When entering ferry/airport details in the trip itinerary screen, there is a drop down list for Company.

To add a new company for this drop down list, go to People/Add person

Select Transporter from the roles drop down list. Click next to "Roles" to close the drop down list then select "Next"

Enter the name of the Transporter Company in the "Company" field and other contact details such as phone number, and address if required.

Scroll to bottom of the page and select "Save". The new transporter will appear in the trip itinerary Company drop down list next time it is opened