Which Sextant can you Trust?

GPS is a wonderful technology. It allows you to glance at your display and see exactly where you are! Chart plotters are even better, granting you the ability to see not only your coordinates, but your live position on a digital chart. Snaking your way through coral reefs at night becomes easy as driving down a country road, just follow the map and keep your digital representation on the map in the middle of your digital representation of a road and hope that there is no new debris in the way that you could bump into.

So we all agree relying too heavily on GPS is a bad thing and that it doesn’t replace proper seamanship and navigation?

If a nuclear bomb detonates in space at the start of World War III or if lightning strikes your mast (both equally probable events), the GPS as well as all your electronic navigational equipment will be toast! This is where backups come into play.

The most reliable and time tested backup is the classic sextant. You see them in movies where they try to make the captain look extra “shippy” by having him look out into the distance and say “Aye, we be nearin’ the coast”. The sextants they show in movies are in fact movie props, but they look like the bronze masterpieces created by expert craftsmen.

For the price of a small boat, you can have a piece of navigational history! You will have an expensive antique that has stood the test of time and is incredibly heavy to hold while you try to sight the sun to find your position.

For that price, you could buy yourself a fancy Raymarine chartplotter and be able to snake your way through narrow waterways on the giant display screen!

What about those significantly less expensive plastic sextants? Are they any good? What are the problems with them? Why are they so much cheaper than the bronze models?

In 2020, we crossed the Atlantic from Cape Verde to Suriname (East to West crossing) using a plastic sextant as our guide. We turned off the GPS and primarily used noon sights to find our way across the ocean.

The plastic sextant did the trick! It accurately records the height of the sun in the sky and is easy to hold while you are doing a reading thanks to its lightweight plastic design.

As for concerns that the plastic sextants are “cheap”: They are a delicate measuring device that needs to be cared for. If you feel that a $2000 bronze sextant needs to live in its case, safely stowed inside the boat, why shouldn’t you do the same thing for your $300 plastic sextant?

We keep our sextant in a specially made box, safely stowed in the cabin away from strong sunlight. If I left it out on the deck, the heat from the sun could distort the arc of the sextant and ruin it; but why would you do that? Take care of your sextant and treat it as a priceless piece of equipment while you are sailing because regardless of the price, all sextants are irreplaceable out at sea.

Some people feel that you get what you pay for and if you paid more, it’s naturally better! Bronze is an expensive metal to make things out of compared to plastic, which is why the bronze units are so much more expensive! A solid gold sextant would be the most expensive option of all, but being made of gold would not make it any better than a bronze or plastic unit. The second part of the cost is the act of making the unit calibrated. Regardless of the material, calibrating the unit is an exacting task which takes money to do, and the result is a precise measuring device made out of different materials. The major cost difference is in the material that the measurements are produced on.

For a reliable backup to navigational electronics, we trust our plastic sextant! It does the job, is light weight, and won’t corrode in the marine environment. If it does die a watery or heat related death, it can also be replaced at an affordable rate compared to a more expensive unit.

Compass Light

A compass is a wonderful tool that revolutionized travel across water. Out at sea in the middle of the ocean, there are no landmarks to guide you. Steering a straight line is remarkably difficult to do, and maintaining a course is practically impossible! A compass works on the simple principle that the Earth has a magnetosphere and the compass is merely a magnet suspended in an oil bath and allowed to orient itself with the magnetic field of the Earth itself. The pretty card that tells you North, South, East, and West is just a cheap card stuck to the magnet to make it look more impressive! The truth relies on the fact that magnetism guides us across the oceans of the world!

While we are talking about magnetism, I find it important to say that we do not have a light in our compass for use at night and this was a conscious decision that we made before we left to go cruising.

Magnetism is a phenomenon that can be created with permanent magnets and also by electromagnets. The mere act of running an electrical current down a wire will produce a, albeit very small, electromagnetic field. Why would you wan’t to put a magnet next to your compass?

Yes, compasses that have lights are shielded to protect them from this influence, making it safe to have a light in your compass so that you can read it while on watch at night.

By day, we can see the compass clearly and we look at it from time to time. The sun illuminates everything and we are sailing along without any issues. This doesn’t mean that we are glued to the compass. When the sun is shining and we can see the compass, we only look at it every few hours to make sure we are still on course.

Being a sailboat, the sails are powering the boat at all times. This means that our direction of travel is not our ideal course but instead the angle to the wind that our sails are set to. We rarely steer the boat by hand as our wind steering does all of this for us. If the wind shifts, the wind steering will alter course to keep the sails to the prescribed wind angle and this means that the sails are always perfectly trimmed, even if the wind shifts.

Wind shifts are why we check the compass. If the wind shifts, we are going to start sailing on a new course and therefore need to adjust our angle to the wind to sail to the desired course. This doesn’t happen every few minutes, instead it happens every few hours, and that is when we look at the compass.

By night, the compass is dark and hard to see (but if there is a full moon, you can see the compass with ease), but this doesn’t matter because the few times on night watch that we need to check the compass, we simply turn on a flashlight and take a look! Once that is over, we turn off the flashlight and let our eyes adjust back so we can continue to enjoy the stars.

Why is the compass of little importance while on night watch? Because the stars are out. On night watch, we simply look up at the sky and locate the North Star. If the boat is maintaining its course, all night long the North Star will stay in the same area of the sky relative to the boat. For example, if the North Star is on the port side just forward of the bimini (when viewed from the helm) then all night it should stay there since the North Star doesn’t move in the night sky. If you look up and notice that it has moved to a different part of the sky (relative to the boat) then you need had a wind shift and need to adjust the sails and windvane accordingly to bring the yacht back on course.

When setting a course, the compass is necessary. I can look into the sky and see where the North Star is but I can’t set a course by it. The compass lets you set a precise course that will get you towards your desired waypoint. Since we are at the mercy of the winds, our acceptable course is +/-20 degrees of our desired course. This means that if our desired course is 80, but the winds only allow us to sail at 74, then 74 is great! If the winds shift a bit and suddenly we find ourselves down to 65, this is still fine and we keep sailing along content with our heading. If we start veering even further and start sailing along at 58, we would consider tacking to bring us somewhere between 80 and 100. We find that we sail with the best VMG (Velocity Made Good) when we are about 70* off the wind. This means that pinching just isn’t worth it for us when we are crossing an ocean. We will sail on an undesirable course for days if it sets us up for a more favorable and more comfortable tack in the future.

All the while, we rarely look at the compass and therefore do not have a light in our compass as the very slight risk that the light might throw off the compass isn’t worthwhile for an instrument that we infrequently use!

Navigating Without a Compass by Night

After the sun sets, the stars come out! If you find yourself on a starry night without a compass, you are in luck!

During the day, you needed to set your watch to find North by using the hour hand on your watch, the “12” position on the face, and the knowledge of when “noon” occurs wherever you are on the Earth. By night, it is a lot simpler!

First, you have many stars in the sky which will tell you a wealth of information. One of the most important stars in the sky is Polaris, the North Star (which is the last star in the tail of the Little Dipper). This star is directly over the North Pole so if you draw an imaginary vertical line down to the horizon, that point is North.

Great, so if you want to go South, do you just turn your head around and keep looking back at Polaris?

Not exactly. Another useful constellation is Orion.

I personally have trouble seeing the entirety of Orion, but I can always seem to find his belt, and that is the important part!

The belt is easy to spot, as its three stars in an almost perfect line. The first start of the belt to rise above the horizon will rise over due East, and the last star to set in the belt and disappear behind the horizon will mark due West. These are handy because if you happen to spot the stars rising over the horizon, you can then have yourself a second cardinal point in the night sky (aside from North thanks to the North Star). Watching the stars set is easier in my opinion because you saw them all night and know where they are as they set instead of guessing which star is the first star of the belt to rise over the horizon.

While the belt gives you a direction at two small moments of the night, it does give you another good indication of South for the entire night. The “Sword” that hangs just below the belt is made up of what look like three stars, even though the middle one is actually a nebula. These three stars are in a perfect line and point roughly South.

I say roughly because there is a little wiggle room for error here. The “Sword” is most accurate when it is high in the night sky and perpendicular to the horizon. At this moment, South is a pretty well pointed area on the horizon. When the constellation is low to the horizon, like when it just rose or is setting, there is a bit of inaccuracy which makes it “roughly” South and not “due” South.

That said, if you don’t have a compass, being guided roughly South is better than

1. Not knowing which way you are going at all

2. Having to crane your neck around to see the North Star behind you

3. Being lost at sea as you sail in circles

The stars will guide you as you voyage across the sea, but do plan on having a compass that is in fine working order so that you don’t have to rely on the stars as your only form of navigation!

Using The North Star

You know how to find it, you know where to look, but do you know why to look?

The North Star sits directly over the North Pole and is a handy indicator at night for “which way is North” but it also serves one more very handy purpose.
The North Star tells you your latitude without any math or calculation. By measuring the angle from the horizon to Polaris (The North Star) with a sextant, you will instantly find your latitude!
Since the North Star is directly over the North Pole, this means that if you stood on the very pole itself and looked directly up, Polaris would be directly over you.
Your latitude would be 90* and the angle of observation in the sextant would also be 90.
If you were at the equator, at Latitude 0*, the North Star would be directly on the horizon (and not too clearly visible).
Therefore, every degree of latitude that you gain in the northern hemisphere, Polaris will also gain a degree of observation from the horizon.
This fact has been known for hundreds of years and in the old times (when navigation was more crude) navigation was performed with a board and a rope!

The board would occupy the void between the horizon and Polaris, and it was held a prescribed distance from the observer.
The prescribed distance was controlled by the rope, which would have knots tied in it. The observer would bite the desired knot and hold the board out away from their face until the rope went tight, then they would position the bottom of the rope so that it would lay at the horizon and the top of the rope so that it would lay at the North Star. If there was a gap between the board and the North Star, they knew they were too far north and needed to steer more south. If the Star was covered, then they were too far south and needed to steer more North until the Star was visible again. If the Star and horizon just touched the board, then they were at the correct latitude for their destination!

There was no measure of Longitude on a ship at that time so they simply sailed to the desired ports latitude and sailed East or West until they ran into it! Thankfully, the ability to keep time on a ship changed this crude behavior as longitude was then able to be calculated and the mysteries of “when will we get there” vanished!

Finding the North Star

Before you can use the North Star, you need to know how to identify it in the night sky.
I personally use three constellations to identify the North Star and confirm it’s identify.

1. The Big Dipper

2. The Little Dipper

3. Cassiopeia

The Big Dipper

Also know as Ursa Major (because it looks like a bear) is a very prominent and easy to spot constellation.

The two most important stars in the constellation are the last two of the dipper. If you follow an imaginary line out and away from the dipper, you will come directly to the North Star.

The Little Dipper

Also known as Ursa Minor (because it looks like a small bear) is a very important constellation in the night sky! This is because the last star in the constellation is actually the North Star! The tip of the tail is actually (in my opinion) the most important star in the night sky when it comes to navigating at sea without technology or electronics.
the Big and Little Dippers actually lay in 69 to each other in the night sky.
If you see The Big Dipper and follow the imaginary line to the North Star, then you should now see the Little Dipper constellation.

I know I was making fun of the constellations for being called Bears because the line drawings I have made look nothing like bears! This is the actual accepted constellation for The Dippers. The full constellation has many more lines and it turns out that the “Dipper” is just the body and tail (very long tails by the way). The constellations have legs and a head, but honestly, you won’t see these features unless you are away from all light pollution on a clear moonless night.
Where can you find that? Out at sea of course!

Cassiopeia

The last constellation I use is Cassiopeia, which looks like a W but is actually a dancing woman!
Cassiopeia lies opposite the dipper of The Big Dipper and about just as far as the Big Dipper is from the North Star.

The reason I use three constellations is because I want to make sure I am looking at the right star. With one I’m pretty sure, with two, I’m very sure, and with three, I’m certain!

The other reason to know multiple constellations (especially constellations that are opposite each other in the night sky) is because if you are near the equator, the North Star will be low on the sky. This means that some of the constellations will be under the horizon and obscured from your view!
Having more visual landmarks in the sky will help orient you and prepare you to better locate the North Star for your navigation at sea.