Sextants on the LMG
This is my first post-via-email so I’m not sure if it will work. I’m not sure if my blog is even running right now…
I have a question from a student: “Is there a sextant on the ship in case other navigational instruments fail? If so, could you take a picture of it?”
A photo is attached. The answer about using it involved a lengthy conversation. The First Mate said that they keep it for show-and-tell, and that if the navigational instruments ever failed there would be a lot more to worry about than navigating with a sextant. This is because we have several dozen GPS instruments on the bridge alone. If all of them or all the satellites that provide the location information were to fail, something else is very wrong with the ship and the world.
In my opinion, all of these failing is unlikely but still possible. One nuclear weapon detonated in the atmosphere anywhere nearby would create an electromagnetic pulse (EMP) which would permanently turn of all electronic devices within range. Unfortunately we live in a world where this is becoming a realistic possibility. Fortunately our ship, located in the Southern Ocean near Antarctica, would probably not be within the target range.
In addition to the above, a sextant requires a) a horizon and b) an object that can be tracked. For the past 2 days we have lived in a black-and-white world. The ship is bright orange, but everything else is a subdued gray. Thick clouds blanket the sky and we cannot easily detect where the sun is, nor where the sky ends and the sea begins.
Therefore, should GPS fail, we would resort to Dead Reckoning. This technique requires your current position to be known, and a compass. (A compass would survive an EMP.) We would point in the direction we want to go, put the engines to a certain speed of X knots (X nautical miles per hour), and then we would just drive in that direction. This technique does not take into account drift due to ocean and air currents.
One of the other mates told me that until 5 years ago all ships were required to carry a sextant. That is no longer the case, and some maritime schools are considering dropping sextant lessons from their curriculum. There exists a generational gap where many older captains require a sextant on board and younger captains my not even know how to use it, or learned out of an appreciation of an historical science, as opposed to a job requirement.
I hope this answers your question.
-k.
