plank: Thick beams or pieces of wood, for which several Hebrew words are used. The Revised Version (British and American) changes "planks" (of fir) into "boards" in 1Ki 6:15, and in a few instances substitutes "planks" where the King James Version has "boards" (Ex 27:8; 38:7, the altar; Eze 27:5). So in the New Testament in Ac 27:44, for sanis.
⇒See the definition of plank in the KJV Dictionary
See SHIPS AND BOATS,II , 2, (3).