Plate seam

A plate seam is the longitudinal butt joint between two plates of the same strake, distinct from a butt (the transverse joint between strakes). Shell, deck, and tank-top plating is joined first into flat or curved panels along its seams and butts on the panel line, then stiffened and assembled into blocks. Seams in hull shell are full-penetration butt welds, commonly run as single-pass one-side FCB submerged-arc welds for speed, and inspected by ultrasonic or radiographic testing. Seam and butt positions are arranged to stagger from frame and girder lines and from each other, a class rule that avoids stress concentration at crossing welds.