R.J. Dickson, Ulster Emigration to Colonial America 1718-1775. Ulster-Scot Historical Series, London: Routledge and Kegan Paul, 1966. Dickson quantifies the history of the Scots-Irish and identifies the ports through which they left Ireland and where they entered the American Colonies. New Castle DE was the port of choice for 1.5% of those who came; Philadelphia admitted 53%; New York City, 18.5%; and Charleston SC, 11.2%.
Dickson’s Appendix D includes a detailed run-down on each ship arriving from Belfast, Londonderry, Newry, Larne, and Portrush, 1771-1775. These facts are taken from the Belfast Newsletter and the Londonderry Journal. These two newspapers also listed the passengers on board from signatures recorded in “letters to the editor” sent to Ireland upon arrival in America.
And there are indexes online for both publications:
http://www.ucs.louisiana.edu/bnl/ Indexed the Belfast Newsletter, 1737-1800. 20,000 surviving pages of the newspaper deliver a final database of information which contains nearly 300,000 items of news and advertisements.
Irish Genealogical Abstracts from the Londonderry Journal, 1772-1784. http://content.ancestry.com/iexec/?htx=BookList&dbid=49206&offerid=0%3a7858%3a0
Your favorite genealogy expert of choice, Arlene Eakle http://arleneeakle.com
PS Other indexes that identify passengers and new arrivals will be forth coming–stay tuned in.