The three parallel texts of Large St Petersburg Tablet, Small St Petersburg Tablet and Large Santiago Tablet makes it possible to compare the first two glyphs with each other; they are two different ways of writing the same (or possibly nearly the same) thing.

And  by comparing with Large St Peterburg Tablet we can see that there the writer has chosen another way to represent the double-canoe:

i.e. as two seemingly disconnected canoes. We can confidently assume though that it is not meant to imply that these two glyphs really should be read as two canoes moving freely from each other. Rather it is just a way to simplify. Everybody knows that they must be connected.