Be careful of the sucker crown mate, they generally harbour ulterior motives.
After about fifteen years of living aboard
, mainly in the tropics and just into the temperate zone, I have found that have both sucking and blowing is necessary.
The first thing I had to do when I moved to the tropics was design some hatches I could leave open in rain storms that were much bigger and had fold down side screens. I could not find any commercially available hatches to fit my requirements so I had some made from alloy and fitted the alloy side screens myself. I then discovered that a fold up louver assisted in keeping the rain out and although it decreased the exit cross section by about half it increased the drawing ability of the hatches.
The home made hatches have at least doubled the cross section of the through-deck ventilation cross section although they don't look half as pretty as the yachty ones they replaced (but then again I don't look half as pretty as I did when I installed the yachty hatches 27 years ago)
The side screened and louvered hatches do a very good job of drawing out the rising hot air down bellow whilst drawing in cool via the companionway
when the boat swings to the wind
in non tidal stream or river anchorages
but on really still, sticky days does not do so well - sucking don't work bro.
To handle really hot humid weather
when I am away from the cooling
seas and not swinging to the breezes I have installed an 18" 12V auto radiator fan in a fold down sub-hatch in the bow hatch
with a speed controller (The speed controller is necessary as even running at 6 volts it blew a gale under that thing) This is the blower configuration where outside air is forced into the bow of the vessel, picks up the hot humid air from inside and exhausts it out the companionway
I also have a number of small, area specific fans in the boat to move and mix the introduced air.
My experience is that you need both sucking and blowing to meet the changing circumstances.