The Plimsoll Line by Year 12 Physics Students

The Plimsoll Line by Ahlaq Hyder 12V

What is the Plimsoll Line?

The Plimsoll line, also known as load lines or waterlines is a reference mark that is located on a ship’s hull that indicates the draught of the ship [4] and the maximum depth in which the ship may be safely submerged when loaded with cargo [2]. It takes into consideration the various conditions of seasons and location that the ship will be in [4]. The positioning of the markings depend on the ship’s dimensions, type of cargo, time of year and the water densities encountered across the locations it travels in [2].

How does physics play a part?

Density is the mass per unit volume of a substance. The temperature of the water affects the level of the markings; this is because warm water provides less buoyancy as it us less dense than cold water. Salinity, or the saltiness of the water plays a part, as fresh water is less dense than seawater. A ship will submerge deeper in freshwater than that in seawater because of freshwater having a lower density, this therefore means that a ship can be loaded with more cargo if it’s travelling only in seawater than it can be in freshwater.

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The History behind the Plimsoll line

Samuel Plimsoll, who was an MP, introduced the Plimsoll Line as a law. He fought a long struggle to pass the law in the English Parliament to protect sailors [1]. Overloaded ships were dangerous as they could sink in heavy seas or rough weather. In the year 1873-74 around the coastline of the United Kingdom 411 ships sank and 506 people died. Overloading and poor repair made some ships so dangerous that they became known as ‘coffin ships’ [3]. Sailors refused to go board these ‘coffin ships’ and were often imprisoned for desertion [1].

Although seafaring merchants understood how dangerous overloaded ships could be, the ship-owners were sometimes tempted to risk it because of the huge profits that they could make when a large amount of cargo was sold abroad. If a ship were lost at sea the owners wouldn’t suffer at all because they could claim their money back in insurance [3][1].

How can the implication of physics be beneficial?

The physics of understanding how temperatures and salinity affect the densities of water provides the benefits of a greater understanding and knowledge of how overloaded ships can be disastrous and how the markings on the ship, based of calculations and the considerations of the dimensions of the vessel, type of cargo, time of year and water densities can provide crucial information to the vessel owners on the limit of cargo they can put on and therefore save people from potential disasters.

Sources of information:

[1] Edexcel AS Physics by Miles Hudson and Patrick Fullick

[2] National Oceanic and Atmospheric Administration (NOAA)

(http://oceanservice.noaa.gov/facts/plimsoll-line.html)

[3] Royal Museums Greenwich – Load Lines

(http://www.rmg.co.uk/explore/sea-and-ships/facts/ships-and-seafarers/load-lines)

[4] The Oxford Companion to Ships and the Sea – Peter Kemp (Oxford University Press)

Plimsoll line by Sambathkumar Uruthirakumar 12G

Brief description

A plimsoll line is a line that is shown on a ship to illustrate the maximum depth of submersion when ship is loaded with cargo.

Physics principles

The Plimsoll line is used so that the weight of a ship produces just enough upthrust in water to prevent the ship from sinking. It also indicates the loading of ships at different temperatures and locations.

History of the Plimsoll line

Samuel Plimsoll, put the Plimsoll line bill forward to Parliament in the 1870s. Before this many ships went missing at sea and sailors died. He fought to pass the law in the English parliament to mainly protect these sailors. The ship owners didn’t care much about the ships due to the fact that they would get the money from the insurance. The law was eventually passed in 1876, and it was compulsory for all the ships to have the Plimsoll line.

Benefits of having the Plimsoll line

There are so many benefits of having the Plimsoll line. The ships and the sailors are safer. Fewer goods are being wasted or destroyed. Financial losses for insurance companies and the goods companies are reduced.

Bibliography

1) http://oceanservice.noaa.gov/facts/plimsoll-line.html

2) http://www.metoffice.gov.uk/media/image/g/m/malhamtarn_snow.gif

3) http://www.rmg.co.uk/explore/sea-and-ships/facts/ships-and-seafarers/load-lines

4) AS physics book page number 54 (unit 1 topic 2 materials)

The Plimsoll Line by Kishok Inderaraj 12G and Jemin Jayapal 12O

Introduction

The Plimsoll line is a marking on ship’s side showing the limit of legal submersion when loaded with cargo under various sea conditions. (1) In essence it shows the volume/weight that a ship can maintain before it cannot displace enough water and sink. The Plimsoll line shows the maximum depth that a vessel can be safely ‘submerged’. As cargo is loaded, the ship will sink lower to displace a greater weight of water and thus balance the new, heavier overall weight of the ship (7)

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History

The Plimsoll line was named after the founder and creator Samuel Plimsoll. Samuel Plimsoll (10 February 1824 – 3 June 1898 and born in Bristol) was an English politician and reformer. As a child he moved to Sheffield and then Cumbria, leaving school at an early age to become a brewery clerk and then manager. In 1853 he moved to London and became a coal merchant, a business that left him destitute and instilled a huge sympathy for the struggles of the poor. (3) ‘But Plimsoll was a determined man. Despite his problems he picked himself up and was soon campaigning against overloaded and unseaworthy merchant vessels, known as “coffin ships’. The ships were overloaded and were in such poor shape and repair, that sailors knew they would sink in high seas. The sailors refused to board the ship and were imprisoned for desertion. So in order to help save lives and provide a safe journey for these ships Samuel Plimsoll invented the Plimsoll line. (5)

Discovery

Initially Samuel Plimsoll began writing a book about the catastrophic effects of overloading ships. When he began to investigate, Plimsoll found the problem was even worse than he had expected. He began to campaign in parliament with the aim of improving safety at sea. Many ordinary people became very interested in his book and his campaign. In 1872, a Royal Commission on Unseaworthy Ships was set up to look at evidence and recommend changes. Despite several defeats in parliament, Plimsoll continued in his fight until load lines became compulsory. He became so famous that several popular songs were written about him.  (5) (6)

An act was passed by parliament in 1876, which made load lines (Plimsoll line) compulsory. This act was named as the Merchant Shipping Act of 1976. Furthermore in 1906 it was made compulsory that foreign ships coming to British ports must have the Plimsoll line. (6)

Benefits

The Plimsoll load line ensures that the cargo-loaded vessel has safe and smooth sailing. They should ensure that the sea level should stay on or below the line (L-R, refer to diagram previously). It might prove to be severely unsafe to the ship as tactless overloading of heavy shipment would sink the ship’s stability. Crossing the assigned limit of the Plimsoll mark or the waterline is considered violation of an international shipping act and can even land the ship’s crew, including the Captain, in deep trouble. (6)

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The Plimsoll line by Teshan Dabarera 12G

The Plimsoll line is a mark, located on the ship’s hull that indicates the maximum depth the vessel may safely be immersed when loaded with cargo. There are many factors that affect the depth of the ship: ship’s dimensions; type of cargo; time of year; and the water densities. After these factors have been accounted for, the ship’s captain can determine the correct Plimsoll line which is needed for the voyage.

TF = Tropical Fresh water

T = Tropical

F = Fresh Water

S = Summer

W = Winter

WNA = Winter North Atlantic

The Plimsoll line is named after Samuel Plimsoll (1824-1898) who was a member of the British Parliament and was concerned with the loss of ships and crews due to vessels overloading. So in 1876, Plimsoll persuaded the British parliament to pass the Unseaworthy Ships Bill, which mandated marking a ship’s sides with a line which would disappear below the waterline when the ship was overloaded and is still used worldwide by the shipping industry. This simple graphic has saved thousands of lives

When insurance was introduced for ships in the 19th century, ship owners purposely sunk their own ships to collect the insurance money. This practice become widespread and killed so many merchant seamen that the overloaded vessels became known as “coffin ships”. Plimsoll fought against this thus leading to the adoption of the shipping regulation “The Plimsoll Line”.

An example of the dangers of overloading was the SS London (1864). It was a British steamship which sank in the Bay of Biscay on 11 January 1866. The ship was overloaded with cargo, was unseaworthy and included 239 people aboard. Only 19 survivors were able to escape the foundering ship to a lifeboat leaving a death toll of 220. If the line had been introduced before the 1866 then this ship would not have been able to depart.

In the year 1873-74, around the coastline of the United Kingdom, 411 ships sank, with the loss of 506 lives because of the overloading and poor repair. At that time many sailors refused to go to sea, in 1855, a group of calling themselves “the seamen of Great Britain” wrote to Queen Victoria complaining about the dangerous of going into seas in these dangerous ships, some sailors who refused were imprisoned for twelve weeks for refusing to sail in ships considered to be unseaworthy.

In the 19th Century working on a merchant ship was a dangerous business, in 1876 the board of trade recorded that 856 British merchant ships were lost within ten miles of British coast, in conditions that were no worse than a strong breeze.

Plimsoll got involved with the problem of ship safety from different attempts, in 1870 Plimsoll who was a coal merchant, became interested after attending a meeting on the subject so he began to write a book about the effects of overloading ships, Plimsoll discovered that the problem was worse than he had expected and began to campaign in the parliament with an aim of improving the safety at sea. Many people were interested in his book and his campaign and in 1872, a royal commission on Unseaworthy Ships make changes, after many defeats in parliament, Plimsoll continued his fight until the Plimsoll line became compulsory till this day.

Another interesting fact is that when rubber sole shoes with canvas tops were introduced in the 1920’s they were known as “Plimsolls” because of the line that divided the sole and upper canvas which resembled the Plimsoll line.

Bibliography

Website: http://oceanservice.noaa.gov/facts/plimsoll-line.html

Website: http://99percentinvisible.org/episode/episode-33-a-cheer-for-samuel-plimsoll/

Website: http://en.wikipedia.org/wiki/SS_London_(1864)

The Plimsoll Line by Karthikeyan Theivendrarasa 12B

The Plimsoll line is a reference mark located on a ship’s hull that indicates the maximum depth to which the vessel may be safely immersed when loaded with cargo. This depth varies with a ship’s dimensions, type of cargo, time of year, and the water densities encountered in port and at sea. Once these factors have been accounted for, a ship’s captain can determine the appropriate Plimsoll line needed for the voyage (see image below):

TF = Tropical Fresh Water

T = Tropical

F = Fresh Water

S = Summer

W = Winter

WNA = Winter North Atlantic

AB = Letters indicating the registration authority (American Bureau of Shipping in the image shown below; the circle with the line through it indicates whether or not the cargo is loaded evenly)

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Samuel Plimsoll (1824–1898) was a member of the British Parliament who was concerned with the loss of ships and crews due to vessel overloading. In 1876, he persuaded Parliament to pass the Unseaworthy Ships Bill, which mandated marking a ship’s sides with a line that would disappear below the waterline if the ship was overloaded. The line, also known as the Plimsoll mark, is found midship on both the port and starboard hulls of cargo vessels and is still used worldwide by the shipping industry.

The Plimsoll Line by Ramz Hkimi 12V

The Plimsoll line is a mark located at the bottom of a ship that shows the maximum depth to which the ship may be safely submerged when loaded with cargo. This depth varies with a ship’s dimensions, type of cargo, time of year, and the water densities encountered in port and at sea. Once these factors have been accounted for, a ship’s captain can determine the appropriate Plimsoll line needed for the sea.

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Samuel Plimsoll was a member of the British Parliament who was concerned with the loss of ships and crews due to ship overloading. In 1876, he persuaded the British Parliament to mark ships’ sides with a line that would disappear below the waterline if the ship was overloaded. The line, also known as the Plimsoll mark, is found mid ship on both the port and starboard hulls of cargo vessels and is still used worldwide by the shipping industry.

This simple graphic design has saved thousands of lives. The Plimsoll line shows the maximum loading point of the ship and lets a third party know, plainly and clearly, when a vessel is overloaded and at risk of sinking in rough seas. If you see that horizontal line above the water, you’re good, if you don’t, you could be sunk.

SS London was a British steamship which sank in the Bay of Biscay on 11 January 1866. The ship was travelling from Gravesend in England to Melbourne, Australia, when she began taking in water on 10 January, with 239 persons aboard. The ship was overloaded with cargo and unseaworthy and only 19 survivors were able to escape the foundering ship by lifeboat, leaving a death toll of 220. So since there was no plimsoll line the ship’s crew had no idea that they had overloaded the ship with too much cargo and the ship ended up sinking.

The Plimsoll Line by Seyar Azizi 12O

What is the Plimsoll line?

A plimsoll line is a line that is drawn on the side of the ships to show how much load it can take before it gets too low and at risk of sinking.

History

The Plimsoll line was instigated by a man called Samuel Plimsoll. In the 1870s, he tried to keep sailors safe by passing a law in parliament, which made all ships that are registered in the UK have the Plimsoll line drawn on their sides. Before this happened, sailors had to risk going out at sea whilst their ships were holding too much cargo, which could make the ship sink. From the years 1873 to 1874 more than 400 ships sunk causing over 500 deaths. Sometimes sailors wouldn’t even board the ships when overloaded and in a poor state, so they were imprisoned for desertion. Even though the cargo was lost, the owners still made their money by claiming insurance.

Plimsoll line

The Plimsoll line indicates the maximum safe draught and the minimum freeboard. The draught is from sea level to the bottom of the keel. The heavier the load the bigger the draught has to be to allow the ship to stay afloat. The freeboard is from sea level to the sheer of the ship. The more load there is on the ship, the smaller the freeboard. When having a smaller freeboard, water can get in more easily and this increases the load on the ship. The Plimsoll line can allow you to see how much overload you can put on the ship before its gets too low in the water. The higher the density of water the stronger the upwards buoyance force is. Density is the mass per unit volume. This means that the density of any solid, liquid or gas can be found by dividing its mass in kilograms by its volume in cubic metres. Buoyancy is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid.

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Sources

The Physics book was published by “A Pearson Company” and follows the guidelines which set by Edexcel and was written by Miles Hudson and Patrick Fullick

The Plimsoll Sensation: The Great Campaign to Save Lives at Sea” which was written by Nicolette Jones in the year 2006

Websites: oceanservice.noaa.gov/facts/plimsoll-line.html” and “cikguwong.blogspot.co.uk/2011/07/physics-form-4-chapter-3-application-of.html

bickfordscience.com/04-Density_and_Buoyancy/02-buoyancy.html

Plimsoll line by Abinayan Rasaratnam 12G

This report shows what a plimsoll line is and why it was created. This report also shows why it is used and what it actually is.

Historical Background

The Industrial Revolution that started in Britain in the 18th century was dependent on trade with foreign countries to supply the raw materials for Britain’s factories. The demand for the importation of exotic goods from abroad was also needed and as an island, Britain became more dependent on shipping.

The rewards from a successful voyage were enormous, but the risks were huge too. Many a ship was lost at sea, often due to overloading with cargo.

Who was Samuel Plimsoll?

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Sir Samuel Plimsoll was Born in Bristol on 10th February 1824, but died in the town of Folkestone 74 years later.

He is best remembered for creating a campaign, which led to the Merchant Shipping Act of 1876 ordering to paint the Plimsoll line on every ship on the hull of seafaring ships to show safe loading limits to prevent accidents.

What is the Plimsoll line?

It’s a marking on a ship’s side showing the limit of legal submersion when loaded with cargo under various sea conditions.

What do the marking represent and what do they mean?

The maximum safe loading depth varies with ocean regions and seasons. In the tropics the water is warmer and therefore less dense than in temperate regions, so the same load ships will float higher in cold regions than in the tropics.

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Why does the density of water matter?

A ship will submerge deeper in freshwater than that in sea water, because the density of freshwater is smaller. The ship can be loaded with heavier load in sea water than in freshwater.

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Sources:

http://cikguwong.blogspot.co.uk/2011/07/physics-form-4-chapter-3-application-of.html

Textbook: Edexcel physics for AS

http://www.barrygray.pwp.blueyonder.co.uk/Tutoring/Ships.html

Plimsoll line report by Milan Divecha 12Y

This report is about the Plimsoll line, any sources of information that have been used have been stated in the bibliography.

Overview

A Plimsoll line of ships is a marking on their hulls, which acts as a reference line marking the loading limit for them (3). It tells you what the maximum height of the water level should be against the hull of the ship. By using this, you can see that if the water level is above the Plimsoll line (or load line), the ship is carrying too much weight so it has been overloaded. If the sea level is at or is under the Plimsoll line the weight is balanced well with the upthrust, so the ship will be stable and will float. The Plimsoll line is named after the man who managed to make it part of maritime legislation, Samuel Plimsoll (1824–1898). (7)

The physics of the Plimsoll line

An object is only able to float and not sink downwards in a fluid if the upwards forces acting on it are equal to or greater than the downwards forces (1). If an object has low weight, when it is initially submerged in a fluid, it will sink as weight is the only force acting on it, but as it displaces some of the fluid, the upthrust pushes it upwards. If the upthrust exceeds the weight, it will rise upwards, i.e. it floats (1). Essentially, we get the inequality: volume of fluid displaced (the volume of water displaced is the same as the volume of the part of the ship that is submerged.) x density of fluid x gravitational field strength is greater than volume of fluid displaced x density of object x gravitational field strength (1). This is the same as saying weight of fluid displaced (the size of the upthrust) is greater than the weight of the object (that is actually submerged in the fluid), in order for an object to float in a fluid. Therefore, in order for a ship to stay afloat, its weight must not exceed the upthrust acting on the ship. That is why when it gets overloaded, the ship sinks. The Plimsoll line helps to check this because when loading the cargo, if the ship starts to sit lower in the water (as the weight starts to exceed upthrust) and the water level starts to go above the Plimsoll line, it tells the crew that there is a dangerous amount of weight on board and the water will not provide enough upthrust to support the weight (7). The position of this Plimsoll line obviously varies for different ships because ships of different sizes displace different amounts of water and therefore will experience a different magnitude of upthrust. Different ships will also have different weights too. So every ship must be assessed by the Classification Society who calculate (using physics principles) where the Plimsoll line should be by considering the density of the ship’s material, the ship’s weight and it’s volume as well as the volume of the keel (the part of the ship that is submerged) (4). Therefore, the implication of physics here is vital as it is used to implement a life-saving feature. Without physics knowledge and the application of physics, people would not be able to determine the load line accurately and so lots of ships could crash and many people could die.

Although in the case of a ship, it is not so easy to work out the upthrust of the water acting on it because it is not like a lab experiment. The water is not pure at sea as it has salt and other minerals, so the density of the water that is actually being displaced could be very different from 1000 kgm^-3 (the density of pure water.) Usually, the water at sea is a lot denser than fresh water because of all the minerals dissolved in it. Sea water has a density of about 1025kgm^-3, whilst fresh water has a density that is much closer to the density of pure water (it is around 1000 kgm^-3.) The density of the water can also vary with location due to the climate of where the ship is; where it is warmer, the water is warmer and so is less dense. This means it provides less upthrust than the same volume of colder water (since upthrust = volume of fluid displaced x density of fluid x gravitational field strength). This creates many problems because a ship may have a reasonable load when it starts its journey in a part of the world where the water is cold and denser, but if its end destination is in the tropics where the water is warmer and less dense, and then suddenly the water provides less upthrust when it enters the tropics. This means that the weight may now exceed the upthrust even though this was not the case when it started and the ship could sink. Hence this is why ships do not have just one general load marking to work with; there are different load lines for different circumstances:

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The markings on the right of the diagram show how the load lines for different types of water where the densities are different differ from the general Plimsoll line. The letters have the following meaning:

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This shows that for the same constant weight of the ship, more of the less dense water must be displaced in order to provide enough upthrust to keep the ship afloat. This is shown by the fact that the water level for tropical fresh water is much higher than winter temperate seawater. As shown, the time of year and the seasons also affect the upthrust on the ship as water temperature varies over the year (so water density also varies).

Historical/Social context of the Plimsoll line

Historically, merchants and product suppliers would overload their ships as they weren’t aware of the danger it caused and wanted to maximise the profit from each shipment (1). This caused the ships to either sink (as the weight was much greater than the upthrust) or it simply caused the ship to float too low above the water. This was also dangerous as it compromised the stability of the ship and made it easier for the ship to sink. In fact, it made it so dangerous that in the year 1873–74, around the coastline of the United Kingdom, 411 ships sank, with the loss of 506 lives. Overloading and poor repair made some ships so dangerous that they became known as ‘coffin ships’ (2). And since global trade was rapidly increasing around this time, the number of deaths at sea increased exponentially. One of the first attempts to get ships to carry loading marks for safety was made in 1835 by Lloyd’s Register, a classification society. Lloyd’s Register introduced freeboard tables for loading, but these only applied to those ships classed by Lloyd’s Register itself. Other ship owners could still do as they pleased when they loaded their ships. If they chose to disregard questions of safety no-one would stop them. This concerned Samuel Plimsoll (a famous merchant and MP) deeply, so he used his political influence as a Member of Parliament to campaign for a bill that improved the safety of ships to prevent the loss of sailors’ lives. He proposed a bill that stated every cargo ship must have a load line by law. Load lines had been as early as the 12th century; ships from Venice were protected by a marking on the side of the ship in the shape of a cross and it acted as a load line. The city of Genoa also marked its ships in a similar way, using a sign made up of three horizontal bars. (2) However, the custom died out, and it was Samuel Plimsoll who believed that is was absolutely necessary for it to be required by law. He believed that legislation would be required in order for merchants to take it more seriously. So eventually after a long struggle, he managed to get the bill passed as an act. The Merchant Shipping Act of 1875 stated that it was compulsory to have a load line marked on the hull of every cargo ship, indicating the maximum depth to which the ship could be safely loaded (3). An International Load Line was adopted by 54 nations in 1930, and in 1968 a new line, permitting a smaller freeboard (hull above waterline) for the new, larger ships, went into effect. (3) Due to the Plimsoll line, there are very few deaths at sea due to overloading nowadays.

Bibliography:

1. Book- Edexcel AS Physics Handbook (Page 54) ISBN: 978-1-4058-9638-2

2. Internet link- http://www.rmg.co.uk/explore/sea-and-ships/facts/ships-and-seafarers/load-lines

3. Internet link- http://www.britannica.com/EBchecked/topic/464810/Plimsoll-line

4. Educational Video- https://www.youtube.com/watch?v=YpCyP1sM_cA

5. Diagram (picture)- http://upload.wikimedia.org/wikipedia/commons/b/b0/Load_line.jpg

6. Book- Notes on Cargo Work: Kemp and Young: ISBN 0-85309-040-8

7. Internet link- http://www.marineinsight.com/misc/maritime-law/what-is-plimsoll-line-on-ships/

Plimsoll line report by Alex Pregal 12I

The aim of this report is to find out when and why the Plimsoll line was created and the physics behind the Plimsoll line which makes it so effective at what it does.

What is a Plimsoll line?

A Plimsoll line is a marking on the side of a ship’s hull which indicates the maximum depth to which the ship may be immersed during the loading of cargo. This depth varies with a ship’s dimensions, types of cargo, time of year and the density of the water the ship is in. This results in the Plimsoll line being in different locations on each and every ship. There are actually many Plimsoll lines on a ship, each one for a different type of water (see table below), the captain of a ship has to decide which Plimsoll line to use when loading the ship.

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Who created the Plimsoll line and why?

MP Samuel Plimsoll was very concerned with the loss of ships and sailors due to the overloading of merchant ships. So he fought a long battle get a law passed which made it compulsory for all ships registered in England to be marked with a marking that indicated safe loading levels for ships in the 1870s. The law, which was put forward in 1876, came to be known as the Merchant Shipping act or the Load-Line act and the marking that was put on ships was called the Plimsoll line.

Physics behind the Plimsoll line

The Plimsoll line works due to the displacement of water and the up thrust it provides. When a ship is loaded with cargo, the weight of the ship will increase, which causes the ship to sink lower and thus displace more water. This extra water that has been displaced increases the up thrust on the ship, as the up thrust is equal to the weight of the water that has been displaced. However, if the ship gets too heavy more water will need to be displaced, as the up thrust of the water is not equal to the weight of the ship, which means the ship will have a net downwards force and thus accelerate downwards due to Newton’s first law. This will result in the ship sinking if it gets overloaded.

The Plimsoll line is calculated using the ships volume and the density of the water that the ship is in. The density of sea water can vary due to the level of salt in the water and the surrounding temperature. This is why Plimsoll lines are at different levels on different ships, and also why they are made up of so many different lines indicating different types of water. The position of the Plimsoll line on a ship is worked out with careful density calculations which will give a safe depth to which the ship can sink to while it is being loaded. The weight of the water displaced at this depth will be equal to that of the ship, which means the ship will float.

Bibliography:

1. http://oceanservice.noaa.gov/facts/plimsoll-line.html

2. Evening Telegraph – Friday 03 June 1898

3. Edexcel AS Physics – Student’s Book

Authors: Miles Hudson and Patrick Fullick

ISBN: 978-1-4058-9638-2

4. http://www.rmg.co.uk/explore/sea-and-ships/facts/ships-and-seafarers/load-lines

The Plimsoll line by Shefali Srivastava 12I

Brief description of the Plimsoll line

It is a mark painted on the sides of British merchant ships which indicates the draught levels to which a ship may be loaded with cargo for varying conditions of season and location. This depth varies with the ship’s dimensions, the type of cargo being loaded, the time of the year, and the water densities at different locations on the planet. The Plimsoll mark shows six loading levels, those which may be used in tropical fresh water, summer sea water, winter sea water, and winter north Atlantic for vessels under 100 metres in length.

Physics knowledge involved

The depth varies because of the various densities of water at different locations. In salt water, the ship will be more buoyant because salt water is denser than fresh water. This is because salt is denser than water and so if you add it to water the resulting solution is denser than pure water. The salinity of the ocean varies, but the generally accepted average amount is 2.5%. So salt water weighs 2.5% more than the same volume of fresh water.

Taking the above information into consideration, we can say that if the temperature increases the density of the salt water increases. This is because as the temperature increases, more fresh water is evaporated and this results in an increased salt to water ratio. This therefore results in increased density of the water. This explains why the Plimsoll line for summer is below the Plimsoll line for fresh water as the ship is more buoyant. Similarly, high precipitation will add more freshwater to the sea water thereby increasing the water to salt ratio making the water less dense. This is why the tropical fresh water Plimsoll line is above the freshwater Plimsoll line as the precipitation in a tropical region is very high and ships are less buoyant. In cold water the water molecules are closer together so it is much denser than room temperature water. This means that a ship is more buoyant in cold water than warm water. This also explains why the Plimsoll line for winter is lower than that for fresh water and higher than that for winter northern Atlantic Ocean as the water in the northern Atlantic Ocean in winter is going to even colder.

The table below shows the density of water at different temperatures:

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The above table shows that as the temperature increases the density of water decreases. This is because as the temperature increases, the molecules of water gain energy and this heat energy is transformed into kinetic energy and the molecules start to vibrate more. This causes them to move away from each other and causes the density to decrease. However, when the water is at 0 degrees Celsius, its density is very low. This is because at this temperature the water turns to ice and ice consists of crystals that are not as densely packed as water molecules.

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Historical context related to the Plimsoll line

Sir Samuel Plimsoll invented the Plimsoll line. According to a newspaper article published on the day of his death, he ‘accumulated facts (on the subject of ships) and examined grounds of complaint, resolved to spare no effort to reduce the wrongs under which the seamen laboured’. In his work titled ‘Our Seamen: An Appeal’, he mentions that before the plimsoll line was invented, there were numerous shipwrecks. He felt that lives were lost from causes that were easily preventable. He recognized that the ships that leave the harbour were so overloaded that ‘it was nearly impossible for them to reach the destination if the voyage is at all rough’. He proved that nearly half of their losses were due to the overloading of ships that would then go out into the sea and sink.

Advantages of the implications of physics

The Plimsoll line reduces the risk of cargo ships sinking. This not only prevents a potential loss of money and fuel but also prevents the loss of life. The knowledge of the density of water at different temperatures and during different seasons is essential for the accurate determination of the plimsoll lines. This shows that the implication of physics is very important in order to reduce the risk of inaccuracy of the plimsoll lines which could result in potential catastrophes.

Bibliography:

1] http://oceanservice.noaa.gov/facts/plimsoll-line.html

2] http://www.mcaorals.co.uk/Loadlines.htm

3] https://deepstop.wordpress.com/2009/02/26/buoyancy-salt-water-vs-fresh-water/

4] Research article by T. G. Prasad titled ‘Annual and seasonal mean buoyancy fluxes for the tropical Indian Ocean’

5]http://fc.codmanacademy.org/branches/geographya/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=6

6] http://lilt.ilstu.edu/ewpeter/GEO360/Water%20Density%20Table.pdf

7] http://www.quora.com/What-happens-to-water-between-0-and-4-degree-Celsius

8] Evening Telegraph – Friday 03 June 1898; newspaper article titled ‘DEATH OF SAMUEL PLIMSOLL’

9] http://www.rmg.co.uk/explore/sea-and-ships/facts/ships-and-seafarers/load-lines

10] http://cnx.org/contents/031da8d3-b525-429c-80cf-6c8ed997733a@7.61:95/College_Physics

11] Edexcel AS Physics Student Book (Edexcel A Level Sciences) by Miles Hudson and Patrick Fullick published 14th July 2008, Unit 1 Topic 2 Materials page 54

The Plimsoll line by Vinnoja Thurairethinam 12V

Ships are used to transport passengers and cargos and as the load in ship increases, it sinks more in water. Moreover, if loaded beyond a certain limit, the ship may sink completely. The Plimsoll line is painted onto a ship’s hull to indicate the maximum depth to which the vessel can be safely immersed in water when the ship is being loaded, under a variety of water and climate conditions.

image

The basic symbol is made of a circle with a horizontal line passing through its centre. The letters on either side of the symbol specify which organization had certified the load level. The location of the line depends on many different factors, such as the hull shape, the length of the boat and the type of cargo.

image

AB = Letters indicating the registration authority (American Bureau of Shipping ; the circle with the line through it indicates whether or not the cargo is loaded evenly)

The additional lines located to the right of the symbol indicate the limits for different water types and climates conditions. These lines are crucial because different temperatures of the water lead to a variation in densities.

In tropical areas the sea water is warmer and thus it is less dense that in colder regions. The ship sinks lower in the water, as cargo is loaded, to displace a greater weight of water. This will balance the overall weight of the ship. Warm sea water produces less upthrust than cold water due to its lower density. Fresh water also produces less upthrust than sea water. This means that a ship with the same load would float higher in cold regions or in areas of fresh water than in warmer areas. Seasonal changes have similar consequences. Therefore, a ship travelling in fresh water or through warmer regions can be loaded with heavier cargo.

Historical background

In the early days of the British navy, ship owner would often overload a ship with goods to be sold in other countries, before sending them off on their trade routes. Due to being overloaded, the ships sank easily during a storm at sea and thus only few sailors survived the trip while most where ‘missing, presumed lost’. In only one year, 411 ships were wrecked along England coast and over 500 sailors drowned.

As a result of this, sailors become reluctant to work on these ships and many of them were willing to spend twelve weeks in prison for disobeying orders than to set sail on what they considered dangerous ships.

image

Samuel Plimsoll, a member of the British Parliament, was concerned with these circumstances and the “coffin ships” of the times. After several denials of his proposals for safety regulations, he eventually persuaded Parliament to pass the Merchant Shipping Act of 1876. This law forced ship owners to paint load lines on the sides on their ships, which would disappear below the waterline if the ship was overloaded. Loading the ship had to stop as soon as this line reached the water level and ship owners who would overload their ships would be fined or imprisoned. This line soon became known as the Plimsoll line and is still used worldwide by the shipping industry.

Glossary

Cargo – the goods or the load transported on a ship

Density – the mass per unit volume of a substance at a given pressure and temperature

Hull – the main body of a ship

Upthrust – the upward force that a liquid or gas exerts on a body floating in it

Vessel – a ship or a large boat

Weight – the force caused by gravitation; weight varies with the strength pf the gravitational field

Biography

Internet:

http://oceanservice.noaa.gov/facts/plimsoll-line.html

https://www.teachengineering.org/view_lesson.php?url=collection/duk_/lessons/duk_float_mary_less/duk_float_mary_less.xml

http://www.physicslocker.com/physicslocker/ks3/2%20Exploring%20Science%20-%20KS3/Y7/Acrobat_Files/Units_and_Skill_Sheets/7K/7Kb5.pdf

http://cikguwong.blogspot.co.uk/2011/07/physics-form-4-chapter-3-application-of.html

Books:

Edexcel AS Physics

Student’s Book

Miles Hudson, Patrick Fullick

Pearson Education Limited, 2008

Page 54

Newspaper article:

The bottom line about Mr Plimsoll

Simon Garfield

The Observer

Sunday 25 June 2006

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