Yes you can. If the boat is docked and you are spending some time on it (like a houseboat or larger boat with a below-deck area) it is considered to be a temporary housing, and castle doctrine kicks in. (sort of like at a hotel room) However, if the boat is moving, the same rules apply as in your car. So you need a CCW if the boat is in motion, but you do not need a CCW if you are docked. At least, that’s what a certified NRA instructor told me.

I don't live in Michigan, but here is a link to a site that seems to have a pretty comprehensive list of the guns laws by state: http://www.handgunlaw.us/states/michigan.pdf

Even though it is a PDF document, there are several links to state offices for more specific information.

Scott

A point to consider if carrying in the Great Lakes; If you wander past the international boundary, you're carrying in Canada, and that could get sticky.