At right angles to the keel of a ship.
At right angles to a ship's length or keel.
Alongside or at right angles to.
The ship drew abeam the cove.
Abreast (of) the middle of a ship's side.
(nautical) Alongside. [Mid 19th century.]
She came abeam the crippled ship.
Origin of abeam
a- (“in the direction of”) + beam (“keel”)