adverb / preposition
abaft
uh-BAFT/əˈbæft/
Toward a ship's stern or farther toward it than something else aboard.
The orange life ring rests on the deck abaft the mast.

Etymology
The elements combine into an expression meaning “at or toward the back.” Sailors preserved this formerly general rearward expression for positions toward a vessel’s stern, the “after” part of the ship.
In context
we need to tip the balance so the wind is pushing further forward of the balance point. To do this, we have to take away the sails abaft of the mainmast in preparation for the wear.