My 23' diesel SeaCraft would cruise at 12-15 knots and I was always trolling between spots. Caught bigeye to 115 lbs. yellowtail to 32 lbs. and lots of dorado and albacore before we got to the "fishing grounds". In places like Panama I sneak a lure over doing 18-20 knots and catch wahoo, tuna etc. but you can get spooled at that speed if the reel doesn't have the line capacity. I've also noticed that the fish seem to come in easier after being yanked around at that speed.