Not very easy.
I won't say impossible, as Mr. Murphy always seems to be looking over my shoulder when I'm replying to this question, but it isn't easy to turtle this boat. I have heeled mine to the point where the rub rail (the black strip around the outer edge of the boat) spent a little time in the water, but it was VERY windy that day, and I the boat was trying to tell me I had too much sail up. When the boat heels this much, it tends to lift the rudder out of the water and the boat will turn itself into the wind. Don't worry about the heel too much- Soon, it will become an enjoyable part of sailing!--Jon BastienH25 'Adagio'(formerly a H23 owner)