Charlotte Doyle is understandably nervous about what people in Providence will say when they find out that the captain of the Seahawk and his first mate are dead. She's old enough to realize that, if there's the slightest suspicion that anything untoward happened during the ship's voyage, then she and Zachariah could find themselves in a whole heap of trouble.
Even though it was mad Captain Jaggery who killed his first mate Mr. Hollybrass, Charlotte was found guilty of his murder at a hastily convened trial presided over by—who else?—Captain Jaggery, the real murderer. In due course, Jaggery falls to his death overboard after trying to kill Charlotte.
Although it was an accident—albeit not a particularly tragic one, all things considered—Zachariah and Charlotte are all too aware that Captain Jaggery's death, coupled with that of Mr. Hollybrass, will look mightily suspicious to the good people of Providence when the ship's voyage finally comes to an end.
But Zachariah, for one, isn't all that worried. He says that he and Charlotte will remind the owners of the Seahawk that they managed to bring their ship into port with its cargo intact. Zachariah's sure that for hard-headed businessmen like the ship's owners, this is what they care about most of all, not the deaths of the captain and his first mate. Sure they died, but they died doing their duty, a not unusual occurrence on the high seas.
As Zachariah assures Charlotte, the owners of the ship may be sorrowful for the loss of Captain Jaggery and Mr. Hollybrass, but
Their tears won't be water enough to float a hat.