Table of Contents

Class Prep

Class 1
Class 2
Class 3
Class 4
Class 5
Class 6
Class 7
Class 8
Class 9
Class 10

>>Topical Articles<<
Assumed Longitude
Casio fx-260 Solar II
Emergency Navigation
Making a Kamal
Noon Sight
Pub. 249 Vol. 1
Sextant Adjustment
Sextant Skills
Sight Averaging
Sight Planning,
  Error Ellipses,
  & Cocked Hats
Slide Rules
Standard Terminology
Star Chart
The Raft Book
Worksheet Logic

Emergency Navigation

The first and best strategy for emergency navigation is to make sure that catastrophic emergencies never occur to begin with. Protect at least one quartz timepiece in a Faraday cage (see below). Get a Casio fx-260 Solar II calculator and protect it in your Faraday cage as well. Carry a mechanical watch to sea with you, and keep it wound and rated while you are under way..

Keep your sextant on a lanyard around your neck whenever it is not in its case. And as T.S. Lecky said over 100 years ago, "Never loan another man your horse, your gun...or your sextant."

Protecting Your Electronics: Faraday Cages

Lightning strikes on sailboat masts are rare...but even more rare is to video record such a strike as it happens. Here is a strike that happened in Boston in July, 2019:

When this bolt struck, there was some damage due to the direct effects of the current, of course. But a lightning strike also produces a powerful electromagnetic pulse (EMP) which can induce a current in microcircuits that fry the electronics of any nearby device. In the case of this vessel in Boston, the news article associated with the video said that the boat had to withdraw from a race it was scheduled to participate in, since the vessel's electronics were damaged in the strike.

You should also verify the accuracy of your steering and hand-bearing compasses if you have been struck by lightning. You can do this using a sun compass or other celestial technique. Celestial objects, our "lighthouses in the sky", are the only invariably correct guide to directions that cannot be spoofed, hacked or damaged.

The key to lightning/EMP protection is to be proactive. First, your mast should be grounded. This will reduce the risk of lightning killing all of your electrics on board (including your cabin lights, navigation lights, and the starter motor for your diesel engine).

Second, you should protect some key electronics with a Faraday cage. This is NOT wrapping a hand-held GPS in aluminum foil and dropping it into a plastic baggie, which gives you the sequence:

      electronics → conductive material → insulator.

Rather, you need the sequence of:

      electronics → insulator → conductive material.

You can certainly use aluminum foil, but there are suggestions that thicker, more robust metal may provide better protection. My wife is always on the lookout for tea/cookies/crackers that come in metal tins. So I have an array of different sizes of metal containers that can all be used as Faraday cages.

Here is my sailing lightning-safety kit:

  • bubble wrap, to go around all the electronics, to provide electrical insulation, as well as to cushion against shock
  • a Casio fx-260 Solar II calculator (you already have an fx-260 calculator aboard, for making GC calculations; this is a second unit in case the first is killed by an EMP)
  • a quartz pocketwatch (this one is available for less than $10 CDN, including shipping)
  • (my cellphone is not pictured, as I was using it to take the picture)
  • a metal can to hold it all
  • There is room in the can for a small, handheld VHF radio, to communicate with passing vessels
  • A 15° kamal
  • A standard length string for making a boathook kamal to measure a broader range of angles
  • A longer string for attaching to a boathook kamal
  • A Sharpie permanent marker to put degree marks on a boathook kamal, plus a 1 page list of intervals for those marks.
  • A short ruler with a scale of millimeters...for measuring out those marks on your makeshift kamal.

After wrapping them in bubble-wrap, putting all your electronic items in zip-lock bags would provide an additional layer of EMP protection, as well as some resistance to water damage.

Suspenders AND a Belt

Lightning is nothing if not unpredictable. So you might consider preparing to navigate effectively with zero electronics on board. The key here is knowing the time.1 I recommend picking up a mechanical pocketwatch for cheap from While aboard, wind it once a day, and note how much it has drifted compared to your electronic timepieces. Record this in the same log where you note wind/waves, so you can correlate the rate at which your mechanical watch gains/loses time with the conditions (likely, your watch will run faster when the boat is pounding to windward in high waves, and slower if you are becalmed).

The process of recording the rate of change in a watch is called, appropriately enough, "rating the watch." Once you are have done this, you can say "the watch has been rated."

A mechanical watch is nowhere near as useful as a quartz watch (which also should be rated), but it is a good bit better than nothing, particularly if you are rating it on an ongoing basis. The price of this watch + shipping comes out to around $15 CDN.

If you want a more reliable mechanical watch, you should get one that has "17 jewels". This is indicative of less friction in the movement, and generally higher quality of contstruction. The least expensive jewelled watch I can find is this one.

I don't know that you need to keep a mechanical watch in a Faraday cage...but it wouldn't hurt to keep it in a zip-lock baggie, to protect it from moisture.


You have no Sight Reduction Tables (e.g. Pub. 249)

The Casio fx-260 Solar II calculator:

  • can do sines/cosines/tangents
  • can be used under water for short periods (i.e. is extrremely water resistant)
  • will float
  • is cheap - $10 CDN at Staples

I recommend that every sailor keep an fx-260 calculator in a Faraday cage, along with a quartz pocket watch and a cellphone. Even if the cellphone does not survive, you can use the watch and the fx-260, in combination with your sextant and Nautical Almanac, to do celestial navigation.

This quartz pocket watch will easily fit in an Faraday cage you might have...and costs less than $10 CDN, including shipping.

In addition to an fx-260, you might consider packing a slide rule that is capable of doing trig. eBay always has rules for sale. If you choose to buy one, be certaint it has the S, T, and ST scales.

You have no Sextant


If you use a small kamal to measure angles angles between 1° and 15° the error can be less than 15'. If you use a boathook kamal for larger angles, you can have an error of less than 45'.

While this is not sufficient to let you hit the mouth of the Strait of Juan de Fuca, which is just 9 miles wide... certainly WOULD guide you adequately if you decided to make landfall 100 nm north of Juan de Fuca, and then pilot yourself down the coast until you found the strait visually. This web page has instructions for making a kamal.

Zero-Altitude Shots

One time you can be certain of the sun's altitude is at the instant the upper limb goes below the horizon. Treat that as an hs = 0° 00.0', and add in dip (there is no index error), and reduce the sight as normal using the Nautical Almanac, your watch, and Pub. 249.

(So far, I am using only Pub. 249 for zero-altitude shots. The Bygrave equations do not seem to want to deal in negative values. I am working at understanding them better, as it OUGHT to be possible to do direct calculation of a zero-altitude shot.)

You have no Accurate Watch

This is where the classic noon and Polaris sights come into play. They were popular in the 1800s and before, when there were no affordable, accurate timepieces available.

And frankly, for the recreational small boat sailor, noon and Polaris sights continued in their popularity up into the middle of the 20th century. It was not until 1966 that radio station WWV started sending time signals around the world by shortwave radio, and not until 1969 that Seiko released the first quartz watch to the market.

Noon/Polaris sights could give you your latitude, without knowing the time...which was a good bit better than nothing. If, for instance, your destination is Cadiz, Spain, and you are coming in from the west, all you have to do is to sail down the line of 36° 32', and you are guaranteed to hit Cadiz. You cannot miss it.

The classic strategy when you are latitude sailing is to keep your DR position current. That is, you will know your latitude for sure, from noon/Polaris shots. You estimate your longitude based on speed and time. When you get within what you estimate to be 150 nm, you acknowledge your uncertainty about longitude by heaving-to at night.

If you don't heave-to at night, you run the risk of getting into the situation in which the Apostle Paul found himself in Acts 27: "About midnight the sailors sensed they were approaching land [Bob's Note: They "sensed" it because they could hear the sound of waves breaking on the rocks!]. They took soundings and found that the water was a hundred and twenty feet deep. A short time later they took soundings again and found it was ninety feet deep. Fearing that we would be dashed against the rocks, they dropped four anchors from the stern and prayed for daylight."

Heaving-to at night increases the odds that you will approach the shore during daylight hours when you can safely navigate yourself into harbor.

You can download the Noon-and-Polaris sight worksheet here. See the Stellarium screen capture) to help you with your Polaris correction.

Longitude Without Time

The experienced mariner can use the moon plus a star-fix to determine the time. Click here for a description of the method.


1 "Do not change your watch time at sea. You might be tempted to change it as you sail into new time zones, or perhaps reset it to remove the watch error once in a while, but this is a dangerous procedure since it is easy to lose track of the correct time if you push the reset buttons in the wrong sequence (also the buttons themselves are a candidate for failure that does not need testing underway). It is far better to wait until you make yur landfall and then reset it to the local time. The convenience at sea is not worth the risk, and you have more to remember if you keep changing it."
      Burch, David, Emergency Navigation (Camden, Maine: International Marine/McGraw-Hill), 2008, p. 12. [return]