Canvas cover, air scoop.
Natural cooling works best at anchor, or moored, so the boat can swing to point into the wind. In addition to the bimini, we rig a tarp over the boom. It complete the shade in the cockpit, and keep the cabin temp down.Then I rig a wind scoop (low cost item at WM) over an open bow hatch. This funnels air through the whole boat. If we are at the dock, and the wind is the wrong direction for the scoop, we run a fan on the shore power. Either solution works fine on Lake Erie. The night air right on the water gets reasonably cool even if the days run up to 90 degrees. We have just bought a 12 volt fan for really hot days - but haven't need it yet. I would permanently mount one in the big aft cabins all of the new models have - otherwise the air can get really dead there.DavidLady Lillie