Because I have the seven volumes of THE FAMINE IMMIGRANTS (covering 675,000 Irish entering the US at NY between 1846-1851) I had to look for the listing for John Thompson and I did find it. The RIVERDALE arrived at NY on Nov 12, 1851 from BELFAST. He is shown as a 29 yr old Laborer
Interestingly, there is also a Jane Thompson 28 Spinster and with her is a ten month old girl, Catherine. Maybe they're connected in some way to John. Wife, Sister, Niece???
Food for thought.