I have heard you can put an air conditioner on the 23, and power it with a quiet generator. Hmmm, wonder if there is an inverter/battery combo that would run it more quietly even than that?
Would the batteries fill up the boat?
Anyway, I use some of these pads people put their pets on to absorb heat. It will cool your back until you get to sleep, and then maybe you will make it till early morning. That and a decent fan are all I have. Some nights, after great sailing, it is too hot to sleep. This year, I will try more anchoring out to be cooler than at dockside, and try the screen in a hatch with a breeze whatchacallit funneling air below. Light air, anchor stern-to, from the cleat on opposite side from quarterberth I sleep in.