Hatches and portholes are wonderful for ventilating a yacht when it is nice outside, but these big holes will let rain into your yacht during a storm at anchor.
When the rain comes, you will need to close your yacht up nice and tight to keep rain droplets from soaking your interior. When you do this, you then rely solely on the ventilation provided by your dorade vents. These cowls will draw air in and separate the rain out, giving you nice dry airflow when the boat is all closed up.
The truth is, most yachts don't have enough dorade vents to supply the airflow needed for "comfort" when you are in the tropics. To remedy this issue, we have found a little trick.
Flipping the dinghy over the hatch will serve as a way to keep rain out. The hatch opens up into the dinghy and air flows under the dinghy and into the open hatch. This is nowhere near the air flow of an unblocked hatch, but it is still much better than a hatch that is dogged down.
A very important thing to do though is to make sure that your dinghy is tied down. An inflatable dinghy sitting on the deck is just asking for the wind to pick it up and send it flying! Be sure you tie it down well, and have the hull centered over the hatch so that the hatch can open into it..
If you have more than one hatch, and have more than one dinghy, then you are in business! We keep our hard dinghy over the salon hatch, and the inflatable dinghy over the forward hatch (when it's raining). This lets us keep the boat open and airy in a rain storm.