Born in San Francisco, Mohrmann became a seaman at 13 years of age. He sailed the world's seas for 18 years, settling in Antwerp for a time where he specialized in ship portraiture.

Preferring to give attention to the ships he depicted instead of his career, Mohrmann sailed the globe creating excellent quality ship's portraits. Today the artist's works can be found in collections throughout America, Europe, Scandinavia and England.