You'd be surprised at the places I go with 28' beam. The amas only draw about 18" so when it comes to channel depths I focus on the center hull (unless there's something hard in the way). For instance, entering Lake Tashmoo I don't give much thought to the beach on each side of the channel. My amas come within about 10 feet of shore as we squeeze through.

After all, the difference between 14' and 28' is only 7 feet on each side. If people laid out moorings so the boats didn't have much more room than that -- they wouldn't be able to swing together without hitting. So long as boats are longer than wide, length is all that matters in mooring spacing.