they take into account local values of wind, pressure, and river runoff, which the static harmonic NOAA station predictions do not account for.  

For the moment, we can see these new current forecasts online two ways. One is the NANOOS presentation, shown below. This works great for the Salish Sea data but there are not as good IOOS presentations for the other 14 regions around the US where we have OFS predictions.

The above source is established and dependable, but NOAA has a new online viewer called OceansMap and it promises to include the currents and a lot more information, with versatile display options. As of now, it is still in beta form, so sometimes not all data are available. Also for now we can only see the time scale in EST (PST +3h).

Historically there have been several local guidelines for predicting the channel currents based on a single value of the tide height at La Conner or Seattle. Google "Current speed in Swinomish Channel" to see a few of them. And indeed some may work in some average conditions, but they cannot be dependable because of the wide range of environmental changes plus the area frequently has unusual tide patterns, such as the above example taken at random with high tide nearly all day long—essentially a diurnal pattern where it is normally semi-diurnal. 

In the picture below we used the SSCOFS data viewed in OceansMap and stepped through a days data, one hour at a time, and recorded the tide heights at the north and south ends, as well as the current near La Conner.  Then we did the old school method of subtracting the tides and plotted that along with the current.

So we see very nicely that this is the driving force of the current, which just confirms our original approach with modern data.  

But we no longer need this analysis. We just open one of the two apps above and get the current. Eventually the OceansMap will be the working tool as it has that neat meteogram optional display at the bottom that could be copied and saved in a phone.

Below are a couple more of these meteograms that compare currents in the channel with tide height at La Conner. Sometimes there is a correlation; other times not.

Earlier models of the Victoria Clipper, traveling from downtown Seattle to Victoria, BC, did sometimes transit the Channel when conditions in Puget Sound were very bad. This OFS data should make that planning better in those cases where it might come up again. The new Clippers are larger, so such careful planning is even more crucial.  

The channel has a mean tide height of 6.1 ft, with mean high water of 9.4 ft and mean low water of 2.7 ft. With dependable tide and current predictions, the Channel might be a more frequent option to Deception Pass for low-powered vessels, which then have the bonus of a visit to La Conner, which is a popular NW destination for good food, good art, and friendly people.

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For completeness, let me add that the wonderful GRIB versions of the OFS data we can get from Expedition and LuckGrib are fantastic for optimum routing over inland waters, but they must compromise on the grid size when converting the NetCDF to the GRIB format, and the resulting resolution is not adequate to use for the narrow Swinomish Channel. For this we need the two resources cited above. Also it seems Panoply which does load the full original data files, cannot resolve the data to that level either.