As already noted, the ship had a sail (and therefore a mast). It must have had a rudder, and a deck/hold arrangements, since all went “down into the ship” (v. 6).
Narrative: Laman and Lemuel were sufficiently humbled that they worked on the ship under Nephi’s instructions (1 Ne. 18:1). Nevertheless, Nephi takes responsibility for the project, and continues to indicate that “I… built the ship.” This does not contradict his statement that Laman and Lemuel worked on the ship, but simply highlights his lead role. Nevertheless, his emphasis in this verse is not on the pride of accomplishment but on the reaction of his brothers. They contemplated the finished result feeling further impressed and humbled. Nephi is not obliquely paying himself a compliment. Nor does he mention anyone else’s reaction. Laman’s and Lemuel’s uncharacteristic humility is important for Nephi’s spiritual lesson—their cycles of humility and disaffection.