27 - I have sailed on the Great Lakes each summer for the last three years. I shot the trips for our TV show, resulting in a two-part episodes for each season. They turned out to be pretty popular, which surprised us, as most of our content comes from sailing in more "exotic" locations. I can tell you from experience that these bodies of water are definitely better defined as inland seas than just "lakes". If I hadn't produced those Great Lakes segments for the show, I don't know if I ever would have sailed there. I'm sure glad I did...
The first year, we sailed out of Traverse City on Grand Traverse Bay and Lake Michigan. On that trip we ran from a summer storm on Lake Michigan, ending up back on the bay for protection. The next day we made a passage across the bay that the guide book said took 5-6 hours. We surfed it downwind in a Catalina 30 in 3.5 hours in very tough conditions. And that was on the bay with 6-8 foot waves (the big lake had 10-12 foot waves). It was my introduction to the Great Lakes, and I was suitably impressed. Other than that 24 hour period, the rest of the trip was nice and mellow, with winds ranging from non-existant to 15 knots. Got to visit some nice little towns, too.
The second year we cruised through the Apostle Islands on Lake Superior. Once again, we had the same range in winds, and dealt with a summer squall one day (sustained winds of 45 knots). That squall was typical of what you'd find out on the ocean, in that it came upon us very fast and lasted about 30 minutes. We were in the protection of the islands, but even so we had friends who ended up with torn jibs and other damage as a result. I have a clip from that particular episode up on YouTube, and although it's just an excerpt, it can give you a glimpse of what you can encounter sailing there:
Last summer for our third trip we sailed from Bayfield, WI to Isle Royale on Lake Superior. It's about a 115 mile passage that we did overnight. And when you're out of sight of land in the middle of that huge body of water, you know you're not just lake sailing.
I can say without hesitation that everyone should try sailing on the Great Lakes at least once. There are some incredibly beautiful locations, it's right in our own backyard, and you can experience a full range of sailing conditions, from placid gunk holing to gnarly open ocean tempests. My favorite place so far is the Apostle Islands on Lake Superior. It's a very remote, natural location with relatively few boats and people. The charter company there is the best, both in terms of people and boats. Their web site is http://www.superiorcharters.com
If you'd like to be able to visit towns and put in at a marina every night, Lake Michigan and Grand Traverse Bay might be more your style. The charter company we used there is Bay Breeze Yacht Charters, which is at http://www.bbyc.com
There are other resources for sailing on the Great Lakes, such as regional magazines and web sites, but I can't recall them off hand. Hopefully some locals can give you that information.