Describe how Alec managed to reach land after the ship sank

Soon the ship begins sinking; Alec sees the black stallion break free of his stall and begin to swim so Alec grabs hold of the rope hanging from his halter and the Black pulls him along. He ploughs on through the water all night until morning when they finally reach an island. It is completely deserted and Alec realizes that he and the Black are the only survivors of the shipwreck.