I was in Kona in early May....a time recomended by one of the divemasters. Water was great - one day it was like glass. One of the few places I have been that actually delivered on the promise of Manta Rays. Although one can get sick from different conditions......I found the boats at Jack's Diving Locker to be big, smooth, not crowded - and best of all - no diesel fumes! Hot fresh water shower right on the boat was nice too.