Spray on the foils… good or bad?

Dear Curmudgeon: The AC 75s throw up a huge quantity of spray which has been likened to a fire hose. Is this simply the nature of the beast or a result of less than optimal design? Does it represent wasted effort and could better design minimize the amount of water thrown up and increase speed? – America’s Cup fan

Dear Fan: I understand it’s a bit of both… it is a source of drag and as such there are efforts to minimize it but equally it’s not a huge amount of drag in relation to the drag of the whole foil. The spray is caused by the pressure on the water around the foil being an order of magnitude higher than that in the air so the water “squirts up”. In theory, teams could reduce it by changing the pressure distribution around the foil but the pressure distribution is causing the foil to do the things they want; lift the boat, generate side-force, etc, so it needs to be worth it. In essence, teams probably have bigger fish to fry. – The Curmudgeon

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