Graphic: Oracle BMW USA-76 unveiled

Oracle unveiled perhaps the most traditional of keel bulbs when it unveiled USA-76 this afternoon, a genuine dolphin shape with curved winglets right at the rear.

USA-76 also had a tapered keel fin which, wider at the hull than at the bulb.

With a design team led by New Zealander Bruce Farr, the Oracle boat is also the narrowest of those left in the contest. Farr said the boats might look different, but they might still have similar performances.

"There's a combination of features that go together to make a successful boat.

"So I think the designs are driven by the biases in the experiments and even biases in the designers' beliefs. The fact that they look quite different, well the performance could still be fairly similar."

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