E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
He has tumbled into a nice berth. A nice situation or fortune. The place in which a ship is anchored is called its berth, and the sailors call it a good or bad berth as they think it favourable or otherwise. The space also allotted to a seaman for his hammock is called his berth. (Norman, berth, a cradle.)
To give a wide berth. Not to come near a person; to keep a person at a distance. The place where a ship lies in harbour is called her berth: hence, to give a wide berth is to give a ship plenty of room to swing at anchor.