Dorade vents come in all shapes and sizes, but basically they consist of a box with a baffle inside and a vent on top. Fresh air and any spray enter the box through the vent. The air finds its way below through an offset vent in the deck, while the water drains out through small holes in the sides of the box.

To improve airflow in harbor, some boat owners shift the exterior vent on their dorades so they are directly over the cabin vent in the deck. Adding an extension pipe to raise the vent will also increase ventilation. If mosquitoes are a problem, it is easy to incorporate a small screen to keep them out.Dorades work well at sea, but need a shut-off plate for when there’s solid water on deck. Some folks also add a fan to suck in more air or to blow out cooking fumes.

A windscoop can be rigged over a hatch in harbor to force more fresh air below. Some have a relief hole in the back to help vent heavy gusts that might rip the scoop off the hatch.

If rain is expected, an aft-facing hatch can be rigged with a scoop like this. Air will still blow below, but most of the rain will be kept out.

When a boat is tied to a dock, this cross-shaped windscoop can catch some breeze, regardless of where the wind is blowing from.

Ships of old ventilated their holds with tall windsails. Some yachts use similar devices while at sea in the tropics. The bottom section is a strong waterproof material sealed to the hatch with a bolt rope and gaffer tape.

To increase airflow through an opening port you can use a strip of plastic or a cut-up water bottle to create a scoop vent.

A cloth scoop can be pulled through a port and secured to a stanchion post or lifeline. A stiff plastic frame with a mesh net secures the scoop on the inside.

Some traditional wooden hatches have hinges both fore and aft and can be opened either way to catch a breeze or keep out spray. Triangular side panels can be added to create a more efficient vent; a louvered panel at the open end will help keep the rain out.