Wednesday, July 17, 2024

Nautical Chart Carriage Requirements When Traditional Paper Charts No Longer Exist

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)


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

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 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,

CG-NAV Policy Letter 01-23


Key takeaways include...

• 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.

• We have a portal of NCC related links at

• 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.

• References:  NVIC_01-16 (ch 2), Enclosure 1, Sec B1, A2, B2. Enclosure 2, Sec B7c.

• 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


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.


Our text and reference books on ENC usage can be seen at


I will be adding a series of videos on the background for this post, starting with this one:

The US Nautical Chart Revolution,
Part 1: State of NOAA Charts, Last Half of 2024

Thursday, July 11, 2024

Wake Low Winds: When you thought the worst was over!

By David Wilkinson
Starpath Instructor

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!


·      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


·      American Meteorological Society Glossary

·      Modern Marine Weather, 3rd ed.

·      Storm Prediction Center