I would look and see how many other charter companies are out there first. It is easy enough to set up a company, But you will need qualifications up to the Advanced Powerboat Certificate a Commercial Endoresmet or Local Authority Boatmans Licence (as a guide), You will need a suitable rib again coded to MCA or Local Authority depending on where you want to go.Enough wet weather gear and lifejackets for each passenger plus two spare.
Then you have to get the clients away from already established companies who have a loyal customer base in most cases. Then add to that advertising moorings , Insurance, engine servicing and fuel .Then work out how much you could make on if you are lucky one charter a week for again if lucky 20 weeks.
Charter companies come and go or merge it is not a easy game as the weather can work against you . The clients cancel at the last minute or the engine play's up . As a sole income I would think again, most of the people I know have other strings to there bow, Simon is a Solicitor and I run a training centre and charter is a small part of it.
Hope not to negative but there is not a pot of gold to be had from it .