Complex sentence: In port, her small crew (eight or nine men) served double-duty as longshoremen; unloading 75,000 to 80,000 board feet was an average day's work.
Split into simpler sentences: In port, her small crew of eight or nine men were also responsible for loading and unloading the ship. Unloading 75,000 to 80,000 board feet was an average day's work.