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Describe the Afra tanker scale.
AFRA uses a scale that classifies tanker vessels according to deadweight tons, a measure of a ship's capacity to carry cargo
Why was the Afra tanker scale developed?
The term is based on the Average Freight Rate Assessment (AFRA), a tanker rate system created in 1954 by Shell Oil to standardise shipping contract terms. Due to their favorable size, Aframax tankers can serve most ports in the world.

Question: What are supertankers
Self-contained rewrite: What are supertankers?