I can never resist adding redundantly to a perfectly good thread, but here goes. Yes, the bull engine was an auxiliary steam engine used to raise large sails. Why "bull" I have no idea, except it was big. It could also be called a donkey engine, as in "The Donkeyman's Christmas," a short story about an engineer who pretends the 'donkey' won't work, so the Captain can't go in the direction he wants. The ship is blown across the Date Line in such a way that the crew gets two Christmases. It wouldn't come up by title on Google and I can't recall the author. Sorry. Someone above mentioned that the 'track' seemed incongruous, as if mixing a railroad track into things. My understanding is that the engine exerted its pull by means of a cable between it and the yardarm. Introducing such a moving part into the mass of 'standing' rigging would be begging to foul something or other, so the cable ran through a track attached to the mast. That would have to be kept free of obstructions also, so "clear away the track and let the bull 'gine/ bulgine run." I love the notion that "low back car" is an ebonic mondygreen for something Irish. Simplified my life.