Not Maintenance per se
That was a question I had several years ago and according to Marine Service Center on Lake Union in Seattle the keel bolts should be tightened after the first year or two. The keel is bedded with sealant at the hull joint and it needs to be put in compression much like a head gasket on a car.Torque values are available from Hunter customer service and they're based on the size of the keel bolts. When you call for the torque values you can ask them about the frequency. My guess once should be about enough.For sockets I found that deep sockets aren't deep enough. I took a regular socket and cut it in half with an abrasive saw and welded a section of pipe in the middle.