Navigation in today’s world may come with all sorts of technology-enabled frills, but knowledge of the ‘dits’ and ‘dahs’, and other analogue sailing practices will come in handy in the most dire circumstances
Originally published by Seafarer Asia Security and Welfare Issue on March 2016
Modern day navigation utilizes all available means to maintain good watch keeping.
But even with the advent of new technology, thorough knowledge of old sailing practices remain relevant and necessary.
“You will never know when electronic equipment would fail, so every sailor should still have the basic knowledge of celestial navigation for the purpose of fixing the ship’s position,” states Chief Mate Renante Garcia, dean of Academics of Maritime Academy of Asia and the Pacific.
Here’s a rundown of the old-fashioned seafaring instruments and hacks that could come in handy:
A sighting mechanism with a 60-degree arc, a sextant’s primary function is to determine the angle, or the altitude, between an astronomical object and the horizon that is used to calculate a position line on a navigational chart. Determining a fix (position) requires at least three intersecting position lines. Often, these three lines would form a triangle called “cocked hat”, which tells the vessel’s current location.
A sextant is also used to find: 1) the latitude, by sighting (the act of using a sextant) the sun at solar noon or the Polaris (north star) at night in the northern hemisphere; and 2) the longitude using lunar distances (the angle between the moon and other celestial bodies), a function equivalent to today’s GPS.
“For six months we didn’t have GPS due to some technical problem, so I taught my British third officer how to do celestial navigation as it was the only thing we could rely on to get us to our destination,” shares Garcia.
To this day, the sextant is commonly used to compute what is called the “gyro-error” or the difference between the geographic north and the gyro-compass north (a gyro-compass is a non-magnetic compass continuously driven by gears parallel to the earth’s axis of rotation).
Dead Reckoning (DR)
From a fix, one can perform a “dead reckoning”. Although DR is subject to accumulative errors, this is the process of estimating the ship’s position without the aid of celestial observation, where the current course of the ship, speed, time taken, and the known or estimated drift (external forces applied to the vessel) are applied to the ship’s last position.
Radar plotting sheet
The use of radar plotting sheets may be the most important means of manual calculation in avoiding collision at sea. The main goal of using this is to determine your vessel’s CPA (closest point of approach) to another vessel, the time of CPA, and the other ship’s aspect (the actual way it will approach you). This is done by calculating the relative motion towards your vessel, allowing you to maneuver away should there be a risk of collision.
Performing a radar plot requires data from radar (relevant range and bearing). Radars equipped with ARPA (Automatic Radar Plotting Aid) and MARPA (MiniARPA) perform this function, but the know-how in plotting on a maneuvering sheet will definitely be useful should they fail.
The Polaris or North Star is a distinct direction marker in the northern hemisphere. It is the 50th brightest star in the night sky that lies on the constellation Ursa Minor, also known as the Small Dipper or Small Bear. At present, it is 0.75 degrees away from the earth’s pole of rotation and revolves around it in a small circle 1.5 degrees in diameter, an almost insignificant err in navigation. As the earth rotates, the celestial sphere (an imaginary sphere concentric to the earth where all objects in the observer’s sky is projected) seems to rotate for the observer except for the celestial poles (an imaginary extended pole of the earth geographical pole) where the Polaris lies, making it a fixed marker of the true geographic north.
There is no marker in the south hemisphere with such characteristics. The nearest is Acrux, the south star of the constellation Southern Cross (Crux). The celestial pole is approximately three and half of Acrux’s length from Gacrux, the north star of the constellation, towards its (Acrux) south.
A latitude hook is the simplest and earliest navigational tool that will keep you travelling straight eastward or westward on the same latitude (in the Northern hemisphere). Its principle is the same as almost all navigational instruments—it takes into consideration the angle of Polaris, the horizon, and the observer. These three points form a right triangle. If you can maintain Polaris’ apparent angle from the hook, you are assured of travelling on the same latitude with an allowance of one degree (60 nautical miles) drifting north or south. If the Polaris moves upward by the hook, it means you are heading a bit north; if it moves downwards, it means you are heading a bit south.
Clocks and chronometer
The earth revolves its axis once every 24 hours, which means the sun completes its apparent revolution, or 360 degrees, at the same time. In one hour, the sun appears to move 15 degrees; in one minute, it seems to move 15 arc minutes, and so on. If you will subtract the GMT (Greenwich Meridian Time) to your local time and cross multiply its difference to the above-mentioned ratio (with the longitude as the unknown), you will derive with your longitude what will be “west” of the Greenwich Meridian if the value is negative, and “east” if positive.
For this procedure to be effective, you will need a very precise clock—a chronometer. Introduced in 1761, it is a specialized timepiece that is not affected by gravity and the ship’s motion. Although there are many means to keep accurate time at present, most, if not all, ships still keep a chronometer for celestial navigation and emergencies. Modern marine chronometers can be based on quartz clocks periodically corrected by GPS signals or radio time signals.
“Modern navigators must be competent and confident enough to use a number of positioning tools and techniques, including but not limited to celestial observations,” notes Chief Mate Peter Katipunan, shipboard training officer of Mapua-PTC College of Maritime Education and Training.
Chief Mate Peter Katipunan says some new officers who lack knowledge and experience become so dependent upon navigational equipment that they don’t get to harness their manual skills.
Flags and pendants
Signaling flags are commonly-used communication signals between two ships or ships and shore. There are 26 flags, each depicting a letter in the alphabet, 10 numerical pendants, three substitute pendants or repeaters, and one answering pendant.
Each letter in the alphabet corresponds to signals like handling dangerous cargoes (B flag or bravo), pilot onboard (H flag or hotel), requiring tug (Z flag or zulu), and “yes” or “no” (C Flag and N flag correspondingly). Hoisting two or more flags depicts messages as well, such as requiring a helicopter (BR), asking for your position (FA), in distress and requiring immediate assistance (NC), and many others.
Flags can also be used in semaphore. Flag semaphore is an early telegraphy system using two flags held in different positions to convey signals, letters, and numbers. It can be substituted by lighted rods at night. This was the most reliable means of in-sight distance communication in the 19th century before radios were introduced onboard.
A whistle or horn, usually the latter, is widely used to this day to send signals, particularly during restricted visibility (thick fog, heavy rainfall, etc). Through a patterned prolonged and short blasts in proper intervals, as stipulated in Rule 34 of IMO’s COLREGS (The International Regulations for Preventing Collisions at Sea, 1972), you may inform nearby vessels whether you are underway, aground, restricted to maneuver, your relative distance (should your radar be working), and many others.
When in sight of one another, vessels may express their intention to alter course, overtake, perform astern propulsion, and even agree or disagree with the other vessel’s intentions through sound signals. This could also be performed using light signals (torch, signal lamps, etc.).
Morse code is a method of transmitting text information through a series of on and off tones or light. It is a sequence of short and long signals, represented by a dot (.) and a dash (-) called “dits” and “dahs”, conveying alphanumeric characters to a receiver.
From its development in the 1800s, amateur radio officers relied on this system to deliver and receive long-distance information until voicecapable radio transmitters were developed in 1920. Most countries permit Morse code on all amateur frequency bands (low frequency to ultra high frequency) while some have dedicated bands for it, making it very reliable in sending distress signals or SOS (…—…). Some amateur radio operators still use the Morse code, although it is not a proficiency required by many countries today.
Ravens and flocks of birds
The Vikings had a very intuitive way to determine whether they were approaching land nearby. During the early voyages for discovery, they would bring ravens with them and release them one by one after long voyages in uncharted waters. These birds would either fly over the nearest land giving out directions, or otherwise circle above the ship.
On April 1982, a naval architect and sailor named Steven Callahan, who had been drifting in the Atlantic for 76 days, was rescued by nearby fishermen after spotting a flock of birds circling above his life raft.
“Celestial navigation is important for survival given that navigational aids like GPS are not available in life boats; including the possibility that this positioning system may also jam onboard,” says Chief Mate Katipunan. According to him, some new officers who lack knowledge and experience become so dependent upon navigational equipment that they don’t get to harness their manual skills.
“Proper training and education in maritime schools are needed,” asserts Katipunan, noting that maritime instructors must also be wellexperienced onboard to fully impart why celestial navigation is still important today.
“The safety of navigation is at risk when the officer on watch (OOW) relies too much on navigation aids instead of employing ‘good seamanship’ practices. These analogue practices should be reiterated to every seafarer when they are doing their duties and responsibilities as an OOW,” states Chief Mate Garcia.