The "green" travel trend is gaining momentum. A recent Lonely Planet survey of 24,500 people found that 93 percent intend to travel more responsibly in the future.
Likewise, a 2012 TripAdvisor survey found that 30 percent of respondents choose a destination because it is considered environmentally friendly.
While a growing number of resorts and hotels have green certifications, when it comes to a cruise vacation, the obvious choice for an eco-conscious consumer is a sailing vacation aboard a tall ship cruise.
Star Clippers' fleet includes the world's largest and tallest sailing passenger ships -- Royal Clipper, Star Clipper and Star Flyer.
"At Star Clippers, we maximize the time we are under wind power so our guests can experience a true tall ship sailing experience," said Captain Farhat Shamim, vice president of operations. "Of course, this also reduces the amount of fuel we consume and therefore is entirely environmentally friendly."
Shamim said that in the Caribbean, where winds are most predictable, the ships operate under wind power up to 60 percent of the time. But even when sailing, the ships run their engines to power air-conditioning, refrigeration, lights and more.
The tall ships use high-quality low-sulphur gas oil. Star Flyer was the first ship in the world to receive the International Air Pollution Prevention Certificate, followed by Star Clipper and Royal Clipper.
The ships' size also contributes to a smaller carbon footprint. Unlike cruise ships carrying thousands, Star Clipper ships carry only 170 on Star Flyer and Star Clipper, and 227 passengers on Royal Clipper, which means less water is consumed and less waste is produced.
The ships also have an advanced water-treatment Bio Reactor system to treat sewage and water from sinks and showers. Treated water is clean enough to use for deck wash and can be discharged safely overboard.
But that's the only thing that goes overboard. Oily bilge water from the engine room is offloaded to a facility on shore, and all waste and garbage is disposed of ashore.
"We dump nothing in the water," said Shamim.