The Thunderbolt still runs once a day in each direction. Departure time from Corozal is 7am, and 3pm from San Pedro. The boat will stop at Sarteneja. Years ago, it ran twice a day, so maybe you've found an out of date website.
https://www.facebook.com/Thunderbolt-Water-Taxi-532625906838707/
Email: thunderbolttravels@yahoo.com
Contact number: 501 610 4475
Last year, a second water taxi, Isla Norte Water Taxi, began running once a day, but the links I have to that company no longer work, so maybe Isla Norte is no longer in operation. They had a 3pm departure time from Corozal. If you find out anything about Isla Norte, let us know.
Edited: 6 years ago