In The Witcher 3: Wild Hunt, sailing is an available form of transport facilitated through the use of small sailing boats.
Boats can sink if they take too much damage, and their health is indicated by an on-screen display that appears when traveling by boat. Enemies will try to attack while you're sailing, and they can rip apart a boat quickly. Sailing into rocks, beaches, and dead bodies can also damage a boat; so careful navigation is required.
Geralt can also Fast Travel while on a boat, but only to destinations accessible via a water route. To Fast Travel by boat, open the panel for World Map while at the helm of a ship. You can travel to any point marked with an anchor symbol.
By default on PC, to use a boat, board the vessel then take the helm using the E key. To navigate, he can use W to move forward, A to steer towards the left (port) and D to steer to towards the right (starboard). He can also reverse by using S. Pressing Shift will make the boat go faster.