Thursday, October 8, 2015

Use of the Mintaka Duo Log Pressure Option to Set Ship's Barometer to SLP

Ship captains often prefer their barometers set to read sea level pressure (SLP) to simplify weather reports and comparisons with weather maps. 

Recalling our jingle "point four-four per floor" as a reminder that a 12-ft change in elevation corresponds to a pressure change of 0.44 mb, we see that a large ship could easily have a correction of 3 mb or more, depending on the instrument height above the water. Also it is not always easy to  determine the actual barometer height above water level when it is 5 or 6 levels above the main deck. Sometimes the value historically assumed on board could be more an anecdotal value than one rooted in an actual measurement or taken from ship's drawings.

This question and be answered—or even by passed—with an accurate, portable barometer. First, such a barometer could be used as an accurate altimeter to measure this height difference in feet or meters, or as we note here you can use it to circumvent this question, and set the ship's barometer directly without the intermediate step or knowing or measuring its height above sea level or a specific water line, such as the Summer Load Line.

In short, we just measure the pressure at sea level with an accurate portable barometer then proceed to the ship's barometer and set it to that value. This involves writing down the pressure at sea level because it will change (decrease) as soon as we move up the ship. And since this process must often be done in a short time with numerous distractions, this writing it down offers a chance for error that could have long term implications to the weather work of the vessel.

The Mintaka Duo barometer offers a convenient way around this using its Log Pressure function. This function automatically stores the pressure and tendency at the synoptic times into a custom data file of these pressures.  But we can force a pressure into this list whenever we choose with the Log Now function. Thus you can digitally "write down" the pressure you need with a button push.

Step 1.  Hold the Duo at or near sea level for 12 seconds or more and then log the pressure.

The Duo button steps are: 

                 [EXIT]  to see main menu
                 [+] [+] to  Log Pressure and [SELECT] [SELECT] to log the pressure.

Then see the logged pressure marked with an *.


 Step 2a.  If you just want to set the ship's barometer to SLP, then go directly to the ship's barometer and set it to the logged pressure. (See Note 3 below on the possible influence of tide height on this adjustment.)

Step 2b. If you want to know or check the elevation of the barometer above sea level or a specific water line, then carry the Duo directly to the height of the ship's barometer and record the new pressure. It will be somewhat lower than it was at sea level. Then find the Pressure Difference:

Pressure Difference = [Duo pressure at sea level] -
[Duo pressure at Ship's barometer height]

Find the ship's barometer elevation from:

Ship's barometer elevation above sea level = Pressure Difference x (12 ft / 0.44mb)

See Note 2 on the use of different reference levels.


1. We need to hold the Duo near sea level (or at any reference level we are using) for at least 12 seconds because the instrument reads the pressure every second, but then averages the 10 latest pressures for display and logging. Thus the pressure you see on the screen that updates every second is actually the average over the past 10 seconds. 

2. We have shown Step 2b schematically using the waterline as a reference for the height measurement, but it could be done using the summer load line level for this reference. Our jingle for the size of the correction keeps this difference in perspective.

3. The height measurement in Step 2b, regardless of reference level selected, does not depend on tide height.  But the Step 2a procedure of setting the ship's barometer to read sea level pressure does in principle depend on the tide height.  In many cases this will not matter, but in harbors with large tidal ranges it could well be that the height of the water does not represent mean sea level. We have discussed this issue in an earlier note called Mean Sea Level, Tides, and Barometers.

Monday, October 5, 2015

AP Release on Tragic Loss of El Faro is Misleading.

When it was finally concluded that the vessel had been lost in the storm, the AP release included this statement:

It is indeed true that when the ship left the dock in Jacksonville the system was a tropical storm. I am not sure what they meant by "still a tropical storm" but it was indeed a tropical storm. But that is not the issue at all.

At the time they left the dock, this was the forecast from the NWS.


1500 UTC TUE SEP 29 2015




34 KT.......  0NE  60SE   0SW   0NW.
12 FT SEAS.. 90NE  90SE  60SW  90NW.


FORECAST VALID 30/0000Z 26.4N  71.5W
34 KT... 30NE  60SE  20SW  20NW.

FORECAST VALID 30/1200Z 26.3N  72.4W
34 KT... 30NE  60SE  30SW  30NW.

FORECAST VALID 01/0000Z 26.2N  73.1W
50 KT... 30NE  20SE  20SW  30NW.
34 KT... 50NE  70SE  50SW  50NW.

FORECAST VALID 01/1200Z 26.1N  73.7W

50 KT... 30NE  30SE  20SW  30NW.
34 KT... 70NE  70SE  70SW  70NW.

FORECAST VALID 02/1200Z 26.0N  74.0W

50 KT... 40NE  40SE  30SW  40NW.
34 KT... 90NE  90SE  80SW  90NW.





Below here we see that the forecast at the time of departure was indeed very good, and when you fold into this the standard Mariners' Safety Rule 1-2-3, we see that there was not any way to bypass this system on the way to Puerto Rico.  See also the similar warning at the end of their forecast.

In short, the AP note on what was there at the time and not saying what was actually forecasted at the time is negligent reporting.

Mintaka Duo Barometer at the Annapolis Boat Show

The Starpath Mintaka Duo barometer heads east for the Annapolis Boat Show.  See it at the Weems & Plath booth (40A and 40B) in Tent C.  Weems & Plath are a world leader in barometer production and distribution and we are pleased they will  be presenting the instrument at the show.

 Read about the instrument here (Mintaka Duo), which also has an extensive support page.  Below is a screen capture from the new computer (Mac or PC) app called Mintaka Commander for displaying data and interacting with the device.

Tuesday, September 29, 2015

Manual of Barometry (WBAN) Now Online

This is the biggest news of our day, Sept 29, 2015.

While  working on updates to our Barometer Handbook, we found that the 1963 Manual of Barometry (WBAN) has now been scanned and available as a free download.  Apparently it was scanned the year following the publication of The Barometer Handbook.  I would like to think that our promotion of this rare, amazing book contributed to this?

WBAN is the Bible of mercury and aneroid barometers, as well as the basics of measuring barometric pressure... in fact, i wish there were a stronger way to put that description... maybe the Mother of all books on barometers... and altimetry.  It is the monumental work of Louis P. Harrison, but other than a note in the Preface he does not often get credit for it as he was an employee when he wrote it and this was an official "US Weather Bureau" document, numbered WBAN.

(The US Weather Bureau evolved out of the US Army Signal Corps in 1870s. It spent the 1880s in the Dept of Agriculture, and then became an agency of its own in the early 1890s. It moved into the Department of Commerce in 1965 where it resides today as the NWS in NOAA.)

We have had an extremely rare printed copy for many years, without which our work on barometers in general would have been much more difficult, and probably not as thorough.

It is not easy reading; most of the thousand or more pages are pretty technical... in some cases really specific (ie taking into account your latitude and the shape of the earth when computing the weight of mercury and your height above mean sea level), but if you have a question about how to use barometers for getting accurate pressure, then this is the primary source, and we list is as such in our own books.

It also includes one of the first compilations of the fudge factors used to convert observed pressures at higher elevations to realistic sea level pressures, the need of which was first recognized by the American scientist William Ferrel in the1880s. He called this the plateau effect and these constants are still in use today.*  Ferrel also discovered the Buys Ballot law (which was even acknowledged by Buys Ballot himself) and he was first to apply the concept of Coriolis force to the circulation of global air masses, and as it is generally used today,  can be thought of as having invented that as well... though this has a bit more nuanced history.

Find the pdf here:

What you do with accurate pressure once you get it is discussed in our books Modern Marine Weather and The Barometer Handbook.

Note that the title page calls the book Volume 1, and the Preface refers to what was intended for Volume 2, but to our knowledge, there is no Volume 2 — when you finish this one, I am sure you will be dying for more, but I am afraid this is all there is.

* Ferrel in the 1880s also showed that the outside air temperature needed to make the conversion between station pressure (ie at elevation) to sea level pressure should not be the present air temperature, but rather the average of the present temperature and that of 12 hours earlier.  We did a study in 2013 that confirms this is indeed the case. See Air Temperature Dependence of Sea Level Pressure Conversions

Saturday, September 26, 2015

Grib Viewers — New Developments and Special Features

Modern weather work underway relies on “grib data.”  This is sailor’s jargon for surface analyses and forecasts presented in a gridded binary format called “grib.” These are vector data given for each point on a Lat-Lon grid. High resolution data can be as fine as 0.12º (7 nmi) between points,  on up to 1.0º (60 nmi) between points. A grid spacing of 0.5º often meets ocean route planning needs.

Wind speed, wind direction, and sea level pressure are the primary datasets needed for planning, but also available and often useful include the height of the 500 mb surface and wind speed at that level, sea surface temperature, precipitation (rate and accumulated), wind gusts, and air temperature. There are also dozens of other atmospheric parameters that are available in this format that we do not often use at sea.

Most of this grib data now in use are the direct computer output of numerical weather prediction models, the most popular of which is the US Global Forecast System (GFS).  Thus we are looking at the same data the professionals use to make their official forecasts. The professional forecasters at the NWS, however, also look at models from other nations, some of which do better than the GFS in some cases. They also have more varied ways to look at the GFS data itself.

Thus it is our obligation underway to check the grib data we use, i.e. GFS, with the final forecasts of the NWS. These two forecasts (GFS and NWS) will be very close more often than very different, but for crucial decisions, or for fine tuning routes as when racing, we must rely on the NWS forecasts, which brings us to one of the main points of this note.

There is increasing  awareness and availability of the National Digital Forecast Database (NDFD) in grib format.  Unlike all of the other grib datasets, this one is actually created by professional meteorologists who are looking at all model predictions before they create the NDFD forecast. The NDFD grib data are the same we see in the NWS graphic maps. The first entry in the NDFD grib set (h00) is the surface analysis, h24 is the 24-hr forecast, h48 the 48-hr forecast and so on. The difference now is we have these every 3 hours, not just as the traditional synoptic valid times shown on the graphic maps. Unfortunately, the global coverage of the NDFD is limited, but for extended US coastal waters we have good coverage.

You can get the NDFD grib data with an email request to saildocs (, and now we are pleased to see this appear in commercial products like WeatherNet for PC from Ocens ( They offer both standard and high resolution NDFD data in the traditional convenience of the WeatherNet interface. Resolution becomes a key factor underway when we are downloading by sat phone or HF radio.  The very high resolution of NDFD (0.12º) is not needed for open ocean sailing and it can make the files very large. The high res data are best reserved for forecasts near tropical systems or along coastal waters where you might want to detect diurnal changes in the wind closer to shore or within bays.

The other exciting news from Ocens is they now offer the ASCAT scatterometer data in grib format through their WeatherNet service.  This wind data is not a forecast; it is the true wind speed and direction measured on the ocean surface as the ASCAT satellite passed over it—normalized to a height of 10m, the same as the GFS winds are.  We only get this unique data about once a day for any one location, but it is a definitive evaluation of a forecast at the time, which we need in crucial decisions.

It is not a surprise that Ocens would be the first to offer this ASCAT grib data as they were indeed the pioneer in this field. In collaboration with the NWS, they offered the first ever grib scatterometer data from the QuickSCAT instrument back when that scatterometer was working. Unfortunately, it stopped transmitting the type of wind data we need in 2009, which was rather before many mariners got to know the power of the data source. So scatterometer grib data is back, and we hope to see more of it.  In the interim, the Indian Met office launched the OSCAT instrument, which provided very good data for a while, but it too has failed.

The latest scatterometer news is the US RapidSCAT instrument on the International Space Station.It provides a broad swath of data (as QuikSCAT and OSCAT did) but its data are in a form that is more difficult to convert to the type needed for our typical grib viewers. The ASCAT instruments (on satellites MetopA and MetopB) are part of the European Space Agency. You can see and access graphic images of all scatterometer data at Ocean Surface Winds Team website  (google ASCAT).

Another new development in grib viewing is a low-cost, high-quality grib viewer and data source for Macs called LuckGrib ( It was developed by Pacific NW sailor Craig McPheeters, created in large part while underway in the South Pacific. LuckGrib has an elegant design and convenient interface, with several unique features added to the standard functionality we expect from a high-quality weather tool.

For more background on the important role of grib viewing software and the acquisition of grib files underway in Mariner's Checklist Before Departure.

Special Features of Selected Grib Viewers

There are many grib viewers for computers and tablets with as many different styles of data presentation and unique features, so I have focused here on viewers that can show NDFD grib data, regardless of where the data files were obtained. It is not uncommon to download a file from one source or viewer and then display it in another viewer. We hope to eventually see more sources offering the NDFD grib files, because these are likely to be the best global data available for the waters it covers. It will take a lot more study to decide if a regional model such as COAMPS or NAM might be better for near coastal waters in some cases. Discussions that favor these over GFS (an almost certainly a valid conclusion near shore) may not have made the same comparison with NDFD.
Special features of several grib viewers are shown in the graphics below.

Figure 1. Ocens Grib Explorer for PC showing ASCAT data on the left.  Each of the individual wind arrows is tagged with the valid time of 1743z, Sept 8, 2015. This is a crucial step in the practical application of this data.  Some viewers capable of showing the Ocens ASCAT grib files do not yet include this important time information. Each ASCAT file includes multiple satellite passes (data swaths) and these swaths have different valid times. On the right is the GFS forecast for 1800z for comparison. Also shown is their “route planner” tool that lets us draw a line between selected waypoints and view the wind and pressure at a specific time along that route.  The tiled display is a unique feature of Grib Explorer for PC.

Figure 2. LuckGrib for Mac has a “measure distance” tool that can be used for route planning. It can be marked in intervals, such as  distance run in one day. Then we can move the valid time slider back and forth to watch wind and pressure vary along the route. The high performance of LuckGrib makes this a smooth and informative demonstration of what we might expect. Then we can adjust the route and look again. This is also a convenient way to study and forecast special diurnal winds such as the Coromuel off of La Paz.

Figure 3. ViewFax from Saildocs is a popular grib viewer for PC with numerous special options. Its overall design is very basic, but it includes sophisticated features in a functional manner.  It displays both ASCAT and NDFD data. It has a direct approach to route planning: you select the starting location of your vessel at the h00 time, along with the intended course and speed.  Then each time you advance the forecast time to the new map, the vessel moves to the corresponding location it would have at that time based on the entered speed and course and a pop-up shows the wind and pressure at the vessel. Also shown here is an over lay of the 500-mb surface heights, which offers a good way to evaluate the stability of the surface pattern and dependability of the forecast. See Modern Marine Weather for details.

Figure 4. Expedition from is a premiere sailing performance and navigation program that includes sophisticated weather routing using grib files. It automatically finds the best sailing route to match your polar diagrams, taking into account not just the wind, but also ocean currents and sea state. You also have the option to scale or rotate the grib files to match actual observations.  Though a long established product, we include it as it does show NDFD data and it has a newly enhanced meteogram feature for viewing wind and pressure over time at a specific point. The examples shown illustrate the different behavior of wind shifts on the two sides of a tropical storm. See an expanded discussion of this topic in an earlier post.

(The popular ugrib viewer from also has a meteogram function, but it will not show NDFD data and does not have any route planning features.)

Meteogram display from ugrib.

Figure 5. Coastal Explorer from is a popular echart program that also shows grib weather files obtained from other sources, and indeed it will display the NDFD data. Shown here is one easy way for a quick overview of weather conditions. We set multiple range rings on the h00 vessel position at 50-nmi intervals (6h run at 8.3 kts), then we can step the forecast forward with an estimate of where we would be at that time. This program and the others illustrated here will also show ocean currents to help with route planning. The RTOFS or OSCAR ocean current data are readily available in grib format by email request underway.

Monday, August 31, 2015

Sides of a Tropical Cyclone, Part 2 Meteograms.

In Part 1 of this topic, we looked at a way to study the wind and pressure on both sides of a tropical cyclone (TC) using any grib viewing program. There are many such programs available and the method outlined does not require any special features. Any of them could be used.  In this note we look at another way to study this that takes advantage of a special meteogram feature of the navigation and weather program Expedition.

In the presence of an approaching TC, we can judge where we are relative to its path by watching the wind speed, wind direction, and pressure from the perspective of being on one side of the storm's path or the other. In the Northern Hemisphere (NH) the right-hand side when facing in the direction of the storm's motion is called the dangerous side, whereas the left-hand is generally more manageable, at least if some distance away from the center, and it is called the navigable side. Part 1 included background on this and references.

The names are in large part based on the fact that the approaching winds on the dangerous side tend to push you into its path, whereas on the navigable side the approaching winds push you away from its path. The sea state on the dangerous side is also notably steeper and more chaotic.

A meteogram is just a plot of the wind, pressure, temperature, etc as a function of time. Time can be plotted forward (a forecast) or backward, a history.  The latter plots are a nice way to see, for example, that wind direction undergoes a prominent veer at the passing of any front.  Using a meteogram as a forecast we can show graphically the behavior expected on each side of a TC, as shown in Figure 1.

Hurricane Guillermo on Aug  3-5, 2105. The same example was used in Part 1. The background and meteograms are from Expedition, version 10.0.12.
Here we see in a much more direct manner what we discussed in Part 1. The blue stripe in each case marks the conditions we would observe from a stationary position over the day the system approached.  The two side points are about 70 nmi to each side, with all 3 being about 200 nmi off—which before any further discussion we have to say are all three very close to this system.  Such intense systems to not emerge suddenly, or if so, extremely rarely.  In this case we would have had at least 3 days earlier to know where this storm was going to be at this time. Thus how we ended up in one of these positions is an entirely different issue!  In short, we would have to say that we are primarily thinking about rare situations in which we did not have contact with the outside world and thus did not have the official forecasts.  But then, even with that assumption, we have to assume further that we did not have a $200 SW radio on board that would have told us the storm location and motion at least once every hour. Such a radio runs on batteries and is not dependent on the ships power.

Looking at conditions during the blue bar, we see first one important factor.  In all three locations we did not see much interesting at all for the first 6 hr, and that is because the closed isobars of the system had not yet reached us.

Once the closed system reaches us we see the expected behavior. On the right the wind builds and starts to veer. On the left we see the wind backing, but it actually falls off a bit, and in any event this far off the axis it never does build much.  This illustrates the value of getting as far as possible from the center of the storm as it passes.

In all three cases we see the pressure going down as the Low center approaches. There is more discussion in Part 1. The main goal here was to shown this new way of studying this behavior.  As it turns out, we have three very large systems in the Pacific right now, so I will try to grab some data and make a video of the use of these metorgrams.

There are other ways to generate meteograms using online resources, once you know the Lat-Lon and time you want. Most of these must be near live times, however. One example is  but I recall others that are easier to use.  I will add them here as i find them.

Wednesday, August 26, 2015

Commercial Echart Ad is Food for Thought

It is not clear that they have thought through the marketing logic here, which only adds to the challenges we face moving into the realm of modern navigation.

[Recall MacDonalds long term request that we "Put litter in its proper place," which has to mean throw your trash on the ground... else it would not be litter.]

From an August 26 email ad.

If they do indeed make 2,000 corrections per day, what is it they are correcting? 

The true charts themselves are not changing anywhere near that rate, even on a global basis. So this simply means they are mostly correcting their own errors in their own proprietary electronic charts. [*]

Thus we learn several things. Good—these charts are getting better every day. Bad—they indeed do have a lot of errors in them. (See related note.)

So the recommendation we make remains the same. When using electronic charting we are still better off with raster charts (RNC) when available. These are direct copies of the latest official charts, which these days are updated every week at no charge. Then if we want the convenience of some commercial vector chart such as this one in a packaged set of electronics of software program, we can then check it with the latest RNC or ENC.


[*] To be fair, maybe they are not just correcting actual errors but adding new information, to an otherwise correct chart. That would have to  be checked, and evaluated. If the addition is something that is already on the official charts, then is that an "error"? If it is adding something that is not crucial, then that is what it is. 

The reason vector charts (official or commercial) will eventually be our main resource is they offer so many layers of information, and are indeed easy to update, even remotely. Some of the information in deep layers is not crucial often, but could be in special circumstances. 

So the 2,000 updates a day shows they are working on this.  My comment here has more to do with the choice of marketing idea. My first impression was with that many updates, they must have a lot to fix.

Sort of like advertising ones level of experience in navigation by citing all the hurricanes they have sailed through.  I would tend to listen more to the person who has sailed all their lives and never been in a hurricane.

Monday, August 17, 2015

Mariner’s Weather Checklist Before Departure

 It is fundamental to safe efficient weather work at sea that these items be checked off and tested before departure. Having it all onboard without prior testing does not count!

(1) Barometer. This is key instrument to any ocean or coastal passage. Check it over a large pressure range using free service at,  or just interpolate the isobars to get the correct pressure for your location at the synoptic times from unified map at For electronic barometers, be sure it is on and running for a few days before departure. Ideally, record the pressure for a week or so before leaving and compare what you recorded with the official values mentioned above.

(2) Wind instruments.  To measure apparent wind speed and apparent wind direction, and they should be calibrated.

(A nice backup to both of these is the small handheld Kestrel 3500. The barometers on these that we have tested have been excellent. It is easy to check the windspeed driving along in a car holding it out of the window. Using one of these to check your onboard instruments, remember that wind at the masthead can be notably different from wind on the deck.  Might have to take it up the mast.)

(3) Calibrated knotmeter and magnetic Compass, and calibrated heading sensor.

(4) True wind from Apparent solution. We need some procedure to convert apparent wind to true wind that is well tested and practiced. This can be done within the wind instruments themselves or some other electronics box they plug into, or it can be done by inputing the data to a computer and computing it there,. Or it can be done by hand with a calculator, which is best done with one that is programmed to do this. There are numerous smart phone and computer apps for this.

(5) Laptop computer. There are certainly ways to do safe weather work without one, but  a computer makes everything related to weather very much easier, more versatile, and better. I would consider it a required item since so many of our best resources are obtained via the computer. In fact since computers are so inexpensive these days, it is not even unreasonable to set up one with all your nav and wx software and connections and then just clone it to another one which you take as a back up.  The back up could be a notebook size that might cost only some $300 or so.

(6) Communications.  This would mean either a sat phone or an HF radio with Pactor modem.  The sat phone is definitely easier, but day to day usage is more expensive.  HF radio work could be near free once set up, but the investment would be notably more than a sat phone to set up from scratch.   It would be nice to have both, that is if the boat is already set up for HF radio then add a sat phone for convenience and dependability.  If not set up already, it would be harder to justify the expense compared to sat phone only.

There are these days all sorts of other communications options, from satellite broadband to systems that connect everything on the boat wirelessly.  However, the basics are in item (6) and they should be there regardless of the other luxuries.  In a sense, the more you have the more that can go wrong, so you want to be able to pick up the sat phone and make a call, or plug it into your computer and send an email.

(7) Software for email. We need software to send and receive emails with attachments… with no restrictions on what we say or include, which rules out the basic ham radio programs. There are numerous options. Airmail from Saildocs is one. Ocens, Xgate, or UUPlus are a couple other options. Each has unique services or features; the prices vary somewhat, but not a lot.

With (6) and (7) in place you can send and receive emails and email attachments by satellite phone.  All of these offer the option in setup to switch between communicating by sat phone or communicating by Internet.  Underway you will use the sat phone, but once in a harbor with Internet, you switch to that.

On the other hand, for getting set up and tested before departure you would also primarily use the Internet connection, but it is crucial that you just spend the air time and do several transfers by sat phone. You want to be 100% certain that this system is working, i.e. send and receive emails with attachments. Turn it on and off, computer on and off, reboot, close all, start again, switch back and forth between sending by sat phone and by Internet, try multiple types of files (discussed below), etc. The main point is to be sure this is all working well before leaving and that you have used it for a couple of weeks at least getting your weather information, as outlined below.

(8) Software for GRIB viewer. Many, if not most, echart programs include the option to overlay GRIB formatted weather data right on the echart you are navigating with.

I assume you will have some echart program in a laptop for navigation that is tracking your GPS position. ( If this has not been planed, i.e. you have a console unit from your navigation electronics doing this tracking, then you may want to consider adding the laptop navigation option. You can do very much more with your own echart program in a laptop than possible with any of the packaged units which are then restricted to just the chart formats they provide as well as limited navigation tools.)

In any event, it pays to have a stand alone grib viewer in your laptop. There are numerous options. For the PC there is Viewfax from Saildocs, Ocens Grib Viewer, Ugrib, and many others. For the Mac there are fewer choices, but both very good. LuckGrib is one and Ocens GribViewer for Mac is another.

(9) Source for grib data. Establish and practice with some source of grib weather files. Saildocs is an excellent source. Many of their download options are included in a convenient Viewfax utility called “Get Data”, but they have much other data that are not listed there that must be obtained by email request to saildocs.  Ocens offers convenient download options from within their pay for use WeatherNet service.  The unique and very valuable option WeatherNet offers is the ability to download the ASCAT scatterometer wind data.  Ocens WeatherNet also now includes NDFD grib data as well. NDFD are also available from Saildocs.

And again, it is crucial to download some of the files and learn to use these forecasts before departure.

(10) Text forecasts. Don’t forget the text forecasts. Practice receiving by email the crucial text forecasts, as outlined in another note in the references below.

(11) Seawater temperature. When sailing in the Gulf Stream or any other strong current system, or when sailing in the tropics in general, it is extremely valuable if not crucial to have a through-hull seawater temperature measurement, or some other permanent way to continuously read and display seawater temperature.  For ocean currents the water temperature marks the boundaries of various features, and for the tropics the water temperature is a measure of TS development, i.e. hurricane formation usually require seawater > 80º F.


High Seas Forecasts and Tropical Cyclone Alerts by Email Request

Weather by Satellite Phone

Modern Marine Weather

Barometer Handbook

Mariner's Pressure Atlas

Sailor's Logbook



Thursday, August 13, 2015

High Seas Forecasts and Tropical Cyclone Alerts by Email Request

In several articles we point out that standard analysis and forecast maps of tropical systems do not have nearly enough information on them to make weather routing decisions.  We need more information. One approach is to download a GRIB formatted numerical prediction. The GFS is the most popular; the NDFD would be superior if that were available to your waters.

With or without these GRIB files, it remains valuable to also obtain the text forecasts from the NWS, in part because the GFS—or any one single model—can sometimes be quite a bit off on the tropical system intensity.

We have three basic text reports that might be of interest: high seas forecasts, high seas discussions, and tropical cyclone alerts. The basic ones we need to supplement the maps are the forecasts, and these are easy to get.

In principle we can get all of the text reports we need from the NWS FTPmail service, but this requires a very specific format and list of file names. An alternative is the excellent services of Saildocs, which have proven very dependable and versatile; it is relied upon by thousands of mariners worldwide, so we will limit the source to this one.

The eastern half of the Pacific Ocean is in the IMO GMDSS forecast zone called Metarea XII; the western half of the Atlantic Ocean is in Metarea IV. 

To get text report and forecast for Metarea XII (North Pacific)

send an email to with the body of the text blank except for 
send met.12  You can put anything in the subject line, which can serve for finding the mail for a repeated request. Be sure there is no signature or other text or graphics in the body.

This is all there is to it.  Try it here.

You can also subscribe to this request to have it sent to you automatically every day.  Send a blank email to for details.

For other metareas, use these Saildocs abbreviations

Code Metarea description
Met.1a      North Part of North Atlantic Ocean (High Seas)
Met.1b      Northeast Part of North Atlantic Ocean (Offshore)
Met.2       East Part of North Atlantic Ocean
Met.3e      East Mediterranean Sea
Met.3w      West Mediterranean Sea
Met.4       West Part of North Atlantic Ocean
Met.5       North Part of South Atlantic Ocean
Met.6n      South Atlantic Ocean North of 60S
Met.6s      South Atlantic Ocean South of 60S
Met.7       Southeast Atlantic Ocean + extreme SW Indian Ocean
Met.8n      North Indian Ocean
Met.8s      Southwest of Indian ocean
Met.9       Red Sea, Gulf of Aden, Arabian Sea, Persian Gulf
Met.10ne    Northeast of Australia (Pacific ocean)
Met.10n     North of Australia
Met.10w     Southeast of Indian ocean
Met.10se    Southeast of Australia (Pacific ocean)
Met.11ior   West part of the North Pacific Ocean (from China)
Met.11por   West part of the North Pacific Ocean (from Japan)
Met.11sW   West part of Pacific Ocean, 0-12S 90E-142E approx
Met.12      East part of the North Pacific Ocean
Met.13      Northwest of Pacific Nord and part of Arctic waters
Met.arctic  From SW corner 67N, 44E to NE corner 80N, 165W
Met.14s     South Pacific south of 25S
Met 14trop  South Pacific north of 25S
Met.15      Southeast Pacific
Met.16      Southeast Pacific between 18S and 3S)

We can also see these reports online two ways. Directly from the IMO see

and we have similar reports from the NWS from this folder:

The files matching metarea XII and IV are  north_pacific.txt  and  north_atlantic.txt

If you are sailing across one of these oceans, you would want to set up a schedule with Saildocs to send you the text report at least once a day, automatically.  This will supplement your maps and GRIB file weather analysis.

You can of course get this information from the HF radio. The USCG broadcasts voice versions of the above forecasts 4 times a day. See

* * *
Any of these services that might potentially be used underway 
should  be thoroughly tested before departure. 

* * *

Tropical Storm Side Determination

In principle if we have all of our weather resources working properly, then we can see where we are relative to an approaching tropical storm or hurricane, and from its forecasted motion we could determine which way to best proceed.

Unfortunately, life is never quite so simple in the real world. First, what are these “resources” referred to here?  We have more details elsewhere, but they would include the weather maps (surface analysis and forecasts), and they would include the GRIB files of numerical weather predictions such as those from the GFS.

We shall see in the videos below, however, that the maps themselves are often not detailed enough if we happen to indeed be inline with, or close to, a TC. The GRIB model predictions on the other hand, give us very detailed forecasts for wind and pressure, but we must be aware that these unvetted model predictions could be wrong!  This is actually more likely with a TC than with more climatically normal forecasts, and indeed more likely to be wrong during the first day or so of formation.

Thus it turns out that perhaps the most crucial official weather information we have underway in a case like this are the email text or radio broadcasts that give the official NWS numerical information on the location, motion, and extent of the systems. These are available at least 4 times a day, and often hourly on the storm warning broadcasts segments of the WWV and WWVH HF radio.  We can pick these up with a standard, battery-operated SW receiver.  The voice broadcasts are usually a voice synthesized rendering of the text reports. Here is a note on how to get these text forecasts by email.

From these text reports we learn the Lat-Lon of the system at a specific time, and we learn the speed of the system in kts, and the true direction it is moving—this might be stated as “northeast or 050,” in which case the numbers are the more specific value; this phrase is not a range of directions or an uncertainty statement.

For the best work here we need an accurate barometer and calibrated wind instruments. Many places elsewhere we discuss barometers and how to check that they are reading properly. This is fundamental to ocean voyaging.

Wind instruments are frankly harder to calibrate properly, but the more accurate they are at this point, the better off we are. The crucial point here is we need to know true wind speed (TWS) and true wind direction (TWD). We get this from the apparent wind speed (AWS) and apparent wind angle (AWA) along with our COG and SOG from the GPS. Some instruments will make this conversion for us, which is a great convenience once it is tested to be working properly. Otherwise, we can use a calculator to convert the AWS and AWA to TWS and TWA, then we can combine the TWA with COG to get the TWD.

Without any wind instruments, you can look into the waves to estimate the true wind direction. The TWA will always be aft of the AWA. That is if you have instruments telling your the AWA is near the beam; the TWA will be more on the quarter, etc. Then add this to the true heading of your vessel at the time, being the compass heading corrected for variation.

The barometer is dropping and the wind is building. Which side of the storm am I on?

Simple enough question, but it needs all kinds of clarification. First of all a reminder that we are talking primarily about “tropical” systems, either within the tropics, or those that have moved out of the tropics…. and we are discussing another rarer type of system which is a “tropical storm” that formed well outside the tropics.  An example of the latter is TS Claudette from July 2015 that formed off the coast of NC and moved NE.

The key characteristic we are calling “tropical” means a small and well defined system with closed isobars. A typical extra-tropical storm in the North Atlantic or North Pacific does not qualify.  Which side of these is rarely a question we face—the other side could be more than a thousand miles away. A tropical storm is typically a few hundred miles across, or less. These are the ones whose sides we care about in this discussion. We can also have the barometer dropping and wind building with an approaching frontal system, but this discussion would not apply to that situation at all.

When sailing in the tropics, however, we are not often confused by what is going on. We are used to glorious trade wind sailing, with the wind and barometer pretty stable. In fact, the barometer is actually more stable than the winds. We can see the trades vary from 10 to 20 kts with not much change in the barometer.  Throughout the tropics summertime pressures will be 1011 to 1014, depending on month and location, and more to the point, the standard deviation (SD)  in this pressure will be only 2 or 3 mb. In the absence of a tropical system, a pressure drop of 2 SD occurs only 2 or 3% of the time. Thus if you see the mean pressure drop 4 or 5 mb then you have a very good warning that a system could be approaching, even if the wind has not started to build. Note we have to say mean or average pressure because within the tropics there is a semi-diurnal variation of the pressure with an average amplitude of 1.7 mb.  Worldwide pressure statistics and how to interpret them is covered in the Mariner's Pressure Atlas.

Now a video review of the key issues of wind shifts as a closed system of isobars approaches and passes.

Storm Side Detection Part 1, Background and References (10 min)

Step by Step Procedures
(1) On a chart or universal plotting sheet, plot the latest known location of the storm.  Also then, look into your logbook to see where you were located at that time, and plot that position on the chart as well.

(2) Using the forecasted course and speed of the storm and your known position now, plot your present position as well as the DR position of the storm at the present time.

(3) Now plot the forecasted track of the storm and its forecasted locations.  We are getting this information from the text reports if we have them (see below).

(4) If we have this data, then we have a picture of what is taking place and where we are relative to the storm. More specifically, you see how far away the storm is and how close it will pass if you do not move.

(5) Now the crucial check to see if the forecasts are correct by recording our barometer and wind speed and direction at least every hour.  With a good barometer, you might learn something on an hourly basis. (Examples in the videos below.)

(6) You might also at this point do a reality check with the Buys Ballot law (refer back to Video 1). Namely, with your back to the true wind direction, i.e. true wind blowing against your back, put left arm out and rotate it forward by 25º. Now check the compass to see which way you are pointing and record that, then convert that compass direction to a true direction.  Then you can go back to your plot and draw a line from the boat to the storm and see if that direction is the same as you just measured with Buys-Ballot.  If yes then you can try this again once the wind direction changes enough to detect it.  If still pointing to the storm, then you are indeed inside the closed isobars of the storm.

If the Buys Ballot direction does not match your plot, and you checked both, then chances are you are not quite into the closed isobars.  This could also be indicated by a pressure that is not dropping or dropping very slowly.

Now we have a couple specific examples.

Storm Side Detection Part 2, Hurricane Guillermo 2015 (17 min)

Storm Side Detection Part 3, TS Claudette 2015, Value of a Good Barometer (15 min)

Now that you see the pressure dropping and wind maybe building, and you have from Buys Ballot a good check on the direction to the storm, you are prepared to consider a course of action.  They key issue is almost always getting as much separation from the storm center as possible at the time it passes you… or with confident knowledge, the possible choice of getting across the front of it before it gets to you. This is especially true with these TC that have strong winds. These strong winds are usually located fairly close around the system… that is, we see that 80 or more nmi gain is usually a huge safety factor.

The video examples we have show this, but we can use the data from a typical TC to see this for other cases.  You can also go to  and choose any of hundreds of storms to check this.

Here are a couple examples.  For tropical storms or for TS stage of a hurricane, the safety radii are smaller, so it is easier to get out of the way of them.


0900 UTC MON AUG 03 2015



64 KT....... 30NE  25SE  20SW  20NW.
50 KT....... 70NE  40SE  25SW  35NW.
34 KT.......115NE 100SE  50SW  70NW.
12 FT SEAS..300NE 200SE 270SW 310NW.

(skipping a few reports)

FORECAST VALID 04/0600Z 17.5N 148.1W
50 KT... 50NE  30SE  15SW  30NW.
34 KT... 90NE  80SE  40SW  60NW.

2100 UTC TUE JUL 14 2015



34 KT....... 60NE  70SE  60SW   0NW.
12 FT SEAS.. 60NE 120SE  60SW   0NW.


Once you see where you are and how the storm is moving, you can then figure the best plan of action.  Here is a video showing a couple choices. It uses the program Expedition, which does automatic routing, but that powerful feature is not required for a good judgement. Also since the sea state will likely be much larger than usual, chances are any polar diagram you have might be an overestimate of performance.

Storm Side Detection, Part 4 Maneuvering from a Known Side (15 min)

Before making a major decision such as trying to cross in front of a system you are nearly in line with, it is best to run for a while in the chosen direction to know true SMG and CMG possible. In some cases, like the example shown, it will be pretty clear if you can or cannot make it across to the navigable side.

That choice, however, is crucially tied to the proper identification of where you are relative to the storm path… and projected storm path.  Recall if you do not have any data at all from the NWS, we must rely to some extent on the known average trend of a storm turning poleward at some point.  The statistics of storm speeds and directions as a function of age is discussed in the text book, and hundreds of actual examples are online at the NHC to test these averages.

Please post your questions or past related experiences as  comments and we can follow up here with that discussion.

Sunday, August 2, 2015

New GRIB Viewer for Macs

For years we lamented to our Mac friends and students that there were so few good marine applications for the Macintosh that they were better off biting the bullet and buying a PC for their marine navigation and weather applications. This litany followed us right into these modern times when we ourselves started running our own PC programs on virtual machines in a Mac.

But sure enough, when the demand grew high enough, these apps have started to appear. In the weather department, our neighbors at Ocens were the first to bring high-quality weather products to the Mac with a series of valuable applications.

And the bar keeps rising, in this case with a new GRIB weather data viewer for the Mac called LuckGrib. As it turns out, this is also a product of the Pacific Northwest, though its developer Craig McPheeters happens to be underway sailing in the South Pacific at the time his product will first appear in the App Store sometime in August.

In keeping with Mac standards, LuckGrib has an elegant design and convenient interface, with several unique features added to the standard functionality we expect from a high-quality weather tool. Besides its versatile display options, it also offers a way to download the data from an Internet connection. Built in data sources include: GFS, WW3, and CMC Ensemble.

Though we tend to reply mostly on wind and pressure for routing, and the 500-mb data for evaluation, and sometimes the precipitation, this new LuckGrib app offers very much more. In a deep Advanced Option you can request any of the 320 weather parameters predicted by the GFS system, including temperatures, humidity, cloud cover, convective properties, and many more at essentially any altitude level in the atmosphere. You would have to be a professional forecaster to make use of much of this info, but it can be found here if desired.

Other outstanding features include:

• Fast operation and smooth performance on all options using even relatively large files. 

• Convenient data selection and request interface. It is always, however,  the navigator’s job to select only the data needed, only over the region needed.

• Versatile track pad pinch zoom and pan. A slider bar can also adjust the zoom level, and standard mouse click and drag also works to crisply adjust the map view.

• User added identification notes to stored data files, along with clear organization of downloaded files to access for updates.

• Many options for personal preferences in color schemes and actual data display configurations available for each of the data types.

• A dynamic feedback option that shows the values at the cursor not just of wind arrows, but also wind speed contours, pressure, or any parameter or combination of parameters. A very informative way to look at the distribution of data.

• A min and max point display within the wind contour option offers nice way to see strongest parts of a storm.

• Option for selecting GFS resolution of 1º, 0.5º, or 0.25º.

• Time to next update for each model. A very nice feature that prevents users from extraneous data downloads underway.

• A draw route leg option, with ticks at specified user-selected intervals. This can be used as an electronic range and bearing line to read the maps, or as a route leg to check wind along a path at a fixed time—or it has the very useful application of setting a day or two route leg, and then sliding the time marker to continuously watch the winds all along that path.

• Time control allows for interpolation of wind fields at times intermediate to the forecast times, which is valuable for comparing with satellite wind data, or making wind predictions at specific times.

• Low price—which has to be considered a practical outstanding feature. It is predicted to be $20, which would make this a must have app for all sailors using Macs for weather work. There is one other high-quality GRIB viewer for the Mac called Grib Explorer for Mac from Ocens, which has many outstanding features of its own. In the ideal world we would have both of these fine tools, but at $199 for the Grib Explorer it requires a larger budget plus an external source for downloading the data.

We have used the beta version of LuckGrib extensively for several months. The LuckGrib viewer is elegant, fast, and functional. Regardless of other weather tools you might have, this tool will add new functionality that will improve your weather work.  If you have not used GRIB forecasts at all, LuckGrib is an excellent way to get started—but we must remind all GRIB users that unvetted numerical weather prediction data (such as GFS GRIB files) should always be compared with the actual professional forecasts prepared by the NWS and their counterparts around the world.

Tech support and related information can be found at

We will add illustrations later and a video on standard and special operations.

Tuesday, July 28, 2015

The New Inland Navigation Rules

Last year about this time, the USCG changed the US Inland Navigation Rules and their Annexes. These are the rules that apply inside most point-to-point lines across coastal bays or inlets leading to the ocean—notable exceptions are all of Puget Sound, AK, and HI waters. There has been little notice of these changes despite a couple details of interest to sailors. Knowing these details could save you up to one hundred dollars; not knowing them could cost you a couple hundred dollars. The official discussion of the changes is an interesting insight into the rules themselves.

The goal of the changes was to bring the wording and format more in line with that of the International Maritime Organization (IMO) Convention on the International Regulations for Preventing Collisions at Sea, known as the COLREGS, or in many places simply the International Rules. Another goal was to address recommendations made by the Navigation Safety Advisory Council (NAVSAC), which we are proud to say one of our past Starpath instructors, Pamela Hom, was a member of for several years.

The changes were intended to “harmonize domestic and international law by reducing and alleviating equipment requirements on vessels, addressing technological advancements, such as wing-in-ground craft (WIG), and increasing public awareness of the US Inland Navigation Rules.”

They also changed the title of the USCG publication previously called NAVIGATION RULES, INTERNATIONAL — INLAND to now read, with a new subtitle as shown below:

The new subtitle reflects the handbook nature of the new publication in that several documents often needed by professional mariners are now in this one book. The book’s cover design is unchanged but for the new title. The inclusion of the edition date in the title might portend an easier way to tell when new editions become available, but that is just a guess. Previously, it was difficult to tell if you had the latest edition.

Following the recommendations of NAVSAC and other professionals, the proposed changes where published, and the public invited to make comments.  Apparently only ten public responses were received, addressing 49 specific points. They were described as mostly favorable, with most addressing the key issue of nomenclature, ie use of “section” versus “part” versus “subpart” versus specific CFR (Code of Federal Regulations) article reference. This aspect has definitely been improved, but anyone looking at this book for the first time would have to wonder what it looked like before improvement.

In a sense with the new handbook content and ubiquitous reference to CFR article numbers, ie 33 CFR §83.25(d)(i), the book itself looks more complex now than it was. But not to worry about that; there are only 18 half pages of content we need to know to be safe in most encounters, namely the Steering and Sailing Rules—though needless to say, proper identification of lights and sounds could also be crucial at other times. Flash cards or special pubs can help with that.

WIG Craft

First the easy part, which does not affect sailors unless they are testing for a USCG license. WIG craft rules are now all the same for Inland and International waters. WIG rules used to apply only to International Waters, so this must be looking ahead to seeing more of these “vessels” here. These strange boats that can fly are more popular in Asia and Europe than in the US.

Rule 1(g) on Carrying a Copy of the Rules

Next there was a proposed change that they did not make, but the official discussion of the decision brings up several interesting points. The USCG considered, and then rejected, a NAVSAC proposal to require vessels down to 16 ft overall length to carry a copy of the Rules on board. At present only (self-propelled) vessels of 39 ft or longer are required to carry “a copy of the Rules for ready reference” on Inland waters. The argument for smaller motorboats and sailboats to carry the rules was the obvious one that they also must obey the Rules; the argument against it that prevailed was “lack of quantifiable benefits to justify a high regulatory burden on recreational vessels.” They stated that 6.5 million vessels were within this (39 ft to 16 ft) category and they listed the GPO Nav Rules book price at $23, and then they multiplied the two to get what was described as “unnecessarily costly” boater expense of 150 million dollars. (With the actual street price of $10, the actual cost to boaters would be more like one six-pack of beer in the lifetime of each of these boats.)

They went on to point out that the skippers of only 14% of boating accidents (in this vessel category) that led to a death had ever taken any navigation training, and only 9% of those were sanctioned courses, and noted that fatal accident statistics have gone down as sanctioned training has gone up over the years. Thus they argued that more navigation training is more important than requiring Rules carriage.

This is obviously true, but I must add that the Nav Rules were not designed to prevent fatal accidents, but to prevent collisions, and I state again our premise that the Navigation Rules is the most important book in navigation.  They also failed to point out that every collision (between vessels of any size) involves the violation of at least one of the Rules by both vessels involved­—in other words, it is statistically impossible to have a collision if you obey all the Rules, regardless of what the other guy does.  But you have to know the rules on what to do when he does not obey the Rules.

I agree that it does not make practical sense to extend the carriage Rule to smaller vessels. Furthermore, it does not matter; the Rules must be obeyed by all vessels, regardless of having a copy on board, and in fact regardless of even having read them. I would hope that somewhere in the state boat registration process there is at least a statement saying you must know and obey the Rules. This would be interesting to track down.

The requirement for larger vessels (>39ft) on Inland Waters to carry the Rules at least gives mariners a chance to look up relevant rules after the fact as a means of ongoing education. There will always be encounters, lights, or sounds that we wish we knew better at the time. Why there is no similar rule in the COLREGS is beyond US law or USCG control.  The international consensus must be that International Rule 1(a) that you must obey the Rules is enough to go with. There are IMO regulations that all commercial vessels must carry a copy of the Rules, but that is independent of the Rules themselves.

With all that said, if you did not know about this Rule, do not feel too bad. It was always the law, but it was buried in Annex V, §88.05. Now with the new changes it is up front in Inland Rule 1(g).
To me the most interesting part of the discussion of the carriage requirement included the phrase “electronic copy,” but only as an afterthought, in an awkward sentence structure, without any implied price to that option, which would have befuddled their cost analysis. In short, a “copy of the rules for ready reference” could indeed be an electronic copy, and the USCG offers a free ebook copy online (pdf) that would run quite well in smart phones or tablets. Furthermore, in another part of the USCG website we find this direct statement:

“Electronic copies of the Navigation Rules are acceptable, however, only if they are currently corrected to the latest Notice to Mariners and can be made available for ready reference.  The unwritten rule of thumb: ‘readily’ means that you are able to avail yourself of a Rule(s) within 2 minutes of the need to do so.”

[Note that the "unwritten rule" seems now to be quite well written.]

"Two minutes" is a cake walk with a well designed ebook version (ie Starpath Pocket NavRules) and even trivial with the USCG pdf version that you can mail to yourself and open in your phone. Click the attachment and choose open in iBooks (a free app from Apple), which will save it there.  Practice once or twice looking up a rule, and you are always legal.

Rule 8(a) — Action to Avoid Collision

This rule is the fundamental description of how to maneuver to avoid a collision. It was always intended to be the same in both Inland and International rules, and it remains so, but there was uncertainty in the wording of the Inland Rules. Now the wording is the same in both International and Inland rules to read (italics and underline added):

Rule 8(a). Any action taken to avoid collision shall be taken in accordance with Rules 4-19 and shall if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

They added the precedence statement (shown here underlined) to the inland rule.  Also interesting, though not part of the rule itself, this USCG document also effectively defined “in accordance with” by adding this sentence to their description of the rule change: “It is our intent that Rule 8(a) should be taken with full knowledge and compliance with Rules 4–19” (italics added).

Rule 33 — Equipment for Sound Signals

In the previous version for Inland Rule 33(a), it was required to carry a whistle and a bell for vessels ≥ 12m (39 ft), but the International Rules required the bell only for vessels ≥ 20m (65 ft). The new inland rule now matches the International rule, so you do not need a bell on board till 65 ft or longer—so off to the swap meets with these, or make dinner bells at home. A brass bell that meets USCG requirements can easily cost $100.

This rule change affects several of the USCG’s trickier license exam questions, so keep in mind an older data set of these questions may now have the wrong answer.  The new dataset of Rules questions online have these answers changed.
Rule 35 - Sound Signals in Restricted Visibility

Rule 35(g) and 35(h) in both International and Inland rules calls for ringing a bell when anchored or aground in restricted visibility. The rules do not specify vessel lengths. In the old inland rule you had to ring a bell for 12 to 20m, now you don’t, because you don’t have to have a bell at all. Now you are forgiven for all the times you were anchored in the fog and did not ring your bell!

Rule 25 - (Lights on) Sailing Vessels Underway and Vessels Under Oars

Here we have another seemingly very simple Inland Rule change that has notable implications to sailors of smaller boats, or dinghy rowers running back and forth to larger boats. It is also notable in that it goes contrary to the harmonizing goal of the changes in that it willfully makes a US Inland Rule different from the corresponding International Rule that was previously the same.

The new US Inland Rule reads (with underline and italics added):

Rule 25 (d) (i).  A sailing vessel of less than 7 meter in length shall, if practicable, exhibit the lights prescribed in Rule 25(a) or (b), but if she does not, she shall exhibit an all around white light or have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.

The lights of 25(a) referred to are sidelights and a sternlight; the lights of 25(b) are a tricolor on the masthead.  They have added the all-round white light option to the Inland Rule, otherwise the two rules would be identical.

Now inland-waters boats, under sail or being rowed, that are less than 23 ft (7 m) long can run with a steady, all-round white light. If you choose that option, it definitely means only the all-round white light; no other lights allowed. It also of course means no engine or outboard running, just actual sailing or rowing.

So what are the implications of this change? There are certainly a large number of boats in this category that could end up sailing or rowing (ie a dinghy) at night. We still have the previous options of full sidelights and a sternlight, or no lights at all with just a bright flashlight at hand to warn approaching vessels. But now we have a third (Inland) option of a fixed, all-round white light.

For many sailboats (again <23ft) you can now sail at night running your anchor light from the masthead—but turn off your sidelights off if you have them. The anchor light was used by some sailboats in the past, but it was not legal then (sidelights and a masthead light looks like a power-driven vessel). Those who knew that may have thought it was better seen than legal, but just like the other common sailboat lighting error of running deck lights and tri-color (also illegal) these lights can get fined.

I know of a case from many years ago where a fine for running both tricolor and deck lights was $50. Modern exposure is higher: “A civil penalty of up to $500 may be imposed by the Coast Guard for failure to comply with equipment requirements...” from a USCG Special Notices to Mariners.
Frankly, it is unlikely to be fined for just wrong lights, but in the event of a collision at night, illegal lights guarantees you a large part of the liability, regardless of who was at fault.

Tech developments that may have impacted this decision are bright LED lights, which even the smallest boat can run for long periods on a small battery.  This new rule also now makes the kayaker with a white light on his hat legal as well, which in the past it was not. Granted, you will look like a sternlight, but in principle that would not be a problem. Anyone approaching a sternlight should go around it.

At this point we can add that one of the USCG’s stated motivations of the changes (“more public awareness”) has just been achieved—you have read an article on the US Inland Rules! To know where they apply, check 33 CFR Part 80, in the back of the new Navigation Rules Handbook.


See a preview of our Starpath Pocket Navigation Rules Handbook for a very convenient presentation of the new rules and all related documents.... or better still, open it in your phone and bookmark it.