Gravy Bollocks

Why do they call it the Gravy Boat? Is it because it looks a bit like a boat? Tenuous link. Maybe after grandma has had a few sherries it starts looking like a boat.
I have heard of the Gravy Train. Why not call the gravy container the gravy train and then people would get it. Maybe they could make a little gravy server in the shape of a train.
But while we have the Gravy Boat, why doesn’t a gravy maker do ‘Gravy Boat in a bottle’ and it is a bottle of gravy and when you have poured out all the gravy there is a boat in there. You wash it out and have your very own ‘Gravy Boat in a bottle’ on the bookshelf to impress you friends. You could collect a set of them and you wouldn’t know what boat you had till your bottle of gravy was running low.