How many loggerhead sea turtle hatchlings will live to adulthood?

One in one thousand (1/1000 or 0.1%). Lots of resources, but I used the number most commonly used in the literature. A source (I looked at many): Sea Turtle Conservation and Halfway Technology*

http://home.eckerd.edu/~meylanpa/BI200/Meylan_Web_Site/pdfs%20of%20readiings/23-Frazer_1992_Halfway_Technology.pdf