| Date | November 2020 | Marks available | 2 | Reference code | 20N.2.SL.TZ0.6 |
| Level | SL | Paper | 2 | Time zone | no time zone |
| Command term | Outline | Question number | 6 | Adapted from | N/A |
Question
It is estimated that shipping is responsible for between 2 and 3 percent of the world’s total greenhouse gas emissions. The United Nations’ International Maritime Organization (UNIMO) has set targets for shipping companies to reduce their current emissions by at least 50 percent by 2050. In response to this requirement, designers are working on clean technologies to power large ships.
Rotor sails made from carbon glass fibre are one example of a clean technology. Rotor sails were first developed in the 1920s but interest in them was not revived until the early 21st century, see Figure 11.
Electricity powers a mechanism within the cylindrical rotor sail which provides the thrust to move the ship, see Figure 12.
Figure 11: (Left) [Buckau ship] George Grantham Bain Collection, Prints & Photographs Division, Library of Congress, LC-DIG-ggbain-37764.
(Right) [Norsepower ship] © Norsepower Oy Ltd 2020.
Outline one driver for the use of clean technology to develop the rotor sail.
Explain why carbon glass fibre was chosen for the modern rotor sail.
Suggest two reasons why the original rotor sail was a shelved technology in the 1920s.
Explain the role of rapid prototyping, instrumented physical models and computer aided design (CAD) in the design of the modern rotor sail.
Markscheme
international/government legislation/target;
aimed at reducing global emissions from shipping;
reduce fuel/energy consumption;
conserving natural resources/to be more cost-effective;
Award [1] for identifying one driver for the development of the clean technology for the modern rotor sail and [1] for a development up to [2 max].
carbon glass fibre is a composite;
providing high strength to weight ratio/tensile and compressive strength;
requiring less electricity to drive the rotation of the sails/allowing sails to resist deformation;
carbon glass fibre is corrosion resistant;
reducing maintenance/repair;
as sails are exposed to salt water;
carbon glass fibre can be used to make complex/large shapes;
using a matrix and fibre composite (hand lay-up/spray lay-up/pultrusion) with a mould;
to manufacture the large scale sail mechanism;
Award [1] for explaining why carbon glass fibre was chosen for the modern rotor sail and [1] for each subsequent development of it up to [3 max].
environmental issues/energy efficiency were not major concerns in the early 20th century;
using fossil fuels to power ships was more efficient;
even though fossil fuels create carbon emissions/rotor sails minimise carbon emissions;
the technology did not exist in the 1920s;
that required advanced manufacturing/materials to allow it to be mass produced;
rotor sails are large in size;
some countries have legislation regarding the maximum height of ships;
to allow ships to pass under bridges safely;
the sail adds height to the ship;
resistance to clean technology from fossil fuel producers;
may have put pressure on governments to legislate (against the technology);
limiting the adoption of the invention;
the high cost of retrofitting existing ships/buying new ships;
may have been prohibitive for the shipping industry;
running existing ship models was cheaper in the short term;
Award [1] for each of two reasons identifying why the original rotor sail was a shelved technology in the 1920s and [1] for each subsequent development of that reason up to [3 max].
Mark as [3] + [3].
Rapid prototyping
the sail mechanism has internal moving parts;
designers 3D print the sail to test the function/modify the interior mechanism;
by creating a physical model/3D prototype using CAD;
Instrumented physical models
(air tunnels allow designers) to analyse the air flow/structural integrity;
providing accurate quantitative feedback for analysis/with the ability to take measurements;
and use the data to improve the efficiency of the mechanism;
Computer Aided Design (CAD)
utilizes software to create surface/solid models/FEA/virtual prototypes;
to communicate/share information (between engineers, manufacturers, clients);
and gain feedback for further development (of the mechanism);
Award [1] for explaining the role of rapid prototyping in the design of the modern rotor sail up to [3 max].
Award [1] for explaining the role of instrumented physical models in the design of the modern rotor sail up to [3 max].
Award [1] for explaining the role of computer aided design (CAD) in the design of the modern rotor sail up to [3 max].
Mark as [3] + [3] + [3].
Examiners report
Straightforward question with good responses.
A good question which allowed a good range of marks to be obtained. Candidates were able to obtain 1-2 marks but few were able to get 3.
A good question with multiple clusters that allowed a range of responses and opportunities to gain marks. The most commonly identified responses related to the fact that environmental concerns were not an issue of the time and that the technology did not exist in the 1920s.
A difficult question for many based on the context of different modelling types relating to the rotor sail. The concept of FEA (in the CAD cluster) also appeared in Q1bi. A number of candidates provided generic answers for CAD and rapid prototyping, trying to give definitions rather than explaining its role in the design of the rotor sail.
