Wow .......That was quick 
Didn't think that one was a "slam dunk" easyone ......
I personally figured the answer was somewhere in the 20 mile+ range. It came about as we were cruising around this past (gorgous) Saturday showing friends, new to the Lake, the Bahre Estate- I popped my GPS into "Go To" for Center Harbor to give them an idea of distance "down" the lakes midsection.
Keeping in mind that I was back near the Red Top off Clay Pt and I have my GPS "waypointed" well off the Docks at Center Harbor in addition my "Go To" function will "hop right over" small islands i.e. straight line "Go To" function
I got
15.6 miles indicated
WiFi -- I'd say you hit it pretty much Right ON, given there are a few obstacles that needed circumventing in the path !!