You want to be near the bottom, so however many pulls it takes to do that. Generally about 50 feet or so, which would be 20-25 pulls. I am never that precise.

One note, use gear that doesn't get you fishing too far from the boat, or you're just going to get tangled with other folks. Use a size 20 jet planer, in clear or green (I spray paint mine flat black). You catch fish going both ways against the current, which, depending on the tide, will be flowing either upstream or down.