Jim makes a good point, although I have got the equipment to add big vetus dorades next to the after hatch. I like them because you can close them tight from inside using a mushroom vent. I have always been afraid that a big dorade box could get washed off the deck with big seas--although I will probably never encounter any such seas in the simple coastwise cruising I do. WE all dream of the long distance voyage. Anyway, I am going to put them aft by the main hatch because I did not want them up where sheeets would catch them. I have had to construct bases for them. I made these out of round pieces of 2" micarda (resin soaked linen), but any upgrade book will have a picture of the standard and traditional dorade box if you want to go htat route. For appearance, I assume you will want to have the vents themselves vertical, which means forming the bases to take into account the camber of the coach roof. One other thought: if this is for underway, yes you may want more vents. But if this is for anchor, construct a couple of wind scoops for the forward hatch and the coach roof hatch. I have used these in the Caribbean to good effect. I think West Marine sells such an item, too. Get the one up forward high, with a hailard, and you collect whatever little breeze comes by.
