The Earl of Abergavenny

Transcription

1 The Earl of Abergavenny The Earl of Abergavenny was an East Indiamen ship built in On the 1st February 1805, she sailed from Portsmouth heading for the Bengal and China. Three days later she sank with the loss of 300 people. Why do you think that she sank? What evidence would you need to make a decision? What questions should you ask? At 5pm, the crew thought there was no danger. Then the ship s carpenter discovered a serious leak and the pumps were set. No distress signal was released because it was not thought to be too serious. By 6pm more leaks were found and the ship was thought to be in serious trouble. Signal guns were fired but by 10pm the ship was full of water and began to sink. On the 4 th February, near Portland Bill, the wind dropped and the tide took the Earl of Abergavenny towards breakers. (Rough waves over shallow rocks). At 11pm a rough sea hit the ship and she quickly sank before most of the passengers and crew had reached the lifeboats. Write your hypothesis on the next page. 1 of 9

2 Why do you think that The Earl of Abergavenny sank? 2 of 9

3 Ship building At the time that the Earl of Abergavenny was being built, a number of changes were taking place in ship building. The knee (the part of the ship joining the deck to the hull) of ships used to be made of wood. Now they were being built of iron for extra strength. Could the iron knees have caused the ship to sink? Write your new hypothesis below. Have you changed your hypothesis? Why do you think that The Earl of Abergavenny sank? 3 of 9

4 Composite ships (ships using wood and iron) were being built at this time and did not show any real problems with rusting. Sir Francis Drake s ship, the Golden Hind, was built in a similar way and survived over 100 years. This means that the iron knees can t have just rusted away. The only way to find out what happened was to dive to the ship and investigate further. Look at the following page for information about the dive. A cross-section of a composite ship showing more advanced iron and wood construction. 4 of 9

5 Diving to the ship The dive to the ship was obstructed by poor visibility and the fact that the knees were very heavy to raise. Eventually a number of knees were brought to the surface to be analysed. Analysis of the knees showed far greater corrosion (rusting) had taken place than was expected. The knees had worked loose around the pins that held them to the hull and deck. This allowed the planks of the hull to move and let in water, causing the ship to sink. Why did the knees rust so quickly? Chemical analysis showed that the pins used were not made of iron but were cheaper copper. Did this make the difference? Raising the knees. A photograph of the pin hole on the iron knee. Large amounts of rusting can be seen. Go to the next page to update your hypothesis. Salvaged knees (taken from another dive). 5 of 9

6 Have you changed your hypothesis? Why do you think that The Earl of Abergavenny sank? You can look at your previous hypotheses on pages 2 and 3. Go to the following page for your next piece of information. 6 of 9

7 Sacrificial Anodes Modern ships are now made of metal. There are a number of methods to prevent them from rusting. Sacrificial anodes are small blocks of metal (normally magnesium or aluminium) which are bolted to the hull. The blocks corrode whilst the ship stays safe. Sacrificial anodes made from Magnesium. See the following page for the last piece of information. 7 of 9

8 The reactivity of metals Rusting corrosion can be prevented by connecting iron to a more reactive metal (eg Zinc or magnesium). This is referred to as sacrificial protection or sacrificial corrosion. The more reactive metal in the pairing is preferentially oxidised away (corrodes), thus protecting the other metal, leaving it intact. The picture above illustrates what would happen after a few days. How does this compare to the iron knees on the Earl of Abergavenny? The reactivity series of metals K Potassium Most reactive Na Sodium Ca Calcium Mg Magnesium Al Aluminium C Carbon Zn zinc Fe Iron Sn Tin Pb Lead H Hydrogen Cu Copper Ag Silver Au Gold Pt Platinum Least reactive (added for comparison) Go to the following page to write your final hypothesis. 8 of 9

9 What is your final hypothesis? Why do you think that The Earl of Abergavenny sank? You can look at your previous hypotheses on pages 2, 3 and 6. AQA Education (AQA) is a registered charity (number ) and a company limited by guarantee registered in England and Wales (number ). Our registered address is AQA, Devas Street, Manchester M15 6EX. 9 of 9