At the beginning of the storm in chapter 15, what did they do to survive?

At the very beginning of the chapter, Timothy and Phillip simply take cover in the hut that they have constructed for themselves. Timothy literally hangs on to the hut in order to keep it together for as long as possible against the ravages of the storm. The hut is eventually destroyed, and Timothy has Phillip lie down. Timothy covers Phillip with his own body in order to better protect the young boy, and they remain like that for two hours. After that, Timothy, Phillip, and Stew Cat make their way toward a palm tree and lash themselves to it with rope. Timothy orients them so that his body takes the full brunt of the storm and protects Phillip as much as possible. They remain like that for an hour, and then they are in the calm eye of the hurricane. Timothy sounds ragged at this point, and he is in some serious pain.  

He was cradling his head in his arms, still making those small noises, like a hurt animal. 

The trailing end of the storm then hits them, and they are bombarded with wind, rain, and storm surge. Phillip and Timothy struggle to keep their heads above water and eventually pass out. Phillip wakes up to find that the storm has passed, and Timothy is barely clinging on to life.  

Timothy had been cut to ribbons by the wind, which drove the rain and tiny grains of sand before it. It had flayed his back and his legs until there were very few places that weren't cut. He was bleeding, but there was nothing I could do to stop it. 

Timothy falls asleep again out of exhaustion. When he wakes up, Phillip discovers that Timothy has died. The chapter ends with Phillip saying that he is now "blind and alone on a forgotten cay."