I believe that this question is asking about something that Timothy tells Phillip in chapter 3. When the chapter begins, Phillip and his mother are still on the ship. They are forced to begin loading into a lifeboat after their ship is hit by a torpedo, and in the process of getting that boat into the water, Phillip is hit and knocked out.
When he wakes up, Phillip finds himself on a raft with Timothy. Phillip isn't happy about this, and he genuinely thinks their situation is terrible. Ever the optimist, Timothy tells Phillip that they are actually having good luck. Timothy tells Phillip that the water keg isn't broken, so they have some fresh water. Timothy also points out that they have a few biscuits, some chocolate, and the matches in the tin are dry. He says that all of these things indicate good luck.
Phillip is absolutely not convinced, and his facial expression shows it. Timothy instantly reads the look and continues with his optimism. He comforts Phillip by telling him not to despair and that they will be found soon since they are in a busy shipping channel. Phillip doesn't argue and falls asleep again. Phillip will eventually learn that Timothy's optimism is one of their most valuable resources.