I dont know if this is true but I read in some cases venting gaimed around 1000 rpm and 5mph. But every boat is different. Also it said that a non vented tunnel creates a suction and creates drag and sucks the boat down a little lower. I dont know if that is true or not. Venting the tunnel breaks the suction and reduces drag. I believe people were venting the tunnel running in shallow water and then closing the vent running in a chop helping keep the boat down. This is just what I remember reading when I was looking at a tunnel hull. Whether its true or not I dont know
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