The organization tree has objects for systems and sub-systems. Include mechanical systems for your vessel (such as the engine) and each sub-system. There are no limits on systems or sub-systems. Then, you can add maintenance schedules or spare parts for each subsystem. Each vessel may look very different based on the equipment on-board and approach to systems maintenance by the owner.
Like mechanical systems you may also keep systems that do not require maintenance or parts--such as electronics. Critical information is gathered (if you wish) and stored to make access quick and easy.
Some equipment on-board is not necessary to operate the vessel but may be needed for the crew. You can add gear to track warranty periods, manuals and documents and other information with the same functionality for mechanical or non-mechanical systems. Having this information in the database can also help with insurance claims or acquisition.