Dang! Eighteen Inches? You'd have a place to camp out up there on the mast! Hell, you and yer sweetie could do some close dancing up there. 12's the only way to go. It's like a white tool box, a router somebody left on the mast. Talk about windage, on the Ariel that big ole saucer would be a dangerous airfoil and in the right wind would take over and lift the boat right out of the water.