In 2020 NOAA announced that this was the last year they were going to authorize an annual set of tables for tides or for currents. The tables were called:
Tide Tables
2020 East Coast of North and South America Including Greenland
2020 Europe and West Coast of Africa Including the Mediterranean Sea
2020 Central and Western Pacific Ocean and Indian Ocean
2020 West Coast of North and South America Including the Hawaiian Islands
Tidal Current Tables
2020 Atlantic Coast of North America
2020 Pacific Coast of North America and Asia.
Prior to 2021, these were "the official sources." All other third-party printed or electronic presentations of US tide and current data, readily found along the waterways and cybersphere, were derived from these, sometimes mixing up actual locations or confusing standard times and daylight times.
These are what we called "The Tide Tables" or "The Current Tables" that were either required or recommended to be on all vessels. These tables included daily data for numerous Reference Stations and then a Table 2 that included corrections to be applied to thousands of Secondary Stations.
That ended in 2021. And despite the fact that some third party companies still print these tables including the Table 2 data that they reproduce from the 2020 tables, the data are not valid. Hundreds of those secondary stations have been discontinued and values for many others have changed.
But more to the point at hand, up till just recently, the USCG license exams still tested on the Table 2 procedures using the old Table 2 data, which has been totally wrong for nearly 5 years now. Many schools around the country still teach this method as well.
The USCG has now corrected that and their new exams treat tides and currents in the modern, correct manner, which is outlined below. This greatly simplifies this important part of navigation. We wrote several notes on this in the past:
You can review these for background and in the second one for step by step procedures for most efficient access to the new data, including how to make your own set of annual tables
Another aspect of the simplicity (progress) is that tide and current questions are now essentially the same for entry level OUPV license exams as they are for unlimited ocean master.
Here is an example.
The diagrams included are:
The solution to #36 is fast. Go to the time on the graph and read the speed, then note that the harmonic directions are given in the figure titles.
That is the right answer to the test question, but not at all the guaranteed answer on the water. These currents are treated as pure reversing, with two directions only, but in practice they rotate, flowing with some strength in an ellipse of directions. The direction given is just the average direction around the time of peak flow at the long axis ends of the ellipse.
Question #35 asks about rotary currents, which is interesting in that the discontinued annual current tables did have a Table 5 listing details of rotary currents along the coasts. But like Table 2, much of the Table 5 data were not considered unreliable, so they have been discontinued. If we want coastal tidal currents, we should use the OFS model forecasts, which are very good. Nevertheless, we can answer this question by looking up any coastal station along the East Coast and seeing how long it takes between successive floods or ebbs, and it will be about 12 hr.
The tide problem, #37, is just as direct. We are between two stations that have different heights but we are only asked for time, and that is the same for both. If they had ask for height the answer would, presumably, be (0.51+0.29)/2 = 0.4 ft.
(Tide heights are pretty uniform over large areas of open water, so the tide values are more likely to be correct out on the water than the current values — assuming the atmospheric pressure is about normal, and the wind has not been strong over the past 12h, and there is no unusual river run off, all of which can throw the water level predictions off a foot or two.)
Likewise for the other end of the license exam spectrum, unlimited master.
This the same as #36, but we have to adjust the time. Starting at 0130 we must travel 15 nmi at 10 kt which takes 1.5h so we get there at 0300.
Question #6 for unlimited master is the same as the #37 for OUPV.
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So the summary is the USCG exams now follow the existing procedures for tides and currents, which is tremendously easier and faster than it was before. It is a pity that the invalid Table 2 data (for tides and currents) are still being published by third party printers, but we should just know this, and move on.
Our main resource for all tide and current data is now www.tidesandcurrents.noaa.gov. Please refer to the article above (What do we do now?) for the exact steps for the most efficient use of the NOAA site. The best procedure is not intuitive. What might seem an intuitive approach can lead to other types of data that you likely do not want. We want the types of data shown in these USCG exam diagrams. In that article there is also a video showing the steps.
The article also shows how to make annual tables for any station. It takes just 4 pages per year, per station. We do not need the historic books that covered all of North America. We need just the stations covering the tidal waters we navigate.
Our book Inland and Coastal Navigationcovers the use of the NOAA website, and our Navigation WorkBook 18465Tr has practice exercises. In practice a new challenge arises in finding the nearest station you care about (illustrated in the links above), or you can use a program like qtVlm or OpenCPN that used tested harmonic data from NOAA and they show where all the stations are.
Here is a video summary of this article, which includes a demo of our recommended approach to the NOAA data.
* * * Thanks to Seattle Maritime Academy instructor Robert Reeder for alerting us to these USCG exam updates.
The International Hydrographic Organization (IHO) describes light symbols as the most complex electronic navigational chart (ENC) symbols in their own published standard for the symbols called IHO Pub S-52, Annex A, Presentation Library. Anyone can download Pub S-52, but the Presentation Library costs 500 euros! Draft copies found online have many errors, and can lead to hours of wasted time with no productive results.
But the IHO does not give themselves all the credit they deserve regarding complex symbols. Let's take a look at the rules for wreck symbols on ENC, for example.
There are six wreck symbols presented below with the official IHO Symbol Explanations, followed by our notes on the required attributes, which are explained in more detail later in the post. Five of the six are essentially the same wreck symbols used on paper charts, but the complexity comes into play because now we know the rules that determine which symbol is used for which category of wreck, and this new specificity is both a virtue and a challenge to those who must display the proper symbols or write books on their meanings. Plus we have the all new concept of isolated danger symbol unique to ENC.
This type of symbol inquiry is good practice working with ENC objects and attributes, which will become more important to mariners as we learn to live without traditional paper charts, relying on the ENC as the only official nautical charts.
IHO Symbol Explanation: wreck showing any portion of hull or superstructure at level of chart datum.
Attributes: VALSOU not given; CATWRK = 4 or 5 or WATLEV = 1, 2, 4, or 5. This symbol means there is no sounding given for the wreck and some part of it is showing at all stages of the tide.
The IHO reference to "chart datum" means "sounding datum," which is always zero tide height on all ENC from any nation.
IHO Symbol Explanation: non-dangerous wreck, depth unknown.
Attributes: VALSOU not given; CATWRK = 1; and WATLEV = 3. In other words, no sounding given, it is charted as not dangerous, and it is always underwater.
IHO Symbol Explanation: dangerous wreck, depth unknown.
Attributes: VALSOU not given; CATWRK = 2; and WATLEV = 3. In other words, no sounding given, charted as dangerous, and always underwater.
Some symbol reference books imply that "dangerous" or "non-dangerous" is determined by the location of the wreck relative to the safety contour, but that is not the case. Dangerous or non-dangerous is coded into the ENC by the Hydrographic Office that made the chart, using rules they set. As noted below, NOAA charts all wrecks known to be shallower than 20.1 m as dangerous, keeping in mind that these are wrecks whose exact soundings are not known.
Wrecks can also be plotted as a generic hazard (meaning rock, wreck, or obstruction) with one of these symbols when the value of sounding (VALSOU) of the wreck is known.
IHO Symbol Explanation: underwater hazard with a defined depth.
Attributes: VALSOU less than or equal to the mariner's choice of Safety Depth. The known sounding is then printed in the center of the symbol. Black if less that the safety depth; gray if deeper.
IHO Symbol Explanation: "underwater hazard with depth greater than 20 metres." [SIC]
Attributes: VALSOU greater than the mariner's choice of Safety Depth.
The official IHO Symbol Explanation given above, taken from the latest edition Presentation Library, is not correct. There is a detailed Conditional Symbology Procedure (CSP) explaining when to use this symbol, and it is based on the Safety Depth, not on a fixed 20 meters depth. Both the US and the UK Chart No. 1 booklets include the incorrect reference to 20 meters. Consequently, some navigation apps (ECS) also do not make this depth distinction correctly, so the symbols in those apps do not change from blue to clear at the correct sounding. It is not a major effect navigationally, but reflects the complexity of the symbol.
The known sounding is then printed in the center of the symbol. Black if less that the safety depth; gray if deeper.
IHO Symbol Explanation: isolated danger of depth less than the safety contour.
Attributes: This is a complex, but valuable symbol unique to ENC. It automatically replaces hazard symbols depending on the depth and location of the hazard. It warns us of hazards (based on our own definition of safe depth) that are located in deeper water where we would not expect them.
Specifically, if a wreck is outside of the displayed safety contour and it has a sounding less than the requested safety contour—or its sounding is not given—then the wreck symbol is replaced with the isolated danger symbol—depending on several other properties of the wreck. That procedure applies to all hazards (rocks, wrecks, and obstructions).
Most ENC users are familiar with that role of the isolated danger symbol, but not so many realize that the reference sounding is the requested safety contour, not the displayed safety contour, and this is not at all clear in the IHO Symbol Explanation.
We have in practice two safety contours. We have the one we requested, say 8 m, and we have the one displayed on the screen, which might be 10 m, because only contours native to the ENC can be assigned as the displayed safety contour. This special contour is then made bold and it separates two prominent water colors, and also triggers various alarms when crossed. If our requested contour is not in the ENC, the next deepest contour is selected for display.
For example, we request a safety contour of 8 m, but there is none in the ENC, so the active safety contour displayed is at 10 m. On the deep side of the 10 m safety contour there is a wreck with a sounding of 7 m. This is shallower than our requested 8 m and outside the displayed safety contour at 10 m, so this one will be replaced by an isolated danger symbol.
If we then change our requested safety contour to 6 m, the displayed safety contour will stay at 10m, but now our wreck is deeper than our requested safety contour, so it will not be replaced with an isolated danger symbol.
I might stress that this symbol depends on a value of the safety contour; whereas the distinction between DANGER01 and DANGER02 above (blue or clear inside a dotted oval) depends on the value of the safety depth. Some nav apps (ECS) do not follow the IHO and IMO guidelines of having a user selected safety depth in addition to the safety contour, so they then use the same value for both symbols.
Those are all of the possible symbols for a wreck. Any wreck on the chart will be one of those symbols. The tricky part is how does a specific nav app (electronic charting system, ECS), decide which symbol to show? This is not such an easy question. The rules (outlined briefly above) are spelled out in the S-52 Presentation Library, which in turn depend on the specific attributes of the object WRECK. These attributes are encoded into the ENC using rules from another IHO standard called S-57.
The attributes of the object WRECK that determine how it should be plotted are:
WATLEV, water level effect
VALSOU, value of sounding
CATWRK, category of wreck
EXPSOU, exposition of sounding
Every WRECK must have a WATLEV, plus it must have either a VALSOU or a CATWRK. You can review these attributes at caris.com/s-57.
WATLEV describes the visibility of the wreck as the tide changes. The options are:
ID Meaning
1partly submerged at high water
2always dry
3always under water/submerged
4covers and uncovers
5awash
6subject to inundation or flooding
7floating
A wreck with WATLEV = 3, always submerged, with no sounding given, will have one of the traditional wreck symbols we are used to from traditional paper charts, WRECKS04 or WRECKS05.
VALSOU is a single number, the depth of the water over the wreck when the tide is 0. This can be a positive number, such as 3.5 m, meaning when the tide is 0, the top of the wreck is 3.5 m below the surface, or it could be -3.5 m, meaning when the tide is 0, the top of the wreck is 3.5 m above the water. Negative soundings are drying heights. Depending on the range of the tide and the location of the object, it could be underwater at all tide levels, or it could cover and uncover with the tide, or it could be always visible to some extent regardless of tide height. A drying height sounding is shown underlined on the screen. We see wrecks that cover and uncover with known drying heights along or in the foreshore.
A known VALSOU means the wreck will be shown as one of the the three danger symbols shown above, and not the type of wreck symbol we were accustomed to on traditional paper charts.
The VALSOU relative to the mariner's choice of Safety Depth determines the symbol DANGER01 vs DANGER02, regardless of other attributes.
CATWRK can have a direct influence on the symbol used. The options are:
IDMeaning
1non-dangerous wreck
2dangerous wreck
3distributed remains of wreck
4wreck showing mast/masts
5wreck showing any portion of hull or superstructure
Each nation making ENC have to establish how they are going to define a wreck as dangerous or not. It is not spelled out in the IHO S-57. NOAA's own Chart Manual, Vol 3, Section 6.3.2 on ENC production states that all NOAA ENC will encode any wreck as dangerous if it is known to be shallower than 20.1 m. They do not need to know its actual sounding, only this limit.
EXPSOU has a more subtle effect on the symbol. The options are:
IDMeaning
1within the range of depth of the surrounding depth area
2shoaler than the range of depth of the surrounding depth area
3deeper than the range of depth of the surrounding depth area
This attribute only affects whether or not a wreck symbol (or any hazard) can show up as an isolated danger symbol. If the exact sounding of a wreck is not known, but it is known that the depth of the wreck is deeper than the shallowest contour of the depth area it is in (ie EXPSOU = 1) then this wreck will not show as an isolated danger symbol. The goal is to avoid the unnecessary display of isolated danger symbols.
This last detail (some hazards not showing up as danger symbols when similar ones do) is not crucial in practical use of ENC because the first thing we learn is we must cursor pick any object that might be crucial and the pick report will tell us all about the object and its attributes. Furthermore, isolated danger symbols are an all new concept in ENC that we are not familiar with on paper charts, so it would be rare to even know something is unique about any specific example.
Also we note the commonality of all hazard symbols on ENC. For most encounters it does not matter at all if we are avoiding a rock, wreck, or obstruction, and indeed more often than not they have the same symbols.
Here is a graphic summary of the wreck symbols
1. Top of the wreck is 3 m above the water when the tide is zero. The underline means drying height.
2. Sounding not known, but some part of the wreck must show when the tide is zero.
3. Same as 2, but can be in deeper water if tall enough to show when tide is zero, i.e., if it is 5 m tall it could be in a sounding of 4 m.
4. Sounding to the top of the wreck is 5 m, which is less than the safety depth so the sounding is printed black.
5. Encoded in the ENC as dangerous wreck, with no sounding given.
6. Same as 5.
7. Wreck located on the deep side of the displayed safety contour with a sounding less than the requested safety contour, which is usually same as safety depth, or the sounding is not given.
8. Sounding to the top of the wreck is 15 m, which is more than the safety depth so the sounding is printed in gray. Black vs gray on the sounding color is a property of the sounding itself, not the wreck. It changes at the safety depth for all soundings on the screen.
9. Encoded in the ENC as a non-dangerous wreck, with no sounding given.
Note this display uses the 2-color option, but using the 4-color option does not affect the wreck symbols.
A couple last details about the object Sounding (SOUNDG).
A wreck with known sounding can also have an attribute Technique of sounding (TECSOU), and value 6 means "Swept by wire drag," so the the sounding is accurate. When TECSOU=6, the sounding gets underlined with a horizontal bracket, as shown below, which is in a sense a different wreck symbol, but it is actually the sounding symbol, not the wreck, that is different. These are fairly common in some areas.
In contrast to that precsion, we have the opposite condition of a sounding or position that is uncertain, in which case we would see this wreck plotted this way,
A circle around any sounding, not just those on a wreck, means the value of the sounding is uncertain. There is an attribute QUASOU, quality of the sounding, that applies to wrecks and soundings in general, which can take on values of:
1 depth known
2 depth unknown
3 doubtful sounding
4 unreliable sounding
5 no bottom found at value shown
6 least depth known
7 least depth unknown, safe clearance at value shown
8 value reported (not surveyed)
9 value reported (not confirmed)
10 maintained depth
11 not regularly maintained.
Any value 3, 4, 5, 8, or 9 will trigger the circled sounding, which is SY(SOUNDC2).
Likewise, an uncertain position of the wreck, can also trigger SY(SOUNDC2). The attribute QUAPOS, quality of the position, can have values of:
1surveyed
2unsurveyed
3inadequately surveyed
4approximate (the old PA from printed charts)
5position doubtful (the old PD from printed charts)
6unreliable
7reported (not surveyed)
8reported (not confirmed)
9estimated
10precisely known
11calculated.
Any value not equal to 1, 10, or 11 will also trigger the low accuracy sounding symbol SY (SOUNDC2).
If there is such a QUAPOS value for the wreck, then an additional low accuracy symbol (?) will be attached to the wreck symbol as shown. This is symbol SY(LOWACC01). These can important annotations to the symbols, being the ENC equivalent of the "PA" (position approximate) or "PD" (position doubtful) labels that were very common on paper charts. Very few non-ECDIS nav apps can show these symbols. Turn on Low-accuracy symbols in qtVlm to see them in action.
One thing we miss in the new NOAA Custom Charts (NCC) is the lack of these low accuracy indicators. The information is programmed into the ENC that the printed NCC are based upon, but the present version of the NCC app does not print them.
We are in the midst of a revolution in US nautical charting. Traditional paper charts (TPC) have been discontinued by NOAA — a process that started five years ago and is essentially completed now, Fall, 2024. There are a few TPC that can still be purchased from the NOAA print on demand (POD) outlets, but these are all marked "Last Edition" and none have been updated for many months, and never will be.
In short, there are no more TPC for marine navigation, but this is not such a shocking state of affairs as it might appear. There is a new style of paper chart that is intended to replace the TPC called NOAA Custom Charts (NCC) and going forward we will use these for our traditional chart plotting just as we did with the discontinued TPC.
These new charts have in fact notable advantages over the TPC: one being we can make our own NCC using a NOAA online app that lets us choose the area we want to cover — we are no longer bound to the old, fixed regions of the TPC.
We can also choose the chart scale we want and the paper size we want. The products we create are high-resolution precisely-scaled PDFs that we can print as we see best. We have an article on NCC printing options for the several standard NCC sizes. Quite a bit of money can be saved if we do not need the largest sizes printed on high-quality chart paper. If we do want big charts on traditional chart paper, then we can have our own creations printed at one of the POD outlets by sending them your PDF, or you can without doing anything online, just contact them and ask for an NCC version of your favorite TPC.
The new version you will get for a favorite TPC will be essentially identical with regard to the charing in the water, even using the same ATON symbols you are used to. The land areas will have less detail for the time being, but this will improve in the coming months. In the end, the land areas of the charts could well have much more useful detail than the TPC they are replacing.
The NCC are based on the latest electronic navigational charts (ENC), which are updated daily at about 0500 UTC.
The most important fact about these new charts is this: the way we plot our courses and solve for piloting fixes on a paper chart is exactly the same on NCC as it was with TPC. We will just be using chart sizes and areas of our choosing, rather than the fixed TPC options we had in the past. Now we can have a chart of our own Bay on 11x17 paper that we print at home or at the local Office Depot, or an overview that spans three of the past TPC.
Navigation schools also have much more freedom to set up practice exercises in various parts of the country since chartlets can be printed on letter paper. Note that when making your NCC, you have the option to add compass roses where yu want. So this, too, is an advantage as you can place these where ever you think best.
One handicap that they should overcome shortly is the absence of the Mean High Water (MHW) value for the chart. We need this to predict the range of lights and hilltops as well as to compute bridge clearances. Thus we must learn to look this up at www.tidesandcurrents.noaa.gov and then write it on the chart somewhere. Strangely, this important number is not so easy to find at NOAA, the video below shows how to find it from the ENC in the background of the NCC app. MHW was always on every TPC, but they have yet to figure how to add it to NCC.
We have several related resources you can use to get involved with the new charts. Here are a couple:
How to make a simple NOAA Custom Chart
The State of NOAA charts last half of 2024
Resources on NCC including links to NCC app and videos on its usage.
Part 1. I know the name or number of the discontinued chart I want.
(a) Go to Part 3.
Part 2. I do not know what charts were available that no longer exist.
(a) First we need to find out what charts existed. There is a list of all charts at NOAA but we cannot tell from that what they covered, so we use a trick to learn the names of charts and what they covered. Download this file Historic_NOAA_charts.kml that we will then load into Google Earth (GE), which will show all the historic chart outlines.
Above is what you see after dragging the KML file onto GE, or maybe just double clicking the file might open GE and load the KML file. Then you can zoom into see the charts.
(b) Mouse over a chart outline to highlight it then left click to get the info. This is an example of a discontinued chart, 18433 Haro Strait Middle Bank to Stuart Island. We once had a full set of these spanning the San Juan Islands at 1:25,000 but they are all gone. For now there is just one 1:80,000 for the whole region—but we should get new reschemed 1:22,000 set of ENC sometime early next year.
(Note that if the chart still exists, you can click one of the preview options and see it, but it is easier by other methods to do that....see starpath.com/getcharts.)
For this example, we assume this is the only one we want, ie we want a copy of the Last Edition of this chart, which was discontinued about two years ago—so the one we get is going to be out dated.
(c) Now that we know the chart we want, we can go to Part 3.
Part 3. Get a copy of a chart whose name or number I know
(b) On the first page, click the link to Hide the map search.
(c) Then enter the chart number... space is too small but it will take it! Then press Search.
(d) Now we see the chart we want, Last Edition of 18433. We can download a JPG of PDF of the image. These PDFs are not georeferenced, like the NCC PDFs are. So if we want to load this chart into a nav program, we might as well use the JPG, which we can manually georeference in several nav programs.
We can also take a look at the chart with the Preview link. Again, we are looking at an historic item. We could have several reasons to want this, but we must remember it is outdated.
Same image zoomed in to show it is a high-res image.
Part 4. How to load a historic chart (georeferenced) into a navigation program
(a) To be added. It takes just a few steps and a minute or two!
Traditional paper charts will all be gone in six months; most are gone now. Here is a summary of the USCG's official chart carriage policy, followed by a short background, some details, and direct links to the references.
(1) A non-ECDIS vessel that is required to carry nautical charts may meet that requirement with NOAA Custom Charts (NCC), providing they are up to date (within 6 months) and made at adequate size and scale needed for safe navigation in the waters covered, and preferably on adequate paper quality for routine navigation plotting underway.
(2) A non-ECDIS vessel on inland waters that is required to carry nautical charts may meet that requirement in lieu of any paper charts on board with an ECS of their choice, providing they are viewing official NOAA ENC, using an adequate size screen for safe navigation (large tablet or computer), and the ENC are up to date.
(3) Vessels in coastal waters, when relying on electronic charting alone, must display official ENC on an ECS that meets more stringent environmental standards that are outlined in NVIC_01-16 (ch 2)—and under further development at the moment. The ECS manufacturer must provide a declaration of conformity. In the meantime, appropriate NCC can be used in coastal waters.
Sample section of a NOAA custom chart (NCC)
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Five years ago, NOAA announced to the world that they had begun the process of discontinuing all traditional paper charts and related chart products such as raster navigational charts (RNC), PDF charts, etc. They said it will be a gradual process, but all traditional paper charts will be gone by the end of 2024.
And they have kept their word on this; at the moment, five months from the promised completion date at the end of this year, we have only 195 charts left of the 1100 or so that existed five years ago, and all of those left are marked last edition (LE). They have not been updated for months, and will not ever be. Even these last charts are already historic items. (The last edition of each NOAA chart once discontinued is available at historicalcharts.noaa.gov.)
Traditional paper charts, with their fixed sizes, scales, and coverage areas, are being replaced with new versions of electronic navigational charts (ENC), downloaded at no charge from NOAA. They are updated daily at 0500 UTC. If we want to know what is changed on the LE charts left, we need to check the corresponding ENC.
NOAA is also offering now a new form of printed chart called a NOAA custom chart (NCC) that is based upon the latest ENC data. These NCC play a key role in our chart navigation going forward, as discussed below.
In short, this historic and impactful revolution in charting is indeed taking place. Several major maritime nations have similar plans for ENC to play a larger role in their chart production, but the US will lead the way, as it has historically with other aspects of electronic charting. The UKHO, for example, had announced a similar deadline for their transition to all ENC, but has since postponed the date, perhaps in part because they had not worked out the carriage requirements that is the topic at hand for US vessels.
ENC are not a new concept, even though the new reschemed versions are significant improvements over the legacy versions. ENC have been in use since the mid 1990s. Since 2018, ENC have been required on nearly all commercial vessels on international voyages. These international ships, and other classes of ships in US waters are required to display the ENC using a type-approved hardware and software system called ECDIS (electronic chart display and information system). But these classes of large "ECDIS vessels" are not a subject at hand, because their rules on charts are not affected by the demise of traditional paper charts.
The International Hydrographic Organization (IHO) specifies the standards for the content and format of ENC in a document called IHO S-57. The IHO also specifies how ENC should appear on the navigator’s chart screen in IHO S-52. An ENC of any nation by definition meets the requirements of S-57, and ECDIS chart display from any manufacturer by definition meets the requirements of S-52.
In Jan, 2016, the USCG announced (NVIC_01-16) that all commercial vessels not required to use ECDIS, may use ENC in lieu of paper charts, and spelled out the details required. Chart display systems (nav apps and chart plotters) that do not meet ECDIS standards are called electronic charting systems (ECS)—which is not a generic name, it is an official IHO definition.
This document was then notably updated in May, 2020 (NVIC_01-16_ch2) and added clarification of the use of electronic versions of other required publications such as the Navigation Rules Handbook, Coast Pilots, Light Lists, and tide and current data—recall that in 2020 NOAA discontinued the authorized publication of annual tide and current tables that use secondary station corrections (Tables 2), and since then it is up to mariners to create their own appropriate tables for required stations using the convenient options at tidesandcurrents.noaa.gov. Tables 2 corrections still in print today are not authorized nor dependable.
Then in June, 2023 an historic internal USCG Policy Letter (NAVPOLTR_01-23) explained the crucial role of NCC.
Those two documents spell out the rules on chart carriage and display that govern chart carriage after the end of this year when all traditional paper charts will be gone—and they govern the policy right now for areas where there are no paper charts left of an appropriate scale for safe navigation.
Please read the full documents linked below. My notes here are only brief paraphrases.
Chart Carriage Requirements During NOAA Chart Sunsetting Plan,
• Though not stated elsewhere to my knowledge, this document confirms that NOAA custom charts NCC will be accepted as meeting chart carriage requirements, provided:
(1) They are up to date (within 6 months)
(2) Made at an adequate scale and paper size for safe navigation in the waters at hand
(3) Preferably printed on adequate paper quality for routine navigation plotting underway
• The preference (3) suggests using one of the existing print on demand (POD) chart printers. Several are set up to accept a mariners homemade NCC, and some are offering predesigned NCC options that replicate as near as possible the traditional chart coverages. They are accustomed to chart printing on quality paper.
• The Policy Letter does not rule out individual printing of chart booklets on smaller size paper similar to those used in commercial chart booklets. The economic 34" x 22" option (ANSI D) might meet single chart or booklet applications for smaller commercial vessels.
• The Policy Letter anticipated an important advance in the NCC program that has since been implemented. Namely, in NCC ver 2.0, mariners can save their NCC designs and then return to them and with two button clicks create an updated version of their saved NCC design. We anticipate NCC app ver 3 in mid July.
• Also noted in the Policy Letter is the fact that NCC do not have chart numbers so there are no Local Notices to Mariners presenting proposed or actual changes for specific NCC, but mariners can check on line for latest ENC updates to the regions they have charted and that way decide if a new NCC is needed or not from their saved NCC design—this is a new update to this updates page, making it even easier stay aware of ENC updates that could affect the NCC.
• It should be noted that the Policy Letter has an expiration date of April, 2025. So until something shows up in the CFRs we should be be aware that things could change at that time.
• References: CG-NAV Policy Letter 01-23, 8b (1) and (2)
Use of Electronic Charts and Publications in Lieu of Paper Charts,
Maps and Publications,
Navigation and Vessel Inspection Circular number 01-16, 16700.4
Again, please read the full document; it includes an interesting history of paper and electronic charting. My notes are just brief paraphrases, with these short takeaways...
• The rules for electronic charts only (no paper charts on board) are different for inland vs coastal waters, where "coastal waters" in this context means anywhere on the outer coast, seaward of the MLW line.
• On inland and coastal waters, however, the key factor is we must use official NOAA ENC that are up to date and of adequate scale for the navigation at hand. (This is not a major concern, because most suitable ECS (nav apps), and there are many as noted in the NVIC, offer the option to check for latest updates and load all scales available with a couple button clicks.)
• We stress that third-party charts or charts described as "based on ENC", "modified ENC," "Enhanced ENC," etc, do not qualify. For non-ECDIS vessels to rely on electronic charts only, they must use official NOAA ENC, presumably obtained directly from NOAA, who provides them at no charge, updated daily at 0500 UTC when changes are confirmed. Light List changes take about a week or so to enter into the affected ENC updates.
• A non-ECDIS vessel on inland waters that is required to carry nautical charts may meet that requirement in lieu of any paper charts on board with an ECS of their choice, providing they are viewing up to date NOAA ENC, using an adequate size screen for safe navigation. This is not spelled out more specifically here, but we can note that the IMO Performance Standards for ECDIS, Sec 10.2, calls for a minimum screen size of 270 mm x 270 mm (10.6" x 10.6"), which is about the size of a nominal 13" laptop or an iPad Pro—keeping in mind that ECDIS standards are not required for inland ECS usage.
• Non-ECDIS vessels traveling in coastal waters when relying on electronic charting alone, must display official ENC on an ECS that meets more stringent environmental standards that are outlined in NVIC_01-16 (ch 2)—and under further development at the moment. The ECS manufacturer must provide a declaration of conformity. In the meantime, appropriate NCC can be used in coastal waters.
• This NVIC also clarifies that digital copies (PDFs, for example) of tide and current data, Coast Pilots, Light Lists, and Navigation Rules Handbook can also meet similar carriage requirements—which is a reminder to all vessels, even those not formally required to carry such documents, that they can meet prudent safe-navigation document needs with digital products.
The active government agencies, USCG, NGA, and several divisions of NOAA, make it very easy to download the documents and keep them up to date. Storing them in the library of your favorite ebook reader is one way to organize them, with convenient search, bookmark, and highlight tools. Ship and instrument manuals can be in another library folder.
Sample ENC section of the same region shown above as NCC, viewed in qtVlm. This ENC has a compilation scale of 1:12,000. It can be zoomed to show detail.
Zoomed section of the above. Many ECS offer the option to highlight sector light coverage; in this case we see the green light marking the top of the main San Diego Bay entrance range
Summary
These basic rules for the smaller commercial vessels that do not require ECDIS seem very reasonable and practicable. The ECS "of our choice" to view the ENC could be any of the many commercial and even free versions available now, such as Coastal Explorer, TimeZero, Expedition, OpenCPN and qtVlm. All show official ENC with convenient means of chart downloading and semi-automatic chart updating. They run on computers and some on large tablets, and all include the range of functionality wanted in a versatile ECS. There are certainly numerous others we have not tested.
The NCC program for the paper chart alternative is very attractive and slowly becoming better known. There is certainly room to improve, especially with regard to terrain coverage, but this is understood and on the table to be improved. Indeed, with all the GIS information available these days on elevation contours, roads, building, ground cover, and so on, we can expect NCC of the future to be superior in this regard to the limited but valuable examples on the paper charts being discontinued.
Recreational mariners are not directly affected by chart carriage requirements of commercial vessels, but it is fair that they look up to their rules as guidelines to prudent navigation. And all mariners are, of course, bound by Rule 2a ("good seamanship rule") of the Navigation Rules.
Sailing and Navigation Schools
On the water training of students who paid for the training are required to have a USCG licensed instructor and the vessels are required to have authorized nautical charts on board. Between now and the end of the year, if there is still a traditional NOAA chart available of adequate scale for safe navigation then a copy of that chart will meet this need until Jan 1, 2025. After that, the training vessel must have either an NCC made as noted above, or have a tablet or computer showing official NOAA ENC of the area as explained above. Third party charts do not meet the requirement, and viewing on a small screen (ie phone) alone will not meet the need according to the documents presented.
On the water training in certain restricted waters that do not require a licensed operator do not have these chart requirements, but simple prudence would call for them in any event. As noted, Rule 2a still applies to all navigable waters, as do perhaps local and state rules.
It seems logical that all navigation training should begin the transition to NCC in place of the historic training charts, which have frankly been distractingly outdated for many years. We are now working on NCC replacements for 1210tr and 18465tr. The challenge is creating NCC that have adequate labels so the many standard exercise books and tests in use nationwide for decades can be adapted to the new NCC. We also have a unique challenge of how to cover a significant section of 18465tr that is now only covered by a Canadian ENC.
Even though the historic training charts will remain available, it seems a disservice to students to continue to use them. NOAA has helped with this transition in that they use on the NCC the traditional chart symbols for all ATONS, rather than the official ENC symbols. Presumably that will change in a year or two... or at least we will have the option to show old symbols or official ENC symbols.
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Our text and reference books on ENC usage can be seen at starpath.com/ENC
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I will be adding a series of videos on the background for this post, starting with this one:
Strong winds come from a variety of weather patterns. Some are large like a mid-latitude Low, some mid-size like a tropical wave, and some quite small like those found in narrow gaps between islands. Some winds are transient like a downdraft from a passing thunderstorm while others are more persistent like the strong summer winds along the southern Oregon and northern California coast.
Strong winds from larger, longer lasting weather systems are generally well quantified by weather models and included in the official forecasts. But smaller scale, shorter duration winds can fall below the resolution, temporal and spatial, of weather models and can be better described by how likely they are to occur in generalized areas. Winds driven by Wake Lows fall into this latter category.
A Wake Low is defined by the American Meteorological Organization as:
a surface low pressure area or mesolow (or the envelope of several low pressure areas) to the rear of a squall line; most commonly found in squall lines with trailing stratiform precipitation regions, in which case the axis of the low is positioned near the back edge of the stratiform rain area.
Because squall lines are bands of thunderstorm, (a.k.a squalls when over water) typically ahead of cold fronts, it is useful to look at the structure of a single squall.
The squall has a life cycle that starts with a growing phase. In this initial phase, surface winds flow radially inward at the base. These we watch with a weather eye to see if they may eventually become towering cumulonimbus. If they grow to full maturity, there is a second phase that has a downdraft creating strong wind that comes with heavy rain, perhaps even hail.
Wind patterns with the two phases of the squall are shown in Figure 1. Notice the strong winds from the downdraft are in front of the squall while behind it the wind can be light or flukey. The difference in the winds fore and aft of the squall is because the speed of the movement of the squall adds to or subtracts from the wind circulating in the squall.
Figure 1 (from Modern Marine Weather by David Burch)
In Figure 2, typically the squall movement would be from left to right. In the mid-latitudes that would be roughly west to east or in the trade winds from east to west. Because squalls are embedded in and move with the upper level winds, it is best to review the 500 mb maps or model data or even local soundings to get a sense of squall movement.
Figure 2
Figure 3 shows the atmospheric pressure distribution along the cross-section shown in Figure 2. The Mesohigh is found under the core area of Figure 2 and the Wake Low is in the area under the stratiform clouds.
Figure 3
As the squall moves from left to right, the leading low pressure area experiences strong winds blowing from the Mesohigh and toward the low. This is the source of the common wind gusts commonly experienced on the leading edge of a squall.
On the aft side of the squall, the wind is again driven by the Mesohigh toward low pressure. Because this area of low pressure is on the aft side of the low or in its “wake”, the term Wake Low seems to fit. One key takeaway is that the wind direction will reverse or at least make a very large veer due to the reversal of the pressure gradient as the squall passes. How quickly the wind direction changes would be affected by the strength of the pressure gradient and speed of the squall.
Wind speeds can be estimated using the pressure gradients and scaling provided in Figure 3. With some unit conversions, the pressure gradient in millibars/degrees latitude would be about 4 mb/0.6*. From Figure 4, assuming 45* latitude, this gradient estimates a wind speed of 76 kt! Although this is just a graphic for demonstration purposes, the magnitude of the wind speed is worth noting.
Figure 4
Figure 5 is from a case study of a Wake Low that occurred on September 2, 2010. The National Weather Service analyzed the pressure drop over a 2 hour period (blue dashed contours) of up to -3 mb. The Duluth International Airport actually observed a 6.1 mb pressure drop in only 28 minutes resulting in a wind speed of 50 kt.
Figure 5
Because Wake Lows are a relatively small scale, short duration event, they are difficult to forecast in terms of wind direction and speed at a specific time and location. However, squall or thunderstorm potential is routinely forecast by the NOAA Storm Prediction Center in its Mesoscale Discussions and Convective Outlooks for CONUS and coastal waters, Figure 6.
Figure 6
While the case studies tend to be in the upper mid-west area of CONUS, they do not suggest that Wake Lows would be limited to those areas. It may just be that only over land is there enough observational data to support the analysis of this relatively small-scale, transient event. This leaves mariners to ask whether winds resulting from Wake Lows could happen more generally anywhere squalls are found. After all, strong winds that radically change direction are something to look out for!
Summary
·Wake Lows are atmospheric low pressure areas found on the aft side of squall lines
·Fluctuating pressure gradients caused by Wake Lows can cause dramatic changes in wind direction
·Strong winds are a potential both on the leading and trailing sides of squall lines
·Wake Lows are small scale, transient events that may be anticipated where squall lines are forecast
·For safety, anticipate strong and gusty winds, as well as heavy rain and lightning with cumulonimbus clouds
