If you sign up for the USPS basic boating, or navigation courses, you get one of their proprietary plastic plotting protractors. The course is free, but the protractor and course book are included for a nominal course material's charge. It's perhaps the best value out there.
It's been many years since my wife and I took the course, but I still use my protractor on occasion.
True Blue . . .
sold the Nauticat