[1] Erdmann was born on 15 April 1940 in Czarnków in German-occupied Poland during World War II, but grew up in Karstädt in East Germany.
From 1958 to 1959, he traveled alone to India by bicycle via Southern France, North Africa, the Near East, and Afghanistan.
Because he couldn't afford a boat, he made his living for a couple of years as a seaman in the Merchant navy.
He bought his first boat, a used 25 ft wooden sloop in Alicante, Spain – where he met Bernard Moitessier who introduced him to the art of astronavigation – and renamed it Kathena, arriving back on the German island of Heligoland on 7 May 1968 after 421 days.
Because of the size of his boat, nobody in Germany believed him at first despite Erdmann producing carefully maintained logbooks and documentary evidence of his ports of call.