Cov kab hluav taws xob qab nthab tau muab faib ua grille main rib, auxiliary rib thiab upper main keel system. Lub uniformity ntawm lub ntsiab tav thiab auxiliary tav ntawm cov hniav nyiaj hniav kub hais txog cov hlau hollow slats. Lub gird qab nthab system yog ib qho kev qhib zoo nkauj qab nthab tsim los ntawm kev sib txuas ntawm lub ntsiab tav thiab cov auxiliary tav ntawm cov hniav nyiaj hniav kub nyob rau hauv ntsug thiab kab rov tav.
