Knudsons from Aardal ships/dates(1881?)

My ancestors were from Aardal and Strand. My grandmother was Johanna Knudsen from Aardal, daughter of Knud Thorsen and Johanne Gudmundsdatter, born in 1863, and immigrated about 1881. What I'm trying to find out is on what ship she might of sailed on, and the date of departure and destination. Johanna also had a sister Gundla (or Gunla), born in 1857 and immigrated to America about this same time, or shortly thereafter. Again, I'm trying to find out what ship she may have sailed on and dates. Johanna's mother and brother, Johanne Gudmundsdatter and Knud Knudsen, immigrated in 1882 and I'd like to know what ship they might have sailed on. In "Emigranter, fra 1825-1970, they were listed as #81822 and #81823?." Johanne was born in 1830 and Knud in 1866. I didn't see the name of the ship on that web page or departure date. Any help?