Not P but Moby-Dick (60)

[Mike Jing]

>From Chapter 81:

With a shout, they took a mortal start forwards, and slantingly ranged up
on the German’s quarter.  An instant more, and all four boats were
diagonically in the whale’s immediate wake, while stretching from them, on
both sides, was the foaming swell that he made.

Here, do "slantingly" and "diagonically"(=diagonally) refer to the relative
position of the boats, or is it something else? What exactly is the picture
here?