One of the Thais' many names for themselves is jao naam, the Water Lords, and from the river expresses of Bangkok to the fishing trawlers of Phuket, boats remain an indispensable way of getting around many parts of the country.
Perhaps the most identifiably Thai boat is the longtail boat (reua hang yao), a long, narrow wooden boat with the propeller at the end of a long "tail" stretching from the boat. This makes them supremely manoeuvrable even in shallow waters, but they're a little underpowered for longer trips and you'll get wet if it's even a little choppy. Longtails usually act as taxis that can be chartered, although prices vary widely. Figure on 300-400 baht for a few hours' rental, or up to 1,500 baht for a full day. In some locations like Krabi, longtails run along set routes and charge fixed prices per passenger.
Modern, air-conditioned speedboat services, sometimes ferries (departure every 30 min) also run from the Surat Thani to popular islands like Ko Samui and Ko Pha Ngan. Truly long-distance services (e.g., Bangkok to any other major city) have, however, effectively ceased to exist as buses, planes, and even trains are faster. Safety measures are rudimentary and ferries and speedboats do sink occasionally, so avoid overloaded ships in poor weather, and scope out the nearest life jackets when on board. As of November 2018, ferry service is available between Hua Hin and Pattaya, a 2.5-hour journey for 1,250 Thai Baht on a catamaran with a maximum capacity of 340.