A Poly tarp over the boom
I've found that the best way to stay cool and keep the sun out of the cabin and cockpit at the anchorage, is just a regular poly tarp over the boom. I stretch it over the boom and tie it to the mast, and the end of the boom. I use 3/16" braid lines in each grommet and tie a slipped half hitch on each one to my life lines. It goes up fast and breaks down fast. A nice cool shower in the cockpit, or a dip in the water always goes well in extremely hot weather. I don't have a bimini top, but I usually feel cool and comfortable with a swim suit on and a wide brim hat while sailing. I usually like to wear a towel over my shoulders to keep from getting a sun burn. I've often thought of installing a button and button hole on the towel, to keep it from sliding off. Another trick I use is a bucket with a rope tied to the handle to dip into the water. Then I take a sponge and dip it into the cool water and squeeze it over my head and shoulder areas. I also cool off my First Mate Penelope Pitbull, this way. The most important thing is to have plenty of ice water to drink and stay out of the hot sun as much as possible.