it is a little boat which has sailed across the Atlantic many times
这个句子是个强调句型,which 指代little boat,意思为就是这只小船已经穿越大西洋多次.
Topsail(船名) be in the race across the Atlantic.
这是个虚拟语气的句子,省略了should这个助动词,意思为Topsail本应该在穿越大西洋比赛的途中.而这句话本身隐含的意思却是这艘般并不在穿越比赛中.
Topsail(船名) was in the race across the Atlantic.这句话却是另一种意思,是一个一般过去式,意思为Topsail曾出现在穿越大西洋的比赛中.