I have the offset set so that when the readout says 3.5 I know I am in trouble since my boat has a 3.5 foot clearance.
I certainly have gone thru the mud before. One time at a low tide I actually grounded out, odd sensation the boat no longer moving up and down. Had to wait an hour to get moving again.
Would you rather have the offset set so that when it read zero, your in trouble?, or go with you hull depth? I tend to like the idea of knowing that when it says 3.5 feet, if I measure from surface to bottom, i will get 3.5 feet.