I am guessing, if he is greatly concerned about losing his glasses, it is because he has a large correction and is very dependent on his glasses. I feel for him, because I am in the same situation. I an very near-sighted with an Rx correction of -8.00.

It is very worth while to see well when you are sailing for every reason I can think of. For safety; for recreational enjoyment of seeing the boat, sails, and foam in action; for seeing the scenery; and for seeing the girls! It is worth the risk of loss to see well. With that said, you still don't want to loose them. If you have a high correction, it takes WEEKS to get use to a new glasses, even if its the same prescription.-So I understand the fear of losing them. Glass straps of various kinds will reduce the risk. Or, wear an older pair that are currently sitting in a drawer. Losing an old pair will not be tramatic. Or take advantage of those two for one deals the next time he gets glasses and use the 2nd for sailing.

It is worth it to see when sailing!