Showing posts from September, 2019

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…

Star Names

For navigational purposes, stars have two naming conventions: proper names such as Canopus and a Greek letter designation called the Bayer system such as Alpha Carinae, meaning the alpha star of the constellation Carina. The alpha star means most dominate, or if all are about the same brightness, the first one in a logical sequence of numbering, as in the Big Dipper, which goes alphabetically from Alpha Ursa Majoris (Dubhe) at tip of the cup to Eta Ursa Majoris (Alkaid) at the end of the handle. Officially the constellation name in this system is in the Latin genitive form (belonging to), but Alpha Ursa Major would be adequate for record keeping and communications.

Science fiction readers will likely know of Alpha Centauri, which navigators call by its proper name Rigil Kentaurus, because this is the nearest star to our solar system and perhaps an early one to visit or receive visitors from.

Figure 1.Sample of star names. The red labels have been added. Selected stars called navigation…

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…

Starpath News — April 2019

• Tracking Jacob Adoram  We are in contact with  former Starpath Student Jacob Adoram as he rows from Seattle to Cairns AU. He left on July 7 and now, after some 6,000 miles of rowing, he is just over 1,000 miles from Cairns. To make this event into a marine weather study project we have created a series of Google Earth overlays so you can see live conditions of wind, current, pressure, and sea state. We have an ongoing series of short articles introducing short video discussions of his progress. Start at the first post to get an overview of what we are doing, and check the index of overlays.  Even disregarding the factor there is a row boat somewhere around where we are covering, it is very interesting to see the ASCAT live satellite wind measurements.  For a jumpstart, if you have Google Earth installed you can click here to load the KML file.

Our original goal was to try to get live measurements of ocean currents to compare with the RTOFS and the OSCAR predictions. This has not pro…

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…