From the expanded IRS instructions for Line 20b, Schedule C:
"Enter on line 20b amounts paid to rent or lease other property, such as office space in a building."
https://www.irs.gov/instructions/i1040sc#en_US_2023_publink24329wd0e1653
If the slip rental fee is an ordinary and necessary expense for a charter boat business, then it clearly goes to Line 20b. It's clearly "other property".
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
