[Rhodes22-list] Minimum mooring depth ??

[Rory Orkin]

I am considering  rhodes 22 which draws 20 inches. board up. I have 40" of water .. low tide winter..at my dock with a slip I could tie up at.. I am concerned that unusual weather or tide could cause keel to pound bottom..It is sand or mud bottom but does give me concern.
I am Not here all the time to tend it.
Anyone have any experience securing boat in similar conditions ??
                                Thanks
                                          Rory Orkin