Reading through these old newspapers from San Francisco is interesting and exhausting. They talk about everything under the sun, except work songs on the docks or aboard the ships. And there were plenty of ships, and there was plenty of loading and unloading! But no songs. Here is one little reference to singing at the capstan from 1865 (under "Lover's Promenade"):

http://cdnc.ucr.edu/newsucr/cgi-bin/newsucr?a=d&cl=search&d=DAC18650605.2.2&srpos=2&e=-------en-logical-20--1-byDA---capstan+son

And here is an interesting little article from 1895 by an old fellow remembering "how it was" twenty-five years earlier (about 1870):

http://cdnc.ucr.edu/newsucr/cgi-bin/newsucr?a=d&cl=search&d=SFC18950420.2.146&srpos=1&e=-------en-logical-20--1----sea+shanty-al