Fall Guy - I believe a weak strike contributed some to the lack of detail in the sails. Here's the reverse of a '92 Columbian Expo half I pulled from CoinFacts. Notice how the sails are nowhere nearly fully-struck, yet the coin received a grade of MS64. And the striking issue is not unique to this one coin. Scroll through CoinFacts and you'll find plenty with similar flatness in the sails. If you don't believe me, have a look - http://www.pcgscoinfacts.com/CoinImages.aspx?s=9296
I agree with VF graded stated several times already. I really enjoy these columbian halves. A well designed coin. I must own at least 15 of these coins of all grades, as well as a NGC toned MS 65(old original holder) example. Love em!