Wednesday, December 14, 2016

NPR lets slip poor reporting of the El Faro case started by the AP

In yesterday's news report, NPR carried on a policy that we see in many news broadcasts these days. Namely, one reporter from the agency quoting another reporter from the same agency as their source, which, in itself, is sad enough.

In this case, NPR reporter Rebecca Hersher presented this: 

"As NPR's Greg Allen has reported, Davidson was an experienced captain: When he left port on Tuesday in the El Faro, Joaquin was a tropical storm, not a significant concern. On early Thursday when he made the radio call to the company, Davidson said the ship was listing to one side, had lost its propulsion, was taking on water."

It sounds like she is relaying an evaluation of an NPR reporter, Greg Allen, about the situation, i.e., when they left port, Joaquin was not a concern. Or maybe he is putting words into the mouth of the deceased captain? In any event, this statement is tragically misleading and inappropriate. 

It is true that when they left port there was, in another part of the world, a storm that may not have been a concern—had they been in that part of the world, at that time. However, he was headed in that direction, and the forecast at that time, was that they would meet a hurricane when they got there.  And they did indeed meet the storm more or less right at the spot and right at the time it was forecasted. These forecasts are all archived at the NHC and this can all be checked.  

In short, when this vessel pulled into the ocean, it could be anticipated that they would meet a hurricane, and this is indeed a concern. I posted a short article on this the day the vessel was lost,  which focused on the same misrepresentation of the facts, in this case, by the AP. That analysis remains tragically valid.

NPR (and anyone else parroting this same analysis) is doing a disservice to the NWS and to all mariners by this type of reporting. We teach daily the obvious fact that a storm's condition when you are not there does not matter. What matters is the condition of a storm when you are where it is. We must rely on forecasts.

As I understand, it has not been established why the vessel proceeded on the path it did, but the NPR report flies in the face of all prudent navigation practice. They are presenting, in essence, a navigation and weather routing lesson to their readers that is totally wrong and can be disastrous.

This morning I hear that NPR is proud they do not present fake news—a low bar at best—but the Greg Allen assessment presented is borderline, in that it is a thoughtless statement that distracts from a productive understanding of the tragic event.

I must add, NPR is indeed one of the best news sources in the world. This is a rare transgression, which I mainly point out because I care about them and respect their work.

Friday, December 9, 2016

Wonderful Website on Barometers

We sometimes have things to thank the government for that we might not appreciate. In this case I refer to their propensity to change website addresses, often in more or less random fashion without any apparent improvement. It could be some form of job security. We thank them because when trying to find a nugget they moved or removed, we found instead a goldmine of related info at another location.

The Fischer Precision Aneroid Barometer. An example of state of the art barometer workmanship. 

The NWS, for example,  recently changed many if not most of the links to where they store weather data, but that is not the example at hand.  Sometime ago, we discovered that NOAA had put online a copy of the remarkable book Manual of Barometry (WBAN), the mother of all bibles of barometer related science. In our announcement of this with a short description of the book we included the link to NOAA for the document.  It is that link which has now gone missing.

But in searching for a replacement, we discovered two things. First a really remarkable website devoted to barometers at

I am embarrassed that I did not know about this tremendous resource, and look forward to studying all that is there. Barometric pressure and its trends remain the fundamental tools for understanding present wind and for anticipating wind changes, and this pressure data also remains the most valuable way to evaluate weather maps underway or at home.  Thus we should all be barometer buffs on some level, and for any barometer buff, this site is a goldmine.  (I would add to it our site and the link to our own work on barometers at and this link that applies some of these ideas to the Pacific NW

And sure enough, the Analog Weather site was smarter that we were; they actually downloaded a copy of WBAN and put it online.  We have a rare printed copy here, but this is such a massive reference (>1000 pages of small type, presented in a really convoluted section structure) that searching, book marking,  and annotating the pdf version is a big help in using it. 

The NOAA scan (17 Mb) has useful bookmarks, but you can add your own to refine the sections, which brings up the second point we discovered.  Namely—and I have to guess it is just a coincidence—but with the disappearance of the free NOAA copy from the NOAA site, there now appears a Google scan of the book that is for sale from them for $5. The Google scan (175 Mb) and is is crisper images, though the 17 MB version is perfectly readable; it also has bookmarks but they are not useful. Each has to be named to have any meaning.  So now, it is easy to find this pdf copy in any search engine, but it will likely be the $5 version that is 175 Mb.

If you have any ties to a university, then you can download the Google scan from Hathi Trust, which is another way to look at it online and search contents, or print individual pages.  An in house copy of the Google or NOAA scan from Analog Weather is likely best bet for long term study... and there is no other kind of study possible with this book!

Once again, a hearty thank you to the folks at Analog Weather for their excellent barometer resource.

Monday, December 5, 2016

GRIB Formatted Regional Wind Forecasts – Review and Updates

Each time we have a regional weather routing project to work on, I have to stop and remind myself about what data are available, and what are the specs.

By specs I mean how often and when is the weather prediction model run, when are the data available after that, how far out does its forecast extend, what are the time steps in the forecast, and what is the resolution of the data, ie a wind point every 1.3 km or every 30 km, etc. And of course, what regions do they actually cover, ie how far offshore, how far north into Canada, etc.

To help myself and others with this, I have compiled here a set of notes on available forecasts and summarized the crucial specs in a Table below for quick reference.

There are two broad categories of numerical model predicted wind data: Global and Regional. Global is for mid ocean or well offshore; regional models are for near coastal and inland waters.

The best wind data for US inland and near coastal waters (HRRR model) were only available as commercial products until the last few weeks or so when Saildocs made them available to the public. Commercial products are only legal in sailboat racing up till the starting gun, so this new development from Saildocs will have a big influence not just on sailboat racing—the data can now be used throughout any race—but this Saildocs service has a potentially huge impact on all of sailing across the US. It will likely take many months and well past next summer to fully appreciate this, but stand by for real change.

We remain grateful to the commercial outlets that did pioneer the availability of the HRRR data last year, specifically Ocens and SailFlow, and their presentations of the data within their own systems are still just as convenient as they have been. Indeed, as more mariners learn the value of this data now that it is publicly available, it should only enhance the value of the commercial services they offer.

Shortly, I will supplement this note with even newer developments from the Seattle-based Mac program LuckGrib that add to and extend the revolution. This should be announced shortly. Their next update includes HRRR, NAM, ASCAT satellite winds, and much more. The scatterometer data (satellite winds) are a positive way to confirm any of the numerical forecasts. Having these data available as GRIB files is a boon to our analysis underway.

The main focus of this note are the regional wind and pressure models. For free, public global models, the dominant model in use worldwide is the GFS model from the US, along with various ensemble presentations of that data. Ensemble means the same model is run using different initial conditions and times, and the results are averaged and compiled into a single forecast that should in principle be more dependable than any single run.  Ensemble forecasts will have lower resolution and less duration than the individual runs.

Some argue that the European global model (ECMWF) is superior to the GFS on some level in some cases, maybe even on average, but that model output remains commercial data, notably from Squid Sailing and PredictWind. With access to this EC data we have the opportunity to compare that with GFS in  more cases.  From a practical point of view, considering all related uncertainties in this process, it is difficult to anticipate many instances where the difference in forecasts (GFS vs. ECMWF) will affect our routing decisions. It is not the subject at hand, but all of these global models can be wrong in substance or in timing in various conditions.  And if carefully compared to actual weather maps and text forecasts, the GFS GRIB data should meet the global forecast needs of most mariners. There are standard precautions to be taken.  The GFS specs are included in Table 1 for comparison to the regional data.

NAM (2.5, 6, 12 km), North American Mesoscale Forecast System, is the flagship regional weather forecast model run by NCEP/NOAA.  It is available for several regions of US waters in different resolutions. A good choice for longer term forecasts than available from the 18h max of HRRR, and for comparison with the digital form of official NWS forecasts in NDFD. The convenient coverage area maps are from the LuckGrib viewer. ( In principle this model should be better than the COAMPS version from the US Navy. See model discussions and links. )

NAM North America, 12 km. Would be used when one of the other higher res NAMs was not available.

NAM AK, 6 km.  Note that it covers Pac NW at twice the resolution as the conus N. American above.
We might get the impression from this official coverage map that we have a trick play in the Pacific NW and can get 6 km data from the AK run as opposed to just 12 km from the North American run, but strangely this is not the case. For some reason, the full AK region is not populated by data and we miss the corner we care about, as shown below.

Actual NAM AK data downloaded and viewed in LuckGrib. Note the missing data in the corners.

NAM Caribbean, 12 km, same as N. America, but note the super hi res of the central region below.

NAM Puerto Rico, 2.5 km. This is about state of the art in resolution, covers Virgin Islands as well.

NAM HI, 2.5 km. Likely best for planning approaches till the HRRR is available.
The HRRR is not even as high a resolution as this one, but it is updated every hour, compared to NAM every 6h,
especially important in the presence of tropical storms. 
NAM data are available from within LuckGrib and Expedition (Expedition does not include NAM AK).

NDFD Oceanic (10 km). This is unique GRIB data in that it is not pure model output, but instead is a digitized format of the official NWS forecast. In principle this should be better than any one model for the region covered, because the human forecasters that created this data have access to all models and they have chosen which they think is best at the time.  Unfortunately it only goes out to Lon 133ยบ W, and then is available again in HI, as shown below. It can be useful in the Strait of Juan de Fuca as well. See The National Digital Forecast Database(For higher resolution NDFD updated more frequently see our later note on NDFD CONUS.)

The NDFD data include wind and significant wave height of combined seas. There is no pressure data.  See the NAM or HRRR for pressure.

NDFD data 3 km, goes about half way up Vancouver Island. This coverage map from the NSDF site.
Pac NW limits on NDFD. About halfway up the west coast of Vancouver Island then to top of the Gulf Islands.

NDFD HI coverage, 3 km. Another view from an Expedition screen cap.

NDFD data are available from Expedition, Saildocs, and the Ocens WeatherNet (commercial data).

HRRR (3 km).  The High Resolution Rapid Refresh model is updated hourly, corrected for all the latest observations,  but it only extends out 18 hours. It is available from LuckGrib, Expedition, Saildocs, and Ocens.  If you have live Internet connections while underway, these are likely the best wind forecasts available.

The data are available about 1.5 to 2.5h after each runtime. That is, a model run at 1400 should be available to you by about 1530. Thus if you download an 18-h forecast at 1535, your first data point could be at 1400 and extend to 0800 the next day.  Download at 1525, and your first point would be 1300, extending to 0700 the next day. The resolution between wind data points is fine enough to do some level of automated sailing route optimization, although it will take more experience with this to learn the limits.  Wind and pressure are available.

The HRRR model actually has wind forecasts every 15 minutes, but the 15-min steps data are not yet available in GRIB format from any source I know of.... ie it is indeed rapid in refresh and time resolution, as it was motivated by tornado and squall forecasting, which it can indeed do!

HRRR 3 km. A huge coverage for this timely and hi-res data. Extends N to Seymour Narrows in BC, and covers all of the Great Lakes.
Screen cap of coverage from LuckGrib.
Pacific NW limit of the HRRR data. 

Sample HRRR data. 18h of forecasts. The data go north to Campbell River... ie perfect for the R2AK run to Seymour Narrows.

And for those navigating by portable device, there is a super nice way to see the HRRR wind data underway, but not in a form for numerical weather routing. Use the SailFlow app in iOS or Android, and surf around in the set up to find HRRR.

Summary of the Regional Forecasts compared to the Global GFS.
See the maps above for the coverage regions.

Public Regional Models
Resolution Timing
km nmi deg coverage model run  delay  duration  time step
HRRR 3 1.6 0.03 map HRRR hourly 1.5 to 2.5 18h 1h
NAM 12 6.5 0.11 N. America 00, 06, 12, 18z 3-4h 84h 1h/36, 3h/84
NAM 12 6.5 0.11 Caribbean 00, 06, 12, 18z 3-4h 60h 1h/24, 3h/60
NAM 2.5 1.3 0.02 Puerto Rico 00, 06, 12, 18z 3-4h 60h 1h/24, 3h/60
NAM 2.5 1.3 0.02 HI 00, 06, 12, 18z 3-4h 60h 1h/24, 3h/60
NAM 6 3.2 0.05 AK 00, 06, 12, 18z 3-4h 60h 1h/24, 3h/60
NDFD 10 5.4 0.09 map NDFD 00, 06, 12, 18z 3-4h 168h 3h/72, 6h/168
RAP 13 7.0 0.12 map RAP hourly 3-4h 21h 1h
Public Global
GFS 28 15.1 0.25 Global 00, 06, 12, 18z 3-4h 384h 3h/72, 6h/180, 12h/384
Predict Wind Commercial products, G=GFS based;  E = ECMWF based
PW/G,E 1 0.5 0.01 selected 00z, 12z 6-12h 36h 1h
PW/G,E 8 4.3 0.07 coastal 00z, 12z 6-12h 168h 3h
Public Graphic only, no GRIB
UW WRF 1.3 0.7 0.01 Pac NW 00z, 12z 6-12h 60h 1h

(Note the NDFD Oceanic listed above is more a global model. For the regional counterparts see our more recent article on NDFD CONUS.)

Other Regional Models

PredictWind PWG/PWE (1 km, 8 km). The 8-km data are available in coastal waters,  nearly globally, and the 1-km data are for many popular sailing areas worldwide.  For more data on the model specs and available times, see this link at

Predict Wind commercial hi res data. Large regions are 8 km, small are 1 km. A similar distribution of data options apply globally.
This is a screen cap from PredictWind Offshore app. Set the route across your route and it will select all data needed.

This product has several advantages when preparing for a race or not racing when commercial products are restricted.  First it is super easy to access in Expedition or by email, and the 1 km hi-res models extend out 36 hours,  compared to 18h with HRRR.  They also have a convenient (Mac or PC) app called Predictwind Offshore that lets you either request and look at the data online, or what is often more convenient, it will prepare a template request that you just email to them when you need an update. The larger regions of 8 km are 390 kb each, the smaller regions of 1 km data are 250 kb each.  The 8 km (also hi res) goes out a 7 days—like the lower res GFS, more or less into the realm of the unknown.  The only drawback to the data is its age, since it takes time to incorporate the ECMWF and other adjustments they make, the data can be 8 to 12h old when it arrives.

Predict Wind also has a weather routing/optimizing feature that seems to work pretty well. You can also use custom polars for the analysis.  For inland waters, however, it does not account for currents, which leaves Expedition at an advantage for that— but I should add here, if you do not have good current data, then you could be better off without using currents at all!  PW does offer and use ocean currents for the ocean routing. They remain unique with their new inclusion of ECMWF data.

UW WRF (1.3 km).  Unique to our local Pacific NW waters, we should always remember the UW WRF model, which is likely as good as any, but only available as a graphic format;  there is no grib format. The  model is run at about 00 and 12z daily and data would typically be 8+ hr old when we get it, and indeed they might not be there when you want them. This is a public service of the UW Atmospheric Sciences Dept.,  with no guarantees.

UW WRF model, run every 6h extends out 60h.

This model could be the best model for the region, but it is not updated often enough to compete with the HRRR, which is updated with all the latest actual wind observations every hour.

Nevertheless, it is worth printing out the UW data before the start, and with a good connection offshore, perfectly legal underway.  You can request the image forecast underway using saildocs.

Tuesday, November 1, 2016

Rock Talk 2: RNC to ENC

In a recent note (Rock Talk—Is it all awash, or not?) we discussed minor conflicts in paper-chart rock symbol terminology for a rock that covers and uncovers, height unknown (US supplemental symbol Ka and INT 1 symbol K11). One of the virtues of moving onto electronic navigational charts (ENC) is we no longer rely on the design of the symbol to convey specific information, and instead we get this from a direct query of the ENC database. This database uses an internationally accepted terminology that overrides national nuances.

Below is a summary of common paper-chart rock symbols with a graphic presentation of their relative soundings.

Figure 1. Common rock symbols used on paper charts and RNCs.

ENC charts, however, have simplified the actual symbols, not just for rocks, but also for other objects traditionally shown on paper charts. Part of this difference is schematically shown in Figure 2. Going forward, we can abbreviate "paper charts" with RNC (Raster Navigational Charts), because that form of an electronic chart is just an image of the actual paper chart.  The figure caption also refers to INT 1, which is the International Hydrographic Organization (IHO) standard for paper chart symbols.

Figure 2. Rock and terrain symbols are greatly simplified on ENCs. Left is a hypothetical RNC (paper chart, INT 1); right is the corresponding ENC. The six or so INT 1 rock symbols used on paper charts are presented on ENCs as just two symbols, with detailed attributes found by cursor pick. Likewise the attractive but challenging INT 1 tree symbols are replaced with a generic tree and cursor pick. Using ENCs, navigation schools will have to forgo tricky test questions distinguishing INT 1 coral from rocks, as these two are a single generic symbol on ENCs. Click the symbol to find out which. (We leave it as an exercise to decide which is coral and which is rocks in the RNC.)

The use and meaning of rock symbols on ENCs are not the same as they are on paper charts. We have gone from seeing some 6 or 7 "rock symbols" that tell us much about the rock from the symbol alone and knowledge of the tide height, to seeing just two different rock symbols on an ENC, some of which may not show at all, depending on how we have the optional soundings set—which brings up the crucial ENC topic of the "isolated danger" symbol, which is a powerful new feature of ENCs; the subject of a later note. 

When using ENCs, we must learn to get crucial information from clicking the symbol (called a cursor pick) and reading about it in another window. The rock symbols alone no longer convey detailed information.

This change in chart reading practice required when using ENCs can be a challenge, depending on individual experience. Having used paper charts for 30 years, my initial attitude toward these simplifications of the symbols, and rock symbology in particular, was negative, and I was not timid in complaining about it. However, the more I have used ENCs and studied the goals of the IHO in their "new" system (it is actually some 10 years old at this point!), I have changed my opinion on this. 

Although we might miss our traditional symbols, there is much virtue in not having to learn all the nuances of the traditional US rock symbols in the first place. In fact, many mariners who did not need to know these details to pass a navigation exam may not have been aware of all the information contained in the paper chart symbols. It is not even that transparent when searching Chart No. 1, without training on the use of that important publication.

Using ENCs, we only have to teach that there are two types of (common) rock symbols, an isolated asterisk or an isolated plus sign in a dotted circle. To know more about that rock, just click it. The procedure is easier to learn than memorizing multiple symbols, and probably a safer way to use charts. We must train ourselves to click every rock that is near our route. 

An asterisk is a rock that covers and uncovers as the tide changes between 0 and MHW (a K11 or K12 rock in INT 1), and a circled plus sign is a rock which is covered when the tide is 0 (K13). Note that we see a plus sign with or without a ring of dots on an RNC, but it aways has a ring of dots on an ENC. A ring of dots in all charting means a special hazard.

The way we learn more specifically what an asterisk rock means on an ENC is a cursor pick. Then we will be told the "value of its sounding."  An asterisk rock with the (9) beside it on an RNC will report a sounding of -9.0 ft in the ENC. In ENC reports, a negative sounding is a drying height.  

Figure 3A K11 rock shown on an RNC (left) and on an ENC (right).
Note drying heights are negative numbers on ENCs. Here the drying height is 0.8m = 2.6 ft.

A plus sign with 4 dots on an RNC (INT 1 symbol K12), will show up on an ENC also as a plain asterisk, and a cursor pick will report sounding of 0.0. Recall that all soundings are relative to 0 tide height, so when the tide is zero, this rock is right at the surface.

Figure 4. A K12 rock shown on an RNC (left) and on an ENC (right).
A sounding of 0.0 means this is a "rock awash" in the IHO definition, but not in the Bowditch definition, a point we discussed in 
Rock Talk—Is it all awash, or not?

Figure 5. Another example of a K11 (NOAA Ka) rock shown on an RNC (left) and an ENC (right).

Figure 6. Example of a K12 rock shown on an RNC (left) and an ENC (right).  Both are official Canadian HO products. Note the slight color pallet differences between US (Figure 4) and Canadian RNCs (Figures 5 and 6). ENCs meeting IHO standards all use the same color pallet, regardless of national origin, which is another small step forward. 

Note, too, that on paper charts, a ring of dots is an indicator of extra danger placed around a single rock, group of rocks, or just a rocky area. On ENC, the underwater rock symbol includes the ring of dots regardless of the sounding on the rock if known—there is no plain plus sign rock symbols on ENC.

Notice in both Figure 5 and 6, how much "cleaner" and more precise the chart looks on an ENC in these examples, compared to the largest scale RNC for the region. This often can be an aid to navigation, BUT we must be careful when over zooming, as shown in both of these pictures. Over zooming an ENC maintains the sharp lines, which gives the impression of a higher accuracy, which might not be justified by the actual survey data the chart is based upon. Both RNCs and ENCs are intended to be used at their native scale, although in practice we often over zoom them. The difference is the RNC gets fuzzy and pixelated, which is a warning of sorts, but the ENC does not.

Here is a summary of the comparison of ENC and RNC rock symbols:

Rock Talk — Is it all awash, or not?

We are preparing new training materials on the use of electronic navigational charts (ENCs), which brings up an issue navigators face when moving from paper charts to ENCs—namely, rock symbols and how these differ between the two formats.

The most common rock symbol seen on a paper chart is a simple asterisk. This is a rock that shows above the surface when the tide is 0 or less, but it is covered by water when the tide is at or above mean high water (MHW).

Figure 1a. Rock symbols.

If there is nothing printed near the asterisk on the chart, then that is all we know about it. On the other hand, if there is an underlined number in parenthesis near it, ie (6), then that 6 is the drying height of the rock, meaning when the tide is 0.0 the top of the rock is 6.0 ft above the surface. At a tide level of 5 ft, the rock is just 1 ft above the surface, and any tide height greater than 6 ft covers the rock. The number is in parenthesis so it is not confused with nearby soundings.

When we start to work with ENC rock definitions, however, we run across a bit of a stumbling block in the definition of this isolated asterisk rock when there is no drying height charted.

For a historical perspective, we refer to the definitive American reference on chart symbols, the booklet called NOAA Chart No. 1, and specifically to the 8th edition, issued Nov, 1984. We see the rock in question as entry O(a) in Figure 1, which is distinguished from the same symbol with a drying height charted, which is rock O2.

Figure 1. Page from 8th edition of Chart No. 1, 1984

The plain asterisk rock, (Oa), is defined as  "Rock awash (height unknown)."  

Most symbols and labels used in the 8th edition of Chart No. 1 were based on those of an IHO (International Hydrographic Organization) resolution from 1952.  But note that the label of the "rock awash," (Oa) is in italics, in parenthesis, and not part of the normal sequence of rock labels in Section O. This is explained in that edition to mean that this is a symbol that does not have a counterpart in the 1952 IHO list of symbols. In short, this is a unique NOAA symbol, not an internationally adopted symbol, but there is more to this story.

When we move to the 9th edition of Chart No. 1 (April, 1990) we see two things. First, rocks are no longer in a Section O—Dangers, but are now in Section K—Rocks, Wrecks, Obstructions, and we see a new subsection of Section K called Supplementary National Symbols. The rock awash symbol is now called symbol "a" in this new list, which we might call Ka.

The change in section labels (ie O goes to K), and the motivation to separate out unique US symbols into a list called "Supplementary National Symbols" is likely due to the appearance of the first edition of the the IHO paper-chart symbol standards called INT 1 in 1987—between the 8th and 9th editions of US Chart No.1.

After the appearance of the IHO's  INT 1 standard, we find that the cataloging of common paper-chart rock symbols has remained essentially unchanged in the US from those of the 9th edition. A sample of the latest edition (12th, dated April, 2013) is shown below. 

Figure 2. Selection of paper chart rock symbols from NOAA Chart No. 1, 12th ed, 2013. (In this latest edition, "Aquaculture" was added to the K section.)

Notice that rock Ka is still a supplement and still called "rock awash." In contrast, if we look at the corresponding page of INT 1 (also called Chart No. 1) from Canada, UK, or elsewhere, we see: 

Figure 3. Selection of Canadian Chart No. 1, which follows INT 1. 

Notice that the US Rock Ka is part of the INT 1 K11 group, and it is in fact presented that way by all other nations.  Check the US definition of K11 and this rock is not included—that is, an isolated asterisk without any drying height specified.

You may fairly ask at this point—if not earlier!—why we care about such details?  The answer is this. Once we move to ENC usage, most rock information is included in the text descriptions of the rocks. The symbols are greatly simplified and we have to "cursor pick" (mouse or trackball click) the rock to read what kind it is. So a precise description of the rock is crucial.  We are also trying to figure out why this US Ka rock is left as a US Supplementary Symbol and not just moved into the K11 group.

It seems we are being called back to the definition of "rock awash." USA Chart No. 1 has always pointed out that if you need more help understanding the terms, refer to Bowditch, American Practical Navigator. Below is the latest Bowditch definition of "rock awash."
Figure 4. Bowditch Glossary (2002)

"Rock awash" with this definition (first part) is what we have called the symbol of a simple isolated asterisk rock on US charts for many years. (The second part applying to the Great Lakes where there is essentially no tides, is not relevant to the present discussion.) 

But we have to admit that the rest of the world does not use this terminology, and that fact comes more to the front when we start using ENC. The isolated asterisk rock K11 in INT 1 is defined as a "Rock which covers and uncovers, height unknown." This is frankly better and more precise terminology. 

The word "awash", outside of a US navigation context, means what we think it means: the top of the thing is above the water to some extent, with water washing up against it or just over it. Thus the US rock symbol Ka called "rock awash" really means "a rock that will be awash at some tide level, but we do not know what that level is." In short, it is a rock which covers and uncovers, height unknown, which is the definition of INT 1 rock K11.

It is not clear why NOAA maintains this definition of the Ka rock, unless it is tied to the tradition we see in the still active Bowditch definition and in navigation school training manuals (like our own). It seems that the rock Ka could be moved to K11, just as in the INT 1, and redefined as a rock which covers and uncovers, with height known or unknown above chart datum.  (We raise this point, but we are aware of the perspective: NOAA and its forerunners were making charts and explaining symbols long before most nations were, so they have history on their side.)

The word "awash" could then only appear in the definition of K12 (the plus sign with 4 dots) which is defined by both the US and INT 1 as "a rock awash at the chart datum," and which is, indeed, the IHO definition of "rock awash" as presented in S-32 the official IHO Glossary.
Figure 5. IHO Glossary, S-32, 5th ed, 1994. This is not the same as used in Bowditch (Figure 4), so we propose that the next edition of Bowditch include this alternative meaning.

It seems that change would simplify US paper chart symbols, and lead to an easier transition into the use of ENC. I know of at least one navigation school, who will no longer refer to the isolated asterisk as a "rock awash."

In a follow up note (Rock Talk 2 — RNC to ENC), we look at how rock symbols are presented in ENC. But before leaving I want to stress that the latest edition of NOAA Chart No.1 is a major milestone in such publications in that starting with the 12th edition, NOAA Chart No. 1 includes for each paper chart symbol the corresponding symbols used in electronic navigational charts, specifically those following the IHO S-52 standard used in ECDIS (electronic chart and display systems).

NOAA Chart No 1 is now more than ever a unique and especially valuable publication for all navigators, worldwide. There is a free pdf version online. To appreciate how lucky we are, the British Admiralty publishes this same data in two books NP 5011 ($35) and NP 5012 ($34).


A special thanks to Brian Voss, Librarian of the NOAA Library in Seattle. He has shown us many times the crucial value of real libraries and real librarians in this Google age.