The boat is a fixed asset; you cannot begin deprecation deductions (or expensing) until such time as the boat is placed in service, which would generally be the date your business begins operations (in this case that would appear to be in 2020).
Your LLC will most likely adopt a calendar year as an accounting period for federal income tax purposes so you might be better off waiting until next year (2020).
Regardless, you should absolutely seek professional tax and legal guidance if you are not familiar with the law and accounting practices with respect to starting and operating an LLC.
