Boat tours are a popular part of any tourist visit.  Depending on the season and location, some of these tours are available non-stop, which can contribute to a significant carbon footprint when all these activities are frequent. Alcatraz, the famous former prison near San Francisco, now a museum, operates boat tours on a daily basis. They decided to do their part in reducing environment pollution by introducing a hybrid boat which uses wind and solar energy to power its on-board electrical installations, but also for the purpose of propulsion. Here's a schematic of the power system:

Naturally, the main propulsion power still comes from diesel fuel combustion, but this is a step in the right direction none the less.

Source: Inhabitat.com