Finding your way at sea
In this learning sequence students find out about latitude and longitude and how they are used to plot positions on the Earth’s surface. Use real data to create and interpret distance time graphs. Investigate how icebreakers traverse the southern oceans and how the speeds of vessels change in different conditions. Create a hypothetical rescue scenario and use graphs and positional data to explain how the rescue takes place.
Setting the scene
How far how fast?
Share this article with students – highlighting the difficult conditions the icebreaker and crews face travelling in southern waters.
Locations at sea: Latitude and longitude
How far is it to the Antarctic stations? Share the voyage track for the 2015/2016 season. Which track is the one referred to on the article?
Ask students what they can see from the map. Draw attention to the grid reference used – to find students prior knowledge of latitude and longitude. Some questions to stimulate thinking and discussion:
- What is the latitude and longitude of Hobart, Macquarie Island, Casey Station?
- What is the latitude and longitude of the south pole?
- The map is flat – but the Earth is not. What does this mean about the shapes and sizes of the landmasses on the map? Where is this distortion most pronounced? Is it possible to use this map to measure distances between places?
Speed at sea
Share one of the SITREPS (situation reports). Discuss what this is. Why is it done?
Points to draw out:
- Knots to km/h (see notes at bottom of page for conversion)
- Heading – what is this?
- Distance in the last 24 hours (convert to average speed)
- Air temperature/sea temperature (note time of day!)
- Nautical miles (see notes at bottom for conversion)
- Links to map – how this relates to the coordinates given
Explore and research
Disaster at sea
What happens when an icebreaker gets into trouble at sea?
Explore the conditions leading up to the icebreaker going aground as described in the article above.
Using the SITREPS from the voyage (V3) have students work out what day the ship went aground. (Hints for discussion: What station was the Aurora Australis moored at when she went aground? What would her average speed be during the days leading up to the incident? How can you pinpoint using the SITREPS data? What does the report say during this time?
Create a table or spreadsheet and record the distance in the last 24 hours for the days leading up to the incident. Plot this as distance/time graph. What can you say about your graph? Choose three days of interest, and describe the conditions onboard and how they relate to the distance covered. What does the slope of the graph say about the speed of the vessel? How far has the Aurora Australis travelled in total over the period of your graph?
Explain and share
How would you convert these distances to speed? Create a graph of average speed versus time and discuss how it relates to your distance graph. What can you say about the average speed? Does this mean the icebreaker was always moving at this speed?
Elaborate and apply
Breaking the ice
Use the V1 data to explore the icebreaker’s speed and position and the changes based on weather conditions and ice conditions. Draw a graph of distance versus time for this voyage. Does the icebreaker slow down in sea ice?
Have students explore a hypothetical situation where the Aurora Australis runs aground near one of the stations and the crew need urgent rescue. Students choose a station, and create a SITREPS log for the day. As part of the voyage leader's notes, ask them to calculate and explain the following:
- How far does the Aurora Australis have to travel to get back to safe harbour?
- Explain how long she would take to reach safe harbour using what you know about her average speed under different conditions.
- If she was stuck aground and unable to move, how long would it take rescuers to reach the station by a) plane, b) high speed catamaran, c) the new icebreaker? (You will need to research the speeds that these craft reach in ideal conditions and then infer a worst-case estimate for speed in Antarctic conditions, justifying your choices.)
- Create a hypothetical distance-speed graph of each of the rescue craft and explain the differences in each graph (it may help to plot them all on the same set of axes.)
Cross-curricular Extension investigation:
What would happen if a ship ran aground near an Antarctic station and needed rescuing in the early twentieth century? To consider:
- How would the crew communicate the disaster to station?
- What sorts of ships were exploring Antarctic waters in the early 1900s?
- What is the average speed of these vessels?
- Could they traverse ice sheets like the modern icebreakers?
Write a hypothetical SITREPS for such an incident, including the voyage leader's notes. Use an example from the 2015/16 SITREPS as a model for the report. Create a distance-time graph for the rescue boat, explaining how the slope of the graph changes over the course of the rescue.
At various points in the learning assess to what extent students:
- represent positions using coordinates (latitude and longitude)
- interpret simple linear graphs and model real life situations
- with guidance, draw distance time graphs that model real life and hypothetical situations
- demonstrates how the slope of a distance time graph relates to speed
- solves simple problems involving average speed.