There are all sorts of surveys, but the best source I've found for real data on how much these boats are used is this official report on fuel usage (2013): htt

There are all sorts of surveys, but the best source I've found for real data on how much these boats are used is this official report on fuel usage (2013): https://www.fhwa.dot.gov/policyinformation/pubs/pl17012.pdf https://www.fhwa.dot.gov/policyinformation/pubs/pl17012.pdf Basically, it indicates that recreational boats use 1% of the fuel of all passenger cars.