Both of you get certified in offshore sailing school. Just don't do it together. That will give you moe confidence in yourself and in him. If he continues to be the daredevil and will not consult your need to build up slowly then he will give up his dream or you. Try to discuss this calmly but forcefully. That this is best for both of you and your dreams. Unless he is a complete ogre he will tone it down.
All the best.