Showing posts from October, 2019

Tracking Jacob Adoram: An Exercise in Wind, Waves, and Currents

Jacob Adoram is rowing his custom vessel Emerson from Neah Bay, WA non-stop to Cairns, AU. He departed July 7, 2018 and now (Jan 26, 2019) is located about 1,100 nmi SW of HI making good about 40 nmi a day, with Cairns about 3,000 nmi to his SW.  He has good navigation and weather resources onboard as well as good satcom connections. His position is being posted online, updated hourly at his Where's Jacob? link at A segment of that display is shown below.

Figure. 1 Display of Emerson's position from his PredictWind tracking display, with a model wind and pressure forecast.
That report is being executed via a PredictWind app (PW) in an iPad connected to an Iridium Go (GO) satcom transceiver with wireless router. The GPS position is being transmitted automatically from the GO every hour to a PW website that is linked to from Jacob's webpage. These positions are updated at 43 min after each hour and labeled with that time, but the actual position shown is from…

How to Wirelessly Transfer Files Among Computers and Mobile Devices at Sea

These days there is more and more use of tablets and phones for navigation, weather work, and communications, but it still is often the case that the best navigation programs for optimum navigation or GRIB file viewing for optimum weather analysis are PC or Mac computers.

We combine that with the fact that the most cost effective source of data at sea is often sat com via a dedicated receiver  wirelessly connected to mobile devices.  The Iridium Go, for example collects data efficiently but interacts only with dedicated apps in tablets or phones, not computers. So if you download a GRIB file from one source, you may want to move it to another.

One clear example of that is the use of LuckGrib or Ocens Weathernet on an iPad to download a weather file and then move it to a PC running Expedition. Or you get mail and attached GRIB files by iPhone and Iridium Go and then want to move them to a PC or Mac to run in OpenCPN. And so on.

One way to do this is to use iTunes, but that is often not…

Brightness of Stars and Planets

In our cel nav course we provide two textbooks: Celestial Navigation and The Star Finder Book.  A question came up in class the other day that reminded us that we have many folks learning cel nav on their own using our main textbook who may not have the second book. These folks were then missing our discussion of star brightness. This note corrects that. In the next printing of the book, we will replace Section 11.20 with this new section of star brightness. Sadly enough, Section 11.20 was the one covering time tics and storm warnings from the NIST on the HF broadcasts from WWV and WWVH. These were both discontinued on Jan 31, 2019. I will have a post on that topic later. 

*  *  * The brightness of a star is often a valuable aid to its identification. Brightness is specified by the body's magnitude. Star magnitudes are given in the star list at the back of the Nautical Almanac, not on the daily pages; star magnitudes change very little, if at all, throughout the year. The magnitud…

Moving Files Around on an iPhone and iPad

In a recent post I discussed a slick way to transfer files among iOS, Android, PC, and Mac wirelessly at sea (away from the internet)—or at home as needed using your normal wifi connection. The process works great, and away from the internet you can use any local network of your own. The Iridium Go device creates such a network, as does the RedPort Optimizer and the Ocens SideKick—the latter two being devices used to wirelessly share files downloaded from a sat phone to apps on other devices.

We also show (in a video linked in the post) that the $20 HooToo portable router does this job fine if you do not have any of those satcom instruments, and it is literally plug and play. Just use the USB cable provided to plug it into your computer or a phone charger, and you will see, in the wifi setup of all devices in the room, a new network (TripMateNano-xxx) that you can use to share files.

At this point, if you only care about Apple products (iOS devices and Mac Computers), you are done.  C…

Does Accurate DR Matter in Cel Nav—Verb vs. Noun

When doing cel nav by traditional books and plotting, we often stress that our choice of the assumed position (AP) based on our DR position does not matter—we can always find out where we are; we do not have to know where we are to find out where we are. Once we have a fix, we can then look over the plot to see if we might gain accuracy by redoing the AP, but this is not often called for.

In other words, we do not need an accurate DR position to ultimately get an accurate fix.  Indeed, at the end of this note, we will illustrate this by doing a fix in the middle of the Pacific using the Golden Gate as our as our initial DR position.

This reasoning rather quickly brings up a conflict that sharp students spot immediately. And, indeed, we got this vary question again just recently. Namely, do we need accurate DR for cel nav? Let's answer the cel nav part first, because more broadly speaking accurate DR is the absolute fundamental aspect of all navigation,  especially ocean navigatio…

Check Assumed Positions After Plotting Cel Nav Fix

A question about DR came up in our cel nav course that took us back to a couple basic points. One is the difference between manual cel nav solutions using tables and plotting sheets compared to doing sight reduction and position fixing with a computed solution using a computer or mobile app. We discuss most of these differences in our textbook, but realized today that one important difference is not stressed in the book, although it is covered in many places in our online course.

The issue at hand is evaluating a fix based on the dimensions of the plot itself. In other words, we look at the lengths of all the lines involved. There are two kinds of lines on the plot of a cel nav fix: the lines of positions (LOPs) themselves, and the lengths of the azimuth lines that run from the assumed positions to the LOPs (the a-values). A sample is shown in Figure 1.

Figure 1. Crucial lengths defined.  If any of these are approaching 60 nmi long, we should use the fix for a new DR and redo the sight…

New PDF Edition of a Classic NWS Pub... With Related Notes on FTPmail

There is a new edition just out, dated April 11, 2019 of the long standing publication, now called 

We refer to this document in our teaching by its file name "rfax.pdf" rather than its title for a couple reasons. First, even though the content and title of the book have changed over the years, the filename since it was first put online has not changed; you can always find this with a search for "rfax.pdf." 
This is now a free PDF, but back before internet it was a must-have nav pub for ocean navigation. In those days, in keeping with its earlier title (below), the pub included the voice broadcast schedules as well as radio fax schedules, including valuable global diagrams of the forecast regions. 
Oldtimers with memory of ocean sailing before the internet will recognize this book that everyone had on board. For historical interest, old versions are online.
Secondly, beyond containing all the radiofacsimile schedules f…

How to Fold a Chart

Ask a dozen cruising mariners how best to fold and store charts, and you will likely get a dozen different answers. So with that background, we boldly go on and proclaim what the best method is!

First though, we should say that if you have just a few charts, it really doesn't matter much how you keep them, it will always be easy to find what you want. The crucial issue of chart storage comes into play when you have a lot of charts, because then the situation can get very much out of hand in just one long trip or a season of day sailing with multiple charts.

The long tested solution is to fold them chart-side in, blank white paper side out, either once or twice, depending on the chart size. Most charts take two folds. Then label the corner with the chart number, as shown in Figure 12.26-1. It is best to use a consistent size and style of lettering. We’ve found that a bold Sharpie pen is ideal for this.

Figure 12.26-1.Best method for folding charts: chart-side in, labeled on the fold…

Finding UTC of LAN with the Starpath Custom Sun Almanac

We published a short book last year that is intended to be the bare minimum celestial navigation training that will serve as a backup to a loss of GPS. In keeping with the backup concept, the book is presented in such a way that it is totally self-contained, which means the book also covers how to use the simple Davis Mark 3 sextant. This is a small device, for under $50, that could be used to safely circumnavigate the world.

Our promise is that this book could be opened up and read for the first time when it was actually needed, and it would be adequate to teach how to take the sights, and then find your position from them using only data in this small book—a large part of which is a custom Sun Almanac designed to make the position solutions especially easy.

GPS Backup with a Mark 3 Sextant
The techniques taught in this book are finding Lat and Lon from "noon sights" (local apparent noon,  LAN) as well as Lat by Polaris in the Northern Hemisphere. What we forgot to include i…