The answer to this question can be found in Chapter One of this great historical novel. As Kit finally sees the shore of America, the new land where she hopes to live, she finds out that one of the ladies on the ship who has been friendly towards her, Mistress Eaton, the Captain's wife, will be leaving the ship at this point. When Kit tells her she thought the ship was her home, Mistress Eaton tells Kit about her living arrangements:
But I was born in Saybrook, and in the spring I get to hankering for my house and garden. Besides, I'd never let on to my husband, but the summer trips are tedious, just back and forth up and down the river. I stay at home and tend my vegetables and my spinning like a proper housewife. Then, come November, when he sails for Barbados again, I'm ready enough to go with him.
We can therefore see that Mistress Eaton spends the summer in her home in Saybrook, living the life of a "proper housewife." She does not spend the summer on the ship with her husband, prefering to get a dose of life on land for a change, before leaving again with him to escape the cold winter and journey to warmer climes.