What significance do the glass bottles with ships inside have?

Susie and her father had made the ships in a bottle
together, and they are a reminder to him of her death. Jack, Susie's father, looks at
the snow globes and the bottles with ships inside as perfect little worlds that are so
fragile they can easily be destroyed. They symbolize how Jack's family has been
shattered by Susie's brutal murder by a serial killer. After Susie's death, the family
falls apart, and Jack is obsessed to find her killer. Susie's killer has destroyed
Jack's perfect little family, and there was nothing Jack could do to prevent
it.