A boat cruise in Rio usually means a 2-4 hour trip leaving from Marina da Glória or the pier near downtown. You'll motor past Sugarloaf, the Christ statue from the water, and the beaches of Copacabana and Ipanema. Expect loud music on party boats, calmer vibes on sunset sails, and a chance to see the city from angles you can't get on land. The water isn't crystal clear and the boats range from basic to fairly nice; don't expect luxury unless you book a private one. It's a solid way to beat the traffic and see the coastline, especially if the weather is good.
Best time is May to September when it's drier and temperatures are milder. December to March can be hot and rainy, with a higher chance of rough seas or cancellations. Expect to pay around $40-90 per person for a standard group tour with snacks and one drink included; private charters start higher. Food and extra drinks add up quickly on board.
Pick a late-afternoon departure so you get the sunset and the lights coming on across the city. Skip the full-day tours that include swimming stops unless you're okay with mediocre beach clubs. Bring sunscreen, a light jacket for the wind, and don't overpay for VIP sections that mostly just get you a slightly better view.