here is some really bad advise by the DBK.
Its seems to me that 20 feet is about a deep as a boat goes in most situations. The landing under Palouse Falls cant be much more than that. But I could be very wrong. Dropping 50 feet, you want to be in the OR tuck so you'll go deep. You'll want water juggs in the bow. that will push you deeper. So, 20 feet should be good.
Bound is boatless man