E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Be off, get you gone. To weigh anchor is to lift it from its moorings, so that the ship may start on her voyage. As soon as this is done the ship is under-weighi.e. in movement. (Saxon, wægan, to lift up, carry.)
Get off with you; come, come! weigh anchor.Sir W. Scott: The Antiquary.