My interpretation of the lines has always been the same as that given by Charley Noble and thurg. The song is very much in the Romantic style, with psychological realism and practical seamanship taking the back seat.

"We're not worried about that sound 'cause it shows just how fast we're going home."

Rumncoke's interpretation of "boom" as limited to fore-and-aft sails may be correct in current usage, but here's what Admiral Smyth had to say in "The Sailor's Word-Book" in the 1860's:

"Studding-Sail Boom. A spar rigged out for the purpose of setting a studding-sail, and taking its name from the sail it belongs to."