meaning larboard or left side, is an abbreviation of porta il timone (carry the helm). Porting arms is carrying them on the left hand.
“To heel to port” is to lean on the leftside (Saxon, hyldan, to incline). “To lurch to port” is to leap or roll over on the left side (Welsh, llercian).
She gave a heel, and then a lurch to port, And, going down head-foremost, sunk in short.
Port. An air of music; martial music. Hence Tytler says, “I have never been able to meet with any of the ports here referred to” (Dissertation on Scotch Music). The word is Gaelic.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894