I keep the "cruising log" and the "maintenance log" separate.
The cruising log is basically a journal. There are really nice ones with entries for lat & lon, boat speed and all kinds of details about the sail. I tend to just put a date and a narrative.
We keep a 3 ring binder on the boat with empty and completed maintenance log items. When something is noticed it is logged by the date and what's wrong. Some things get deferred and some things we take care of right away. There is a column for the corrective action.
For maintenance expenses we use quick books pro and have set the boat up as a cash business. All assets - basically the boat and mooring
deposit - are listed and then we log anything we purchse for the boat by category - sails
maintenance, mooring fees
The next owner will have a completely detailed log of our upgrades and expenses.