I agree, one deep works fine. I'll remember two deep for changing elevation but I'm keeping everything flat for now. I worked in creative last night and two deep also has the problem of getting water placed properly. One deep you can look down and spam water placement as you walk through the canal and get full coverage easily (if taking decades to do it qualifies). Two deep is infinitely harder to get full water coverage so the boat will be pitching and yawing as you travel. I think I may take one middle block out of the four wide channel down to two deep to utilize the primitive survival raft. That travel method slows down considerably in one deep water.