Since Germany did not exist as a cohesive nation until 1871, it's not entirely accurate to call them German immigrants. Most of the colonial-era immigrants from the future Germany are referred to as Palatines, a reference to the region controlled by the Elector Palatinate, but this too is inaccurate. Looking just at immigrants coming from the Rhine River valley, there were numerous other territories from which they originated. Württemberg, for example, was a large region on the Rhine which was occupied by French troops during the winter of 1741-42 (one can easily imagine that people living in Württemberg may have been very motivated to emigrate to the new world after the French army finished ransacking their towns). However, for a variety of reasons, "Palatine" has become the generic term for immigrants from this region during this era, regardless of their actual point of origin.
|Detail of map of Germania published for Benjamin Hederichs in 1742.|
From Geographicus Rare Antique Maps
The best resource I've found on the topic is The Palatine Wreck by Jill Farinelli. I have a pile of scholarly books and articles that focus on specific aspects of German emigration during the 18th century, but Farinelli's book does the best job of describing all aspects of migration from the Rhineland to America. She focuses on a specific, tragic shipwreck in 1738 and presents some wonderful research into the individual passengers, discussing their possible motivations for leaving Europe and detailing all of the steps involved in getting here.
The typical journey involved traveling by barge down the Rhine to Rotterdam, where English shipping companies loaded up their ships with migrants. I had assumed that travelers from the Rhineland would go directly into Rotterdam, but as Farinelli explains, Rotterdam didn't want them. Instead, they had to stay at a migrant camp just outside of the city until their ship was ready for boarding. The waiting period could last weeks.
After finally getting onto a ship, the travelers would be at sea for approximately 12 weeks, encountering the miseries of seasickness for the first time. There are some marvelous first-hand accounts of the journey that are either currently in print or available through archive.org and Google Books.
Here is a bibliography of some of the best sources I've found on the topic of 18th century German immigration:
Gottlieb Mittelberger's Journey to Pennsylvania in the Year 1750 and Return to Germany in the Year 1754..., Translated from the German by Carl Theo. Eben. Philadelphia: John Jos. McVey, 1898.
The Notebook of A Colonial Clergyman, Condensed from the Journals of Henry Melchior Muhlenberg, Translated and Edited by Theodore G. Tappert and John W. Doberstein. Minneapolis: Fortress Press, 1998.
Stephen R. Berry, A Path in the Mighty Waters: Shipboard Life & Atlantic Crossings to the New World. New Haven and London: Yale University Press, 2015.
Jill Farinelli, The Palatine Wreck: The Legend of the New England Ghost Ship. University Press of New England, 2017.
Aaron Spencer Fogleman, Hopeful Journeys: German Immigration, Settlement, and Political Culture in Colonial America, 1717-1775. Philadelphia: University of Pennsylvania Press, 1996.
Farley Grubb, German Immigration and Servitude in America, 1709-1920. London and New York: Routledge, Taylor & Francis Group, 2011.
Rev. H. Harbaugh, The Life of Rev. Michael Schlatter; With a Full Account of His Travels and Labors Among the Germans.... Philadelphia: Lindsay & Blakiston, 1857.
Charles E. Kemper, "Moravian Diaries of Travels Through Virginia," The Virginia Magazine of History and Biography, Volume 11 (April 1, 1904).
William J. Mann, Life and Times of Henry Melchior Mühlenberg. Philadelphia: G. W. Frederick, 1887.
A. G. Roeber, Palatines, Liberty, and Property: German Lutherans in Colonial British America. Baltimore and London: The Johns Hopkins University Press, 1998.
Marianne S. Wokeck, Trade in Strangers: The Beginnings of Mass Migration to North America. University Park, PA: The Pennsylvania State University Press, 1999