In the seven volumes of the subject books covering 675,000 Irish entering the US at New York during the time noted are many, many McCrackens listed. Most of them boarded ship at the Northern Ireland ports of Belfast or Londonderry or Glasgow, Scotland. There are others that left for the US from Liverpool.
Another significance was that there were several weavers listed.
Just thought I'd post this and if someone has immigrants arriving in the US about 1846-1851, drop me an E-mail with the name and approx age during that period or date of birth and I'll see if I can find them. Also, names of others that might have been traveling together.
Al O'Brien