16' of line in 12' water would allow the lures to run 1-3 ft down considering lure/line wgt and other concerns. This works great when fish are suspended. Generally longlining will require MUCH more line as you will be moving faster. Generally 10-40 YARDS of line or a 'decient cast' length. If the lure starts hitting bottom, indicated by small ticking of the rod tip, either speed up a little or reel up a couple of cranks.