Play through the prologue again to see what this boat looks like. It is the boat that you and Carlos escape on. In order to acquire this craft, you must fly a helicopter (with missile pods) and hit it once or twice. Do not worry about it blowing up as six missile hits are needed to set it on fire and seven missile hits are needed to destroy it, making it one of the strongest vehicles in the game. When you enter a Convict, your wanted level will go up a lot but it will not add stars. You will also not lose wanted level while in one. The best place to find this vehicle is near the prison. There is another version of the craft, but it is hard to find and resembles a fishing vessel.