French to English Tech/Engineering Ships, Sailing, Maritime undocking

I have very little context. The report is mainly about damage to a crane but there is a small section that describes how it got damaged - it got hit by a ship that they lost control of while undocking! The relevant phrase is:

durant l’appareillage, on dédouble l’amarrage, on reste sur les gardes avant, les travers,

which I am, so far, translating as:

during casting off, you remove one of the two moorings, remaining on the front and beam moorings,