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Engineering Navigation – Searching The Longitude

Mahesa Abeynayake Head of Quality/ Act. CEO/Consultant Marine Engineering, Fiji Maritime Academy Just as oil and water do not mix, the Captain of a ship and the Chief Engineer are
03 May 2017 11:00
Engineering Navigation – Searching The Longitude
John Harrison

Mahesa Abeynayake
Head of Quality/ Act. CEO/Consultant Marine Engineering, Fiji Maritime Academy

Just as oil and water do not mix, the Captain of a ship and the Chief Engineer are usually not the best of buddies.

Disputes ranging from the optimal speed of the vessel to the quality of food served on board runs rampant in a division of management discipline on board.

In modern day shipping, the Captain or the Master is in charge of navigation and the operation of the vessel. The Chief Engineer ensures that the prime mover propels the vessels and that all machinery is in the proper condition in his care.

 

A traditionally known fact is that while the Captain assumes   that the ship navigates through the waters because he pulls and pushes levers on the bridge, the Chief Engineer thinks that the ship is just a shell to take his beloved machinery around the ocean.

It is undisputed that it is skillful work for the navigation officers to find their way around the ocean and get the ship to the destinations.

What is not well known is the lifetime effort of an Engineer’s dedication to ensuring Navigation Officers can find the position of the ship at sea.

To know the position of a ship one must know the coordinate.

Coordinates are a unique identifier of a precise geographic location on the earth, usually expressed in alphanumeric characters. Coordinates, in this context, are points of intersection in a grid system.  Coordinates are usually expressed as the combination of latitude and longitude.

In the 1700’s, with only the latitude available to position the ship, vessels used the method of dead reckoning to find the position using chip logs to calculate the speed in knots.

This method was not only unreliable but inaccurate as there was no way of measuring time accuracy at sea.

The cause of one of worst maritime disasters in that time was the navigator’s inability to accurately calculate their positions.

Narrative of finding the “Fix” begins on 22 October 1707, when four warships of the Royal Navy floundered off the Isles of Sicilyships causing loss of 1550 lives.

Ships using dead reckoning and not knowing their position at the longitude losing ships of the Royal Navy caused an uproar  in England.

Identifying that the method of dead reckoning depending on just latitude to fix position were both inaccurate and flawed, a Board of Longitude was formed in 1714. The Longitude Act offered a reward to 20,000 pounds for anyone who could find a method of determining longitude accurately at sea.

 

Chip Log and Knots

In the days of sail, the measuring of speed was calculated by throwing a log attached to a rope knotted at regular intervals. Sailors counted the number of knots that passed through their hands in given time to determine ships speed. The timing was done with the aid of an hour glass.

 

 

Dead Reckoning (DR)

In the absence of modern day Global Positioning System (GPS), the method of finding the position of a ship at any time was the process of Dead Reckoning (DR). The process began with a known start position then recording heading speed of the ship and plotting the new position on a chart.

With all this effort, the ships could only work with horizontal lines dividing the globe separated by the equator into Northern and Southern Hemispheres called the Latitude.

Use of DR has several flaws causing the ships like the Naval Vessel fleets to wander off the course.

The method did not take into account the currents of the oceans and wind speeds.

The biggest obstacle was to keep the actuate time. In the absence of clocks and the modern day chronometers, an hourglass was used to time knots. Imagine counting knots for an hour?

 

Longitude

The east-west position of a point on the earth surface expressed in degrees was the critical missing link inaccurate positioning of a ship at sea in the 1700’s.

The calculation of the angular distance from the prime meridian which passes through the Royal Observatory in Greenwich required an accurate clock.

 

 

The problem of Finding Longitude

Clocks made in those times were made out of wood and worked with a pendulum.

The swinging weight dangling at the end of a string was useless at sea as a pedal powered wheelchair. The wooden cogs failed eventually due to lack of lubrication.

The motion of the sea rendered the device working with a pendulum inaccurate.

The search for the longitude became an obsession of one man, a carpenter from Yorkshire John Harrison (pictured)

 

Having built his first long case clock in 1713 at the age of 20, John with hisbrilliant engineering mind and exceptional carpentry skills,  made three clocks in search for accuracy and durability at sea.

With the help of his brother James, they managed to overcome the lubrication problem by using lignum vitae, a type wood which is self-lubricating. The material is used for stern tube bearings on ships mechanical components up to this day.

Solving the swinging issue

Finding a suitable time keeping the device to swing accurately at sea took a little longer.

In 1730, John Harrison traveled to London with his marine clock to compete for the prize. It was another five years before the wooden clock, named H1, was built.

In 1741, H2 was built with many improvements but still was not good enough. After 17 years with the third clock, H3, using circular balance mechanism, John appeared to be closer to his goal.

This particular design left two legacies that are still being used in engineering up to this day – bimetallic strip and caged roller bearing.

Harrison’s first successful sea watch, the H4, with a winding crank was made with metallic material and not wood and took six years to construct. The final testing on a voyage from Portsmouth to Kingston Jamaica in 1761 saw it lose only 24 seconds in nine days at sea – a remarkable feat for time technology at the time

Like many other pioneers, John met resistance from many quarters of skeptics and non-believers but persisted on his beloved project.

The Board of Longitude and Astronomer, named Neville Maskelyne, was his major obstacle, but in the end, persistence prevailed,  and the Marine Chronometer was born.

With the clock timing the distance accurately from the starting point, a ship’s position could now be fixed with Latitude and Longitude with precision.

After five clocks, taking 48 years of work, John had built an accurate time keeping machine which earned him the fame “clock maker who changed the world.”

With his H5 clock,the sea calculation of Longitude was now possible.

Ship positioning has come a long way since the days of chip logs, and  DR. GPS, Electronic Charts, Atomic Clocks, and radar are now modern navigation aids. If all fails, it is back to basics with the Marine Chronometer, Sexton and paper charts  that are still part of the Bridge’s equipment.

All these modern instruments still depend on Longitude and Latitude to “fix a position.”

Let’s not forget that it was a carpenter with persistence and an extraordinary engineering mind that paved the way for safe and accurate navigation..



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