I've seen quite a few comments about concerns that opening ports will eventually leak. I had a NorSea 27 aft cabin with 9 (count 'em) 9 opening ports. When I sold her last summer she was 17 years old and not one single port leaked. I made sure they were dogged down properly which means alternating the tighteneing sequence from one dog to the other and not cranking one down all the way tight before tightening the other, like torqueing down a valve cover. I never had problems with the seals. During the five years I owned SeaGray, I opened each port and cleaned the seals with vinegar and put a light coat of mineral oil. Vaseline is a killer. NEVER use it. I have 4 opening ports on my M17, Seafrog, and so far, so good. You do have to remember to wipe up any water on the outside before opening them, as they do tend to accumulate a couple of ounces of rain/dew. As I mentioned before, I wouldn't have a boat without them. It's amazing how much air comes through a 6" hole. One tip I got from reading one of the Pardey books was to get a 6" plastic flower pot and cut out about a third of one side. Stuff it in the port upside down and you have ventilation if it rains. Regarding dorades. I've been very lucky to crew on a number of delivery passages on some really nice yachts. (Nothing like being on a boat that you'll never own with the owner a thousand miles away) Anyway, I never found one boat with a dorade that ever provided more than a baby's breath of air unless the wind was over 20kts. Granted they would help a teensy bit if it was raining where you couldn't have a hatch open but I don't recall that many nights of rain and when it did rain it was usually over in a few hours at most. I still prefer a forward opening hatch. And if that isn't enough a wind shoot is the answer to a poor man's air conditioning. Joe Seafrog M17