Do boats use gas like cars?

Most speed boats, especially with outboards, use gasoline engines.

Larger vessels such as ships and commercial boats, generally use diesel.

For raw power and performance, gasoline engines are still best. Big chevvy V8s are popular choice for powerboats with internal engines.

Water and electrics (for the spark) do not mix well, so gas engines need to be maintained and looked after well and can be temperamental.

For economy and reliability diesels are best. Which is why commercial vessels use them.