Well, I think I'm getting somewhere. I've checked voltage both running and not. When not running, voltage was 12.5V and it hit right at 14.45V when the engine is on and running. I also checked voltage from the battery lead to the engine block ground post - figuring if the ground cable from battery to block was bad, I'd see it - and the voltage was consistent. Since it seems like the ground cable is good, I checked voltage from the lead on the starter to the ground post on the block and that was good too.
Earlier today when I had it in the water, I turned the key, the starter clicked and then finally turned and the engine started. Once I got home and tried to turn it over a few more times, the starter only clicks. Everything else electrical seems to work, so I am beginning to think this whole thing was just a bad starter. I've cleaned all the connections and pounded on it with a hammer and still can't get it to free up.