The marina where I winter haul has nominal depths of 3 1/2 feet at low tide. They regularly moor boats with 5 and 6 foot drafts in their field. Normally this results in boats with paint and gel coat ground off the bottom (the "mud" is of course filled with rocks, clams, barnacles, etc. .. VERY abrasive.) The yard doesn't mind as repairs for this type of damage is fast an easy - goop on some epoxy, cover with paint.
This past summer, a particularly bad storm sucked most of the water out of the harbor. Many boats bottomed out, hard. This winter, the array of damage is amazing - bent/broken rudders, keels ground down to bare fiberglass, big holes, fin keels bent, horizontal stabilzers broken & distorted. To say nothing of the unseen structural damage.
Go find a mooring with enough water for your boat.